klumb15

I have a 90 corvette motor, and i read somewhere that the compression was 10 to 1 or something like that, and that I should be running premium...i've been running 89, but should i be running premium or doesn't it make a difference?

ME Leigh

It has aluminum heads, so 89 octane will be fine.

unvc92camarors

aluminum heads don't exactly mean it's ok to run 89
in the lt1's, it is 10.5.1 compression and it has alum. heads, and it reccommends premium (but has a knock sensor device that can retard timing to accomodate lower grade gas i.e. i use 93 and my buddy uses 87 in his 96)
you don't have that though, so i would reccommend 91+ (whatever it is in your area) just to be on the safe side

the best way would be to see if it pings or not using that
if you're trying to save money, i think you could use it but at your own risk

aklim

Lets say I blindfold you and place you in front of me and randomly punch at you. 3 different scenarios. Tell me which hurts more.

1. You are 2 feet away and you have to stand still and not move.

2. You are 2 feet away and when you feel me hit you, you duck a little. If you get hit again, you duck a little more and so on till you don't feel yourself getting hit.

3. You are 10 feet away.

#1 is like the cars of old without a KS. #2 is relying on the KS to retard timing. #3 is like using premium gas.

My vette tells me to use premium gas so your vette motor should need it too. BTW, it is 10.3:1 compression.

aklim

The only way you can tell that is to see what the KS is hearing with a scantool. Anything else is a SWAG. In the summer, I get more knocking than in the winter. The last owner used some 87 octane gas. I had to let it run out before I changed the filter and put in 93. In the meantime, I did see more knocking on the scantool than with 93 at WOT.

doug791

aklim has it right. The only way to know if its okay to be using cheaper gas is to hook it up to the scan tool because youre not going to know if your car decides to pull a couple degrees of timing or whatever. I run 91 to be on the safe side.

Theoretically you want to run the lowest octane gas possible without getting premature detonation.

ME Leigh

True the only true way to tell is hooking it up and find out the knock counts. But aluminum has a much higher heat conductivity then iron, so 10:1 with aluminum heads is like 9.5:1 or lower with iron heads. But then again it is a L98 with a crappy combustion chamber design so.... I spoke to soon, but i still think you should be fine.

axoid

If you are getting knocks and you still want to run the cheep fuel, you could just retard the ignition timing 4-6 degrees.

aklim

If you are that worried about having to run premium fuel which amounts to about less than $2 a full tank, why would you put a high performance motor in the car? 350s are a dime a dozen. You could have put in any one of 10000 350s and be fine with 87 octane.

Lowering the timing means lowering the power of the car. Which might also make it need more rpms to make the same power for basic movements. That might eat away any savings you get.

For the extra $1.40 a tank or so, I get about 200 miles in the city and 300 cruising, I think I can afford the little extra especialy when you divide it over the 200 miles or so which comes to less than a penny a mile. BTW, that is with 3.73 gears and hot ******* when I can. YMMV

klumb15

are you talking to me? the reason there is a vette motor in my car is because i bought it with one in there...the previous owner had a 5.0 that overheated so therefore there is a vette motor in there..and yes i will start running premium..