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Old 08-09-2014, 08:04 PM   #401
Rae876
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Default Compression

Quote:
Originally Posted by Crystal_Imprezav View Post
So I just went from an effective 8.5:1 .030" quench Wiseco piston, cosworth cam setup to a 9.2:1 .038" quench high compression Manley pistons and Kelford 272/268 setup...

All things being equal, HTA3586 + FIC 1680 (at 53 base pressure); I am making 80-100whp less than before... This does coincide with what I have seen previously with high compression setups so I am not really shocked... I was hoping with E85, it would be different from C16 which is what I have dealt with in the past HC setups...

The car will take almost as much timing as before. It likes a little less down low around peak TQ but will take as much as before up top and not knock. However, it makes more power with 1-2* less than the previous setup which means it is at MBT at 1-2* less timing but it is still 80-100whp underpowered than my previous setup...

That being said, I really have yet to see someone prove that high compression in a Suby will make more power than the standard 8.2-8.5:1 compression we typically run even on E85 which should theoretically really optimize a higher compression ratio. Just a bunch of unproven hearsay of the typical "oh it spools faster" "oh it has better off boost" yada yada.

Let the discussion begin... No newb or unbacked data/opinions allowed
Question with the higher compression engine build, u made less power???
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Old 09-02-2014, 01:05 AM   #402
JMlegacy
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I think u skipped over the whole thread :P

He couldn't make the same power as the lower compression setup.

Question for Crystal_imprezav, do you think the ej20 bottom end would be better suited for HC setup?
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Old 09-02-2014, 08:07 AM   #403
fastblueufo
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Originally Posted by JMlegacy View Post
I think u skipped over the whole thread :P

He couldn't make the same power as the lower compression setup.

Question for Crystal_imprezav, do you think the ej20 bottom end would be better suited for HC setup?
No, because the head combustion chamber is basically the same design except smaller. And your dealing with port injection.
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Old 09-02-2014, 08:48 AM   #404
2Fast4U1DAY
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People seem to carry over the high compression theories from NA cars, which DO NOT APPLY TO FORCED INDUCTION setups... we dont rely on compression ratio increase for power.

If you are trying to make more power, upgrade the turbo/injectors and tune on stock or lower compression. It will give results you are looking for. Cranking up the static CR is going the wrong direction as shown in the OP of this thread.
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Old 09-02-2014, 10:59 AM   #405
fastblueufo
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Originally Posted by 2Fast4U1DAY View Post
People seem to carry over the high compression theories from NA cars, which DO NOT APPLY TO FORCED INDUCTION setups... we dont rely on compression ratio increase for power.

If you are trying to make more power, upgrade the turbo/injectors and tune on stock or lower compression. It will give results you are looking for. Cranking up the static CR is going the wrong direction as shown in the OP of this thread.
You are partially right. You are actually wanting to raise the cr to make more power. With turbo or supercharging your raising the cr with the forced induction. Only difference is with forced induction your dealing with more oxygen in the cylinder than if raising cr with an engine using atmospheric pressure Vs forced induction.
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Old 09-02-2014, 01:20 PM   #406
2Fast4U1DAY
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My point was that we dont rely on a bump in STATIC compression to make our power, we add boost and timing to make more cyl pressure, versus milling heads to make a smaller cc combustion chamber , or using a piston with a taller compression height (or in our instance less dish)

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Old 11-28-2015, 07:56 AM   #407
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Bumping this from nowhere.

What did the actual results end up being? got a before & after dyno?
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Old 01-04-2017, 12:27 AM   #408
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Originally Posted by vicious_fishes View Post
Bumping this from nowhere.

What did the actual results end up being? got a before & after dyno?
Just bumping to say the results are invalid as he changed cams as well. If he did the same test with the same cams, with just a change in CR then we could say something.

Last edited by JMlegacy; 01-04-2017 at 01:24 AM.
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Old 08-13-2018, 08:50 AM   #409
iamturbo
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Quote:
Originally Posted by JMlegacy View Post
Just bumping to say the results are invalid as he changed cams as well. If he did the same test with the same cams, with just a change in CR then we could say something.
I guess you didnít read the whole thread, he switched pistons and retuned car from high comp back to low comp and made more power! So his results are very valid.

Crystal, hows the car running? Iím curious how big of a difference did you see with Kelford cams compared to previous? Iím about to do anouther build here In next month or so and considering changing from BC280 about same lift as coast to Kelford 199d or GSC s3 because both have about 1mm more lift.

I too had very similar issues trying to run high comp about 8 years ago, tried running 9.5:1 with stock cams same heads used on previous shortblock and couldnít make the same power uptop and had one hell of a time tuning it. Did make crazy spool and low transient boost response with a 30r sized turbo but top end power was down about 50whp at same boost level as before. I was chasing fastest response and gave it a shot but never was satisfied because top end felt so flat at 495whp compared to 540-550. Needless to say that motor ate bearings in about 10k miles because the added cylinder pressure is my belief and running aggressive timing. I tried it and have since gone back to basics and run really low comps and high boost, which has always worked for me on just about everything from Suby, Honda, Evo/4g63 to sbc and even a 280z build I did about 2 yrs ago on the non turbo motor. Lower compression give you more space to fill with air, and lower effective cylinder pressure at a given power/boost level which will help motor to last longer, put less stress on bearings, and block.

So for all of you that still want to try and do high comp, it can work but is really not worth it, many have tried and the risks and lifespan of the motors goes down drastically for a slight bump in off boost and transient response.
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Old 08-14-2018, 09:37 PM   #410
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I've heard my tuner complain about two things - crappy gas from Canada, and motors with high CR (I think he said 9+).
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Old 08-20-2018, 03:07 PM   #411
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I've heard my tuner complain about two things - crappy gas from Canada, and motors with high CR (I think he said 9+).
Who's your tuner?
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