Octane question???

[bornatiger]

I have a 93 tune on the car from BrooksSpeed. I am going to the track tonight and was wondering if it would hurt to put a few gallons of unleaded 101 that the track offers in the tank. I am gonna show up with about a 1/4 tank of 93 already. Cool or not cool?

 

[Shake&Bake]

Yeah you will be fine. You can run 93 and above with that tune.

 

[Tunedprt91]

Yep correct me if im wrong but you can always go up in octane but never down.

 

[98BABCobra]

Yep correct me if im wrong but you can always go up in octane but never down.

^^^ This. You can always run higher octane than you are tuned for but NEVER run lower octane than what you are tuned for.

 

[bornatiger]

Thanks for the help. I have read a little about it since I posted. Seems the gains are not worth $9.50/gallon.

 

[CJK440]

But why run more octane than your need? You won't go faster unless your tune is off.

 

[racecougar]

Thanks for the help. I have read a little about it since I posted. Seems the gains are not worth $9.50/gallon.

Gains? You won't see any gain whatsoever unless it's oxygenated fuel, and then you need to tune for it. Stick with the fuel you're tune for.

 

[DVJ38]

Gains? You won't see any gain whatsoever unless it's oxygenated fuel, and then you need to tune for it. Stick with the fuel you're tune for.

Yup, not going to make any difference. You'd just be wasting your money.

 

[mwolson]

In fact, it will reduce your HP a bit. The higher the octane, the slower the burn. If your engine is well tuned for 93 octane, your peak cylinder pressure will hit at the optimum crank angle for torque. With higher octane, the peak cylinder pressure occurs later, after the optimum crank angle, leading to slightly lower HP.

But you run less risk of detonation with higher octane.

 

[STAMPEDE3]

In fact, it will reduce your HP a bit. The higher the octane, the slower the burn. If your engine is well tuned for 93 octane, your peak cylinder pressure will hit at the optimum crank angle for torque. With higher octane, the peak cylinder pressure occurs later, after the optimum crank angle, leading to slightly lower HP.

But you run less risk of detonation with higher octane.

This^

 

[laddanator]

What happens if you are tuned for 93 and run octane below that?

 

[mwolson]

What happens if you are tuned for 93 and run octane below that?

The flame front in lower octane fuel burns faster, so peak cylinder pressure will occur before the optimum crank angle. This tends to put all the energy down into the bearings, main caps and up into the head and head bolts turning it into heat. It can also cause detonation, which is an uncontrolled explosion of the air/fuel mixture. That can destroy your motor.

Knock sensors listen for detonation, and when they hear it, the PCM will retard the spark, moving the peak cylinder pressures closer to the optimum crank angle, but I wouldn't trust the knock sensors on our cars...

 

[Royal purple]

Good info!

 

[ZAPPY]

Thanks for the help. I have read a little about it since I posted. Seems the gains are not worth $9.50/gallon.

This is a waste of money since ur tune is setup for 93 octane. The purpose of the higher octane is to take advantage of more timing so u wont see any gains with a 93 tune on higher octane fuel. Jmo :rockon: