What are the pros and cons of having 9:0:1 compared to 8:5:1?

[Hobbes =^.^=]

Just like to know what the pros and cons of having a 9:0:1 compression. Thanks.

 

[BoostinAWD]

Pros: More low end grunt, quicker turbo spoolup.
Cons: Detonation on pump gas unless you like running low psi.

 

[Beemer]

You could squeeze a bit more boost out of 9:1 using a water/alcohol mix injection system, but overall, if ya want to have fun on the street and not be mortgaging your house for a race gas delivery system under your garage floor, 9:1 is a bit much. However, with water wetter, moderate boost, and a h20 injection system, you might be able to get away with 10-12 psi on a cold day on 92 octane amoco ultimate. Might get a bit more if you can find 94-5 octane at the pump somewhere.

 

[Tevenor]

I run 16psi on 93 daily on my 9:1's. Don't blame the higher compression for bad tuning.

 

[BryanK]

Holy smokes Batman, 9:1 compression hurts boost #'s THAT badly? I always thought that if you wanted more insane boost than you should use like 8:1 compression... but thats if you're pushing over 25 psi. I always thought that with the right tuning on a S-AFC, 650 or 750 injectors, walboro fuel pump, and all the other supporting mods that you can run around 20 psi on a 9:1 compression car without seeing hardly any knock. Make no mistake, I know none of this difinitively, all just info I've read on here. This scares me though, because I'm going with a 6 bolt 1G rod/95 piston engine that I'm told will run 9:1 compression. Anyone else, any input?
Thanks,
Bryan

 

[NDgsx]

Originally posted by BryanK
This scares me though, because I'm going with a 6 bolt 1G rod/95 piston engine that I'm told will run 9:1 compression. Anyone else, any input?
Thanks,
Bryan

Huh? 2G pistons are 8.5:1.
Boost is a relative term. You can run as much boost with 9:1 as with 8.5:1, but not with as much timing advance. It's all in the tuning.

 

[motofool]

tuning is what u loose when going higher compression meaning your window for tuning gets small less room for error ina higher compression motor my build is gonna be around 10:1 and with good tuning eventually will hit around 20psi on the 2.4 litre goal is 400-450hp

highercompression turbo cars are not for beginer tuners or people who dont have good knowledge of how motors work...

the lower compression easyier to tune the more boost u have to run to make the same power asa higher compression motor with less boost

Bill

 

[motofool]

oh and for 9:1 u shouldn't have to worry about race gas if u keep your intown boost down if u run max boost all the time yea u'll have knock and detonation without proper octane ....

my car with 10:1 will only be boosting the bar minimum and ill turn it up when need be and i go to the track...

 

[rdrkt]

Originally posted by Tevenor
I run 16psi on 93 daily on my 9:1's. Don't blame the higher compression for bad tuning.

Word

The difference between 8:5:1 and 9:1 is minimal. But you cant definitely notice a big difference in the spool of the turbo going from 7:8:1 to almost 9:1. I noticed it in my 1g rod 2g piston motor and I cant wait to see how it spools my buddy's big 16g. Something tells me that will spool it up likes it’s a stock turbo.

However keep in mind when buying new pistons and building your motor that you have to account for decking the block and milling the head which will also slightly raise compression.

 

[Slowboy]

I run 9:1 compression and 25 psi with a 60 mm compressor wheel in a t3/t4 on 94 pump gas with no problems. No, it is not easy and there is a lot of tuning to do, but most of it is in the timing like a previous poster commented on.

I would do 9:1 on any street car!

Part of me wants to go low compression and run big boost though....

Mike Huml
www.slowboyracing.com

 

[HighPsi91]

A freind of mine had built a small 16g car with real high compression. It was around 9.5:1. That thing had some insane response. It was a monster on the street at even 16psi. 16psi was about the limit on pump gas however. After that it would detonate pretty easy. Back then there were no dataloggers and such so tuning for knock, etc wasnt really even considered. It was all done old school. This measly small 16g car made most 20G and larger cars feel stupid.... well at least untill he broke a piston

 

[AndyFL]

If my wallet ever gives the oppurtunity I am gonna rebuild with 7.5:1 venoila's from extreme. Just because I have seen what crazy power can be made on low compression without sacrifice.

 

[Cody Morris]

What is ExtremeMotorSports running for internals? Is it those exact pistons they sell that are running insane amounts of HP and low 8's or 9's.

 

[Thalomos]

So, 2G pistons are stronger right? So it's definantly worth going with the 2G pistons on a rebuild... ?

