416ci (LS3) 12.4:1 CR, race gas to pump gas?

Hello,

I'm interested in purchasing a Corvette that has been heavily modified for road course/track use. The engine is LS3 based, 416ci with a 12.4:1 compression ratio and runs strictly off race gas, it puts out 800 hp. My question is if it would be possible to modify the tune to run off pump 91/93 gas without having to lower the compression ratio or change engine components? It is a deal breaker for me as race gas is $11 per gallon, and at $200 per tank, that makes the car too impractical for me. But if I can switch between tunes, for street (91/93 octane) and then track (98/100 octane), I could make that work. What are your thoughts and opinions? Thanks in advance!

Do you have an accurate number for the Dynamic Compression? Else what's the Cam's Intake Valve Closing at 0.006"?
The simple answer is to run a fuel composition sensor and fraction of ethanol (flex fuel) not lower than 30%. So e30-e100.
That's what I do with my daily 13.5:1 that likely has an earlier IVC as well (higher dynamic).

Which race gas does he run (what brand, what octane rating)...?

As pir4te said, what is the DCR and what are the cam specs (dur, lsa, adv)...?

CR in the low 12's is marginal, you may be able to run on 93 octane... probably requires cooling system to be in good condition, and CAI must be able to pull in cold air always.


Does he have tune and log files you can look at...?


The HO spark table could be edited to run a little less timing at higher load.

Quote:

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Originally Posted by pir4te

Do you have an accurate number for the Dynamic Compression? Else what's the Cam's Intake Valve Closing at 0.006"?
The simple answer is to run a fuel composition sensor and fraction of ethanol (flex fuel) not lower than 30%. So e30-e100.
That's what I do with my daily 13.5:1 that likely has an earlier IVC as well (higher dynamic).

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Dynamic Compression calculates as 10.56:1 per the specs I have.

We have e85 here, would I be better off running that?

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Originally Posted by n8dogg

Dynamic Compression calculates as 10.56:1 per the specs I have.

We have e85 here, would I be better off running that?

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Seems high, what is the IVC @ 0.006"
Yes no problem with 93 either just keep ethanol fraction above 30% (e30). e85 is 1/10th price of the other cocktail so yeah.

Quote:

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Originally Posted by pir4te

Seems high, what is the IVC @ 0.006"
Yes no problem with 93 either just keep ethanol fraction above 30% (e30). e85 is 1/10th price of the other cocktail so yeah.

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Here are the specs that I have on the cam to figure our the IVC, Duration @ .050= I 252 E 262, Lobe Separation= 108.

Duration (252)/2= 126 + lobe separation (108)= 234 - ground in advance (?) - 180= 54

Not sure what the ground in advance is.

Quote:

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Originally Posted by joecar

Which race gas does he run (what brand, what octane rating)...?

As pir4te said, what is the DCR and what are the cam specs (dur, lsa, adv)...?

CR in the low 12's is marginal, you may be able to run on 93 octane... probably requires cooling system to be in good condition, and CAI must be able to pull in cold air always.


Does he have tune and log files you can look at...?


The HO spark table could be edited to run a little less timing at higher load.

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Thanks Joe, I'll pull the tune out of it late this week and take a look. He runs VP Racing 100 octane. He said it can be run with 98 octane. He suggested lowering the compression ratio to run 93 octane.

Cam specs are 252 duration, 108 lsa, I don't know what degree advance the cam has, I'm trying to find it in the paperwork.

74.4 cc pour volume so pistons are 5.5cc dished. Nominal CR is 12.43.
If ICL = 108 then DCR = 9.5 to 9.9
If ICL = 103 then DCR = 9.9 to 10.3
Need IVC @ 0.006" to be accurate, but at a guess DCR is 9.5 to 10.3 (safe combustion of 93 really depends on squish / quench of piston), so possibly OK but yeah tune needs safety margin / limiting for daily on 93.
E30-E85 is all good.

Running E30-E85 as Pir4te said is inherently good in that alcohol content raises the effective octane and helps to keep combustion chambers cool.

LOL, thats cam specs at 50..... You need to use specs from when the valves actually open.