91 vs 94 octane tune

[weSS1LEy]

How much difference would getting a cam kit and then tuned with 94 ethanol free chevron or 91 shell? I always use 94 and my car is currently tuned on it. My cam installer is 6 hours away and only has 91

[pnwdan]

fill up with 91 there and add octane booster

[PepeLePew]

Gasoline with higher octane will give you better knock protection and allow for more timing. If your car was tuned for 94, then you may get knock retard running the lower octane gas. If you are retuning the car and the tuner only has access to 91, then you won't notice a difference to running 91 or 94. The only thing I would be cautious of is the actual octane rating of the fuel mixture in the tank at the time of tuning. For instance, if you had a a couple gallons of 94 in the tank and your tuner added 5 gallons of 91 before tuning, then you may experience a little KR if you ran pure 91 from that point forward.

In terms of HP, I would expect a difference of about 10 at the wheels between a tune on 91 vs 93/94.

[PepeLePew]

Originally Posted by pnwdan

fill up with 91 there and add octane booster

I agree... if you go this route, make sure to get an octane booster that is lead free. Royal Purple makes a good one that will raise your octane by level by 3. Just be careful, if you raise it to a mixture that is higher than 94 while tuning, you may become dependent on the stuff and it isnt cheap.

[weSS1LEy]

Sounds like some room for error with octane booster. I could maybe fill up with 94 and also bring a jerrycan. Or maybe ship my car on a truck

[PepeLePew]

Originally Posted by weSS1LEy

Sounds like some room for error with octane booster. I could maybe fill up with 94 and also bring a jerrycan. Or maybe ship my car on a truck

Don't overthink it... pnwdan had a great idea with the octane booster. The stuff works. Just try to do the math on how much you add to keep it at 94 or lower while tuning. I'd say shoot for 93. That way you don't get a tune with too much timing if you can't get 94 on the trip. Shipping the car on a truck might cost you a lot and driving that distance with a bunch of gas cans in the car might kill you on fumes.

[pnwdan]

Originally Posted by PepeLePew

Don't overthink it... pnwdan had a great idea with the octane booster. The stuff works. Just try to do the math on how much you add to keep it at 94 or lower while tuning. I'd say shoot for 93. That way you don't get a tune with too much timing if you can't get 94 on the trip. Shipping the car on a truck might cost you a lot and driving that distance with a bunch of gas cans in the car might kill you on fumes.

Yes good point. Was thinking that after I posted. Need to make sure mathematically you stay at or below 94 so you don't get over tuned.

[weSS1LEy]

Lol yes good point!

[Blueovalman]

There should not be worlds of difference here between 91 octane and 94 octane fuel. The difference in timing your tuner can run will be very minimal really. Use whatever fuels are available. I ran our 10 SS on the dyno using ethanol free 91 octane Chevron fuel and it ran great on the dyno!

[pnwdan]

Originally Posted by Blueovalman

There should not be worlds of difference here between 91 octane and 94 octane fuel. The difference in timing your tuner can run will be very minimal really. Use whatever fuels are available. I ran our 10 SS on the dyno using ethanol free 91 octane Chevron fuel and it ran great on the dyno!

That's like saying there isn't much difference between 87 and 91 though but there is.

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[Blueovalman]

Originally Posted by pnwdan

That's like saying there isn't much difference between 87 and 91 though but there is.

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What octane fuels to use would be what fuel octane is most available in your area 91 octane or 94 octane? It really depends because from what I have seen 91 octane is more readibly available in my area so I choose to use that when I got my dyno tune. For my 91 octane tune I use that for street duty and I use my 100 octane tune at the track. A lot of the people I see here are favoring E85 fuel. GM recommends only using top tier gasoline in your SS I know Chevron/Texaco and Shell are top tier gasoline’s. If you do run 94 octane your tuner can only tweak the perimeters so much more comparing to use 91 octane yes there is a difference but not by a lot. It is up to you if you think it is worth it??

[weSS1LEy]

All I know is my car is fast for a bolt on and 94 tune and I want to keep it that way lol ! My tuner here loves our 94 chevron.

[acammer]

Originally Posted by weSS1LEy

Sounds like some room for error with octane booster. I could maybe fill up with 94 and also bring a jerrycan. Or maybe ship my car on a truck

^^^ THIS! You really want to tune on the fuel that you typically expect to run.

It is true that these cars are absolutely capable of burning a wide array of fuels under a many different conditions - closed loop fueling and knock sensors ensure that you can run 94 octane at sea level in the summer and then 87 at the top of Pikes Peak in the dead of winter and still have the car run reasonably well.

But - you're not going for reasonably well, you want to tune with a purpose for the conditions where the car will most typically be operated, and then keep a safety net for conditions that fall outside that.

Tuning the car on the fuel you typically use is always a good idea - especially if that's significantly different from what might be available near your tuner. 94 to 91 is significantly different. A good tuner will work up the spark to the best it can be for your 94, and should be retaining the safeguards the factory affords (knock sensor, knock learning) for instances where you may have to get a tank of less than stellar fuel. As the operator, you want to be aware of situations where you have to run fuel different from which the car was calibrated for and take measures to avoid areas of high knock potential anyways (no WOT, avoid lugging the car in high gears at high loads and low rpm).

I definitely wouldn't just dump in a bottle of octane booster - you don't know what sort of final octane number you're going to arrive at, and again the whole point of tuning is the get the calibration spot on for the combination you have - and that includes the fuel you most typically use. Two 5gal cans that have quality spouts, keep them in the trunk, and plan you fill ups so that you can arrive at the tuners just about out of fuel, and then "fill up" to a half tank with your home-town good stuff that you are going to run 99% of the time you drive the car. It's a small step to take in order to have things optimized the way they should be.

[pnwdan]

Originally Posted by acammer

^^^ THIS! You really want to tune on the fuel that you typically expect to run.

It is true that these cars are absolutely capable of burning a wide array of fuels under a many different conditions - closed loop fueling and knock sensors ensure that you can run 94 octane at sea level in the summer and then 87 at the top of Pikes Peak in the dead of winter and still have the car run reasonably well.

But - you're not going for reasonably well, you want to tune with a purpose for the conditions where the car will most typically be operated, and then keep a safety net for conditions that fall outside that.

Tuning the car on the fuel you typically use is always a good idea - especially if that's significantly different from what might be available near your tuner. 94 to 91 is significantly different. A good tuner will work up the spark to the best it can be for your 94, and should be retaining the safeguards the factory affords (knock sensor, knock learning) for instances where you may have to get a tank of less than stellar fuel. As the operator, you want to be aware of situations where you have to run fuel different from which the car was calibrated for and take measures to avoid areas of high knock potential anyways (no WOT, avoid lugging the car in high gears at high loads and low rpm).

I definitely wouldn't just dump in a bottle of octane booster - you don't know what sort of final octane number you're going to arrive at, and again the whole point of tuning is the get the calibration spot on for the combination you have - and that includes the fuel you most typically use. Two 5gal cans that have quality spouts, keep them in the trunk, and plan you fill ups so that you can arrive at the tuners just about out of fuel, and then "fill up" to a half tank with your home-town good stuff that you are going to run 99% of the time you drive the car. It's a small step to take in order to have things optimized the way they should be.

Wouldnt he need to have enough gas for the return trip too since he's tuning for 94? Wouldn't wanna tune for 94 then run 91 on the way home.

It's easy to read the directions and just add the correct amount of octane boost to the correct amount of fuel. Its simple math.


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