Or should i blow the money on 9.1:1? Spool-up sounds nice, and wouldn't the lower boost be made up for the higher compression?

Also how much horsepower can the 2G pistons hold?

 

[Pennywise]

asuming you have 9:1 cp with some finely tuned haltech you should be fine right?

 

[Pennywise]

if you ran 25 psi on pump gas with 9:1........ 30psi on pump gas with 8.5:1?

 

[rdrkt]

Originally posted by Pennywise
asuming you have 9:1 cp with some finely tuned haltech you should be fine right?

You can run 9:1 fine with just a safc. With the inclusion of a Haltech I have seen people run 10:1 safely on pump gas. Its all in the tuning.

 

[Pennywise]

10:1 !!!!!!!!!!!. on pump gas !!!!!!! you can push what, 15 psi max right? or could you push 25 psi on pump gas?

 

[rdrkt]

Originally posted by Pennywise
10:1 !!!!!!!!!!!. on pump gas !!!!!!! you can push what, 15 psi max right? or could you push 25 psi on pump gas?

No it would be low boost but spool would be insane. I know Magnus has a few customer cars running around with that setup. It seems to work out pretty well. You should see what Altered Atmosphere does with high CR motors. You can look here for the results. That is a brutally fast gorgeous Civic.

 

[G-Ell]

Originally posted by Tevenor
I run 16psi on 93 daily on my 9:1's. Don't blame the higher compression for bad tuning.

Originally posted by NDgsx
You can run as much boost with 9:1 as with 8.5:1, but not with as much timing advance. It's all in the tuning.

Originally posted by rdrkt
Its all in the tuning.

I hate to be a dick, but peeps, there is the answer to your questions on "Will my car be fine with this set-up?". Everything else is just guesses. No one can actually tell you how much boost you can run, or how your car will run with any list of mods.

 

[Pennywise]

So running a higher cp would enable you to run a bigger turbo due to the quiker spool up? I would go no higher than 9:1 but I wouldn't want to any lower. the 9:1 could really take 25 psi on pump gas? I wouldn't run that all the time just at the track, but would a higher cp be better for a street car so you would have little lag? does a higher cp give you more power at higher boost levels or low cp?

 

[rdrkt]

Originally posted by Pennywise
So running a higher cp would enable you to run a bigger turbo due to the quiker spool up? I would go no higher than 9:1 but I wouldn't want to any lower. the 9:1 could really take 25 psi on pump gas? I wouldn't run that all the time just at the track, but would a higher cp be better for a street car so you would have little lag? does a higher cp give you more power at higher boost levels or low cp?

Originally posted by Pennywise
So running a higher cp would enable you to run a bigger turbo due to the quiker spool up? I would go no higher than 9:1 but I wouldn't want to any lower. the 9:1 could really take 25 psi on pump gas? I wouldn't run that all the time just at the track, but would a higher cp be better for a street car so you would have little lag? does a higher cp give you more power at higher boost levels or low cp?

Maybe I am confusing the point a bit so let me give you an oversimplified answer. Higher Compression Ratio would mean LESS boost especially on pump gas.

Higher compression SHOULD help your turbo faster. I noticed a pronounced difference between stock CR and the CR on my 91 rod 95 piston motor.

The amount of boost that you are going to be able to run is all dependent on your turbos efficiency levels. You wont be able to run a T25 to 20 lbs on pump gas but I can get away with running 20 lbs on my 60-1.

Regardless of turbo size 25 lbs is A LOT of boost on pump gas. There are a few super tuners that might be able to get away with that but most mortals wont be able to do that even with a standalone.

 

[Pennywise]

IYO what cp would you recomend for a street driven car? I personaly think that 7.8:1 is to low I was either thinking 8.5:1 or 9:1. this will be partnered witha built engine and a finely tuned SAFC. so it will be okay for high boost seting. I understood all that stuff, I know you can run higher boost settings on lower cp b/c it wont det. lets say you have 2 cars both runing the same turbo, both runing 20 psi but one has 7.8:1 and the other has 9.0:1 which one has more power?

 

[jw]

The 9.0:1 will make more power at the same psi IF you tune properly so it dont knock and timing retard. You can run any boost you want on pump gas, the question is if you can tune with good timing curve and yet not detonate? As someone already stated, lower compression allow more room for error and running more boost on pump gas. With higher compression and bad tuning, it means you will be blowing more HG.

 

[Pennywise]

I live in dallas who is a bad a** tuner? I need help I know no dsm shops around dallas, good ones at least. I can pull this of with a SAFC? or would haltech be better?