What's the Best Compression Ratio for Tech House
03-29-201309:16 PM #ane
Veteran Member 4 Rings
going with custom pistons. What's the best compression ratio and why?
Going use custom piston set and the CR is basically anything from viii.5:ane-nine.5:1 and more or less with shave or thicker hg. Part of me likes college CR for better spool but its a trade off for peak end. I was wanting to encounter some examples and impressions for both ends.
thanks
03-29-201309:41 PM #2
Veteran Member Four Rings 
How much ability are you chasing? With my current engine I placed in stock pistons from the AEB that have a college ix.5:1 CR versus my original ix.3:1 pistons (cheapest route available at the fourth dimension for twenty mm wristpins). If I had the money to spare, I would have sourced AMU pistons that have a 9:1 CR. Depending on your power goals, my personal stance is it isn't that big of a deal. And with that being said, I plan on going ix:1 83mm stroker pistons on my adjacent engine.
I hate information technology when my automobile acts similar a little bitch, treating me like a bitch
03-29-201309:54 PM #iii
Veteran Fellow member Three Rings 
You'll want eight.v-nine:1 for a FI awarding for best torque and drivability all effectually.
01 A4 Avant <- TwinScroll T3 jawns
Congenital 06A|Congenital AEB|RR Stg3 Clutch|01E 6MT|lx Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Cracked Dump tube
NefMoto Tuned
03-thirty-201305:38 AM #4
Veteran Member Three Rings
going with custom pistons. What's the all-time compression ratio and why?
Originally Posted past zandrew 
Going use custom piston set and the CR is basically anything from viii.5:1-ix.5:i and more or less with shave or thicker hg. Part of me likes higher CR for better spool but its a trade off for top end. I was wanting to run into some examples and impressions for both ends.
thank you
Off boost, loftier comp would be amend but y'all could however get away with the height cease by running meth injection :)
99.v A4 ane.8TQ MT
i.9L built/blueprinted motor, JE assymmetrical pistons, IE Tuscan Rods-JNL racing custom ported head, IE CVA2 camshafts-BW EFR7064 .92 IWG-Total-race T4 manifold-1150cc injectors +++++++++
Instagram : e85.A4
03-30-201307:09 AM #5
Veteran Fellow member 4 Rings
I take seen guys run extremely high CR before without the issue of knock. I am talking 12.5:1 while running SC62 sized snail in a daily driver making 400+whp. It was actually tuned for more whp but for daily use it just spun the tires. It was in Honda motor and not a VW but this is still has me wondering why not. He specifically wanted higher CR for the off boost characteristics. I know meth works but too me it seems like a band aid that can be stock-still with a proper blueprint and tune. I always somewhat laugh nigh meth since information technology was actually a feature on the first mass produced turbocharged motor dorsum in 1962. Call up well-nigh that, the first mass produced turbocharged motor was an all aluminum V8 215ci that ran ten.25:1 CR and used meth to prevent knock. You would remember in 50 years with all the advances in tuning and monitoring the engines vitals you could run the same CR without the aid of meth, which I am sure you can.
I was leaning toward 9.0:1-9.25:1 though.
Does anyone make a piston that has plenty clearance to brand the motor a non interference?
03-30-201307:47 AM #six
Veteran Fellow member Four Rings 
No. These are interference engines anyway yous put it. As for pinch I run 8.v and won't exist doing it over again. definitely go over 9. but it depends on what fuel y'all want to run. If y'all volition be running e85, I don't see why ix.5 would be besides loftier, I retrieve information technology would be great. Just for 93 I'd say 9.25 should do
"During my service in the United States Congress I took the initiative in creating the Internet." Al Gore, sometime Vice President of the United states of America
2022 SQ5- Wife's ride
2000 A4 Avant 1.8TQMS- Daily Commuter
2000 S4- Working?
03-30-201309:23 AM #7
Veteran Member Four Rings
I am also on the fence wether to go 2.0 or run the ane.9. Ultimately I would trade some torque for a lil more RPM range and from my prior expierences it seems like the smaller cranks spin better. I was thinking about punching the motor out with 83mm pistons and running a balmy prepare of cams like the 210's from Eurospec or mayhap fifty-fifty just their single intake. I really don't think going to 2.0 is necessary to attain what I am trying to accomplish but at the same time I am the blazon that will always wonder what if? I also have a GT3076R that I am contemplating every bit well just for now I am sticking with the GT2871R.
What is the rubber limit of the stock block equally far as RPM'south go (not hp)?
Is there any consenus on which is a ameliorate upgrade as to cams or valves?
WHen I build this block I would like to accept provisions in place for say 500awhp in instance I desire to do something really stupid 1 solar day.
03-thirty-201309:45 AM #8
Senior Member Two Rings
depends on what you want. If you want more bottom terminate torque so go with the higher CR pistons... if higher RPM HP is your goal than go with the lower CR pistons. If you accept the the big port heads I'd exist tempted to run peradventure a ix:1 CR. The viii.5:ane would give you more superlative end but these motors already lack torque and if this is a DD it would suck on the street.
If you have the small port heads I would just stick with the stock CR which I think is ix.5:i... or at least that is what I call back it is for the 2001+ 1.8T
1988 Shelby Dodge CSX-T, 2.5L 4cyl, T04E xl trim w/ .63 A/R, Stg2 Ported 8v Head (Sold) it was a torque monster!!! :(
2001 A4 1.8T turbo dorsum two.5in exhaust, SB clutch w/ 17lbs SMFW, Forge splitter, Revo stage ane flash, 4:i Middle diff, ST Coilovers, 034 RSB, Forge FMIC.
03-30-201310:05 AM #9
Veteran Member Three Rings
going with custom pistons. What's the best compression ratio and why?
Higher CR will not requite you more bottom end. At WOT a 8.5:1 CR engine will out-spool and produce more torque than an identical engine with ix.5:1.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Croaky Dump tube
NefMoto Tuned
03-xxx-201310:17 AM #11
Senior Member Two Rings
Originally Posted past catbed
College CR volition non give yous more than bottom terminate. At WOT a viii.5:1 CR engine volition out-spool and produce more torque than an identical engine with 9.5:1.
I would be really interested in seeing where you got that info because that is the first fourth dimension I accept always heard that before
1988 Shelby Dodge CSX-T, 2.5L 4cyl, T04E 40 trim due west/ .63 A/R, Stg2 Ported 8v Head (Sold) it was a torque monster!!! :(
2001 A4 1.8T turbo back ii.5in exhaust, SB clutch w/ 17lbs SMFW, Forge splitter, Revo stage ane flash, 4:1 Center diff, ST Coilovers, 034 RSB, Forge FMIC.
03-30-2013x:20 AM #12
Veteran Member Three Rings
Originally Posted past juxsa
I would be really interested in seeing where you got that info because that is the first time I take ever heard that before
Its the nature of a FI engine. Look up dynamic compression ratio.
01 A4 Avant <- TwinScroll T3 jawns
Congenital 06A|Congenital AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Intermission|Cracked Dump tube
NefMoto Tuned
03-thirty-201310:41 AM #13
Account Terminated Three Rings
You guys must be joking. Where do some of you get your info from.
Pinch ratio going upward is giving you more power at whatever powerband level. Its simple. All that volume is compressed into a smaller space. When the bang goes off it in plough explodes that much more outward. That is just in lamens terms. High CR will net you more power with whatever turbo on and off heave. You lot will have more torque, faster spool up, and more than area under the power curve all else existence held constant. In that location is just one caveat. When you run a higher CR y'all finish up hitting a wall quicker of how much boost you can run on 93. You can recoup by running e85, meth injection with 93 or e85, or race gas.
Smaller crank spinning better??? What the hell are we talking about. The cranks are the same size. The offset of the crank journal for the rod is but slightly higher. We are talking MM here. Your worried purely about rod to stroke ratio and the ratio is perfectly fine for even high revving motors on out detail engines with out detail stroker kits. No thing how you cut information technology more than displacement will net yous more ability across teh entire RPM rang, spool up quicker, and overall more than area nether the curve. Sound like a familiar argument? More deportation doesnt cyberspace y'all a potential wall with heave though. Its impartial in that respect.
Your cake isnt your rpm limiter. Its your valvetrain. While there is no static number to not cross typically you cant rev college so 8500 (id adopt to say 8000) on our stock hydraulic lifters without going to a solid lifter design. I also would rev past 7500 on the stock valvetrain. Sodium filled valves are rather brittle with historic period and counterbalance quite a chip to comparable options. Really like shooting fish in a barrel to bladder a valve even with upgraded springs. Non a definitive ways of expression here merely good rules of thumb.
Remember there isnt a ameliorate than this or that idea mentality. Everything is a compromise betwixt driveability, where power happens, and durability. You can just compromise and pull from each column not exponentially add together to each column with new shiny parts.
03-thirty-2013x:43 AM #14
Veteran Fellow member Iii Rings
Originally Posted by sweets4style
You guys must exist joking. Where do some of you become your info from.
Compression ratio going upwards is giving yous more power at whatever powerband level. Its simple. All that volume is compressed into a smaller infinite. When the bang goes off information technology in turn explodes that much more outward. That is just in lamens terms. High CR will net you more power with any turbo on and off boost. You will have more than torque, faster spool up, and more area under the power curve all else being held constant. In that location is merely i caveat. When y'all run a higher CR you end up hit a wall quicker of how much boost y'all tin can run on 93. You can compensate by running e85, meth injection with 93 or e85, or race gas.
LMAO. This is NOT TRUE.
You are right virtually the block/valvetrain though.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Croaky Dump tube
NefMoto Tuned
03-30-201310:56 AM #15
Senior Member Two Rings
Originally Posted by catbed
Its the nature of a FI engine. Expect up dynamic pinch ratio.
