Pressure

[Grip64]

Looking for some advice her please fella's.

Is it possible to rejuice cylinder cranking pressure by advancing or retarding my cam timming ?

Grip

[BSB67]

Retarding cam timing will reduce cylinder pressure and reduce piston to exhaust valve clearance.

[elacruze]

 

Why?

[Grip64]

Thanks for the reply's fella's.

I'm trying to get more timing into the motor, ( 28 total with iron heads 10 to 1 comp and 98 gas)before detenation set's in 

Cranking pressure is 180 with the cam insalled stright up !!!!!

Any idea how much pressure could be bled off with retarding the cam

Grip

[elacruze]

There's no way to answer that accurately. It depends on the intake lobe closing rate, and whether hydraulic or solid.

[Grip64]

Its a solid, here's the valve timing from the card...

open @50 int 13 BTDC exh 63 BBDC   
Close @50 int 53 ABDC exh 7 ATDC.

Grip

[elacruze]

I'm sure there are a couple guys in the forum who can answer with direct experience, but my WAG is that if you retard 4* you'll lose 5-10psi.
The only way to know for sure is to do it and measure.

[John_Kunkel]

Retarding the cam keeps the exhaust valve open longer during the compression stroke so some of the compression pressure goes out the exhaust valve.

[BSB67]

John, I think you ment the intake valve.

[firefighter3931]

Thanks for the reply's fella's.

I'm trying to get more timing into the motor, ( 28 total with iron heads 10 to 1 comp and 98 gas)before detenation set's in 

Cranking pressure is 180 with the cam insalled stright up !!!!!

Any idea how much pressure could be bled off with retarding the cam

Grip

180 psi is pushing it for iron heads. Retarding the cam isn't going to make an appreciable difference. What cam are you running that has such an early closing point ? Did you degree it in or just line up the dots ?

One option is to pull some static compression out of the motor with a thicker head gasket....or swap to a cam that bleeds off more cylinder pressure.



Ron

[Cooter]

OR, there's always 110 Octane....