I am using 91 grade gas on my Evo for daily drive, and I am going to track on this Saturday and planning to use 100 gas. will this cause problems to the engine for not using consistent grade of gas?

 

Er, no.

Just mix 50/50 with the 100/91 to save money but still provide a little safety buffer (not that you need it, but it's a good idea). I'm curious what made you think the engine would be damaged by better/higher/different octane.

 

why waste the money on race gas if you're not tuned for it?

 

it just gives you a little cushion.. engine will be hotter and under a lot more strain.. these factors could show knock that a few dyno pulls wouldnt.

isnt not about more performance.. its about a little more safety.

 

We're talking road racing, man. Things are a lot different when you are going full boost for 20 mins straight. You can't compare it to a 12-sec drag run or short dyno pull.

 

edited

 

 

I had to take back what I said cuz I didnt realize I was in the roadracing section

 

Back in '03 when my Evo was almost bone stock (axleback exhaust only), I took it to a road course and filled up with straight 100 octane midday while I was there. Unfortunately, it rained right after that, and the rest of the track day was wet so hard to compare with the morning sessions in the dry.

But anyway, two or three days later when the tank was almost empty, I filled up with 93 octane and the engine felt pretty sick as I pulled out of the station -- like it didn't want to hold a steady idle and like it was "searching" for the correct tune for the fuel. But it cured itself within a few miles and was fine after that.

In summary, I'd suggest that any time you move from higher octane to lower octane, give the computer a few miles to adjust before you get into heavy boost. Going from lower octane to higher octane shouldn't be a problem at all...

 

+1 .... people would be surprised if they datalogged their stock EVOs under high boost/stress conditions with 91oct gas.