compression VS horsepower

J

jhawk

Member
I have been told 50 psi is goal for a stock T, just wondering if horsepower is reduced at a matching percentage ,if all 4 cylinders read 25 is the hp also reduced by 50 % ? thanks in advance! jim :confused:
 
I doubt that there is any kind of reliable formula or chart to determine this. For one thing, cranking compression will be less than running compression, because at slow cranking speeds compression has more time to bleed down. If you have a somewhat leaky valve or worn rings and hand crank slowly, you will have zero compression. Now hook up a 12 volt battery, and you may have 10-20# compression. With the engine running, maybe 30-40# compression. Plus, while running oil is being splashed on the cylinder walls, which may help the rings seal a little more and raise compression a little. All these results will vary depending on engine temperature and wear, carbon build-up, oil viscosity, etc.
 
Interesting. I am getting a Z head to put on my stock 1915 which of course is hand crank only. One of our club members was saying it is low on compression and when hand cranking my fresh rebuilt 1927 with Z head I find that is true.

Hope it doesn't break my back when cranking!
 
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