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

[n8dogg]

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!

[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).

[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.

[n8dogg]

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).


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

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

[pir4te]

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

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

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.

[n8dogg]

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.

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.

[n8dogg]

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.

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.

[pir4te]

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.

[joecar]

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

[ProperTuningOG]

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

[pir4te]

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

Mentioned that, but range is probably between 60 and 70 ABDC I reckon. I think LS3 DCR over 9.3 (without building some mechanical octane) gonna need more than 93. Entirely possible OP is way over.

[n8dogg]

Mentioned that, but range is probably between 60 and 70 ABDC I reckon. I think LS3 DCR over 9.3 (without building some mechanical octane) gonna need more than 93. Entirely possible OP is way over.

I must be missing something on the engine spec sheet from the builders. I'll take another look, any terminology I should be looking for?

[pir4te]

I must be missing something on the engine spec sheet from the builders. I'll take another look, any terminology I should be looking for?

Advertised IVC or IVC @ 0.006"

[joecar]

The cam spec sheet typically has the specs for 0.006" and for 0.050"... post a pic of it if you can.

[n8dogg]

The cam spec sheet typically has the specs for 0.006" and for 0.050"... post a pic of it if you can.

21104

[pir4te]

Interesting cam! Not the info needed to confirm my guess, sorry can't help.

[n8dogg]

Interesting cam! Not the info needed to confirm my guess, sorry can't help.

I'll ask the previous owner if he has those specs.


Here is the tune file for those who are interested in looking at it and want to give their $.02. I expected a touch more spark, my stock block H/C/I C5 Z06 see's 28 degrees timing with 93 octane and no knock. Maybe the tune is conservative being a race car.

21105

[joecar]

Yes, that's some builder's buildsheet, it's not the cam grinder's card.

[joecar]

Looking briefly at that tune:
- stoich is set to 14.08 so he's running something like E10-15.
- PE is not sufficiently rich at EQR 1.14 (EQR 1.175 would be safer).
- it is scaled for VE/MAF/IFR since IFR maxes out at 7.999 g/s).
- HO and LO spark tables have too much timing at high load (consider that LS heads are fast burn design).
- HO/LO separation is not sufficient,
- this tune looks like an E40.


If you do this:
- increase PE EQR to be sufficiently rich,
- reduce HO to 24 degrees at high load,
- set LO suitably wrt to HO,
- run E10+ (set Stoich AFR tp match your fuel)
then I think you'll be able to run safely (power will be down from 800HP since timing will be reduced).

Can you get any logs (showing LTFT's, KR, SPARKADV, MAF, MAP, LAMBDA/EQR, ECT, DYNAIR/DYNCYLAIR/APCYL and the other usual pids)...?