It all depends on the compression ratio. If you're running 9.5:1 or less, you should have no problem on pump gas at all. Up to, maybe a little over 10:1, higher grade gas does the motor good. Higher than that, you should probably use additives. I'm still running the stock 10.25:1 compression on my 350, but I retarded the timing a little bit to compensate for it. I use premium gas, and have never heard her knock. Hope that helps.
Another poor college student trying
to keep a hot Chevelle on the streets.
350/300hp (more than that now)
and a decaying TH350
I don't use any kind of additives in my 1972 El Camino. I have a stock L65 350 w/ 8.5:1 comp. The emmisions sticker on my car said use 91 octane or higher low lead or unleaded gas. It runs fine. If something ever happens, then I'll have the harden valve seats installed.
This one keeps coming up - I read an article some years ago in Popular Mechanics which summed it up well - Unless you are racing, towing large trailers, or otherwise putting a HEAVY load on your engine, unleaded gas should not cause you grief - it may cause valve seat recession but don't actually worry about this until you need a valve job. The lack of lead is VERY beneficial in other areas; longer exhaust life, longer sparkplug life etc etc. You may have a problem with octane levels IF you have a very high performance engine ( 11:1 compression ) but this is unrelated to lack of lead - several additives are available in this case. Don't use these additives UNLESS YOU NEED THEM. They are VERY bad for the environment as well as being very expensive.
Hope this helps
[This message has been edited by swild (edited 11-29-99).]
I have close to 11.5:1 on my 396, and I can run premium and just cruise if I retard the timing a few degrees. If I am gonna go out to take care of business its gotta be premium and octane booster ( I use the 104+ additive in the black bottle for approx 97-100 octane) and it seems to be fine. I check the plugs after every night of "business" and they seem to be fine.
On the advice of a couple of old timers, I ran my 'camel hump 'heads on my old 350 for about 28,000 "pleasure miles" (really beating the hell out of it) after a quick valve job. The guys told me not to worry about the heads because I really wasn't loading the motor down much. They were right, after 28,000 miles, no valve recession, heads are still in good shape, after running mostly premium and retarded timing, and slightly richer fuel mixture with 10.5:1.
I think most people mean premium unleaded pump gas when they say "premium" 92-94 octane depending on where you live. the best additive for it I've found locally are equal parts of 110 octane Cam2 or 115 octane TurboBlue.
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