You should read about the nature of static CR too. What sweet4style said is correct
1988 Shelby Dodge CSX-T, 2.5L 4cyl, T04E twoscore trim westward/ .63 A/R, Stg2 Ported 8v Head (Sold) it was a torque monster!!! :(
2001 A4 i.8T turbo back two.5in frazzle, SB clutch westward/ 17lbs SMFW, Forge splitter, Revo stage 1 flash, 4:1 Heart diff, ST Coilovers, 034 RSB, Forge FMIC.
03-30-201311:03 AM #16
Veteran Member 3 Rings
going with custom pistons. What'due south the best compression ratio and why?
Originally Posted by juxsa
You should read about the nature of static CR as well. What sweet4style said is right
He is correct... For naturally aspirated engines. Are our engines naturally aspirated?
NA engines are VE limited, where ours are knock limited.
So if what he is saying is correct, then why did audi drib the CR from ix.5 to ix for the TT225? Surely audi has some idea what'south going on in the combustion chamber.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Congenital AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Cracked Dump tube
NefMoto Tuned
03-thirty-2013xi:xix AM #17
Senior Member 2 Rings
Originally Posted by catbed
He is correct... For naturally aspirated engines. Are our engines naturally aspirated?
NA engines are VE limited, where ours are knock express.
So if what he is saying is correct, then why did audi drop the CR from 9.5 to 9 for the TT225? Surely audi has some idea what's going on in the combustion chamber.
Because with a lower CR y'all tin run more heave without worrying about detonation. why are current forced induction DI engines running 10.five:ane CR or higher and produce torque at a lower RPM than our 1.8T could ever dream?
The answer is because their CR is crazy high
1988 Shelby Dodge CSX-T, 2.5L 4cyl, T04E 40 trim w/ .63 A/R, Stg2 Ported 8v Head (Sold) it was a torque monster!!! :(
2001 A4 1.8T turbo dorsum 2.5in exhaust, SB clutch westward/ 17lbs SMFW, Forge splitter, Revo stage 1 flash, 4:1 Center diff, ST Coilovers, 034 RSB, Forge FMIC.
03-30-2013xi:27 AM #eighteen
Veteran Fellow member Three Rings
going with custom pistons. What's the all-time compression ratio and why?
Originally Posted by juxsa
Because with a lower CR you lot can run more than boost without worrying about detonation. why are electric current forced consecration DI engines running x.5:1 CR or higher and produce torque at a lower RPM than our i.8T could always dream?
The answer is considering their CR is crazy high
Exactly.
Directly injection is a WHOLE different brawl game. You can't compare a DI to a port injection enginr
01 A4 Avant <- TwinScroll T3 jawns
Congenital 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Croaky Dump tube
NefMoto Tuned
03-30-201311:45 AM #19
Senior Member Ii Rings
Originally Posted by catbed
Exactly.
Directly injection is a WHOLE different ball game. You can't compare a DI to a port injection enginr
the principle is the same merely like the principle is the aforementioned with a forced induction motor as compared to a N/A motor... all turbo motors are N/A motors until they start building boost. I am done with this. I am not trying to be a dick but you tin can become ahead and go along to believe what y'all want, simply don't get telling people wrong data.
Again to the OP, the reward of depression CR is that y'all can run more than boost and take more top cease just at the expense of low end torque because it takes longer to spool the turbo. A high CR will have more lesser end and will be able to spool the turbo faster but at the expense of elevation end due to having run lower boost because of detonation.
1988 Shelby Dodge CSX-T, 2.5L 4cyl, T04E forty trim w/ .63 A/R, Stg2 Ported 8v Head (Sold) information technology was a torque monster!!! :(
2001 A4 1.8T turbo back 2.5in exhaust, SB clutch w/ 17lbs SMFW, Forge splitter, Revo stage 1 flash, four:ane Centre diff, ST Coilovers, 034 RSB, Forge FMIC.
03-30-201311:59 AM #xx
Veteran Member Three Rings
Originally Posted past juxsa
the principle is the same just like the principle is the aforementioned with a forced consecration motor as compared to a N/A motor... all turbo motors are Northward/A motors until they offset building boost. I am done with this. I am not trying to be a dick but you can go ahead and continue to believe what you desire, but don't go telling people wrong information.
Again to the OP, the advantage of low CR is that you can run more boost and have more acme terminate but at the expense of low end torque because it takes longer to spool the turbo. A loftier CR will accept more bottom end and will be able to spool the turbo faster just at the expense of pinnacle stop due to having run lower heave because of detonation.
Ok, we agree to disagree. You say turbo motors are N/A before the turbo spools. You are correct, but even on my laggy as fuck sixty trim, I make positive pressure before ii.5k RPM. That is considered "down-depression" and you volition take knock and less than platonic spark advance with higher CR.
OP, the correct info is use 8.5:1 to 9:1 CR pistons for a turbo engine. Any more and you lot're losing out on ability because of timing pull due to knock.
Last edited by catbed; 03-30-2013 at 12:eleven PM.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Congenital AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Break|Cracked Dump tube
NefMoto Tuned
03-30-201312:15 PM #21
Veteran Member 4 Rings
I was ever taught rule of thumb is to run lower CR if you desire to run more than heave and higher CR for improve off boost driveability. And with the CR you are looking at, you are actually limited to what is offered for our vehicle. Highest on the market would probably be 10.5:1 (usually nine.5:1 is listed but there are college CR pistons out there) and lowest being viii.5:1. I only considered 9:1 to be the compromise between the two. Just an opinion.
I hate it when my car acts like a piffling bowwow, treating me like a bowwow
03-30-201301:12 PM #22
Veteran Member Four Rings
At that place is pregnant difference betwixt DI and port injection. Directly injection allows you to run more timing (thus more torque) down low with college CR since DI really keeps combustion chambers libation past directing the much libation fuel directly into the chamber. Dynamic compression ratio means alot but that is across the telescopic of this thread. It takes in a lot more factors like valve timing and then on. However i take never seen a higher dynamic CR on the same motor with the same valve timing when comparing a higher static CR to a lower static CR. Yous WILL Non Get More TORQUE AT LOWER RPM's WITH LOWER CR THEN WITH HIGHER CR.
Sweet4style you obviously are misinformed almost what I am concerned nigh and what I am not. The cranks are different weight. The mean piston speed for a larger crank per revolution is higher then with a smaller crank. Too force equals MASS * dispatch and then by reducing weights (like forged rods and pistons) you lot reduce the force that is also exerted on the bearings and then along. Now to tie all this together nigh recollect that higher rod stroke ratios is what you want for RPM's. Information technology is IF we are talking NA, yet we obviously are not. In a forced consecration motor you lot need lower rod stroke ratio. A lower rod stroke ratio increases the speed of the piston at TDC opposed to a longer rod stroke ratio that slows it downwardly. A longer rod stroke ratio increases your run a risk of detonation. Besides the rubber average mean piston speed is typically 4200 fpm on motors one.viii and up (this is why those shitty D16 motors with brusque rod stroke ratio seem to concur up so well to turbo builds). This also depends on type of material used and quality of the build. You can spin them alot faster but these are numbers given too me past a company that all they practice is build how-do-you-do operation motors and they consider these safe speeds for your average architect. Obviously newer motors are unlike but a great deal of engineering science went into them to achive this and the VW 1.8 was not i of them.
For a 86.4mm stroke y'all are doing 4250 fpm at 7500 RPM which is more then safe with forged rods.
A 92.8mm stroke your are doing 4566 FPM which honestly should besides exist but fine.
AT 8000 RPM y'all are still at less FPM with the 1.8 crank opposed to the two.0 crank.
The idea would be to balance between the mean piston speed and rod/stroke ratio. However it would seem that you "should" be able to run more than pinch on the two.0 setup opposed to the one.9 since it ultimately has a lower rod stroke ratio and would be less prone to detontantion. However you are also increasing the rod angle which is a lot harder on the crank, bearings, and rod itself. Meaning you lot best have your $h!t correct.
You are also generalzing that deportation is everything when information technology comes to making power. Its not. I would accept a motor that can spin safely to 10,000 RPM that is a 1.6 opposed to a 2.0 that can not go past 7500 if I want to brand hp. My signal of stating that I similar a one.9 with cams and valves is that if I want to spin it to a higher RPM I tin can do so with out a significantly higher quality build (like balanced internals etc). I approximate in fairness I genralised also since there are other things that can be done to aid a longer stroke similar lightened flywheel, caster, etc merely this is taking in that both setups are the aforementioned.
Nonetheless I prefer real world examples.
03-30-201301:21 PM #23
Veteran Member Four Rings
Another general rule of thumb is to not increment bore on this engine to 83mm unless going stroker. It could be speculation, but 82.5mm is what you would want to cease at if staying stock stroke. Reason being is that you lot identify more stress on the piston rings with them being larger in diameter. The longer stroke alleviates this tension, with the added bonus of more displacement. On the upward move of the piston, the rod angle basically would not be ideal with that large of a bore/piston with the stock crank. All in theory though.
I detest information technology when my automobile acts like a little bitch, treating me similar a bitch
03-thirty-201301:40 PM #24
Veteran Fellow member Three Rings
Originally Posted past zandrew
There is significant deviation betwixt DI and port injection. Direct injection allows you to run more than timing (thus more torque) down low with higher CR since DI actually keeps combustion chambers cooler past directing the much cooler fuel directly into the chamber. Dynamic compression ratio ways alot but that is beyond the telescopic of this thread. It takes in a lot more factors like valve timing and then on. However i take never seen a higher dynamic CR on the same motor with the aforementioned valve timing when comparing a higher static CR to a lower static CR. YOU WILL Non Go More than TORQUE AT LOWER RPM's WITH LOWER CR THEN WITH Higher CR.
So why did you start this thread if you lot think y'all already know the answer. What you are saying holds true for North/A like I said before. Non FI.
Quoted from another thread on a unlike forum:
"Dynamic compression ratio, as opposed to mechanical compression ratio. sqrt((heave+14.7)/14.7) * CR = effective compression ratio. Dropping CR allows a greater constructive CR (therefore greater oxygen with which to combine with fuel). Say you driblet from 9:i CR to eight:1, which allows an increase in heave from xv psi to 18 psi without detonation onset and all else being fairly equal. You've lost 3-iv% in power potential as a result of the decrease in mechanical compression ratio, simply you've gained x% in absolute potential, for a net increase of 6-seven%. Could be incorrect, but I incertitude almost people could tell the difference in throttle response in off-boost situations betwixt 8:1 and 9:1. There is a betoken where a lower CR will non be enjoyable in off-boost conditions, simply I don't recall 8:1 or 8.5:1 is it."
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Break|Cracked Dump tube
NefMoto Tuned
03-30-201301:53 PM #25
Veteran Member Iii Rings
Originally Posted by Seerlah
Another general rule of thumb is to not increase bore on this engine to 83mm unless going stroker. It could be speculation, simply 82.5mm is what y'all would want to stop at if staying stock stroke. Reason being is that yous place more than stress on the piston rings with them being larger in diameter. The longer stroke alleviates this tension, with the added bonus of more deportation. On the upward motion of the piston, the rod bending basically would not be platonic with that big of a bore/piston with the stock crank. All in theory though.
Larger bore does non hateful more stress. Quite the opposite in fact. More surface expanse for the aforementioned amount of forcefulness equals less strength per unit of measurement area. I'thousand not sure how yous think information technology relates to bore size with stock crank though?
Besides, the rod bending will NOT change if you only alter pistons. The wrist pin location will stay the same, as well as rod length.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Pause|Croaky Dump tube
NefMoto Tuned
03-30-201302:27 PM #26
Veteran Fellow member Four Rings
does no one ever read my posts? forget all the number bullshit, dynamic this and that, any. the unproblematic fact is lower pinch volition cyberspace you lot less torque low downwardly, simply allow yous to run more heave on worse gas. high compression volition net y'all more torque off heave, but is less stable in high boost and poor octane fuel. boost is obviously skillful, merely if yous cant run whatsoever kind of timing while in boost to keep knock downwardly than whats the point? high compression is skilful but if y'all cant run high heave while in high compression whats the bespeak? the fact is you demand something in between, and my explanation is below, every bit quoted from above. all of the high tech number bullshit is fine, but you cant alter any of it. you lot become Ii numbers to bargain with. bore and compression ratio. choose wisely.
Originally Posted by redline380
No. These are interference engines anyhow you put it. As for compression I run 8.5 and won't exist doing it over again. definitely go over nine. but information technology depends on what fuel you lot want to run. If you lot will be running e85, I don't see why nine.5 would be too high, I recollect it would exist bang-up. Merely for 93 I'd say nine.25 should do
"During my service in the United States Congress I took the initiative in creating the Internet." Al Gore, erstwhile Vice President of the United States of America
2022 SQ5- Wife's ride
2000 A4 Avant 1.8TQMS- Daily Driver
2000 S4- Working?
03-30-201302:31 PM #27
Veteran Member 4 Rings 
A friend of mine is running 12.two:1 in his speed6. Not actually related to this thread though since the MZR is DI, and he's running E85. I just figured I'd share.
03-30-201303:00 PM #28
Veteran Fellow member Iii Rings
going with custom pistons. What'due south the all-time compression ratio and why?
Originally Posted past redline380
does no one always read my posts? forget all the number bullshit, dynamic this and that, whatever. the uncomplicated fact is lower compression volition net you less torque low down, but permit y'all to run more boost on worse gas. high compression will net y'all more torque off heave, but is less stable in high boost and poor octane fuel. boost is obviously good, merely if you deceit run whatsoever kind of timing while in boost to keep knock down than whats the bespeak? loftier compression is good but if you cant run high boost while in high compression whats the point? the fact is you need something in betwixt, and my caption is below, as quoted from in a higher place. all of the high tech number bullshit is fine, but you cant alter whatever of it. yous go TWO numbers to deal with. diameter and pinch ratio. choose wisely.
It is NOT that simple with FI engines.
People keep throwing around the term off-boost. You are rarely off heave at WOT with a streetable turbo, and you volition Non notice a difference between CR at part throttle.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Congenital AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Suspension|Croaky Dump tube
NefMoto Tuned
03-30-201303:10 PM #29
Veteran Member Iv Rings
Originally Posted by catbed
It is NOT that unproblematic with FI engines.
im non maxim its simple. im saying you dont take a option. what are you going to do, order custom crank and piston to get a good rod angle? like i said, for all intensive purposes, you accept two numbers to choose from. bore and pinch ratio. you tin can research the fuck out of pistons, practise math till theres numbers popping out of your donkey, only at the end of the day you will be (for a 1.8/9) running a 86.4mm stroke with a 144mm rod length. those wont modify. and all other numbers rely on those variables. then similar i said, yous got 2 numbers, no matter how you chalk information technology up. no one ever said the vw 1.8 was designed to be a race engine because it wasnt
"During my service in the U.s.a. Congress I took the initiative in creating the Internet." Al Gore, former Vice President of the United States of America
2022 SQ5- Wife'southward ride
2000 A4 Avant one.8TQMS- Daily Commuter
2000 S4- Working?
03-30-201303:29 PM #31
Veteran Member Four Rings
Originally Posted by catbed
Larger diameter does not mean more stress. Quite the opposite in fact. More than surface area for the same amount of force equals less force per unit of measurement area. I'm not sure how you call up information technology relates to diameter size with stock crank though?
