Manifold Mania – Part 3 The Final Chapter, for now . . .

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We test four popular intake manifolds to find which is best only to get answers already suspected.

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By

David Vizard

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At this point the background info you need to know about the hi-tech two plane intakes we are about to test have been reasonably covered. But before looking at the dyno results a few words on the test engine and it’s carburetion would not go astray.

Caption: In this shot our test engine is shown with a polished Edelbrock Air Gap Performer RPM installed. This is topped off with an AED Holley carb. A fairly big Comp Cams hydraulic cam was used along with 1.6/1 rockers on both intake and exhaust.

The test engine was a basic 383 CID small block Chevy. The displacement was achieved by replacing the 3.48 stroke stock crank with a 3.75 inch stroke Scat cast steel series 9000 crank. This was used together with a set of budget Scat 6 inch rods and Speed Pro hypereutectic flat top pistons. These in conjunction with 72 cc chamber Dart Pro 1 Platinum 200 cc port heads gave a nominal 10/1 compression ratio. The cam used through out the testing was a Comp Cams hydraulic flat tappet single pattern grind (Xtreme Energy profile #5447). This produced an off-the-seat duration of 284 degrees and 240 degrees at 0.050. The lobes were ground on the shaft on a 106 degree LCA at 4 advance. After some preliminary carb testing a Barry Grant 850 Speed Demon with vacuum secondaries was settled on as the one to use for the bulk of the testing. There were multiple reasons for choosing the big BG carb. First it was reasonably large so it would go a long way toward satisfying the engine/manifold combinations need for big carb CFM (as we established earlier). On the other hand it was not so big as to fall too far outside of the CFM typically recommended for this sort of application. A hot number here, for the record is 750 cfm. Next the vacuum secondary that we had on the Speed Demon gave the best chance of good low speed torque bearing in mind the cam chosen was quite big. The last factor was in fact more political than anything else in as much as Barry Grant does not produce a single four barrel two plane intake there for the other intake manufactures would not be competing against a manifold specifically design to work with that carb.

Caption: A Barry Grant 850 Demon carb was used for our tests primarily because it was a good compromise between being able to deliver low speed drivability with it’s vacuum secondaries and sufficient total airflow to feed a reletivly big cammed air hungery 383 inch engine.

Dyno Numbers.

Caption: Just how close the capabilities of the four intakes tested can be seen from these tests here. The carb calibration and ignition timing for each intake was extensively explored to get optimal results. As it happened timing requirements were virtually the same across the board but jetting was not.

Ok now for the dyno numbers. Right at the outset there was a strong suspicion that these intakes might produce very similar results and that proved to be just the case in this instance. If you check out Fig 8 you will see that it is very difficult to see much difference between any of these intakes. They were in fact so close that using too thick a line on the graph caused overlapping to the extent that deciphering the results became near impossible – hence the thin lines. The closeness of the results means we need to take a serious look at just how repeatable the engine/dyno can be. Since this was more or less expected the results were garnered from an average of three runs after establishing the calibration for the particular intake concerned. Just for the record they did not all end up with the same jetting. The Weiand required from two to four jet sizes less than the other intakes. Also we got into stagger jetting which threw in yet another factor. For the most part staggering the jets as per Fig 9 worked best and if you intend to follow what was done here this would be a good starting point. However do not assume that because it worked for out for our combination that it will be spot on for yours.

Caption: On our test engine the Edelbrock and Dart intakes responded positively to the stagger jetting shown here by delivering about 4 hp more. With either of the other two intakes the results of any pattern of stagger jetting were somewhat indeterminate.

Although the numbers were close there was, non-the-less, some repeatedly measurable differences where one intake was better than the others. A quick rundown goes like this; top hp number was produced by the Dart intake where it beat the Weiand intake into second place by a whole two HP! Best peak torque was made by the Edelbrock intake where it beat the Weiand and Dart into second place by one lb-ft. The best low speed output was produced by the Professional Products and the Weiand intakes by a 4 lb-ft margin over the second place Edelbrock intake. Best cruise vacuum and idle quality was achieved with the Weiand intake.

Caption: The upper arrow indicates the totally divided plenum employed by only the Weiad manifold of the group tested. Also note the side expansion on the high plenum to even out the plenum volume from side to side.

