Author Topic: idle help  (Read 3271 times)

Offline Cliff Ruggles

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Re: idle help
« Reply #60 on: January 09, 2022, 04:02:31 AM »
Same thing with camshafts, all are good just some better than others. 

Attached is an overlapping dyno sheet showing what happened when a back to back cam swap was made with no other changes.  Nothing fancy about the engine, just a basic Pontiac 400 with a stroker kit installed to get it to 463CID, 9.3 to 1 compression, and factory iron heads flowing 250cfm.  So really no better if as good than a well prepared set of Chevy peanut ports.

The first cam is the "famous" XR276HR Comp Cams HR.  They recommend that cam to nearly everyone that calls them for a HR cam choice.  It was also Butler's (company that specializes in Pontiac engines) "go-to" cam until I sent them the dyno sheets.

Anyhow, the XR276HR cam is pretty aggressive with short seat timing events, tight LSA (110) and ICL advanced 4 degrees (106).  It sports 276/284 @ .006" duration and 224/230 @ .050".

The problem and why it was replaced.  It was too good at cylinder filling and causing pinging/detonation of pump fuel.  Yes, what folks don't realize here is that you can put a small cam in a big engine and make too much cylinder pressure for pump gas even below the proverbial "brick wall" of 9.5 to 1 compression.

My suggestion was to put a bigger cam in the engine on a wider LSA so I recommended using older Magnum lobes with 289/308 duration @ .006" and 236/245 @ .050" and to move it out on a 114LSA and install it with the ICL at 110 degrees.

No other changes made.  The results were no more pinging, smoother idle and a nice power increase over a broader RPM range........

Offline old cars

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Re: idle help
« Reply #61 on: January 11, 2022, 03:29:03 AM »

A few years ago my brother rebuilt the engine in his 1970 GTO 455 4spd , 355:1 rear axle . He has owned this car since new and it is still stock down to the carb and exhaust manifolds. He just street drives now and not that often. This is the camshaft he chose. He says he is very happy with it for what he does.



Part Number: 60918
Pontiac Hydraulic Flat Tappet Camshaft

Pontiac - 287, 301, 316, 341, 350, 370, 389, 400, 421 & 455
Performance level 3 - Torque Beast - Delivers impressive midrange and top end power. Healthy sound. Economical price.
INT/EXH - 288/298 Dur @ .050” Lift: 214°/224° RR: 1.5/1.5 Gross Lift: .444”/.467” LSA: 112° RPM: 1750 to 4500 Redline: 5000

Offline Cliff Ruggles

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Re: idle help
« Reply #62 on: January 11, 2022, 04:22:47 AM »
That cam isn't a Crower grind, it's actually an old "generic" cam that's been marketed and sold under at least a dozen labels over the years.

The companies selling them "juggle" the specs slightly to make it look like their own cam, but they simply buy them directly from CMC then re-box/sell.

It's actually an excellent camshaft for a Pontiac 400 engine build with moderate compression.  A tad small for a 455 but still works pretty well there too.  Marketed by Summit Racing as the 2801 and often called the 068 "high lift" cam in Pontiac circles.  Pretty popular overall and has a lot of seat timing plus considerably more lift than the factory 068 and 744 Ram Air camshafts.  The gentle ramps are easy on the valve train and wide LSA makes for smooth idle, strong low end/mid-range power and good street manners.

Here is a link to some Pontiac camshafts that were sold over the years.  Drop down to 214/224 @ .050" offerings and you will see how many Companies market that grind and notice how the "advertised" specs are different since they are trying to make it look like something they grind "in house".........

http://www.pontiacpower.org/PontiacCams.htm