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Intake Comparo - More Data

March 27 2006 at 8:22 PM

Jay Brown  (Login jaybnve)

For Werbyford - The FPA headers are a tri-Y design. Primaries are 1 3/4" OD, varying from 13" long to 6" long, depending on the tube, secondaries are 2" OD, varying from 20" to 13" depending on the tube, and the collectors are 3" diameter, and extend 10" until the dyno exhaust starts mushrooming out to fit the 6" diameter flex pipes.

For the intakes, here are the Edelbrock A & B measurements:

cast iron CJ: 4.25" / 6.0"
PI: 4.375" / 6.375" (my PI measurements were different than the ones you posted)
F427: 4.75" / 6.0"
Blue Thunder: 4.75" / 6.75"

I can't get the Streetmaster numbers because its installed, but I'd guess there are close to the cast iron CJ numbers, and my Performer RPM numbers agree with yours.

For BB - Get these plots while you can, because they're taking up a lot of my Network 54 space, and I'm going to delete them in a couple of days:

Vacuum numbers (resolution is 0.1"):

Streetmaster exhaust temps:

F427 exhaust temps:

Blue Thunder exhaust temps:

RPM exhaust temps:

CJ exhaust temps:

PI exhaust temps:

Some notes on the graphs above:

1. Manifold pulling the least vacuum is the F427 (least HP). Manifold pulling the most vacuum is the Streetmaster (most HP). Imagine that! The one that doesn't fit this pattern is the BT. Hmmm.....

2. Looking at all the exhaust temp plots, I had almost concluded that my #1 cylinder thermocouple wasn't working correctly. The #1 exhaust temp is flatter, and lags as RPM increases, in every case. EXCEPT with the Streetmaster; this manifold proves that the thermocouple is working. One potential conclusion is that its difficult to make a dual plane intake that feeds the correct mixture to #1.

3. I was blown away by the tight distribution of the exhaust temps on the CJ manifold. This one clearly has the best distribution of all the intakes, with the exception of cylinder #1, which starts out relatively hot, and ends up relatively cool.

On another note, its always interesting to read the comments about tests like this. One that kind of strikes a chord with me is that the engine's tune should have been optimized for each intake. There is some truth to that statement, and that would be an ideal way to compare the intakes on this particular engine. However, in my opinion its not good engineering. For a comparison test, you want to have all variables fixed except one. Then you get true comparison data, applicable to lots of engines similar to this one. On a more practical side, if I had to adjust the carb and the timing for each manifold combination, it would have tripled the number of dyno pulls required to get the data. This is not my job, its a hobby, and I simply don't have the time for that kind of detail. Further, I'm pretty convinced that the relative gains and losses by doing that wouldn't have affected the results too much. The A/F number on the dyno came in between 11.2 and 12.0 for every intake at the HP peak. When we were messing with the timing on the PI intake, we got about a 4 HP improvement out of advancing the timing 5 degrees. So, I don't see that there was a lot to gain or lose by messing with those variables. I'd bet my bottom dollar that no combination of timing and carb tuning would have given the Performer RPM the edge over the Streetmaster.

For all you guys that said thanks, you are very welcome; its been a lot more fun for me than it has been for you, I'll guarantee that. I look forward to sharing more dyno data in the near future.

Jay Brown
1968 Shelby GT 500 Convertible, all aluminum 489" 1030 HP Supercharged FE
1969 XL Convertible, 460
1969 R code Mach 1, 706 HP 511" all aluminum FE, 10.457 @ 127.47, 2005 Drag Week Winner, Naturally Aspirated Big Block

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