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View Full Version : what compression and bore are you 2.0L guys running



v dub'n
10-18-2010, 08:51 PM
I've decided on building a stroker motor and have been looking at pistons, any one running high compression like 10:1 and up? If so where did you get your pistons, I'm looking to run between 10:1 and 11:1.

jrock
10-18-2010, 09:40 PM
Why would you want to run that high? It's a turbo motor...not a naturally aspirated or supercharged motor. What turbo do you plan on using? Most people that I have seen run 9.0 or 8.5. General rule of thumb is the lower the compression ratio the more power you will make off boost.

jrock
10-18-2010, 09:42 PM
O and bore is usually 83 but you can go to 83.5 if you don't mind the thinner cylinder walls.

Sales@RAI
10-18-2010, 10:07 PM
Why would you want to run that high? It's a turbo motor...not a naturally aspirated or supercharged motor. What turbo do you plan on using? Most people that I have seen run 9.0 or 8.5. General rule of thumb is the lower the compression ratio the more power you will make off boost.

It's actually the exact opposite. The higher the CR the more power you will make off boost

jrock
10-18-2010, 10:30 PM
Hmmm?..from what I have heard from a couple sources was that the higher the compression the better the power straight from the engine while the lower the compression the better off boost. Most of turbo cars you see are running at a compression ratio under 10.0 while many naturally aspirated and supercharged cars out there are running over 10.0. It's also much safer to run a turbo vehicle at a lower compression ratio to avoid detonation and should help decrease lag time.

jcb.
10-19-2010, 02:05 AM
Hmmm?..from what I have heard from a couple sources was that the higher the compression the better the power straight from the engine while the lower the compression the better off boost. Most of turbo cars you see are running at a compression ratio under 10.0 while many naturally aspirated and supercharged cars out there are running over 10.0. It's also much safer to run a turbo vehicle at a lower compression ratio to avoid detonation and should help decrease lag time.

WTF?
None of that makes sense.

Forced Induction cars run lower compression as stock to allow some margin of error and avoid pre-ignition/detonation issues when the intake charge temperatures get too high (usually down to the crap charge cooling systems as stock).
This has some draw backs:
Low compression leads to POOR power OFF BOOST (off boost means the engine is just producing the power it would produce if you ran it without the turbo, the same as you describe as "straight from the engine")
Low Compression also leads to LAG (see above).

Advances in ECU control, piston design, charge cooling systems either FMIC or W to A coolers) mean running low compression high boost systems with massive lag are no longer the smartest way forward.
turbo cars in the 80's oftern ran 7.0 or 8.0:1 compression

1.8t is 9.5:1 as stock.

I am running 9.75:1 in an 83mm stroked 2008cc block.
If you plan on running water meth the 10:1 is not an issue. no point running higher IMO. you will just end up with the ECU pulling timing at some stage when you hit higher boosts and temps

gmx
10-19-2010, 05:01 AM
I really would want this answered and cleared up and Clint if you coulde offer any insight that would be good.
They say with lower comp you can run more timing. Where is this timing? Up top only? All over the rev band?
Timing increases response and spool. Would it totally offset and be of equivalent response, lag as to a higher comp motor? At what point?

Since I'm obsessed with more of a usable rev range (yea ok we bought the 'wrong' car for this) i'd rather a coated piston with stock or slightly higher comp.

Keep in mind, the TT & 8L S3 have a DSMIC setup with 9.25:1 Comp.

revolution337
10-19-2010, 05:31 AM
I wouldn't recommend anything above 10:1, and even that is high. You def will need a decent water/Meth setup to keep IATs as low as possible. Timing also becomes a big concern when running high compression. You will be dancing a fine line between power and detonation. What kind of tune do you plan on running?

