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Old 11-14-2012, 10:51 AM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by gmtony55 View Post
ok guys I am learning a little,now I'm in have some decisions made but have a few still questions. As I said before I have the performer RPM intake,but As I read it seems as though it is for a high rpm engine which I dont have. a 400 I am told to build for lower rpm. Keeping with low budget should I buy a performer intake that would fit my quadra-jet carb and just sell my RPM intake? Or would the money be spent better on a new carb and use the RPM intake?
The Performer RPM is just fine. It is though of as being a higher RPM mainfold than the regular Performer, yet in back to back testing the RPM gives up very little on the bottom end while having very substantial gains on the top end. It makes me wonder why Edlebrock even bothers to inventory the standard Performer as I don't see where it has a market except maybe for smaller less than 350 cubic inch engines.

This brings me to the next concept which is as an engine grows in displacement the need to feed the bigger breathing cylinders has the effect of bringing the power peaks of what are high RPM parts when used in a smaller sized engine downward in the RPM band and smoothing such effects as seen with aggressive cams. This is to a large extent effects that are related to mixture velocity.

For example, if you take an intake manifold, cylinder heads, and camshaft that would be suitable for a high performance 350 that let's say has a 400 horsepower peak at 6000 RPM with a semi-rough idle. These same parts on a 400 inch engine will generate 400 horses at say 5600 RPM and will idle smoother. They very likely will not make much more peak power from the 400 inch engine because they simply can't supply any more mixture. A classic test of this was done by David Vizard many decades ago where he use the 300 horse 327 cam on a 350. The 350 peaked out at 305 horses. Now there is a compresison ratio difference in the engines he tested the 327 having a ratio of about 11 to 1 where the 350 being built for unleaded fuel has a ratio around 9 which if corrected might have made a 320- 330 some horse engine out of the 350, but it still is an excellent example of the limiting effects on cam timing and what would be the related components of the heads and intake system as they relate to feeding a larger engine.

For some top notch reading that summerizes a lot of these concepts I'd recommend two of Davd Vizard's many books, these rather bring the detail subjects of his other books into a summary form that makes a lot of the connections between the various components to help you understand the integrated whole how the parts and concepts work together. Go here as many of David's books are out of print so you need to hunt for them. <<< David Vizard: books by David Vizard @ >>>

My starting recommendations are "How to Build Horsepower Volume 1" and How to Build Horsepower: Carburetors and Intake Manifolds, Volume 2". These books really tie the complex engine internal subjects together. When you're ready for nitty-gritty by subject you will see that is covered as well. Some of this stuff you have to read several times to get the concepts and at that some concepts such as how compression, camshaft timing and power output relate are much more subtle than reading most any book makes clear. There is always on any subject an assumption that the reader brings some knowledge with them that isn't well defined by the book. We can help with this so don't be afraid to ask questions.

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