Gas :Super or Regular?

[bradvette]

The octane any given engine needs is in direct relation to the normal operating temperature and the compression ratio of the engine. Given that our cars are "set" to run in the 200 range and the compression ratio is ~9:1 it is going to take a higher octane. There is a chart I've seen that graphs it all out. With my HD radiator my car runs right at 150-160 I could probabally run 89 octane but I choose not to. The General recommends these things for a reason.

Hrtbeat, I'm not sure I quite follow. You have a '90, which is a 10.25:1 c/r L98. The earlier L98's are 9.5:1. The LT1 (and LT4's I think) are 10.5:1. I do follow you on the temperature, and ambient temps count as well.

All things being equal, in stock trim, early L98's can run 89 octane (or probably 87), the 90/91 L98's on 91 octane, and LT1/LT4's should run 93 octane.

 

[Hrtbeat1]

If you lower the cylinder head temperatures (coolant temp) in theory you can get away with running a lower octane without risk of detonation or pinging. I have a heavy duty radiator and a 160 degree thermostat. My car runs right around 150 degrees, sometimes as low as 140 and sometimes as high as 160, but nowhere near the 200+ that it ran at when new. By running cooler I could most likely get away with running lower octane, but as I said I choose not to. I will have to find the article and graph I was talking about, it was in Engine Masters magazine a couple of months back very informative article.

 

[bradvette]

i agree on the coolant/head temps, especially with alum heads. i just didn't understand where the 9:1 c/r that you referred to, was coming from. our '90 are 10.25:1 out of the factory. the earlier L98's were 9.5:1. with a lower c'r like 9:1, you'll most likely be fine with 87 octane, with iron heads.

 

[Hrtbeat1]

OIC I was just generalizing on engines especially considering compression ratios have varied from around 7:1 up to 11:1, depending on the application. My old K5 Blazer was somewhere around 7.5:1. I think the old L-88 was 11:1.

The earlier L98's were roughly 9.5:1 compression. I know the later L98's were 10.25 or 10.5, depending on what reference you use, and the LT-1's were 10.5. Sorry if I confused anyone.

 

[mesteffen]

I always run premium.