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Camshaft Selection for your New Engine

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jamesF:
GOOD INFO.That was a great read...... That made me  pull the trigger.. I ordered a Stump Puller on a 112 from Dave at SD this afternoon for my 455 to replace my XE type on a 110 LSA..

Cliff Ruggles:
Thanks guys. 

The Stumpuller cam is excellent for a Pontiac 455 engine build.  I like to see at least 9.5 to 1 compression with it. Idle quality is excellent, relatively smooth with just a hint of attitude. It produces a very strong/broad/flat power curve and works quite well with stock converter/gearing, but really shows it's colors with a very well made aftermarket converter with a little added stall/torque multiplication but still very well coupled in the "normal" driving range.......Cliff

Cliff Ruggles:
Had a few extra minutes this morning and wanted to put up some dyno sheets here.

It's a great story and on topic about camshafts if you have time for the read. 

The story goes that an engine builder and machine shop owner builds his first Pontiac engine.  He had extensive experience with other engines but never took a Pontiac 400 and installed one of the available "stroker" kits to make it a 455 (actually 467). 

He took on the project and bought the stroker assembly, and topped with an nice set of #96 heads ported to 250cfm on the intake side.  Stock head flow is around 215 or so for those heads.  Anyhow, he computed the static compression ratio and it came in around 9.3 to 1.  So he should be fine on pump gas, IF you believe all the "experts" on the Forums who continue to regurgitate information on that subject.  The engine builder also wanted to upgrade to a hydraulic roller cam with retro-fit lifters.  Comp cams recommended and sent him an XR276HR camshaft.  On paper it really doesn't look too bad for the build, sporting 276/282 @ .006", 224/230 @ .050 duration, .335/.340" lobes (.502/.510" lift) and 110LSA. 

The cams is installed, degree'd at 106ICL and they go to the dyno.  My only contribution to the project is supplying a rebuild kit and tuning parts for the Q-jet they are going to use.  The dyno runs are a bit disappointing and of course everyone is blaming the Q-jet from the dyno operator all the way down to the guy who takes out the trash.  They actually installed their "dyno mule" Holley and cranked up the timing to make acceptable power and blew up the engine on the dyno from detonation.  Yep, pinged it so hard it spun the rod bearing and damaged the crankshaft.

So I get the call from the shop owner and we go over the engine specs and I tell him that the cam is the problem with it and to replace it with a larger cam on a wider LSA.  Of course initially he's a little set-back by my comments not fully understanding that the relatively "small" cam on the tight LSA was simply too good at cylinder filling and making excessive cylinder pressure early in the RPM range.  Yes, tight LSA yanks power down and narrows up the power curve.  This not only hurt power it would not allow the engine to effectively manage pump gas even a little less than 9.5 to 1 compression.  We also talked a little bit about my experiences/track history with long stroke Pontiac engines and tight LSA with early closing intake specs and finding that the wider we go with LSA and bigger the camshaft the better they work when placed in service and the more power we are rewarded with.

So I supplied some cam lobe recommendations, we moved up to a 289/308 @ .006" with 236/245 @ .050" with bigger .381" lobes and wider 114LSA.  I advised to set the ICL at 110 degrees and not advance the cam any further.

The engine was repaired, and the only change done was the cam replacement.  They put it back on the dyno and low and behold it is now fine on pump gas with "optimum" timing/fuel curves, idles better, and cranked out quite a bit more power as shown on the dyno sheets!.......Cliff

Cliff Ruggles:
Bump.

David Haskins:
Very informative article Cliff. You have me thinking about my 69 Pontiac 350 rebuild and the cam I chose to use in it.  I was wondering about the god awful smell in the garage every time I fired it up. I have used nothing but 93 octane non-ethanol fuel ever since the motor has been rebuilt (approx 2 yrs ago and 500 miles)with a Holley 600 that I never could get to work properly.  Gonna need to give some serious consideration to re-camming the bird.  Thanks for your wisdom.

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