After each intake had been meticulously tested with the 850 Demon carb it was decided to run tests using an 850 Holley HP modified by AED to deliver something a little over 1000 cfm. The purpose was to give the intakes as near all the cfm they could use and see where the chips fell. Be aware that we did not explore low speed drivability here. This was a top end output exercise only and if you follow this path make sure you or some one you know is a real expert at part throttle calibration. Anyway back to the plot. The big flowing AED carb allowed our test engine to breathe far better through all of the intakes. The biggest gains in power were seen with the Dart and the Weiand. The reason for the Weiand picking up better than the others (except the Dart) was probably due to the fact it did not have a plenum divider cutout. This makes it a true two plane intake with absolutely no sharing of the carb barrels on the other side of each plenum. The Dart intake looked like it had more runner cross sectional area and as such could possibly be making more use of the bigger carbs additional cfm. The least gain in top end with the big carb was from the Professional Products intake. That said it still made joint best low speed torque with the Weiand intake. So how much was the bigger carb worth? In round numbers the peak torque output went up by typically 5 lbs-ft and top end output by between 8 and 14 hp depending on the manifold.

Caption: As with the Edelbrock and Weiand intakes the Professional Products intake can be had in polished form. Although no comparative tests have been done on a 350 we have had strong results with this manifold on 350’s

After each intake had been meticulously tested with the 850 Demon carb it was decided to run tests using an 850 Holley HP modified by AED to deliver something a little over 1000 cfm. The purpose was to give the intakes as near all the cfm they could use and see where the chips fell. Be aware that we did not explore low speed drivability here. This was a top end output exercise only and if you follow this path make sure you or some one you know is a real expert at part throttle calibration. Anyway back to the plot. The big flowing AED carb allowed our test engine to breathe far better through all of the intakes. The biggest gains in power were seen with the Dart and the Weiand. The reason for the Weiand picking up better than the others (except the Dart) was probably due to the fact it did not have a plenum divider cutout. This makes it a true two plane intake with absolutely no sharing of the carb barrels on the other side of each plenum. The Dart intake looked like it had more runner cross sectional area and as such could possibly be making more use of the bigger carbs additional cfm. The least gain in top end with the big carb was from the Professional Products intake. That said it still made joint best low speed torque with the Weiand intake. So how much was the bigger carb worth? In round numbers the peak torque output went up by typically 5 lbs-ft and top end output by between 8 and 14 hp depending on the manifold.

Caption: The Dart intake was top for our HP figures but by such a small margin that the term ‘experimental error’ has to figure in there somewhere. We have used this intake on three engines now and all to good effect.

As far as output is concerned you can see we are dealing with numbers of around 1% of total output. Even with our careful pre-test calibration checks and dummy runs we are at the very edge of the engine and dyno’s ability to reproduce numbers. Having said that there are sufficient trend indicators here for me to have an idea of what intake I would use for an application that might be significantly different to our test engine. For instance if I was building a 350 I would lean a little in the direction of Professional Products or the Weiand intake.

Caption: When Edelbrock designed the Air Gap Performer they broke new ground. This was such a step forward in two plane design that it set the standard for other manufactures to meet.

e Weiand intake. I have used both of these on 350 and liked the results. Price here would be the driving factor. If max performance on the drag strip was the main criteria and the engine was a 383 incher or more I would lean toward the Dart intake. On a basic 383 with Dart 220 as cast heads and street strip hydraulic cam of 290 degrees (244 @ 0.050) along with an 11.5/1 CR we have topped the 515 hp 500 lb-ft mark on our dyno with this intake. As for the Edelbrock intake suffice to say I have learned more about what it takes to make a good intake work from this manifold than all the others put together. Part of that has been due to the patience shown by Edelbrock by supplying me a manifold for whatever engine I wanted to test on. It is often said there is little that can replace experience and this is a prime example. When I use this intake I am about as certain as I can be that the results will be good. To sum up here the bottom line is that which ever intake you choose you will be getting a highly functional piece of speed equipment.

So are these the definitive tests? It might look that the tests were done with enough care that the results are now set in concrete. Unfortunately that is not the case. Sure a lot of attention to detail was made but a simple factor like having a little tighter or looser quench could completely reverse the order in which the manifolds finished in terms of power. What we can say for sure here is that the bar was set pretty high by Edelbrock and if anyone else wanted to play in that arena then they had better pull the stops out to compete. At the end of the day, apart from dyno testing, the only way you will tell one of these intakes from the other is the odd thousandths of a second or so difference you may see from the clocks at the strip.

Read Manifold Mania Part 1

Read Manifold Mania Part 2