My Evo8 made 496hp @ 27 psi on straight Shell 93 octane with air/fuel ratio's in the 11.2-11.0 range. So I decided to dump in some VP C-16 Race Fuel and see what my car could crank out. I first did a run with the same exact settings, no changes what so ever except for the fuel. To my surprise my a/f dropped from the 11.2-11.0 range to 10.6-10.5 with absolutely no other changes made.

Have any of you tuners experienced the same thing? I had run my car previously @ the drag strip and swapped fuel right there and had noticed no changes in air/fuel ratios.

I raised the boost to 31-32 psi and got a 530hp run, but I could swear that the car runs better on pump gas.


Here's my mods:
AEM/EMS (self-tuned)
1000cc injectors
Custom Dual Pump Setup
Buschur Stage 3 Head
Buschur 272's
GT35R(non HTA) with Hafe manifold/ o2 housing
Buschur Spec Rods and Pistons
Buschur Race Intercooler
Stock Intake Manifold, Throttle Body, and Ignition.

C-16 has a different burn rate than pump gas. It doesn't surprise me one bit that with no changes the tune went richer with C-16.

It needs a totally different AFR and ignition timing strategy.

What would you recommend? What a/f ratio should I target for, and how much more timing?

If it's a drag car I would look at 12 AFR + with C-16

Timing depends on boost and the car. 6*+ more up top over pump gas isn't abnormal (depend on boost)

It's not abnormal to see at least a 60whp gain on C-16 on a GT35 with proper tuning and more boost.

In the end it all depends on what the car likes. I do know you should lean it out a ton though. It is no surprise the car ran like crap with just adding leaded gas with no tune changes.

What a/f ratios do others run while on VP C16? All opinions welcomed!!

Go for 12.0-12.2 afr don't worry. Then change the timing 1 degree at a time and look if something change in whp, I know it will.

Yes, seeing richer AFR's on race fuel over pump gas is completely normal.

The car should make another 50+ whp going from pump gas to race gas.

I have no AFR that I try to target on pump gas or race gas. Each car is different. I rarely ever tune in the 12:1's though, I run cars on the rich side.

Most pump gas is oxygenated and has a lower specific gravity then C16. The two combined will mean that for a given injector pulsewidth, you are getting less fuel mass into the engine. As A/F ratios are mass based, and not volume based, if your specific gravity is lower, you will lean out the mixture.

Often times, the fastest stable burn means the best power because it requires less timing advance to get the peak cylinder pressure at ~15 degrees ATDC. If you are still getting a stable burn on 93 octane at 27 PSI, upping the octane with a slower burning fuel means you are unlikely to gain any power, and may even lose power. C16 seems to be a slower burning fuel and needs more ignition advance to make the same power as other fuels if you aren't at the level that requires the higher stability of C16.

I've used a couple other fuels then C16 and even at the 35+ PSI range found some 112-114 octane non-oxygenated fuels to make as much or more power then C16. Add oxygenation into all of this and it gets real interesting.

In fact I did lose power. My Car went from 496hp on straight 93 octane to 478hp just by adding 1.5 gallons of VP C16.

That is without tuning for the fuel though.

You would likely get the power back with a retune for the C16. C16 is pretty potent, as it has a high energy content relative to other unleaded fuels. The higher energy content helps offset the loses associated with the requirement for more timing advance.

Just like said before by some very qualified tuners......we tune our cars on C16 right about 12.0 as well.

I run ERC 118 and we tune that as well to 12.0

On my personal car going from 91oct (400hp) to the 118oct we picked up a ton of power to 500+

Well just tune the AEM differently once you pass a certain boost level. Change the timing map to be more aggressive over X psi (only prob is make sure you dont go over x psi on pump and use the timing retard for knock). Although it will get richer it should drive better at higher boost if you tune the timing (at least smoother).

Or put a switch and use the NOS tables to add timing and modify the fuel once its turned on for race gas.

So you can have a tune for both in one map (kinda sorta) or have two maps.

Just getting back from the drag strip, not good news. Ran a 11.53 @ 124 mph with a/f ratio in the 10.3-10.1 range. OK, so let take some fuel off, ran a 11.63 @ 118 with big misfires getting towards the end of the track. Datalogs show a/f ratio skyrocket to 18's to go along with the misses. Driving home, both fuel pumps die out ran 12V to them you could here a click but they wouldn't pump.

It's late and I'm tired so more info tomorrow.

Whoa......sorry to hear bout that.

Simple ? but did you have enough fuel in the car when you made the runs?

I would have done an easy pull in 1 gear after leaning it out before going all out in each gear

At what point did the afr's skyrocket and how long were you on it?

My secondary pump was completely dead. The primary would run for a few minutes, heat up and shut down.

I had both pumps tied together with no type of material to separate them, apparently the magnetic field produced, and the heat generated by them was the culprit.