lamboworld

My car is almost done from getting a HCI build. The heads were milled and the compression bumped to 12:1. My car will be tuned for 93 and I am wondering if there is any benefit in bumping the Octane to 105 when I run a 1/2 mile event in 2 weeks. If so, I thought about running the Torco Accelerator.

edmundu

If you are tuned for 93, using slower burning fuel will likely decrease power.

Whis9

I have a similar set up to you I was told to run 100 on a road course. 93 is pushing the limit for our compression ratio. On the street you will be fine. It's from one of the top builders and road course drivers in the country

Nowanker

Octane requirement depends on CR+timing... if it's close to the detonation edge, I'd rather run the "slow" fuel than risk damage.
Seen it several times in the BMW world. Aftermarket M3 tuning is mapped well for 92 fuel, but pushing things on Calif 91. Guys take 'em to the track, and I say "blend in a little 100 unleaded for safety", to which they reply "naaah, it runs great".
And then they pay me to replace their blown headgsket.

rio95

I researched octane boosters this weekend and it seems torco is one of the best options. If you're getting kr I think this would be a good route to take if you don't want to lower timing.

db2xpert

Running 12+ compression, tuned for 93.
Can only get 91 crap here in AZ, so mix 2gals of 100 with 3 of 91.
Gives me 94.6. On hot days I go a tick less than 3 gals of 91, and run about 85.5 octane.

As others said, going too high and you lose HP.

lamboworld

Probably closer to 11.8. My head builder, Advanved Induction, figured the compression for 93. I think that he cut them to 64cc.

Nowanker

Go too high, lose HP
Go too low, lose the motor.
Hmmm. decisions, decisions.

MTPZ06

Knock and detonation are no joke on these motors if you're pushing it hard. At minimum, dump a bottle of Torco octane booster in the tank for good measure.

BLW BY

If you're looking for a top speed # you'll have to run more octane.
If not, you won't realize the full potential.

I milled my heads only .015" and saw more KR on 91, that's why I run meth injection. They say it's equivalent to running way higher than 100+ octane.
If those octane haters are right, my car wouldn't get out of it's own way because I'm also shooting water mixed with the meth.

Sure got rid of KR at peak cylinder pressures between 4800-5400rpms while cranking 24° advance.
See how many dyno pulls are done with that much timing and no KR.

Pulling timing, pulls torque = less horsepower. It's simple math.

lamboworld

Yes I am looking for top speed. My heads were milled at
.030

AzDave47

If you are tuned for 93, mix in enough high octane gas to get your total octane over 93, somewhere in the 94 range is enough. Post #8 gives you the tradeoff.

BLW BY

Tuned to run 93, who buys into that.LOL
The ECM is trying to run what's programed into the high octane table and at the same time be able to pull enough timing to run safely.
For a better part of the time it's running less than what's programed, because the ECM pulls timing from multiple tables. That's why the car feels faster on a cool night. Is that where the 'CAR'S TUNED' to run on 93 or is it tune to run on 93 on the track at 105° ambient temperatures.

Pre detonation is firing the charge before the piston can make efficient use of it and it's like a hammer pounding on your piston. This equates to less power and destructive forces on your engine. You want the force on the piston to be like a hand pushing down and a longer amount of time than a hammer hit.

Or buy into that 'tune to run on 93'.
Just make sure your octane booster is like a flame retardant, like the stuff they spray on christmass to keep them from burning.

Methanol injection was developed in WW2 to help the planes take off on short runways built in Europe. Do you think they were tuned for one octane?

olddragger

water meth is underrated imho.
Also don't forget that the heat you may generate could affect the fuel requirements.
I much rather run a little more octane than needed to compensate for any surprises.
Water meth allows a good bit of flexability. You do have to tune for it--if you just throw it on you will lose 10-20 rwhp depending.
Sure keeps an engine clean

XLR8-R

Mine was tuned for ~93 and last time it was dynoed(with 93) there was knock retard. Dyno operator drained some fuel out, mixed some Lucas Octane booster with it, put fuel back in, KR was gone and picked up 15 wheel horsepower...
Also when you are running a half mile event you are redlining in 4 gears with a real load, not a Dynojet wheel for one gear...(more heat, more load, more chance to detonate)

RichieRichZ06

Also keep in mind that when mixing fuel to add to the tank of a C6, the right hand side tank will be virtually used up before the car switches to the left hand tank. If you have right at 1/2 tank and add 3 gallons of race fuel, it all just went into the right hand side tank. When you use that 3 gallons, the car will now be burning your unmixed fuel from the left tank and it won't have the race fuel mix. I't best to run the car empty, mix fuel in race jugs and then dump the premixed fuel into the car.

Just a little food for thought.

olddragger

now that is a very good point.
I don't now much about our dual tanks---does the pump run a siphon to keep the tanks balanced?

RichieRichZ06

There is a jet pump that transfers a little fuel, but if you start with a totally full fuel load, it will burn through about 90% of the right tank before emptying the left tank.

This is also important to keep in mind when corner balancing C5, C6 and C7 cars because a lot of people think running a 1/2 tank is the best. That's not necessarily true because when the car is at half tank, nearly all the fuel load is in the left side which is also where all the driver's weight is at. It's better to run the car full of fuel to balance the load evenly.

olddragger

Very good to know--thanks for that .

veloz

soo then if i let my tank go down to 1/8 tank 93 octn - which is about 2 gallons i think - and then add 2 gallons of 100 octn race fuel = to 1/4 of tank = 50% mix....wouldnt it be using it from the left side tank all mixed up?