-:vw:-
10-19-2010, 05:43 AM
IMO you want 9:1 especially if you are concerned about off boost throttle response and or power with the 4 cylinder engines. The LOWER the compression the worse your throttle response and or power is OUT OF BOOST. The HIGHER your compression the better your throttle response and or power is OUT OF BOOST. Most N/A engines are 10:1 or 10.5:1 nowadays turbo engines are typically anywhere from 8.5:1 to 9-9.5:1 depending on how good the tune is. 10:1 might be doable with a good tune and relatively low boost, 11:1 = NO. I doubt you'd want either as I'm sure you will want to pump the boost through this engine?

Vrdady
10-19-2010, 10:55 AM
It's actually the exact opposite. The higher the CR the more power you will make off boost

second, I recently saw a honda running 14:1 with a GT40. I couldn't believe it.

somebody5788
10-19-2010, 11:10 AM
I have a friend running small twin turbo's (almost always spooling/ no lag) on a Nascar 350 small block with custom Direct Injection heads (he works for a race team.....) It's running somewhere between 10-13:1 and was making 800 hp all motor... now with the turbo's and all... well.. he hasn't really dyno'd it hahaha he suspects its over 1000 on 93 and 1300-1400 with nitrous and race gas.... Just saying that high compression ratio is totally possible with boost.

capea4
10-19-2010, 11:25 AM
I run a 10:1 1.8 with a pc 16 file K04 and love it. Car acts like a strong v6. Cams and porting help get air in and out. I have had it this way for years, and its the main reason I haven't left the K04.
*Edit* and maybe even a small V8

jrock
10-19-2010, 11:37 AM
WTF?
None of that makes sense.

Forced Induction cars run lower compression as stock to allow some margin of error and avoid pre-ignition/detonation issues when the intake charge temperatures get too high (usually down to the crap charge cooling systems as stock).
This has some draw backs:
Low compression leads to POOR power OFF BOOST (off boost means the engine is just producing the power it would produce if you ran it without the turbo, the same as you describe as "straight from the engine")
Low Compression also leads to LAG (see above).

Advances in ECU control, piston design, charge cooling systems either FMIC or W to A coolers) mean running low compression high boost systems with massive lag are no longer the smartest way forward.
turbo cars in the 80's oftern ran 7.0 or 8.0:1 compression

1.8t is 9.5:1 as stock.

I am running 9.75:1 in an 83mm stroked 2008cc block.
If you plan on running water meth the 10:1 is not an issue. no point running higher IMO. you will just end up with the ECU pulling timing at some stage when you hit higher boosts and temps

Sorry for the mixup but when I said "off" boost I meant on boost.

-:vw:-
10-19-2010, 12:06 PM
second, I recently saw a honda running 14:1 with a GT40. I couldn't believe it.

And he's probably running full stand alone. It's all about the tuning. I suppose if the O.P. could get someone to write him something for the 11:1 or 12:1 it may work but not with whats available in an off the shelf chip tune.

Kyle H
10-19-2010, 02:01 PM
if you want to run that high of compression with boost you better be running 100+octane all the time...

v dub'n
10-19-2010, 03:45 PM
i dont have a stock ecu and this is'nt for a daily driver, i'm looking for a healthier motor off boost.

black99.5a4
10-19-2010, 04:02 PM
fsi's are running 10.50:1 and boosted, they make amazing power, both off and on boost.. sure, you run less boost, but it makes more HP per PSI.. TFSI's run 9.6:1 CR.. there are both making 450-500hp at various shops around.. its in the tuning and fuel at that point.. if you wanna run pump, you wont be running super high boost but you'll make as much or more power as someone on higher psi but less compression.

USP's mk5 is making 605whp on stock pistons and running 10's, its a FSI 2.0t

thenj3
10-19-2010, 05:16 PM
hope you feel like running race gas all the time lol

terraflata
10-19-2010, 05:21 PM
To answer the original question 9:1 with 83mm bore. If the readily available 94 octane (I feel so bad for you guys in Cali) combined with water/meth doesn't work out, compression dropping gasket for the more boost!