what fuel should i run

[mikepasquale1]

Tring to figure out what fuel to run. From what others ha e told me should be ok with 87 but id ratger atretch the opinion out.

I cannot get in touch with the builder. He is long gone and had all the paperwork. It was a $2300 stock rebuild with an added mild cam, cylinders 0.30 over. Nothing real special about it.

Will i be ok with 87 or should i go higher?

I worry myself stupid about things like this

 

[73 MACH 1 MAN]

Octane decisions are mainly based off of compression ratio's if your running 10:1 or less you should be fine w/87 octane if higher you should go with hi-test. Are you getting any pinging? If so it may be you need to run a higher grade or your timing is off!

 

[hyena429]

Octane decisions are mainly based off of compression ratio's if your running 10:1 or less you should be fine w/87 octane if higher you should go with hi-test. Are you getting any pinging? If so it may be you need to run a higher grade or your timing is off!

agreed ..What motor too? 351w? Shouldnt be very high compression..But thats all counts on what they put in...87 should be fine...but punch it going up a hill and see if you hear any pinging in your motor while under load.

 

[73vertproject]

With that build and no stroke done I can't imagine why you would need anything more than 87, Mike. Of course, as the others said, if you get pinging driving uphill or under load, you might go with a higher octane and see if that solves the problem.

 

[mikepasquale1]

No pinging but hvent driven it yet. yes 351w. Almost positive flat top pistons. Just makes me nervous if it does start pinging cause in my mind ill think something is severly wrong and the engine is shot lol.


Also i have no idea what the comp ratio is. Unable to track down builder to find out.

 

[hyena429]

No pinging but hvent driven it yet. yes 351w. Almost positive flat top pistons. Just makes me nervous if it does start pinging cause in my mind ill think something is severly wrong and the engine is shot lol.


Also i have no idea what the comp ratio is. Unable to track down builder to find out.

aww little ping wont hurt anything..but too keep driving it like that for a while will....I would try her out with 87..just dont put to much in at first just in case...You can always fill the rest of the tank up with 91 or 92 if it pings a bit...But it realy shouldnt..It should love 87 with a mild build..It will be alot like a truck motor..And love the low octang gas.

 

[Jeff73Mach1]

Keep in mind that the temperature your engine is operating at, the timing setting, the cleanliness of the top of the pistons restrictions in the exhaust and improper jetting in the carb can all affect pinging and detonation.

If the car runs or more accurately "diesels" after you cut the key off, even just a second, then your engine needs attention.

A light "ping" is a little different than detonation which sort of sounds like a loud rattle or shaking a can full of screws. True detonation is when the fuel mixture is igniting at some point in the engine cycle before the ignition occurs.

Generally speaking if you don't hear detonation, it isn't going on. By that I mean it is an obvious sound that is hard to mistake even over exhaust and road noise. More octane makes fuel harder to ignite, allowing more timing and more radical tuning and more compression. It has always been my understanding that best power comes from using the fuel that has the lowest octane rating that satisfies your engine.

 

[goodnigh]

The owner's manual that belongs to my quench Cleveland says to use 99 0ctane or higher.

That was 1971 though and don't know how that equates today. I use the highest rating I can get, 91.

Runs fine with initial timing around 14.

mike

 

[Darkhorse71]

True detonation is when the fuel mixture is igniting at some point in the engine cycle before the ignition occurs.

That is 'pre-ignition' and if that were to truly happen, it only takes a few revolutions before severe damage is done. Detonation (or post-ignition) is actually a late burning of the fuel after the initial spark. The damage comes from a second flame front (after plug spark) severely heating up the top of the piston. This is what causes the piston to melt and 'pepper' on your spark plugs /dig holes in your piston.

Probably the best I've ever read on the subject....

http://www.streetrodstuff.com/Articles/Engine/Detonation/

 

[mikepasquale1]

Thanks guys. Ill see how it goes.

 

[Jim and Jutta]

More octane makes fuel harder to ignite, allowing more timing and more radical tuning and more compression. It has always been my understanding that best power comes from using the fuel that has the lowest octane rating that satisfies your engine.

I learned something today (again), good stuff, thanks Jeff!

Jim

 

[Jeff73Mach1]

and I did refer to preignition and detonation improperly. Mea culpa