Which Gas?

[71VERT]

I am picking up a 69 427/435 on friday and was wondering what gas to use. the owner said he rejetted the center carb so he could use sunoco 94. He said he had to mix it with racing fuel previously before rejetting in order to get it to run correctly.

Do you add any octane boosters? or lead to the gas?

Thanks

Jerry

 

[JohnZ]

Forget about "octane boosters" or "lead additives" - they're useless; also, carb jetting has little or nothing to do with what octane fuel the engine will be happy with. Assuming it still has the original 11:1 compression ratio and hasn't been rebuilt with lower-compression pistons, you'll need to feed it the best premium fuel you can find at a minimum, possibly have to mix 20%-25% race gas with the premium, and/or back off initial timing and the centrifugal advance curve as well.

 

[Stallion]

This is a great question. John, in my case (1978 L48 8.2:1 compression ratio) what should I go for? Would the premium be enough? Or would I have to look around for something special?

Thanks!!

 

[JohnZ]

You should be fine with 87-octane regular with 8.2:1 compression - you won't have any problems.

 

[MaineShark]

You'll need something to protect the engine from accellerated wear due to running unleaded gas: the engine was designed to have the lubrication of the lead. That's where lead additives are useful.

Joe

 

[Stallion]

But I thought that they were expected to run unleaded? That's what it says on my cover. I figured that was the "norm" to go in my engine. No?

Thanks!

 

[Eric]

But I thought that they were expected to run unleaded? That's what it says on my cover. I figured that was the "norm" to go in my engine. No?

Thanks!

TR,

Joe was referring to Jerry's question about the 69 427. Your 78 was indeed built to run on unleaded. Not to worry.

 

[MaineShark]

Heh. Yeah, I forgot to address the reply to a particular post. You're fine with 87-octane unleaded. The only thing the fancy gas will give you, is better detergents. When I got mine back in November, I asked that question here. The advice I got was to add a bottle of fuel injector cleaner (some companies actually have a formula for carbs) to every fourth tank of gas. That's a lot cheaper than buying the expensive stuff, and probably does a significantly better job of keeping your fuel system clean.

Joe

 

[offshore]

You'll need something to protect the engine from accellerated wear due to running unleaded gas: the engine was designed to have the lubrication of the lead. That's where lead additives are useful.

Joe

FIRST SMART THING I HEARD YOU SAY.

 

[offshore]

I build highperformance boats and on the water the most you can get is 93 but it has valvetech allready added to it if we can't get 93 with valvetech we pour in a pint of real lead (per 150 gal. both tanks= 300 gal.) apprx. 3 hours of running time. But what mainshark said was correct run 93 set your "total" spark advance to 30 deg. and use a 140 deg.t-stat and you will have no problem. you can get valvetech at any good parts store. I run these engines @11:75.1 at 5500-6200 rpm for 4-5 hours at a time with NO detination problems.

 

[69MyWay]

FIRST SMART THING I HEARD YOU SAY.

Your input is very valuable as noted in your last post to this thread. However, these kind of comments have no place here.

If you don't understand, or would like further instruction on the matter, please send me a private message.