Bought 9.5:1 pistons for my SR....Was this a mistake?

[DJ Cool Breeze]

All i keep hearing is that 9.5:1 pistons are not good for turbo cars and that i cant boost the car a hole lot or it will blow up...is there any truth to this? I know a lot of honda guys switch to lower compression for boosting thier cars and i was wondering if i had made a mistake on choosing higher compression.

So to recap ....

1) Can i run like 20-25lbs of boost with a 9.5:1 compression?

2) Will higher compression make my car less reliable? or more likely to detonate?

3) is anyone running a higher compression set up right now? and how has your car run since you bumped up compression?

Thanks,DJ

[CMG]

Uh, I'm not a boost pro, but in all my internet travels I've never heard someone say higher compression is good for higher boost.

[redtop91]

So to recap ....

1) Can i run like 20-25lbs of boost with a 9.5:1 compression?

You can. But you'd need a much higher octane than anything the pump will provide you. The increased compression ratio will make the air fuel mixture more likely to auto ignite on the compression stroke since compressed air and/or fuel mixtures' temperature is proportional to the pressure of the system, Boyle's Law in short. Basically higher compression ratio makes the mixture hotter and easier to ignite without spark, making the engine more likely to knock. Couple that with Boyle's Law in application with the higher compression of your intake air which will make you intake temps already hotter than ideal. You'll have to combat that effect with higher octanes which resist compression ignition. Basically I'm pretty sure you'll knock on pump gas.

2) Will higher compression make my car less reliable? or more likely to detonate?

If you have a spot on tune and a higher octane you should be fine. So for a race car you are fine and dandy. For a street car, not so much.

[Seishuku]

10:1 here, though only 10PSI with a T25, but I inject a 60/40 Water/Alcohol mix into the intake too. It snubs detonation really well, I could probably run 14PSI, but that's about my fuel system's limit.I inject about 120CC/Minute of the mix at 5PSI and above.

High compression + Boost usually doesn't mix well, but with proper tuning and safe guards it will be just as reliable as a low compression turbo engine, and make more power and have better response!

I usually fill my 1.3 gallon reservoir about every 3 weeks during summer, and it usually will last me all winter.

[bgsr240]

I heard that you gain more torque and response with higher comp. pistons. All I can say is make sure that you have an awesome fuel system and tune to back it up.

[xsublimefrekx]

just run a thicker hg and get a good tune. Im at 9.0:1. I have a few friends that are at 9.5 or 10:1 and they are fine.

[CMG]

But what about trying to boost to 2 bars with that high compression? Would running something like race fuel or toluene have the same effect as water/meth injection?

[jerryd87]

if e85 is available could try that, it will use about 30-35% more fuel but it also has right around 105 octane, i saw a supra running 30psi with a 10:1 compression ratio running fine on the street using it so 9.5:1 with 20-25psi should be fine

[DJ Cool Breeze]

Sorry it took so long to reply to my own thread...been away from the computer for a while.

xsublimefrekx:

You said i could get a thicker headgasket...I have heard that a thicker head gasket will lower compression, but by how much? I was looking at getting a a cometic 1.1mm or a greddy 1.2mm headgasket.

I found this company that sells true octane booster: http://www.kemcoindustries.com...Id=61

If i were to mix in this octane booster and have an octane rating at about 97-98 would that be alow me to run say 15-20lbs of boost? or would i still need to go higher?

Thanks for everyones help here



Modified by DJ Cool Breeze at 11:28 PM 1/26/2008
Modified by DJ Cool Breeze at 11:32 PM 1/26/2008

[redtop91]

When you run a thicker HG, being that they are metal, for a good seal, you''l have to deck the head and the block. Depending on lateral runout, they might have to take off so much of your block/head that the HG might not lower compression as much as expected. I was trying to find the exact answer to the question myself and no one seems to know.

[karmakaze]

according to enthalpy with my current setup:

90mm cp pistons (9.0:1 compression ration)gt3076r .64

i can boost to 18psi on 93 octane anything above that i will have to go with race gas

he estimates that i will put down 430-440hp @ 18psi.

[DJ Cool Breeze]

Good stuff to know Karmakaze, and red top.

I have 2 questions for both of you:

Karma- So what kind of octane would you need if you were to up the boost? like 100 octane?

And can i buy a knock sensor? do they make such a device? and how much would it be ?

Redtop- If i were to get a thicker headgasket would the length of the timing chain be a problem? wouldnt it need to be longer? im just thinking since the distance would be greater due to the bigger gap between the head and block?

Thanks guys.

[redtop91]

Redtop- If i were to get a thicker headgasket would the length of the timing chain be a problem? wouldnt it need to be longer? im just thinking since the distance would be greater due to the bigger gap between the head and block?

Thanks guys.

Remember we're talking millimeters here. The thickest head gaskets are about as thick as a credit card. I think the timing chain has enough slack in it to compensate for that but I'll try to verify that and get back to you,

[karmakaze]

Good stuff to know Karmakaze, and red top.

I have 2 questions for both of you:

Karma- So what kind of octane would you need if you were to up the boost? like 100 octane?

And can i buy a knock sensor? do they make such a device? and how much would it be ?

Redtop- If i were to get a thicker headgasket would the length of the timing chain be a problem? wouldnt it need to be longer? im just thinking since the distance would be greater due to the bigger gap between the head and block?

Thanks guys.

I think he said 100 octane to boost to 20-22psi and 110 to boost to 24 IIRC. i need to verify that in my emails before it is gospel.