Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

7028276 air fuel ratios at cruise 15.9

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PonchoVia:
This thread should be required reading. The explanation should really be tagged and posted on the home page.

The voodoo that is understanding a camshaft has been much more difficult for me to grasp than anything else. I   am just beginning to understand the basics.

What engine characteristics are affected by the centerline alignment of the camshaft?

thanks.

Cliff Ruggles:
Moving the cam around effects the intake closing point.  It also effects scavenging across TDC during the overlap period. 

There is a lot of things going on in one of these engines.  From what I've seen the big CID engines enjoy big cams on wide LSA's.  The Pontiac 455 by design is undersquare and fed by cylinder heads with no more cross section than an average small block Chevy head.

Good for cylinder filling down low, but chokes them up quickly at higher RPM's.  They were designed to be low RPM engines with tons of grunt for effectively moving heavy vehicles around. 

I have built a good many here, and consider any cam with less than 230 @ .050" duration too small.  I still see folks put tiny cams in them for "more low end power", but they will make more power than you could ever use at low RPM's with a larger cam, and the larger cam will make a butt-load more upper mid-range and top end power.

I attached a dyno sheet and cam card from a 455 we did here couple of years ago.  It was about 8.8 to 1 compression.  It idled with 14" vacuum and dead smooth clear down to 600rpm's.  I even had Harland Sharp 1.65 ratio rockers on that cam.......Cliff

PonchoVia:
533 torque at 3500?!?! AND 454 horse at 8.8 compression.
These things are amazing when they

Cliff Ruggles:
Yep, actually undercammed it a bit, wishing afterwards I would have went to a .380" lobe with 289/308 seat timing, 236/245 @ .050" and 114LSA with the ICL at 110.  It would have at least 500hp and  still good idle quality and street manners.....Cliff

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