cam timing--moving the power band

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The stock 20R cam is simply too big. Advancing it won't do it.

 

every thing you want to know is in here and another link in there. the aplication is different than yours but the theory is the same.

http://www.jalopyjournal.com/forum/showthread.php?t=331733&highlight=need+discussion

 

Advance for low end torque, retard for top end power. Kinda a general rule of thumb but can become complicated when you take all of the variables into consideration. If that doesn't confuse you I'm not trying hard enough.

Frank

 

Well on a standard sbc one tooth on the cam gear is like 16 degrees(if memory serves). Way too much in my opinion, makes for wierd pulses ie backfires at above 2kish rpms. Although in the lower rpms.......?

I found this out the hard way btw.

 

I think you need an engine with a little more torque... the small bore 4's have little torque and the HP is at a much higher RPM. Why not find a small diesel? CAT/Perkins or ? They are pretty cheap if you look around and they are pretty compact.

 

i would check the cam at overlap to see if it is adv/retarded at tdc before i would mess with it. if the overlap is split down the center between int/exh then try maybe 4 deg. you would probably gain more tq by making some type of velocity stack / cold air sysyem and headers into a long collector...being a car motor you cant expect much in an industrial atmosphere...good luck

 

I've read that some builders have gone as far as 8 degrees from the True TDC mark.

You're sure gonna want to check valve clearance.

4 degrees is the most that's usually recommended by cam manufacturers.

The above figures refer to V8's.

 

I had to advance my cam timing 2 degrees on my O/T 347 stroker in my race car. Rule of thumb, at least with ford engines is each degree moves the power band +/- 200 rpm. I'm not sure if that goes the same for other engines (size, brand, etc.).

 

I read somewhere that circle track guys would advance or retard the cam to obtain max cranking compression. This is supposed to give best low end torque. Never did it. Anyone have any real life experience with this?

 

I remember reading somewhere that moving the timing more than 6° means you really need a different cam. If you can get a regrind, that would be your best bet.

This guy did something similar to what you are after, with an Austin 1L engine.

 

If you get a computer program you can enter all the engine specs then change timing to see what the result is. saves alot of time, and answers alot of questions.