I'm building a 2x4 intake for my 392 Hemi. Since it was a race motor, it has ported heads, and big valves. I want more low end torque than that would normally allow. Is there a way with my runner design that I can increase the velocity of the airflow at low RPMs, even with the big ports? Thanks. Bugman Jeff
This has been done on some 4 bangers in the 70s... But it wold probabaly require you to run your two 4 barrels syncronized. Split the intake passages in the manifold between primary and and secondarys with the primare passages about half the volume of the secondary side. that will increase the speed of the primary intake flow but allow the secondary flow to be unrestricted by a small passageway. I really can't remember but I think it was either Vega's or Peugeot 504s had this in the 70s. Of all the things I've lost, I miss my memory the most....
It's not going to be what you want to hear but on Ford 351 Clevelands I've filled in the intake ports with an epoxy to reduce the port size and runner volume. I had never heard of it, but a friend was using this stuff on these big inch race motors, so i tried it, and it worked great. For 351C they also make plates that block off the bottom of the port, which essentially does the same thing, of course I didn't know they existed until well after I did it my way.
in one section of the Mopar Performance engine manual, they talk about doing this in intake manifolds with 2 part epoxy and popsicle sticks, but I think it is for regular big blocks. They give a measurement and tell you where to put the stick. Could do something similar to that with yours.? Jay
Read these:1 and 2 The theory is the same for cars and bikes.Basically,you can fill the floor of the port in signifigantly,without reducing flow.This improves velocity,which helps drivability,and torque. You could also run a divider down the middle of the plenum,like on a dual plane intake.This would effectively cut the plenum volume in half and increase the velocity through each carb giving better atomization.Real long runners help torque too. For more advanced theory,check out:Endyne
My first thought was to epoxy the ports smaller. I've done it before, and already knew velocity was more important than flow. But I will be running the blower later on after I collect all the accessory drive pieces. I don't want to have to open the ports back up then, because it would require another teardown. Like it was saying, air flows better going from a large area to a small one. It's straiter, and doesn't tumble as much. That's why intake ports flow better when tested backwards. With that in mind, would runners larger than the port opening increase velocity in the port? I know a small runner going into a big port would kill any velocity I gained. -Bugman Jeff
Unkl Ian hit the nail on the head with the velocity verses volume article. When I ran my Weber 48IDA's I got better performance using the smallest venturies available. This set-up worked beautiful on the Individual Runner's. In a sense that is the same theory of dividing and or raising the plenum floor. When I was reading about the Fly's problems I was wondering if Roothawg's Fuel injection might benefit from smaller venturies by the butterflies! My old Hilbourn F.I. didn't give you the option of smaller venturies..., In fact they looked as though they were a straight shot to the piston! So I played around with the Dial-A-Junk till I got it to run better (not best)! Reading this article points out to me that Roots F.I. and my old F.I. were designed to run at 9,000 rpm with a big cube motor with a lot of squeeze and possibly a wild roller cam...! Anything less than this Monster Motor setup wouldn't allow the proper velocity! ?????????????????? SORRY for wandering off your problem a bit..., But I think we have an answer for Root! HEY ROOT..., Guess What...? Mark
Okay I'm new at this velocity enhancing stuff so bear with me. I came up with this idea of a velocity stack that pinches down in the center to increas velocity, maybe it'll work or maybe it wont. In acouple weeks I'll have access to flow benches and was thinking about making a couple and testing, make a straight walled one with the same openings at each end as the one with a pinched waste and see if it'll in creas the velocity. Sorry if I wandered off topic a bit but i've been thinking about this very subject for awhile now. -Jesse
Jesse- When you try that, make one with the narrowest part at the bottom too. It would seem to me(pure spectulation) that velocity would increase at the narrow part, but would slow down again as the tube got wider. I would think(again, just a guess) that if the narrowest part was at the bottom, the air would steadily pick up speed. Sound reasonable to everyone? -Bugman Jeff
The Jalopy Journal