Besides, the rod bending will Non alter if you lot merely change pistons. The wrist pin location will stay the same, too every bit rod length.
I should have worded information technology manner differently. Typed also fast non going with what I wanted to say (I know the rod top wristpin cease does not change position 
). Just the theory was what yous are negating. Once once again, just a theory. For better words, more than like a tilt of the piston that would be in that location if not for the rings (piston to cylinder clearance). Theory is as you increase the bore yous in fact place more tension on the rings. Your statement would agree truthful if information technology were on a straight upwards move with equal strength applied to the sides. But that is not the instance.
Not trying to showtime a debate at all. Only stating what I was taught 
.
I detest it when my car acts like a little bowwow, treating me like a bitch
03-30-201303:44 PM #32
Veteran Member Three Rings
Originally Posted by Seerlah
I should have worded it way differently. Typed too fast not going with what I wanted to say (I know the rod peak wristpin end does not change position ). But the theory was what you lot are negating. One time over again, just a theory. For amend words, more similar a tilt of the piston that would be there if not for the rings (piston to cylinder clearance). Theory is as yous increment the bore you in fact place more tension on the rings. Your statement would hold true if it were on a directly upward move with equal force applied to the sides. But that is non the instance.
Not trying to start a debate at all. Just stating what I was taught .
Not trying to either, only confused as to your statement. Merely, all cleared up now.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|sixty Trim|1000cc EV14s|Bad MAF|Clunking Intermission|Cracked Dump tube
NefMoto Tuned
03-30-201306:39 PM #33
Veteran Member Four Rings 
Expect, not to stir things upwards here, merely Catbed, I think some of your reasoning is faulty. While a lower compression ratio is ultimately going to lower the knock threshold and allow for more power, the advantage doesn't materialize until the lowered knock threshold of a say, 8:1 compression ratio exceeds that of a higher one of say 9.5:1.
So say that all things existence equal, y'all can run 15 degrees advance at 10 PSI from 3000 RPM to 7500 RPM on an 8:one and a 9.5:1 pinch engine, the high pinch engine will ultimately brand more than ability. Yes, there is slightly more space in the cylinder on the low pinch engine owing to the piston dishing, but that's not what's making your power on the depression compression engine, every bit y'all said, it's the increment in detonation resistance.
However, lets upwardly the heave to 30 PSI and all of a sudden I need to first dropping the timing to 5 degrees accelerate for the 9.v:1 or fifty-fifty dropping the boost to 20 PSI vs leaving it at 30 PSI and at xv deg advance for the 8:ane, now the low compression engine starts to brand more power.
What am I trying to get at, your annotate nearly the low pinch engine outperforming the high compression one doesn't concord true until you start running up against the knock limitations of a higher compression ratio, which can exist pretty loftier really. With water/meth I can hold effectually xviii-twenty degrees advance at 30 PSI on my 5556 and that'due south on an AEB CR of 9.five:ane. Then really, you're probably looking at north of the 250-300 WHP range before you lot start seeing the advantage of a depression CR engine and past then you're probably due north of 5000 RPM in your powerband.
Easiest way to look at it is this manner: concord VE at a fixed 100%, assume space amounts of boost and infinite detonation resistance, which makes more than power at a given heave level five:1 compression or x:1? Only every bit you rightly pointed out, information technology doesn't work that way, sooner or later detonation will rear it'southward ugly caput and you'll have to pull heave or timing. You lot merely had information technology a little off on when it sets in, information technology doesn't occur as soon equally y'all hit positive pressure level, it occurs gradually and at a certain cylinder pressure threshold. It'south also probably the case (and I'm guessing, but it makes intuitive sense) that detonation likelihood occurs logarithmicaly every bit heave increases, not on a linear scale.
Likewise, a higher CR will also take the consequence of increasing the exhaust gas velocity every bit the piston raises to expel the exhaust gas from the cylinder. That said I don't know if it'south negligible or not.
Last edited past ZimbutheMonkey; 03-30-2013 at 06:49 PM.
03-30-201308:11 PM #34
Veteran Member Four Rings
BTW, has anyone had a expect at using these pistons in a 1.8T?
http://www.spaturbo.com.br/loja//com...mart/Itemid,1/
SPA makes them and I find it to exist an interesting design. Non and then much for efficiency'due south sake, simply for detonation resistance. Reason beingness is that my understanding of detonation is that it commonly occurs at the border of the flame front closest to the cylinder wall. Basically, the gases there heat upward and ignite earlier the flame forepart has a chance to reach that area.
