Maximum Hp With Manifolds…

[RR3834bbl]

In a January 2005 issue of Mopar Muscle, pages 56-61, they set out to find what components would make the most horsepower in their application while utilizing factory HP exhaust manifolds. There base, a 466CI low deck stroker engine, Edelbrock aluminum cylinder heads, and ‘73 400 HP exhaust manifolds. Then they began dyno-testing the engine using different types of cam, intake, and carburetor combinations. Their favorite carburetor ended up being an AFB style 800cfm Edelbrock. With the dyno results they got, it was no surprise to me that they found that the engine favored a duel-plane Edelbrock Performer RPM intake manifold over the Mopar M-1, and Victor 383 single-plane intakes.

The most interesting find in the article was the cam that they found worked best with the restrictive exhaust manifolds, and this is where I want to focus the topic of this thread.

They began their dyno testing with an old design Mopar Performance “Purple Shaft Mechanical Cam” .528/.528 – 241/241 Degrees Duration @ .50. After that, they tested other cams, which were not mentioned in the article. It would have been nice to know what cams they tested with torque and horsepower numbers, but those were not provided. Anyway, this is what they said about their cam testing. With their combination, the engine did not like anything over 245 degrees duration @ .50. In addition, they said that power went South with anything over the .528 lift. Most interesting, they said that their motor did not like dual pattern cams, quote, “One would think that with the restrictive exhaust you should leave the exhaust open longer to blow out the spent gases, but that theory didn’t work as planned when we tested it.” In the end, even they couldn’t explain why the old MP cam worked so well with their combo, so they just went with it, after all, I guess dynos don’t lie. The final posted RWHP numbers, 527 lb-ft of torque, and 474 horsepower.

So I would like to open up speculation and look into why the old cam design worked well with the exhaust manifolds. Simply because I am planning on using factory HP exhaust manifolds and dual plane intake in my car. Of course I know that there are many other variables involved with selecting a cam, so I am just posing a general question. It would just be great if I could see through all the smoke and find out if one cam design would work better over another, e.g., duel pattern, or single pattern? Old Mopar Purple Shaft, or newer fast rate of lift? One thing is certain, IÂ’m not interested in a mechanical cam as IÂ’m after street reliability; I donÂ’t want to worry about adjusting lifters all the time. Could it be that the Mechanical cam is the reason they got such great numbers over the other cams?

For the complete Mopar Muscle article, go to:

[url]http://compcams.com/Community/Articles/Details.asp?ID=2004

[jelsr]

After an unexpected blow up I installed my Super Stock into my grandsons Bomber to get him by while I rebuilt his engine. The Bomber class required a cast in. and ex. setup and my engine had a Hughes HEV5056BS(.575 in. .587ex. and 252in. 257ex. @ .050) w/headers and single plane aluminum intake. The carb was offended but after some adjusting it ran like a scalded cat. Those HP ex. manifolds will fool you. Pull the socks off of some high dollar Chevvys.

[TK]

The same same cams, do make better low end power, so, it is no suprise, that it ran better on the top end too.
Manifolds, aren't the only deciding factor, head flow, ect, also play a major role in lift/flow rates matched to exhaust, ect.............
You cant say, if it had ported heads, ect, the results would be the same either.
There ain't nothing wrong with manifolds..........LOL

As far as mechanical cams working better with manifolds? I think you will see some gain, with a mechanical cam on anything, manifolds had nothing to do with it.

[George G. Leverette]

The problem with dyno figures is the high RPM needed to get the best numbers, who drives at 6,000 RPM in real life for a long period of time? The Mopar cams are designed for short duration spurts like at the track and really come on at approx 3000 RPM. Bottom end suffers if deep gears are not used, so the Mopar cams are not street friendly and gas consumption is very high. Hughes started the split duration cams designed for Mopars, after using the cam they suggested for a small block, I am highly pleased with the results and would recommend you contact them for advice.

[451Mopar]

I read that article along time ago, and thought the cam selection was interesting too. Problem is they don't say what other cams they tried, and show power /torque curves. I think the combination of the Edelbrock heads, the cam duration, lobe seperation, and overlap may have had part to do with which cam was best?

[DartGT66]

I know they tried a couple of different cams, custom grinds in that engine, but overall the 284/.528" wokred very well in that engine with the exhaust manifolds. The article, and some others he has written, can also be found on Andys web pages: http://www.arengineering.com/articles/articleframe.html