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Not sure where else to put this, so "General" seems like a good spot.
Basically, trying to figure out what I should be running for fuel in my FC race car.
I purchased this car over the winter after it had been sitting in storage for several years.
S4 non-turbo 13B with almost no miles since "race" rebuild
converted from FI to Weber 45DCOE Carb w/ Racing Beat manifold, Racing Beat Header, HKS exhaust.
Heavily ported. On engine dyno (according to reports as I bought the car after the build) car made 270hp at 7600rpm. Idles ok, but it's pretty "lumpy" so my best guess is they did a Bridge Port.
Apparently they used new Turbo II irons when the built the engine, but the car is not Turbo'd.
OMP is disabled (since a leaky OMP is actually what caused the car to blow up the first time.)
Now, most stuff I'm reading says this should run fine on pump gas with pre-mix.
However, notes from the engine builder (very respected racer and mechanic locally for the last 20+ years. I know he's good, but he's not a "rotary" guy. He primarily races Nissans) indicate that the car should be run on VP C-12 race gas or similar.
He indicated that this was more for the lead to lubricate the seals than it was for the Octane. i.e. his notes say it will run on pump gas "ok" with enough pre-mix.
This seems a little bit excessive to me, which is why I'm here.
Any thoughts on the fuel requirements for this thing?
I'm torn between thinking "well, this old-time racer and engine builder must know" and thinking "well, he IS an old-time engine builder and racer and probably thinks EVERYTING should be running C-12 race gas, including his lawn mower."
If he was a rotary specialist I wouldn't even question, but he's not, so here I am.
My concerns are primarily, in order:
A) I want to run whatever is best for my engines life
B) I don't want to burn money I don't have to.
C) I don't want to hurt the performance running 15 pts. higher octane than I need and the engine can barely burn the stuff.
Also, any mid-ground that people have used?
i.e. pump gas with something like Red Line Lead Substitute added?
Any ideas would be great. I've been doing a ton of reading, and everything I read just confuses me more.
A bit of the backstory, for those who care:
It's basically an overbuilt IT/underbuilt GT class car, but should be very competitive in the local regional club-racing I'll be doing with it.
Seeing as how it is local club-racing, I don't want to burn money I don't have to.
The engine was blown up, rebuilt, dynoed, put in the car, car ran 1 lap, blew the clutch, had the clutch replaced, went into storage for a few years and hasn't raced since.
The challenge is, most of the information I have is from the previous owner of the car, who isn't mechanically inclined, but used to own a Mazda dealership, and I know he spared no expense on the car. So, I've got his memories, plus a few notes from the builder and local people who "know the car."
Thanks in advance for any input. I really am having a hard time deciding what to do. The group order for C-12 is going in amongst some people from my race series tomorrow, so I'm trying to figure out if I should get in or not.
86 RX-7 Race car: Full Bridge S5 TII Housings w/ RX8 internals, Weber 51IDA and lots more by RPM Motorsports
04 RX-8 GT (mine)/ 03 Mazdaspeed Protege (Hers)
2 * 88 RX7 Convertibles (1 Turbo) because I need even more projects
12 Impreza WRX daily driver and dog hauler
That's what I was thinking as well.
He was looking at the lead for the seals. It's tuned for more better then pump regular, but doesn't need 108 either.
I actually emailed VP Racing (and got a personal answer back in about a half hour, very impressive) talking aout the car and build etc.
They recommended Motorsport 105L or Motorsport 98L. (The 98L is the spec fuel for the STAR Mazda series) so that looks like the way to go.
High test pump gas ( I use Sunoco 93 octane ) With 1 ounce per gallon of two cycle oil ( Redline or it's equivalent ). This is in a street port SCCA legal EP motor with over 230 hp on the dyno. This is the reccomendation from my engine builder, Jesse @ Prather Racing, who is a rotary perfomance specialist.
Jesse knows his **** but I've seen the results rx7doctor has seen with lower octane numbers. We got the best power with 89 octane and even went looking for 87! It could be the different blends used in different parts of the country at different times of the year. Maybe the 93 is more consistant nationwide?? Who knows.