Quote:
Originally Posted by SSLance
I have pretty much narrowed my cam choices down to these two:
The cam for the SP383
Duration at 050 inch Lift: 222 int./230 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.509 int./0.528 exh.
Lobe Separation (degrees): 112
And the Comp cams XR276
Duration at 050 inch Lift: 224 int./230 exh.
Valve Lift with Factory Rocker Arm Ratio: 0.502 int./0.510 exh.
Lobe Separation (degrees): 110
Is my interpretation correct that the 110 degree lobe separation of the Comp Cam XR276 will bring the power band in just a bit lower in the RPM range than the 112 degree SP383 cam if everything else was the same?
I can put my hands on a pretty fresh XR276 for a great price and I'd have to buy the SP383 cam new. Either way not a big deal, but every penny helps.
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Tighter lobe separation will give you HIGHER cylinder pressures -- will narrow your power band - give you more bottom end torque and should give you a higher PEAK power.... it will also LOWER your vacuum at idle (who cares).
A WIDER LSA will do the exact opposite of the above points.
I'd go with a larger cam - and make sure you get the right one for your application -- i.e., is your block already set up for a roller cam or is it an early block that requires a retro fit roller cam... if it was me - I'd probably choose the XR 288..... but I like a bit of cam in a car. The 288 is rated at 2500 to 6000 rpms.... or at least the XR 282 rated at 2200 to 5800. On the AutoX course - I'd want the little extra RPM's the bigger cam would have.
Rule of thumb -- larger cubic inches "eat" bigger cams. In other words - larger cubic inches tend to make a cam more mild than it would be in a smaller cubic inch motor.... So I like to choose "one up" from what would be correct for a lower cubic inch motor.
Nothing worse than sticking a cam and having it sound like your grandmothers Buick.... My buddy Pierre choose the wrong cam for his 496" BBC.... firing it off makes me want to just turn and walk away before anyone sees me by the car. Sad. LOL