Now, that said, if you subtract the pinch in that region by giving it a concave area, would information technology not stand to reason that you would lessen the compression and hence the possibility of autoignition. Also, every bit SPA claims, it does increase swirl and the homogeneity of the air/fuel mix and therefore lessens the possibility of detonation (part of why the FSI and TFSI engines can run high pinch and run lean at cruise).
***EDIT*** I looked at the website and they're actually designed to run with longer rods to give a one.9L displacement boost. So there'due south that whole rod ratio thing that was being discussed earlier.
Last edited by ZimbutheMonkey; 03-30-2013 at 08:23 PM.
03-30-201308:40 PM #35
Veteran Fellow member Four Rings
Originally Posted by ddillenger
Catbed was right on point when he said we're knock limited.
not trying to sound like an donkey, just duh! all engines are knock limitied. (lets not become techinal on this, y'all know i hateful internal combustion, reciprocating engines) its why back in the days, the easiest fashion to increase power was to increase displacement. the gas was shit back and so, every bit well as the ignition systems. we have the aforementioned limiting factors in todays engines, just to a different caste. if nosotros werent knock express, compression ratios would be ∞:1 and gas would exist 0 octane decision-making the knock now, that is a whole other story and many factors play into it.
Originally Posted by ZimbutheMonkey
BTW, has anyone had a look at using these pistons in a 1.8T?
havent seen them. interesting pattern, simply i feel they are a chip contemporary. im sure they spent a long time desinging them carefully, but whats the point when you tin accomplish the same thing by running better fuel? as i stated a couple times, i really think the sweetness spot for a 1.8 is at 9.25 compression and e85. run the timing sky loftier, crank the boost to whatever, and hang on.
"During my service in the U.s.a. Congress I took the initiative in creating the Internet." Al Gore, former Vice President of the United states of America
2022 SQ5- Married woman's ride
2000 A4 Avant 1.8TQMS- Daily Driver
2000 S4- Working?
03-30-201309:00 PM #36
Veteran Fellow member 3 Rings
Originally Posted past ZimbutheMonkey
Expect, not to stir things up hither,
Then say that all things being equal, you can run 15 degrees advance at ten PSI from 3000 RPM to 7500 RPM on an 8:one and a 9.5:1 compression engine, the high compression engine will ultimately make more ability. Yep, there is slightly more space in the cylinder on the low compression engine owing to the piston dishing, but that's not what's making your power on the low compression engine, equally y'all said, it'south the increase in detonation resistance.
However, lets up the boost to 30 PSI and all all of a sudden I need to start dropping the timing to v degrees advance for the nine.5:one or even dropping the boost to 20 PSI vs leaving it at 30 PSI and at fifteen deg advance for the 8:1, now the low pinch engine starts to make more power.
Yes, but who is running a congenital motor at only 10psi? If someone is edifice a motor to make power, so they will be riding the knock threshold, right? You can give examples of situations where what I said is untrue, simply I'm talking real world situations here. Certain you can build a high CR engine and run low boost, but why would yous do that?
What am I trying to go at, your comment about the low compression engine outperforming the loftier compression one doesn't hold true until you start running up against the knock limitations of a higher compression ratio, which can be pretty high actually. With water/meth I can hold around 18-20 degrees advance at 30 PSI on my 5556 and that's on an AEB CR of 9.five:i. So actually, you're probably looking at north of the 250-300 WHP range before you lot start seeing the advantage of a low CR engine and by and so you're probably due north of 5000 RPM in your powerband.
I'm talking strictly 93 pump gas, as 90% of people aren't running meth. I agree that meth will add knock resistance. And like I said, odds are if you are building an engine, y'all'll be riding the knock threshold.
01 A4 Avant <- TwinScroll T3 jawns
Congenital 06A|Built AEB|RR Stg3 Clutch|01E 6MT|threescore Trim|1000cc EV14s|Bad MAF|Clunking Break|Croaky Dump tube
NefMoto Tuned
03-30-201310:14 PM #37
Veteran Member Four Rings
redline- Gas was shit when? Call back they went to unleaded and leaded gas could handle loads of timing. This is why you tin not achieve the aforementioned level of hp with pre unleaded motors with unleaded gas. Likewise requite you an idea airplane prop motors from WWII ran 130 octane in todays equivalent where equally todays run 100 octane. Manufacturers have learned to work around this though.
I don't have the pick for E85.
catbed- You can run whatsoever ready of numbers any amount you desire. Real world examples requite you better models to work from. Yet its a good idea to accept guidelines to build within.
