General Category > Quadrajet Carb Talk and Tips

camshaft rules of thumb?

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billy 2:
  I agree as well for all the same reasons. billy 2

Cliff Ruggles:
We use roller cams only in engines built here since the retrofit parts have became readily available.  It just makes sense to take "scrubbing" a lobe out of the equation, and I sleep a lot better at night!.....Cliff

Marx3:
I never really understood what to use duration at 050 for... Besides maybe getting a picture of how steep the ramp is.
I think the whole idea behind getting nice civilized idle and response and that strong locomotive feel makes so much more sense than getting some flashy cam that sound great in idle but never really work with the engine since most people do a cam change only. A good example is this cam:
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=708&sb=2

into a completely stock smog Mopar 400 from the mid-70's with 7.5:1 cr.
A friend of mine was advised that this cam was a fine choice for a 400 engine.
I enlarged some things on the idle system on a nice late 70's Pontiac 800 cam unit.
It idles fine, but sound a little like it's got 400 hp, but it has sub 10 hg vacuum in idle and I doubt it makes over 250 hp at the crank.

Are there some guideline to determine minimum lsa from? Or is it also determined by the adv.
duration? I guess you could as much lift and duration into any engine combination if only you where not plagued by overlap?

Shark Racer:
That is a VERY aggressive cam for that little compression ratio. You need to get the compression way up to appreciate a cam like that - the cars that were typically matched with a cam like that had compression ratios around 10.5-11 - on iron heads. (at least on Chevys!)

Duration at 050 coupled with the LSA will determine how well it idles, how much suction is available at idle. I have a much milder cam, 216/216-110 on a roughly 8:1 CR and it's also too much cam for that ratio.

Honestly, I'd go with a cam in the 20x duration range at most with that CR. Better yet, up the CR (thinner head gaskets, smaller cc combustion chambers, different pistons, deck the block, some combination thereof) and optionally go down a step or two on cam.

Marx3:
Yeah dynamic compression ended up around 4.5:1 sad thing is it as a reputable shop that suggested that grind. Jesus Christ... Engine is in a completely restored 68 charger that is going to be sold to free up money for the next build. By that time I am helping him out on building the engine.

Aha! Duration at .050 and LSA determines idle/vacuum quality... VERY interesting.
Can you elaborate?

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