Streetable Compression Ratio

[91nsx85crx]

About two years ago I purchased a 95mm Darton sleeved block from a NSX owner planning on doing a high-compression and nitrous build. I, however, was more interested in building a motor to turbocharge, so I had the high-compression JE pistons milled flat. This gave me a final compression of about 8.9:1. My question is: What would really be the optimum compression ratio on a street car where you were keeping the horsepower around 500? Would it be beneficial to the drivability to run a higher compression but at what risk to the engine from possible detonation or increased load on rods? Also, because the surface area between the 95mm cylinders and the head is so small, what kind boost do you think can be contained without blowing the head gasket? This seems to be the limitation, not the strength of the sleeves, which I'm certain are still much stronger than stock. Comments on all aspects are welcome.

 

[brandonsan]

About two years ago I purchased a 95mm Darton sleeved block from a NSX owner planning on doing a high-compression and nitrous build. I, however, was more interested in building a motor to turbocharge, so I had the high-compression JE pistons milled flat. This gave me a final compression of about 8.9:1. My question is: What would really be the optimum compression ratio on a street car where you were keeping the horsepower around 500? Would it be beneficial to the drivability to run a higher compression but at what risk to the engine from possible detonation or increased load on rods? Also, because the surface area between the 95mm cylinders and the head is so small, what kind boost do you think can be contained without blowing the head gasket? This seems to be the limitation, not the strength of the sleeves, which I'm certain are still much stronger than stock. Comments on all aspects are welcome.

I am going to run 9.3:1 with my low compression rebuild. I would run a max of 9.5:1 with a turbo system. 8.9:1 is fine but you will be sacrificing some power.

 

[JeffShoots]

Depends on who you talk to. Comptech says around 9 and 3/4. So most are going with high 9/1 that I know of.

 

[nsxtcy85]

Is it safe to run a high compression with nitrous build I was always under the impression that its just like boost as its another form of forced induction and its not a good idea for high compression and nitrous maybe Im miss informed.....

 

[brandonsan]

Is it safe to run a high compression with nitrous build I was always under the impression that its just like boost as its another form of forced induction and its not a good idea for high compression and nitrous maybe Im miss informed.....

Yes it is safe but you might have to retard your timing depending on the dosage and compression ratio. Boost and nitrous are 2 completely different animals. I would not use nitrous unless you have a FULL understanding of how it works.

 

[Elite]

8.9:1 is perfectly suitable for FI applications. 9.0:1 is fairly standard practice, so your not far off at all. The lower you go, the less likely you are to knock/detonate(of course it all depends on your tune).

 

[nsxlover]

I run 9.5 to 1 ratio

 

[WOODY]

I also have 9.5:1 at 500 whp. I believe that the HP difference with minor changes in compression ratio are quite insignificant when viewed against the final HP of an FI setup. FYI- I am also using stock head gasket and bolts and have no issues with 50,000 FI miles on the motor.

 

[Vega$ NSX]

Anything between 9:1 and 9.5:1 is good. I'm running the SOS 9.5:1 myself.

 

[Cameron]

Almost anything is possible with C16... :tongue:

 

[adrenaline_nsx]

8:9:1 is very streetable, still to high for my taste but good for street. If you want to make BIG power stick somewhere in the 8's.

 

[legendz4life]

About two years ago I purchased a 95mm Darton sleeved block from a NSX owner planning on doing a high-compression and nitrous build. I, however, was more interested in building a motor to turbocharge, so I had the high-compression JE pistons milled flat. This gave me a final compression of about 8.9:1. My question is: What would really be the optimum compression ratio on a street car where you were keeping the horsepower around 500? Would it be beneficial to the drivability to run a higher compression but at what risk to the engine from possible detonation or increased load on rods? Also, because the surface area between the 95mm cylinders and the head is so small, what kind boost do you think can be contained without blowing the head gasket? This seems to be the limitation, not the strength of the sleeves, which I'm certain are still much stronger than stock. Comments on all aspects are welcome.

If by street you mean pump gas, then lower compression will be more likely to safely make maximum power because you will be able to run higher levels of boost and full MBT ignition timing. Higher compression can improve driveability by increasing low rpm off boost responsiveness of the motor, but on pump gas can require lower boost levels, retarded from optimum ignition timing, and more careful precise tuning to avoid detonation.

That said, the difference in off boost response and peak power between 8.9:1 and 9.5:1 in a 500hp 95mm bore boosted NSX is probably negligible, and the 8.9:1 will be further from detonation.

 

[MiamieNeSeX]

As most usually run pump gas being in the 8s with FI would be the ideal range. But then again the variables are numerous, how much boost you run, how low or high your IATs are how lean you will tune, what fuel will you run etc etc etc. We run 8.5 to 1.


Armando