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advancing/retarding cam

9K views 29 replies 12 participants last post by  Pilch 
#1 ·
Just been playing around with my dyno program before I freshen my 351. Basically its 10.5:1 CR, ported iron 2v's with 4v valves, Crane F238 etc etc.

It seemed to make pretty good power and torque according to the program, 435 hp @ 6000 and 399ftlb @5000.

When I retarded the cam 10degrees, it jumped to 465 hp @6250 and 415 ftlb @ 5000. Not that I would retard it that far tho.

I'm not sure how accurate these dyno programs are, so Iwas wondering if anyone has actually tried retarding or advancing the cam timing with a similar combination and what the results were.
 
#27 ·
brenx said:
Plenty of people in the real world have retarded and advance cams. It's common knowlege. Most don't do it for power though. They retard it to change the power band to ****rpm or visa versa. Most would end up advancing theres as this makes everything happen earlier.
hmmmm..... still didn't get the answer I was after. I'll put it more practically:

If I retard my current cam from reccommend settings far enough to increase the powerband by 500rpm, what effect will this have on idle quality and low rpm running?

ie. will it survive, or will something fail?
 
#28 ·
Pilch said:
hmmmm..... still didn't get the answer I was after. I'll put it more practically:

If I retard my current cam from reccommend settings far enough to increase the powerband by 500rpm, what effect will this have on idle quality and low rpm running?

ie. will it survive, or will something fail?
Results vary from engine to engine. The main thing to be wary of is piston to valve clearance. My 351's cam was advanced 4 degrees.
 
#29 ·
Pilch said:
hmmmm..... still didn't get the answer I was after. I'll put it more practically:

If I retard my current cam from reccommend settings far enough to increase the powerband by 500rpm, what effect will this have on idle quality and low rpm running?

ie. will it survive, or will something fail?
Adjusting the cam timing effects the valve opening and closing events in relation to the piston position in the bore. The most significant cam event they claim is the inlet valve closing point.
Advancing the cam timing would close the valve sooner allowing the piston to build pressure for compression earlier resulting in higher cylinder pressures and improved low end punch.
Retarding would lower pressures allowing greater scavenging improving top end.

My 2 Cents
 
#30 ·
hmmmmm....... fair enough then. I would expect there'd be a point where the cam has been advanced/retarded so far that there would be a lack of compression at the point of detonation causing not much more then coughs and splutters from the engine.

So is there a typical rpm change associated with each change in degree??? or is this a case by case basis.
 
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