The Stovebolt Site Forums The Shop Area Engine Shop milling 848 for 261

Does anyone have data on what compression ratio is for a stock 848 dropped onto a stock 261, plus data showing what compression would result after milling .030, .060, .090, or .120 off the head?

Another question is what is the max compression a guy can go for and still be able to use 87 octane fuel without detonation concerns?

I want as much punch as I can get from idle to about 2500 RPM but fuel economy is necessary. A 3/4 cam kills low RPM performance and drives the peak power way above the RPMs I will run 99.9% of the time. Extra displacement from the 261 and compression boost from a milled 848 is the ticket for me.

There is an old hot rod magazine article available at http://www.selectric.org/55chevy/soup.html
It should answer your questions. Interestingly when the 261 that is the subject of the article was bored out to 278 cid the article states the compression was raised to 8.5:1. I'm thinking it must have been the pistons they used.

If I remember correctly they did use an 848 head as part of the modifications and there is some discussion of that.

Lots of good information but maybe outdated a bit by newer equipment/methods but maybe not.
Jerry

To correct myself. I checked the article and indeed they did say the compression raised to 8.5:1 as a result of the bore being increased 1/8th inch. The author specifically says the compression height of the new pistons was the same as stock. Its important to note that previous to this they had milled .030 from a 235 cyl head (presumably an 848 head). But the point is that compression is claimed to be raised just by boring to a larger diameter.
Jerry
Jerry

When did the 848 head first become available? That Hot Rod Magazine article was published in May 1955.

It seems that the majority of stovebolters need the same information I seek. Someone knows the answers, so PLEASE HELP.

I'm still hoping that SEVERAL folks here that are succesfully running 87 octane with a 261 and milled 848 head will tell us what bore and mill they have implemented.

Also hoping someone can lead us to information on what the maximum compression value can be that allows the use of 87 octane.

Jerry - Thanks for your reply. I have that article and it contains good info but not all info I seek.

Tim - Boring increases compression since you end up compressing more mixture into the "same" space. I don't know when the 848 was introduced but mine came off a 1957 235.

My block has been bored .030 but my 848 is virgin. I want to mill the head the min amount that will give the max compression acceptable for 87 octane.