#3---Intake Manifolds Flow Testing & Port Matching 3/17/2006
Which ones are best?????

Dave Hughes

Revised 10/15


Intake Manifolds


Intake manifolds were one of the original hot rod parts, and they are still one of the first parts changed when more power is needed. Not only that, they are racy looking and save weight.


Technically, they are extensions of the intake ports in the heads. But unlike cylinder heads, porting and flowing of intakes has never received the popularity or interest of heads, and that has been a mistake. There may be thousands of shops in the United States that port cylinder heads. Many of them even have flow benches to test their work. Porting cylinder heads is a very mysterious subject filled with lots of theory, trial & error, lies and myths. But, at best,  manifold exteriors are only painted or polished like some tuner bling. Some may be really tricked out with a "gasket match" woooo!!


A couple of years ago, we noticed that some of the higher flowing aluminum heads were not picking up power like they should have been based on the air flow improvements they provided (promised). Some investigation indicated that the manifolds many racers were using were not flowing as much air as the heads; in other words, the manifold had now become the bottle neck in the system.


In the Fall of 05, we started a program of flow testing intake manifolds. What we found, for one thing, is that the fixturing required is much more extensive than what is required to test cylinder heads. This is one of the reasons shops dont make a concentrated effort to test them. Some attempts to flow them in reverse (air flow backwards) have been done because the specialized fixturing is not required, but these tests dont give a true picture of the flow patterns. We have taken the time to create the unique fixturing allowing us to mount and flow test the intakes correctly. We are testing many manifolds some oldies of historical significance and the newest and latest pieces available.


This testing has not only confirmed that our suspicions were correct about manifolds air flow, but, what we have learned about unequal air flow from one port to another is shocking. Port to port flow varied as much as 60cfm! Unbelievable!  Yes, 60cfm (at 28 DP) from the best to the worst port.


     Some of the old favorites were actually fairly close on equal flow, within 20cfm, - no that is not as good as we would expect from heads, but this is what you have been getting. We were able to improve and equalize some intakes, others were very disappointing. One of the most interesting aspects was that those with the most equal port-to-port spread were the lowest flowing pieces and they are among some of the more popular intakes used in dyno shoot-out comparisons. This might indicate that equal, but lower flow is better than more flow, with some ports, giving a higher average flow. This is a poor trade-off at best, but interesting none-the-less.


    One of the worst spread of port-to-port differences was 60cfm in a single plane manifold. This is unusual since single planes tend to be easier to make equal flowing.


  We have modified some dual plane plenums with good results, mostly the newer pieces. Old dual planes that were modified made poor ports better. However, you would be better off with the newer manifolds. Port matching also provided some interesting results. The so-called gasket match about a 1/2" deep or less that is popular with some magazines and sanctioning bodies proved to be a waste of time or worse. However, a very deep port blend reaching as far as the eye could see, when applied properly, could be worth over 40cfm on some manifolds very significant! Blending is tricky. Some runners responded to inner wall work and some to outer wall, and we now know which works and which do not.


We have come to the conclusion that the 2x4 tunnel ram intakes ran so well, not because of the extra carb as much as the fact that the runners of these manifolds could flow so much more air, especially when compared to the old single carb intakes. Another surprise was the multi-carb inline 2x4 and 3x2 dual plane intakes. These were surprisingly equal in spite of their basic designs dating from the 1950s. Their flow numbers were as equal as or better than many popular single plane intakes available today.


The manifold should flow about 20% to 30% more than the heads or else they will cause a restriction to the flow potential of the system. Most of the manifolds we tested did not equal, let alone exceed, most well-ported iron heads, to say nothing of the Edelbrock, Indy or other aftermarket aluminum heads.


What this testing has shown us is that a manifold can be a great source of previously untapped power. This would be especially true if the heads being used are on the high end of their full potential.


We now have super deep port matching on selected manifolds called Full Port Match. And, yes, they will cost more, but this not something that you can get anywhere else. Actually, in dollars spent per horsepower gain, this may be one of the best deals you can get.



Modified and equalized manifolds are going to be available on a select basis to customers very soon, keep checking our website.

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