Quote:
Originally Posted by vanmor
I don't like either. Look for something with a 270 advertised duration. Also go with a wider LSA. Something like 112 to 114. I like 0.050 durations around 218 to 228 on the intake. 224 to 234 on the exhaust.
I'm not an expert by a long shot, but I have done extensive reading and studying on the subject. I have also talked with people who vary in age about these things over the years.
For a street driven Pontiac with a 2000 to 2500 stall or four speed, 3:55 to 3:23 gear, and 72cc to 83cc iron heads, you can't go wrong with the above cam parameters.
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Look at the timing specs will ya!
http://www.lunatipower.com/Product.aspx?id=1776&gid=287
If he Ran a Summit 2802 which is roughly what you describe which has 114 LSA installs at 110icl iirc, the intake closing will be about the same spot as it would end up with my suggestion. In other words the number of degrees in compression would be quite similar!
The exhaust opening point would still be in a favorable position plus this cam would have less overlap/overlap window.(his combo isnt going to benefit any from more overlap!)
The 2802's best quality is its intake closing point helps where compression is on the edge for pump gas. Its certainly not a better cam than this VooDoo for his application.
BTW, next time you get a chance, degree a cam with the heads off and pay close attention to where the piston is. Not just the degree wheel, but where the piston is relative to the deck, relative to cam timing! Find seat time and other points like .020" and .050" and .100", .200" etc. cam lift.
You should discover that LSA and duration at .050" is NOT how a cam is designed nor how it should be chose! Likewise you dont "automatically" decide 112 LSA needs to be at 108ICL! LSA and ICL are coincidental centerlines of chosen timing events!!! Best used for checking purposes! Likewise duration at .050" tells you little without a whole bunch more info! Again best used for checking purposes.
Cam timing events and ramp rate requirements are based on application. Head thru-flow and stroke greatly determine what cam timings and ramp rates will be required for the result intended.
btw If you want to get a better perspective than my above suggestion, check timing points at the valves on #1 with the head off the other bank where you can observe that #6 Piston wiil be at same position in the bore as #1. This way you can see actual valve movement and all the relationships to what I said above. Even more interesting is to do this with a 350or 400 then put the same cam in a 455 and repeat the process. Keep in mind either engine hits max piston speed NEAR approx 75 deg bbdc.(each will be different fwiw) I'll let you do a little research as to why that is important to know.