This weekend my project is to start the great FE intake comparo, using my 428CJ as the dyno mule. You may recall my last intake comparo, using my brother's 428 engine, where the Streetmaster came out on top for the intakes. I decided that I'd start this comparison test this weekend with the top three intakes from the last test: the Blue Thunder intake, the Performer RPM, and the Streetmaster.
There are some differences between my 428 CJ and my brother's 428, most notably the cam and the heads. The heads on my engine are 428CJ heads with stock valves and a street strip port job. My brother's heads had CJ valves installed, and had some minor porting work, but not as extensive as the work done on my CJ heads. Also, I have the Edelbrock RPM cam in my engine (236/236 @ .050", .571/.571 lift). My brother's engine had a much milder Crane cam (216/228 @ .050, .531/.561 lift). Both engines are .030" overbored, stock crank and rods, and the same forged pistons and compression ratio. My brother's engine used a 750 vacuum secondary Holley carb, and mine uses a 750 double pumper.
I'm only partially through this test, and have done the Blue Thunder intake with a couple of different sizes of open spacers (made it worse in the midrange with no gain up top), and also swapped on an 850 Holley (lost 10 HP). 400 HP is what the engine wants to make with this intake. So, I swapped on the Streetmaster, same manifold as what was used on my brother's engine. Here are the surprising results:
If anything, the BT intake looks better! No big gain for the Streetmaster this time. Looking at the manifold vacuum numbers, I have a theory of what is going on here. My 428CJ can use a lot more air than my brother's 428, because of the heads and the cam. The vacuum in the Streetmaster at WOT, nearly 2", indicates that the small runners are a significant restriction to the airflow with this engine. Whereas my brother's engine benefitted from the velocity of the intake charge provided by the Streetmaster, my engine needs more air than can be supplied by the manifold.
Of course, its only a theory LOL! Tonight I will be porting the Streetmaster, according to Edelbrock's instructions, to try for increased flow. I will run it tomorrow, hopefully along with the Performer RPM, and post the results tomorrow night. Stay tuned - Jay
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