ratnacage

True, but let's look at the big picture. The WOT gains are less than 10 across the board, so even using very ambitious assumptions, that's less than 4% of the output at 3000 RPM (assuming 240 rwtq at 3000 rpm). Now look at part throttle and you're talking gains or losses that are virtually undetectable. The bottom line is you don't need a dyno to find the answer to the original question. This is in no way a swipe at the OP, but too often people get themselves buried in graphs and dyno numbers and fail to step back for a moment to look at the bigger picture.

Norm Peterson

I wonder how closely the single-plane vs RPM-oriented dual plane carburetor manifold comparison works as an analogy here . . .


Norm

ratnacage

I don't think it does. The dual plane manifold reduces the effective volume of the intake runnersto each cylinder. This maintains intake-runner velocity higher, which in turn supports low-end torque. Dual planes develop less torque on the high end than single planes as they become more restrictive relative to a single plane, and the higher velocity is not enough to overcome this. This is the 'Reader's Digest' version - the actual explanation would take several paragraphs, so hopefully this explains the single vs dual plane sufficiently.

The CMP's (charge motion plates)in our cars don't change the overall volume of the intake runners so intake velocity shouldn't change - HOWEVER, air will accelerate around a throttled CMP, and if they're close enough to the intake valves, then maybe they'd have the same effect. But as I understand it, the CMP's serve only to induce turbulence which promotes better fuel mixing at lower rpm. I'll leave open the possibility of being very wrong on that point however.

Norm Peterson

OK, I'm beginning to get a picture. A cc or so of material that provides throttling isn't going to affect the volume enough to matter much, but the effect on the velocity field will, and I'd certainly expect that to be somewhat RPM-sensitive.

Does anybody have any real pictures of the OE CMP's? I'm beginning to wonder if they bias flow toward one of the two intake valves, affecting swirl and tumble within the cylinder.


Norm

UrS4

No swipe taken. I was in retrospect more concerned about the part throttle torque decrease below 3K for normal street driving. And like Norm said, I would be concerned if delete plates in combo with an O/R X would decrease the low end torque enough to feel like I need to down shift more often which would suck as even with the 4.10s I think the bottom end lacks low end torque.

Obviously if I was racing I would be above 3k so the benefit of the reduced restriction would be noticed but unfortunately I don't road race evey day.

danGT06

I've got an O/R h-pipe and CMDP's and I didn't notice any low end torque loss.. I did pick up 14rwhp from the delete plates and O/R pipe. I could care less if I lost torque below 2k if anything it helps me take off easier next to cops. If I'm racing it doesn't even come into effect.