I'm also planning another 500 inch build. Taking the bottom end out of a 496, and will use it in a 400 block to come up with a 512. I will need new pistons, of course. I have a set of Stealth heads on the 496 now, and it seems to run out of breath about 5000 RPM or so. Torque falls off, and it just wont go much faster. So, as has been said, a head that will only flow enough air to get a 500 cubic inch motor up to 4500 or 5000 RPM before torque falls off, doesn't make sense. Especially in a drag race motor. Most heads in production form usually can't supply the flow needed to make them run well at higher RPMS. So off to the professional porter they go, to make them flow more air. I'm sure there is a formula that shows how much intake flow is needed to get a 500 cubic motor to produce maximum torque at say, 4500 RPM. DOES ANYONE KNOW HOW TO DETERMINE THAT? And would you please let us know? Then we can find a head that will flow the right amount of air to make the 500 inch monster run like it is supposed to. Thanks
For the purpose of response I'm going to consider the Stealth head and the Edelbrock RPM head the same, as we can get the same air flows from each head.
I think maximum torque rpm is going to be determined more by the camshaft than the cylinder head flow, and then to a lesser degree, by the intake manifold design.
We ran a 451 stroker with 452 iron heads that flowed around 302 cfm @ .600" and a 496" stroker with Edelbrock RPM heads that flowed 309 cfm @ .600" lift.
The 451 used a Comp Cams solid roller 254/260, .582/.588, 110 LSA.
The 496 used a Lunati solid roller 249/255, .585/.600, 110 LSA.
451 made max torque of 588 lb-ft @ 4,600 rpm and 621 HP @ 6,100 rpm
496 made max torque of 642 lb-ft @ 4,600 rpm and 642 HP @ 5,800 rpm......so we know that 300+ cfm will get a 451-496 engine to max torque with that kind of cam around 4,600 rpm.
Then we used the 451 and a 500" with the same pair of 906 iron heads that flowed 340 cfm and both used the same solid roller 280/288 @ .050, .800/.800 lift.
451 made max torque 548 lb-ft @ 6,200 rpm and 694 HP @ 6,900 rpm
500 made max torque 599 lb-ft @ 6,200 rpm and 730 HP @ 6,600 rpm
What can the well ported (340+ cfm) Edelbrock/Stealth heads do on a 451? With a solid roller 278/280 @ .050 and .780/.780 lift, just one of many dyno sheets from 11/29/09 says.............601 lb-ft @ 5,800 rpm and 773 HP @ 7,200 rpm. I can only guess what the 500" engine would do with the same heads, we never tried them.