I'm about to pick up a RB long primary header. I'll have to fabricate
everything from the dual outlet flange on through. Anyone have any idea
what sort of length would be sufficient to make more power than the
short-primary system, but lighter in weight than the full RB system?
Thinking about 1-3 more feet as a dual pipe, then perhaps a 2>1 muffler and
a single outlet in front of one of the wheels.

Engine will initially be stock '84, but very soon will add EFI with a very
free flowing intake tract, then nitrous, then perhaps the eaton supercharger
if it doesn't pick up enough speed with the nitrous. Not concerned with low
rpm torque, have 4.44 gears and lightweight flywheel ready to go in when the
motor swap is done, but holding out on the gears in hopes of scoring a set
of 4.778, 4.875, or 5.125 gears. I can easily forsee that with the EFI I
won't let it drop below 4500rpm except at red lights. Car will be LIGHT and throw in some stupid short rear tires along with the ring and pinion ratios, and it should rev up there RIGHT NOW.

Thanks in advance!

R

 

The length is not something that you can guess at. It is all based on the exhaust pulse for specific horsepower gains at specific RPM. Paul Yaw have done a great deal of work on this and he has written some great technical articles at (http://personal.riverusers.com/~yawpower/techindx.html) or you can look at the RB manual for specific lengths. Believe it or not you cam make things worse by getting the wrong length.

Good luck

 

Looks like if I took the RB full system and shortened the tubes, each little bit will move the tuned rpm point higher. That's good news! Time to crank some numbers to see.

BUT with the nitrous plus a supercharger later, I think there will be so much flow the exhaust will restricted, and exhaust tuning for scavenging wont' be as possible/critical unless I increase pipe diameter.

Thanks, will dig some more.

R

RB Manual: The catalog?

 

http://www.racingbeat.com/resultset....rtNumber=16119

Hmm. If I duplicate that length to the collector, have a smooth collector, then a gradual increase in pipe size to 2 3/4 or 3", then a straight through muffler, I don't think I'd be hurting myself at all! Ideas?

http://www.racingbeat.com/resultset....rtNumber=16004

Right there I get the idea of length, looks like 2-3" after the collector, overall 14" so guessing 10-11" for the tube length. I was going for 14-18" just for length requirements, but if 14" with the collector and a bit of pipe after it is good enough for them to sell commercially, 10-11" before the collector won't be too short for my custom system! At $46 from them, I might just buy it and flange it and start there. I wish they had it for $60 with 2 flanges on it so I could make it all bolt on, and bolt the rest of my stuff to it. That's what I'll do at the shop, add the flanges to this piece.

However, this short runner setup they have really gets close to duplicating the "streetable" header. ??? What's going on here?

R