How can race gas be "bad" for any car? The higher the octane, the safer the car runs.

On an NA engine like the VQ35, it's probably an overkill. Even with a race tuned map, it probably won't add any significant power. And detonation on an NA engine like the VQ35 isn't as dangerous as opposed to those who are running forced induction. The turbocharged & supercharged VQ35's would definately benefit from the higher octane; less chance of catastrophic detonation. And if they already have a tuned race map, it should yield power for the VQ35 TT/ST/SC.

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"The higher the Octane rating, the faster the gas will ignite which in general is good" ?????

The higher the octane the slower the fuel burns! The point is to create peak combustion pressure [BMEP] at 15-17 degrees after top dead center when this forces the piston down to create greatest torque.

An error eitherside of the correct timing results in less power output.

Ignition fires 40-15 degrees before TDC and thus the flame speed is:
40 + [15-17] or 55-57 degrees at cruise to a 20+ [15-17] or 35-37 at torque peak rpm................how long from spark untill 68% of mass has burned [oxidized/combusted].

Preignition or knock are symptoms of extreme error from the optimum timing.

On a dyno you read peak torque so you use a combination of fuel 0ctane and btu and ignition advance [and A/F ratio which changes flame speed] to zero in on the peak [which occurs at 15-17 degrees ATDC].

Racers use a pressure sensor under each spark plug to measure peak vs degrees and set individual cylinders ignition timing to squeeze out the last 1-2%...............so that each cylinder is creating exactly the same power for smoothness and reduced bearing wear.

Fuel octane is just one of the tools you use.

Knock sensors help zero in on the no knock point which is below optimum with both regular and premium...........racing fuel may take you thru the peak and over on the down slope of curve..................a dyno will tell the truth, if the peak power goes up at all rpms you have your answer.

 

105 race gas with Osiris dyno tune for the race gas map =

 

Fuel facts:

All unleaded gasonline(87-121) has exactly the same energy content. Meaning each grade of fuel has the same potential energy. The difference between the fuels is the additives. The higher octance fuels have more expensive additives which acount for the increase in price. The grade of fuel you engine requires is directly proportional the amount of compression your engine is tuned for. Octane [wikipedia] is a measuring system that determines the resistance of gas and other fuels to knock. Thus using a higher octane alone will have zero increase in performance/maintenance over the recommened 91.

 

Hope all these high octane gases don't have lead because it will ruin your expensive cats.

 

What are cats?

 

true with stock ECU programming... however, higher octane/oxygenated race fuel allows for more aggressive timing without knock - providing "increase in performance".

 

Cats are easy to change out and wouldn't be a problem with straight pipes. I'd be more concerned about the sensors...

 

ther is plenty of unleaded race fuel options... it shouldnt even be an issue or concern.

 

Only slightly correct. Octane is a fuel's resistance to ignite and all unleaded gasoline does have the same energy content; however, there are so many other factors at play. I don't know if this what you were getting at, but higher octane fuels aren't cleaner. Yes, they have more additives, but most are there to raise octane.

Some things to consider:

1) Compression use to play a role in a car's usage of higher octane fuels. The VQ is still a bit old school so it does need the higher octane to perform at peak, but cars with direct injection, fancy combustion chambers, and variable valve timing and lift can get away with running crazy high 11+:1 compression ratios while running happily on 87. Both Honda and Toyota have motors that do this. Toyotas V6 runs a whopping 11.5:1 compression. 10 years ago, that would have required 100+ octane to run reliably, especially on a motor capable of revving to 6800rpms.

2) In colder weather, when the air is dense, the baro pressure is high, and the intake charge is cold, there isn't a huge need for higher octane fuel. It's quite possible that 89 could out perform 91+ in sub 40 degree air. Cooler air means more oxygen and cooler intake temps which means preigntion (what high octane is trying to control) isn't as much of an issue.

3) The VQ series is a pretty finicky motor with a very sensitive knock sensor. It runs a reverse flow cooling system which means the heads are cooled first then the block. This is good at keeping the motor temp consistent, but not so good and keep temps low. High temps mean a higher chance of preignition.

4) It's been shown by Sport Compact Car, that a stock VQ is happier running higher octane and can use it. Their project 350Z consistently gained 5 to 7whp between running 91 and a 91/100 mix (~96 octane).

5) There is a limit to how octane is benefical for these cars. If you're NA and are stock or have the typical bolt-ons and you're racing in 60+ degree weather, it would probaly benefit the car to run 93 to 96 octane.

 

^^^ now that makes sense to me.

 

Q45 and DaveB, nice posts. Many others filled with misinformation - jiminy christmas though everybody seems so confident spewing it forth - lol .

 

if i throw 20 and 20 in of 100 and 93 my car will def be a bit more responsive and pull a touch better

 

Which posts are you referencing? the info I posted is based on dyno observations and track results on my car.

 

90% of you seem to be basing your opinoins on personal experience rather then theory. Here are the facts, well as factual as Wikipedia can be.

"Many high-performance engines are designed to operate with a high maximum compression and thus demand high-octane premium gasoline. A common misconception is that power output or fuel mileage can be improved by burning higher octane fuel than a particular engine was designed for. The power output of an engine depends in part on the energy density of its fuel, but similar fuels with different octane ratings have similar density. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power."
http://en.wikipedia.org/wiki/Octane_rating