Hi compression vs low compression vs fuel quality?

[moturbopar]

Ok the title might be confusing but I do not know which would be better. I am puting a new rebuilt 350 in my work truck. The problem is I am considering doing a few mods to help performance and hopefully fuel economy. The most important question and the one that is most important is would I be better off running higher compression (64cc heads) and run 91octane or run lower compression (75cc=8.5-1) and 87 octane. I am wondering which would be cheaper in the long run more mpg and higher priced fuel or less economy and cheaper gas?

 

[4X4HIGH]

Never run high compression in trucks or you will end up with detonation no matter what grade fuel you try using. Stick with a compression ratio of between 8.5:1/9.0:1 for best drivability and you will also gett better mileage since it won't be detonating and working against itself.

 

[moturbopar]

For high compression I was thinking 9.5 for max, and vortec heads since they have a good combustion chamber, I forgot to mention that
Anyways I am leaning to the low compression (8.5) engine anyways, since it will be cheaper to build and I know I can run cheap gas, which I can get anyplace.

 

[dyeager535]

You want as much compression you can run (without problem) with the lowest fuel grade available, since you are talking about *economy*. Obviously there are a few variables, (cam, fueling, etc) but Vortecs have no problem running at 9.0+ on 87 octane if tuned right. (which is always going to make a difference)

Manufacturers are up around 10:1 on 87 IIRC in some applications, so higher is possible, but not likely on an iron headed 350.

 

[steve_kibbe]

What kind of milage are you wanting to achieve? You can swap in a 6.2 and get 17+ all day long, just might take a few minutes to get there

Then you'll have 18:1 or so

 

[MTMike]

My engine was built for mud racing by the previous owner. It has 10.5:1, Vortec heads, moderate cam and I have to run 91 octane w/ the vacuum advance disconnected to keep it from pinging. Even then I get 4-6mpg

If you're looking for economy, keep the compression in the ~9:1 range.

 

[4X4HIGH]

Manufacturers are up around 10:1 on 87 IIRC in some applications, so higher is possible, but not likely on an iron headed 350.

The only way this is possible without detonation is with FI and an ECM to control everything. Manufacturers are up to as much as 11:1 but like i said, this is with FI and all the sensors monitoring everything.

 

[Chevy305]

I vote for the 64cc heads.

More power equals less lugging and you don't have to be on the gas as hard to get to where you are going.

I say go for more compression!

 

[crometooth]

I'm running a 350 with Vortec heads and about 10:1 compression. I don't have any serious problems with 87 octane. Course, the cam makes the difference, you need some overlap if you are going for higher compression.

If I had to do it again I would stick with 9:1 or so. If turbo or a blower is in your future then 8:1 might be a better choice...