Which would be better suited for road racing? 8:5 or 9:1

Thanks in advance.

I would think 9:1 for quicker spool and more torque, but I'll let another more experienced answer.

Also depends on your class.

the more the better =)

Originally posted by candela
the more the better =)

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Seriously!

The different between 8:5:1 and 9:1 is negligible. If I were building a motor for open track or autox I would go 10:1. Just make sure you have the proper tuning tools and run the proper fuel to make that work.

PS Havent you asked this a few times before?

Originally posted by rdrkt
The different between 8:5:1 and 9:1 is negligible.

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Agreed

Originally posted by rdrkt
If I were building a motor for open track or autox I would go 10:1.

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Well, open track you will be at WOT a lot and seeing some sustained time at high rpm and high egt's. To keep from killing a motor on open track I would limit myself to 9:1...autocross....gimmme as high compression as feasable (10:1).

Remember though...as your C/R goes up your tuning window closes...so it's harder to tune a car without blowing it up.

Originally posted by dyezak
Well, open track you will be at WOT a lot and seeing some sustained time at high rpm and high egt's. To keep from killing a motor on open track I would limit myself to 9:1.

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I honestly don’t know. If you have an turbo running at very efficient boost levels. You have an intercooler keeping IAT as close to ambient as humanly possible. A good radiator and oil cooler. A proper race gas like C16 would the EGT really climb out of control?

Originally posted by dyezak
Remember though...as your C/R goes up your tuning window closes.

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Tuning is tuning. If you have no idea what you are doing you should let some else do it. The turbo Honda guys have been doing some absolutely incredible things on 10:1 pistons. I know that Marco sells pistons at that CR but I would like to see them make it on to more cars.

At least 9:1 mavbe as high as 10:1, but that depends on boost, turbo, cooling, and fuel.

More compression is generaly going to help the turbo spool faster, and it will definently provide more low end grunt before the boost comes up.

um I think that is exactly what rdrkt just said... poeple sure do like to immitate???

Thanks for the help everyone. I believe I did ask some questions a few times before. But whenever I search for them, I can never find them. Are old posts deleted from time to time?

Originally posted by rdrkt

I honestly don’t know. If you have an turbo running at very efficient boost levels. You have an intercooler keeping IAT as close to ambient as humanly possible. A good radiator and oil cooler. A proper race gas like C16 would the EGT really climb out of control?

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A datapoint for you. This past September, I was at VIR in Virginia, running the full course, 3.27 mile, 17+ turn course. At the time, I had a ported 14B, 2.5DP, 3"TP, 3" thermal, Supra pump, Aeromotive set at 43 psi, stock SMIC with foglight removed, SAFC and 450's running 100 octane unleaded.

I started the weekend at 16 psi and it felt great! Had enough power to pull just a little on those stock F-bodies. Temps were in the high 50's, low 60's at about 900 feet elevation. As the weekend progressed, and I got faster, I started hitting 900C EGT's before the end of the straights. My only adjustments on my SAFC to that point were to fix the base FP increase.

I turned my boost down to 13 psi. Still peaking before hitting the end. Started adding some fuel from about 4K on up to 7K. Ended up putting about 7% more in. I was already running my injectors in the mid-90's for duty cycle, so I didn't use the SAFC to add any more fuel.

I "fixed" the problem by shifting to 5th gear instead of 4th. I gave up some speed at the end of the straight, but the EGT's stayed below 900 that way (still hitting about 125 mph at the end). RRE states on their page that road race activities where you are doing more than 1/4 mile at a time will required more fuel than drag racing type events.

Just my experience.

Oh, to the original poster. I think 9.0:1 would be pretty safe. The new EVO is what, 8.7:1? 8.8:1? I can't remember. If it also see street duty, I think 10:1 with boost would start to get a little touchy on pump gas. I don't know. Try it and let us know!

someone should contact like JE and ask them to make 9.2:1 pistons, i would buy em in a heartbeat

Yes several people are saying the same thing. In this case I agree with rdrkt and the others. I was simply adding my .02.

Originally posted by greathuskie
someone should contact like JE and ask them to make 9.2:1 pistons, i would buy em in a heartbeat

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You can call JE and ask them to make any custom piston you want. It isnt a very large price difference to have them make a "custom" piston.

Originally posted by 2-0turbo
Just my experience.

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That is pretty intresting thank you. I wonder if your EGT issues were due to the IC heatsoaking or your coolant and oil temperatures starting to rise hmm. I am trying to get a group of my friends to do a HPDE in June at Summit Point so I will be testing some of my theories then.

Originally posted by rdrkt

That is pretty intresting thank you. I wonder if your EGT issues were due to the IC heatsoaking or your coolant and oil temperatures starting to rise hmm. I am trying to get a group of my friends to do a HPDE in June at Summit Point so I will be testing some of my theories then.

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I don't know either. I was only running 13 psi boost, so my intake temps should not have been too high. With the foglight removed, I should be getting pretty good ram-air cooling at over 100 MPH. Coolant was normal, I don't know what my oil temp was. By the time I do my next IC (in the works now), I will have my intake tract instrumented with TC's so I will know all this great stuff and be able to calculate IC efficiencies.