Also riding the knock threshhold for what reason? Pushing a motor til it knocks and and so dorsum it off a degree or 2 will non yield the nigh ability (though sometimes it can). This is a major misconception that a lot people get suckered into believing. I really believed this myself and tuned a 4AGTE in AE86 to acme 218rwhp. Sold the automobile and the next owner had information technology dyno tuned. It made peak 222rwhp at the same exact psi on the same exact setup. Nonetheless he pulled 8 degrees of timing and gained twoscore lb ft at 3500 RPM.
seerlah - You need to await at the anatomy of piston. The rings are basically springs that push outwards on the walls to go along the compression and frazzle gasses on 1 side. The skirt of the piston is actually what rides the cylinder wall. When you measure out the piston diameter and compare it likewise the spec you lot do so at 90 degree from the centerline of wrist pin. Not the crown. Also give you a specific example I have 82mm forged piston and the skirt is 81.92mm (for a 82mm bore). The area above and betwixt the rings is 81.15mm. The expanse above the oil band is actually narrower and then the skirt. As well the width of the height 2 compresion rings are three.35mm and the groove depth for them is iii.75mm. Most people think the piston is the same bore superlative to bottom
03-30-201310:43 PM #38
Veteran Member Iv Rings
Originally Posted past zandrew
redline- Gas was shit when? Recollect they went to unleaded and leaded gas could handle loads of timing. This is why you can not reach the same level of hp with pre unleaded motors with unleaded gas. Likewise give you an idea plane prop motors from WWII ran 130 octane in todays equivalent where every bit todays run 100 octane. Manufacturers have learned to piece of work around this though.
I don't take the option for E85.
i was talking wayyy dorsum, like 1900-1920ish similar when gas was getting popular. even with pb, the gas was pretty crappy. and lead is a whole other subject field. how awesome would leaded gas be? yeah it kills cats, only like any of us actually run cats. and 02 sensors? id have no problem replacing them in commutation for leaded gas. equally for no e85 option, thats a shame. it really is. its some smashing stuff. in that case, id nonetheless stick with 9.25 pinch, youd just have to kill the timing a bit up top with 93. its not like your motorcar would be ho-hum or anything
Originally Posted past zandrew
The skirt of the piston is really what rides the cylinder wall.
i hate to be a stickler and i know you know better but i similar to clear upward data that can be miscontrued by other users. at no point in time does whatsoever part of the piston, exist it skirt or ring, contact the cylinder wall. there at least should always be oil in between ii moving parts. if they come in contact, they will seize which is kind of a bad thing
"During my service in the United States Congress I took the initiative in creating the Internet." Al Gore, former Vice President of the United states of america
2022 SQ5- Wife's ride
2000 A4 Avant 1.8TQMS- Daily Driver
2000 S4- Working?
03-thirty-201310:44 PM #39
Veteran Member Three Rings
going with custom pistons. What'south the best compression ratio and why?
Originally Posted past zandrew
catbed- You can run whatsoever set of numbers any amount yous want. Real world examples requite you better models to work from. Nevertheless its a expert idea to have guidelines to build inside.
Likewise riding the knock threshhold for what reason? Pushing a motor til it knocks and then back information technology off a degree or 2 volition non yield the most power (though sometimes it can). This is a major misconception that a lot people become suckered into believing. I really believed this myself and tuned a 4AGTE in AE86 to top 218rwhp. Sold the car and the adjacent owner had it dyno tuned. It made height 222rwhp at the same exact psi on the aforementioned exact setup. Yet he pulled 8 degrees of timing and gained forty lb ft at 3500 RPM.
I AM talking real world examples. Where do I throw arbitrary numbers out?
When tuning a machine, y'all shoot for MBT. In the one.8t engine, MBT is knock limited.
And you are saying that your old car gained 40 lb-ft due to pulling 8 deg of timing? That doesn't make a lick of sense. And were the dyno runs on the same dyno, same ambient conditions, and back to back pulls? Didn't recall so.
Last edited past catbed; 03-31-2013 at 03:00 PM.
01 A4 Avant <- TwinScroll T3 jawns
Built 06A|Built AEB|RR Stg3 Clutch|01E 6MT|60 Trim|1000cc EV14s|Bad MAF|Clunking Pause|Cracked Dump tube
NefMoto Tuned
03-xxx-201311:09 PM #40
Veteran Member 4 Rings
Originally Posted past catbed
Yeah, simply who is running a built motor at merely 10psi?
I practice, every fourth dimension my engine is below well-nigh 4000-4200 RPM. in fact, every motor out there runs only 10 PSI right until it hits eleven PSI. The indicate I'm trying to make here is that the OP is asking about overall driving characteristics of an engine. Let's face up it, the majority of a small displacement boosted engine is spent at part throttle and in less than full boost weather.
Until you hit the that threshold where a high compression engine starts to detonate, the loftier compression engine will yield improve torque and power delivery equally opposed to it'due south low compression analogue whenever it's not riding that knock threshold.
Myself, I live at 3500 ft elevation and I'll tell yous, a 1.8l engine off boost tin can inappreciably become out of it'southward own way. That niggling extra bit of power I become from the stock 9.5:ane compression is well worth information technology when I'1000 taking off from a lite or when I become stuck in a position where I need to advance and downshifting to 6500 RPM (like that weird spot in 3rd around 75-80 km/hr) isn't applied.
Source: https://www.audizine.com/forum/showthread.php/532980-going-with-custom-pistons-What-s-the-best-compression-ratio-and-why
0 Response to "What's the Best Compression Ratio for Tech House"
Post a Comment