Compression Ratio with a babbit engine

[Bud]

What is the highest compression ratio Fordbarn members have run RELIABLY with a properly rebuilt babbit bearing engine?

[IndyA]

The best I got was 70# ...

[frank55a]

I have been running a Brumfield 5.9 head with babbit bearings for the last 11 years and have put about 20,000 miles on the engine with no problems. I have a friend that is also running the same combo that has over 60,000 no problems.

[daveymc29]

I have an old engine with 94#, police head and no idea when it was built, several years ago is all I was told. It is quite the best engine of my three cars and I have driven it for three years with no issues. It has a "police" head if that tells you anything. Since I have no idea if it has been milled or not, it doesn't tell me much, just that it is higher than normal. I haven't had the pan off, but no external signs that it is anything but babbitt,

[chap52]

Can't remember where I got these numbers, but I wrote them on a note page in my Model A stuff;
Standard head=60#
Police=70#-75#
5.5/6.0=90#-100#

[Y-Blockhead]

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Originally Posted by chap52

Can't remember where I got these numbers, but I wrote them on a note page in my Model A stuff;
Standard head=60#
Police=70#-75#
5.5/6.0=90#-100#

That's pretty close to what I got on my otherwise stock engine... Stock head=65psig, Snyder 5.5=100psig.

BTW, the OP asked for highest ratio, not psi.

[Jim Brierley]

I have raced on babbitt for years. B rods, drilled for pressure C crank. Ran 153 MPH at Bonneville on my Cook OHV conversion, 12:1, on nitro and many drag-race runs on gas at 116 mph, 12,20 e.t. I changed to aftermarket rods with inserts in 2008, the babbitt B rods were beginning to look a little shakey. Am still running babbitted mains with 7.5:1 compression and a turbo, 167 best speed to date. Babbitt was run in Offies for years!

[George Miller]

The babbitt does not care what the compression is. The running pressure is what matters. They still use babbitt for high load bearings. What makes a difference is the quality of babbitt and the quality of work done. Also the way you drive the car. Like driving it with the spark all the way advanced going up a hill with your foot down hard on the accelerator. That will help take the bearings out.

[PC/SR]

Have a 6.8 CR Weiand head, used for street and hillclimbs for 8 years no problem on babbitt. RPM is the limiting factor in an A engine with stock splash oil system, not compression ratio, because of oil supply at higher RPMs.

[Kohnke Rebabbitting]

RAJO dual overhead cam head, with Hemi valve chamber, race car ran 14:1 compression.


Herm.

[Gasnutte]

I have a "B" head I put on a fresh rebuild 1989 Still running good. Running full advance will shorten bearing life. also have counter balance crank and lightened fly wheel the combination makes for a long lasting engine. Don't forget a good air cleaner.