16 replies to this topic

[superfly_GTR]

Im looking at fitting a new cam in my worked 186 to boost power and make it pull harder through the rev range, at the moment I am running a 30/70 crow cam with 280/290 IN./EX. duration and .440"/.465" valve lift with an effective power range of 2200-5200.

Im looking at maybe a 40/80 crow cam with 300/300 duration and .450"/.450" valve lift and a pwer range of 3500-6800. But then i get worried because apart from valve timing (40/80) the specs dont seem much bigger than mine, and with the crow cam list if you go lower in the valve timing you sometimes get more valve lift and/or duration and maybe go higher in the valve timing and sometimes get less valve lift and/or duration.

What i want to know is what combinations do what, what goes good with what and so on. Im just trying to get my head around cam specs.

The car is street driven daily but no real traffic work its either open HWY or residential streets but I am looking at getting into some track work, hillclimbs, sprints, motokhanas and the like.

My engine specs are 186 + .040" Fully balanced and decked with flat top pistons, Shaved Yella Terra stg 3 open chamber head running 9.5:1 comp, electronic ignition, extractors, and a 390 4bbl holley (thinking about 1 3/4" SU's)

And I am looking at the Crow range of Hydraulic camshafts

http://www.crowcams....e-Holden6.shtml

Thankyou, and all help and knowledge will be appreciated. Matt

[superfly_GTR]

what im wanting to know is what is better high lift and short duration, or low lift and long duration or a bit of both and what each combo does, also what does the valve timing spec do? ie: differance between 30/70 and 40/80 also what is better combo for inlet an exhaust because i noticed most have different specs for both. I am running 3.08 diff gears with an M20 but was thinking of going to 3.36 if mine kicks the bucket.

Cheers Matt

[Tiny]

Actually.. Thats a pretty good question matt.

Ive seen this covered in a few magazines in depth, but i wonder if we have any members on here who may like to put together a tech article on what is a cam, how do they work, and what do all these funky numbers MEAN...

I used to have a reasonable grasp of the works of cams, but to be hinest.. ive forgotten it all!

If anyone's got the info, or maybe i'll look into the magazine articles ive kept and try and post them up for more people to see and learn about cams.

Cheers!

[Tiny]

Dave. I fully understand that we'll never become experts, but maybe i was thinking of an explaination of what things like base circle, lift, duration, overlap means and a possibly ( And i know this is wehre the diffuclty comes in) how they affect a basic engine.

I understand too that this knowledge is the money of any engine builder, and by no means do i want to take that away from anyone!

I was thinking of some basic info for people's knowledge ( and to stop em using that damn rediculous "Stage 58" terminology that shits me so badly!!)

Cheers I'll try and find the magazine articles i had with this info and scan em up if i can!

[micklx]

A cam with a long duration will give a lumpier idle, whereas a cam with a shorter duration but more lift could flow a similar amount but have a smoother idle due to the inlet and exhaust valves being open together for less time.