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Intake Manifold Comparo - Interim Report

March 25 2006 at 8:51 PM

Jay Brown  (Login jaybnve)

Three down, and three to go. I may not get them all done this weekend, but I'll do at least two more tomorrow, and maybe the third. Today we tested the PI, CJ, and Performer RPM intakes. Results:

PI Peak HP: 357.1
CJ Peak HP: 363.0
Perf RPM Peak HP: 374.6

Here's a chart that shows the results a little more clearly. The green (bottom) line is the PI, red is the CJ, and blue is the Performer RPM:

Although the peak differences in the PI and the CJ were not that pronounced, the CJ shows a wide band of higher torque and HP than the PI. The Performer RPM is clearly better than either of the factory intakes.

I'm running a little behind schedule because we had some issues to solve with the engine prior to getting meaningful results. These were mostly related to my brother's lack of experience in building engines (this is his first one). On break-in, we had very hot exhaust temps, and it turned out we were running leaner than indicated by the dyno's A/F meter because two of the vacuum ports on the base of the carb had been left unplugged, and also no carb gasket had been installed on one side of the 4 hole 1/2" spacer. Then, we were blowing tons of oil out the exhaust, and it turned out that the cork end seals that my brother had installed were holding the intake too far up, preventing the bottom of the ports from sealing against the gasket. So, on 7 of 8 holes we were sucking oil into the intake ports. We pulled the PI intake and replaced the gaskets, and went with silicone on the end seals instead of the cork, and then finally the engine started to run reasonably well. We were going to run all the pulls to 5500 RPM, but the engine has a single point distributor, and point bounce started getting us at 5300 RPM, so we limited the top speed to that. The engine wants to peak in HP around 5000 RPM anyway, so even with that limit we are getting the data we need.

A word on the leaky cylinder (see my original post lower on the page). We checked it after two minutes of running, and leakdown had gone from 40% to 50%. Then, we checked it again after cam break-in, and it had gone down to 30%. Finally, we checked it again after the last dyno run of the day, and it was at 36%. I can't account for the variations in the readings, but in any case it seems to be staying about the same after a couple hours of run time on the engine. I'll check it again during and after tomorrow's tests.

The BT intake is on the motor now, and I'll be running that one early tomorrow afternoon, then switching it off for the F427. I'll do the Streetmaster tomorrow if I have time, but if not sometime next week, and post a full report after I have all the data.

Thanks go to my brother (well, its his engine after all...), an old friend of mine who stopped by to help, and also Shoe, who was here for most of the afternoon and evening. I couldn't have gotten all this work done without those guys. The four of us pulled off the CJ to Performer RPM manifold swap in 50 minutes, trying to beat my self imposed deadline of no dyno runs after 8:00 PM for sake of keeping the neighbors happy.

Can't wait to see how the BT will do...

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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