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-   -   Built 350 stops making power at 5000 rpm??!! (http://www.hotrodders.com/forum/built-350-stops-making-power-5000-rpm-2742.html)

chevyelc81 06-11-2002 09:36 PM

Built 350 stops making power at 5000 rpm??!!
 
Ive got a 1981 camaro with a 350 that i just rebuilt, Its got a forged crank fully balanced, forged pistons, 1.94 heads, Ive got the performer RPM intake and cam power package which is rated at 1500 to 6500 rpm. I put new performer valve springs in, and im running a 650 cfm edlbrock carb with full length headers and a flowmaster force II exhaust system. Its got good torque and you can feel the horsepower incrase as the rpm's go higher but as soon as I hit 5000rpms, the motor stops pulling, I don't get it. It should pull to more than 6500rpms. Im thinking it might be my distributer. Its stock but I have the accel coil with the 8.8mm wires. Ive tryed retarding and advancing the timing but nothing seems to help. Some suggestions would be good....

4 Jaw Chuck 06-11-2002 10:28 PM

The cam ratings are estimates and are only intended as a guide, other factors such as porting and carburation will have a greater effect at higher rpm than will the cam. What's it do on the dyno, sounds like a hp/inch setup to me? Just because a cam is rated for a 6500 rpm power range limit doesn't mean your engine will continue to build power to that rpm. You would need a cam with 310-320 duration to reach that kind of rpm and still be building power, but stick some restrictive heads on that engine and it would fall on it's face long before it reached 6500. The entire engine is a package and the heads are a very big part of that package and so is the header design and carb size.

The other part of this is what I call manufacturer padding, the mfg knows that everyone out there will want to put the biggest cam in their engine that they can buy but nobody wants an engine that barely idles at 1200 rpm and stalls when the weather changes. Therefore they overstate their street cams abilities somewhat knowing full well that their largest cam is probably all that the typical consumer is willing to put up with.

Have a look at the circle track grinds and do some comparing, you will see a big difference in lifts and durations as they relate to rpm in comparison to their street profiles. In racing they don't care one wit about idle quality and only want power in a certain rpm range plus the mfg is confident the hardware will be there to support the big lifts and durations. If you want to be making power at 6500 that would mean you would be shifting around 7000-7400, that is Nascar territory man and it might surprise you what kind of hardware it takes to reach this level of power range. Think 850 double pumper and brodix heads with huge single plane intakes and 3/4" header tubing diameters. Your stock type heads are not ready for this and neither is your stock type reciprocating assembly. You would need to go up to 2.20" valves and do some serious porting to a factory head to get there.

Enjoy what you have, to get power in the range you are suggesting is not comfortable for the street and totally out of line with street oriented off the shelf consumer parts. Now if you want to get serious I would suggest looking at what a typical circle track sprint car runs for parts and go from there, leave the factory stuff for the grocery getter.

Sure would be nice to banging shifts at 7200 though wouldn't it?

F-1Rodder 06-11-2002 10:33 PM

I think QuadJaw is onto this one pretty well. You may not be that happy with an engine that actually runs strong through 6500rpm. To me this spells dog at streetable rpms. It will probably run through 6500, it just doesn't have the same pull at that range. The manufacturer states a range of operation, they don't say where it is best for a given demand. If you want the best of all worlds, buy a VTech engine.


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