Chevy Car Questions & Answers - Performance Q & A

Kevin McClelland Oct 1, 2009 0 Comment(s)

Too Many Choices
Q: I have a '74 Chevy Nova with a 406 SBC in it, and I'm having trouble deciding if I should change my intake. The current setup is 11.5:1, AFR 210 Eliminator heads, a Comp XR294HR cam with 1.6 Pro Magnum rockers, Total Seal rings, a Speed Demon 850 (changing to Mighty Demon 750), and all forged internals-everything with ARP studs. Currently I have a Victor Jr., but when I read the CHP article with the 16 different manifold test on the 383 ("Manifold Learning," Sept. '08), the Jr. didn't impress me. The car is a street/strip car that weighs 3,550 pounds with me in it and has 3.70:1 with 26-inch tires, a 3,000-stall converter, and a TH350 transmission. The best e.t. is 11.54 at 117, with a badly slipping Third gear (on pump gas). The trans is being rebuilt as I write this. My cam is relatively small for my displacement, and I want to keep the rpm in the 6,200-6,300 range because it's a factory four-bolt block. I was thinking about switching to the RPM Air Gap because of my cam, but this year I'm planning on throwing a 150hp shot of juice at it (plate kit), and I don't know at that point which manifold will work best. With my setup, will an Air Gap be too small? Thanks for the help.

Jason Gielish
Albany OR

A: What a nice package you've assembled, mid-11s out of your combination that is street driven in a fun car! When you present 16 manifolds tested on one engine, it can be somewhat misleading, and how the data relate to every engine combination can vary somewhat.

Now that we've gotten past the disclaimer, let's talk about your manifold selection. A standard 2975 Victor Jr. manifold usually works best with 2 inches of open spacer under the carb. The plenum volume is inadequate in most cases (back to the disclaimer), and Edelbrock was trying to stay within a hood clearance/packaging constraint. What Edelbrock came up with was a great all-around manifold. Will the dual-plane design make more torque below peak and in the meat of the torque curve? In most cases, yes. Will that give you more trouble getting off the line without spinning the tires? Maybe. Again, it all comes down to working out your own combination of parts.

On top of all that you want to add a plate nitrous system. This adds another layer of possibilities. Usually we prefer to add nitrous to single-plane manifolds over dual-plane ones. You get much better mixture distribution to all cylinders with the single-plane design. Can you run a plate system on a dual-plane? Sure, it is done all the time. However, when pushing the tuning we'll go with a single-plane every time. The last thing you want to do is have a distribution issue with nitrous on one cylinder and push the tuning until you find which cylinder is lean on fuel, not nitrous. Unfortunately, you could be adding spark advance and watching the performance increase and one cylinder is going into detonation. The other seven cylinders may be happy as can be with the spark and the car runs quicker and faster. This is when it will be too late.

There is new technology out on the nitrous plate designs with the perimeter- and diffuser-type plates. This atomizes the fuel and nitrous much better, but with the dual-plane designs having sharp turns and elevation changes, the chance of mixture separation is much greater than with a single-plane manifold. If it was our engine below the plate, we'd stick with the Victor Jr.

Sure Stop
Q: I could sure use your help. I have safety concerns about the rear brakes on my '98 Chevy Silverado pickup. The rear brakes' stopping power is very, very slight, if any! The brake shoes after 100,000 miles still appear OEM new, regardless of continual adjustment, cleaning, and roughing the surfaces of the rear drums/shoes. Symptoms include the front rotors hot-spotting, three sets of front brake pads, and a long brake pedal stroke, and the occasional actuating of the antilock system at really slow stops. The ABS or its sensors are not at fault, I am sure.

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