Originally Posted by
Epstein
Oh I know all about how torque and horsepower are related. How power under the curve affects acceleration, where gearing comes in, etc. I built the knarliest spreadsheet around for comparing 2 setups, all coded by hand. It'd be a different story if GM had some OHC motors so they could actually make power over 6000 rpms where your tq/hp multiplier is higher. LS7 might make 475tq but that drops to about 350tq only 1800rpms later (8000rpm). Torque is all about peak cylinder pressures and displacement. It has a lot less to do with flow rates, which was the point I was making against your flow rate arguement. Lets compare 5L class engines then, since we're equating displacement with torque. Lexus 5.0L 2UR makes 371tq. The most powerful 5.3L L-series (including LS4 and the truck L's) is 340tq. Hey, what happened??
HP = airflow end of story. Your L92 (or L99 or whatever) head is great for having 300cfm in, but the 200cfm out is the limiting factor here. You might as well only have 250cfm in. If I can completely fill a 5.0L motor 7000 times a minute and you can only fill your 7.0L motor to 60%, guess whose doing more work?
Here's a little exercise. Car1: 500hp at 7500rpms, which is 350tq. Car2: 500hp at 5500rpms, which is 477tq. That's all just math. Adjust gearing so that they're going the same speed while making 500hp. Figure out which one has the most acceleration. GO!
Make up your mind, first you post the K20 head as an example of something that flows awesome, LSx heads cant touch it modified, then a stock casting, truck head outflows it, both intake and exhaust, then you run off trying to complain about the exhaust flow, when it still flows more than the K20 head, on both sides of things.
Uh comparing the 5.3L lame production truck engine to a performance lexus sedan engine ? Really now ?
As far as the 500 HP car comparison goes, like I said show me a comparison of the two dynographs overlayed, good adjust the gearing so both are at the same speed @ 500 HP, great for a theoretical comparison, now adjust the gearing so the LS7 is in its torque range within a useable speed range, with the included transmission, chances are you are going to end up with something that has you over 400 ft lbs from 1800-6800 or so, oh whats that you say the V10 from your audi doesnt even make 320 ft lbs ?, the bmw engine barely into the 400's ? Ouch. I know which i'd rather install, oh yeah, pssssttt by the way, thread was for v8 discussion, i think was his point above, as now everyone wants to bring in honda 4 cyl heads, and bmw / audio V10 engines to make weak attempts at putting down the Gen3/4 sbc platform.