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Old 08-27-2012, 04:06 PM
oldbogie oldbogie is online now
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Quote:
Originally Posted by dave350v8 View Post
Hi
bogie and engineczar both of you are spot on! It does seem to at least match the camels at lower revs but then it wants to rev further than them!
The advertised duration is 280 and at .50 intake/exhaust is 230 degrees.
To be honest I dont fully understand these figures.

Skip whites website states with a cam around 480/510 lift it dynos at just over 400 horsepower on a 350.

Do you think changing rear gears and a bigger carb will help, I was considering a cam change as well if you have any suggestions?
Thanks again
Certainly a bigger carb say around 750 CFM on an Edlebrock Performer RPM intake with long tube headers of 1-3/4 or 1-7/8ths tubes combining Skip's deep breather heads with this cam, the engine ought to go to over 400 horses I guess somewhere from 5800 to 6200 RPMs. It's likely to be peaky; it also may take 1.6 rockers to get there.

This whole thing, and this includes the performance from your older camel humps, really gets the engine into an area where in a systems integration sense, sum of the parts and the tune, it can gain or lose gobs of power on incredibly small often seemingly innocuous changes/exceptions/deviations of things. So with a change, as the one you did with the heads, can make it difficult to dial it back in. You just have to mess with it and that could include as was suggested advancing the cam a few degrees, I havent used a Skip White cam so I don't know if he grinds them straight up or advances them as Comp and others do. So you've got to be a bit thoughtful here. Comps come with about 4 degrees already in them so sometimes adding more isn't helpful. I just don't know if Skip's cams are the same way of not. Like Jim Miller, he touches base in here sometimes maybe you'll hear from him about this.

Your cam numbers tell you that the valve closed to closed timing is 280 degees, SAE (Society of Automotive Engineers here in the U.S.) specify this measure at .006 inch lift, whether that is really done here I don't know. 230 degrees is the duration measure from the point where the valve opened to .050 inch and is .050 inch from being closed. The difference between these two points is mostly ramps to ease the lifter and valve train motion into opening smoothly without flexing the pushrod and sitting the valve down without bouncing it. The .480/.510 inch measure would be the amount of intake and exhaust opening, respectivly, over the peak of their lobes. This is valve opening not lift at the lobe, there is a rocker between these two places. For the Chevy Small Block this is usually given for a 1.5 to 1 rocker ratio. So the actual lift happening at the lobe would be 50 percent less or .320/.340 inch. A 1.6 to 1 rocker would add 1.067 to the 1.5 rocker ratio and lift so that lift at the valve would go to .512/.544 inch with this cam.

Stiffer gears would improve acceleration performance by increasing the mechanical advantage the engine has over the mass it needs to move. Plus, it moves the RPMs higher for any given road speed to where more engine power is available. So gearing is a double advantage in terms of power delivered between the tire and ground. The downside of stiffer gears is higher fuel consumption, noise, vibration and wear.

Bogie
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