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Originally Posted by crochunter
Yeah i know a F260 cam is good but it has the same lift on exhaust and inlet. Isnt it better to have more on the exhaust side. Perhaps Davis knows.
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I wouldn't touch a flat tappet camshaft for this application. There are others who may disagree, but a roller cam is the way to go if the springs will work with it.
There is no real cost differential between a custom roller cam and an off-the-shelf roller cam, so a custom cam can be made to order specifically to the application.
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Originally Posted by crochunter
351 bored 30 thou
grout filled
eagle rods
forged pistons
comp is 11.5
4v closed chamber heads
2" pacemaker extractors
TFC Manifold
port stuffers
750 ultra hp series holley
This car will be used mainly at the drags and motor is in a XY falcon. So if anyone could help me with a camshaft that would be much appreciated. He is hoping for 500 hp if thats possible.
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A camshaft is like the "brain" in an automotive application, particularly non-computer controlled applications. Note that "application" doesn't just mean a few engine parts. The entire application needs to be considered. What transmission, converter, tire diameter, gear ratio, etc. all need to be considered. Also, the weight of the vehicle must be considered. I don't know what an XY weighs, so I can only speculate at best.
A 750 carburetor is too small for a drag racing application at 500+ HP, IMO. He'll want 800-950 CFM, with probably a reasonable minimum of an 850. A bit of this will depend on the gearing, tires and converter (if applicable), but anything less than about an 850 will reduce the ET potential. If your mate already has the 750, he can try it, but that is a small engine carb for a mildly worked 355 Holden, not a fire-breathing Cleveland.
The 2" diameter primary extractors are likely too large without a larger carburetor. For that much extractor, you need some fairly serious RPM and/or fairly serious displacement. With larger extractors, higher RPM power is aided at the expense of some lower-end torque. Every part in the combination has an effective RPM range where it is contributing effectively to the goals. Every part also has an effective RPM range where it is detracting from the goals. A lot of these ranges on both the + and - sides of it will be overlapping. Too much in one or two areas will take away from something else in one or more areas.
I'm guessing that your mate doesn't have the budget for a lot of testing, so he probably wants something that is going to work fairly well out of the box. The cheapest way to do this without nitrous is to use more displacement. A larger engine will make more usable power at a lower cost than a smaller engine. If he is able, consider using a stroker. The money spent on a 393 will be well worth it. The added lower-RPM torque will help get things moving along very well, too. Of course, then the chassis design comes into play and whether or not traction will be sufficient enters the equation.
However, assuming that your mate intends a responsible gear ratio of about 3:90-4:33, depending on tires and assuming something under 3500#, I would likely recommend a solid roller camshaft with about the following specifications:
.680-.700" lift w/1.73:1 rocker arm
252* intake @ .050"
254* exhaust @ .050"
108* LSA
37* valve overlap
900 CFM carburetor (use a restriction plate to fine-tune flow for off-the-line performance and maximum MPH through the lights)
Add a pyrometer to at least the #1 cylinder to get an idea of how much heat you're making.
Polish the combustion chambers in those iron heads until you can use them while shaving.
Run a crankshaft scraper.
Carefully balance and weight match every single rotating component to within +/- 1gm.
Ensure that the block machining process is extremely exact. Any amount of bore taper or deviation exceeding about .0002-.0003 is way too much, IMO.
Mirror polish the crank main and rod journals.
Use head and main studs. Be sure to use the studs during the block machining process!
Pay special attention to the finish hone of the cylinders.
...there are probably 9000 other things to consider, but I hope that this at least gets up to the plate.
:davis:
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