I read you now, LR-dude.

Too bad I don't have an engine dyno (and an engine) so I could just tell you what to do and send you a bill .

Ryan

 

If ya had a definitive answer I WOULD pay for it just to know.

 

More Boost? Give Big Dave a hug for me.

Make the whole y-pipe out of the same oval tubing?

 

BOOST? We dont need no stinkin' BOOST


$$$$$$CHA CHING$$$$$$$$$$$ $400 Y pipe

Brady you lurker you.


David

 

Definitely use a clearance tube on both. Things get a little tight on the driver side.

As for what's going to happen... who knows. You'd need a multi-dimensional math model to "calculate" and/or simulation with accurate component models. So, considering you can't calculate (too complex for most) or simulate, you're left with an educated guess. Either that or you spend some time and test. That's how I've arrived at my collector length and diameter through 4 different engine builds now. Yeah it costs you someone elses time and your money but what else are you going to do besides make a guess. An engine I put together last summer for a friend was built to make 600 hp at the flywheel. A good friend of mine uses a Burns collector system which allows you to slip on different length/diameters and see what you get. A friend of mine builds the headers from flange to primary and we go from there. Our first guess said, use a 3-1/2" diameter but the testing showed that the 2-3/4' was worth more avg. hp/tq. Who would have figured? On my last engine ~650hp, a 3-1/4" collector (merge) diameter made the best hp/tq. On the new engine, 3-5/8" (merge) worked best. It's just an opinion I have but my guess is that alot of people run too large a collector diameter, that's also too short. It's experience however, that things don't always work out like you think they should.

Everything with these cars is a compromise. We all know what we'd like to do but then we have to work it out around what the General gave us. Either that or build a tube chassis, sheet metal floor pans and throw the body on it. I seem to remember that stuff being expensive too.

Can't help with the collector geometry issue. I do know that if the area is constant, there shouldn't be a problem where flow is concerned but what else can be said. I reviewed two books by Winterbone & Pearson titled, Design Techniques for Engine Manifolds & Theory of Engine Manifold Design just to see what I could find that might cover your situation. "Theory" is very heavy in mathematical models and some design elements while the "Design" book goes into more build detail. Of course neither mentions pipe boundaries with oval cross sections, collector or otherwise.

I'd test or be content to settle for form over function. Well I lied... I'd build a full oval exhaust. $$CHA CHING$$

Who said this was gonna be cheap.

-Mindgame

 

Thanks MG,
I think I will get two and make it equal. They will be most of the collector and total about 16" long. Still have had nobody tell me if the engine "see's" the collector with the same size "Y" pipe behind the collectors along with a full exhaust. Or the 3-1/2" collector is just another part of the "Y" pipe according to the engine.

Don't mention the money. David will have a fit. He wants a full exhaust for 29.99 a 3-12 "Y" pipe into a 4" out the back.. Each one of these bends are 25+ dollars and there are a few. That's allright POP will get her done. And done right, as right, as I know how....

I'm up for the tube chassis with a 706BB and 15 x 33's.

 

Those flat bends are 80+ dollars each.

More boost would do it,I just have to be careful not to overboost. The pop off ain't set right yet.

 

Dont mention money LMAO..we won't go there $29.99 will only by ONE of the many bends on the shop table..and hey I got a brother inlaw deal on the Mufflex..doesn't hurt to be frugle.It was a free even swap for a SLP 2OTL, well I had to pay for the reducer and to have them swapped over.

MG did your collector tests show HP differences with FULL exhaust attached? And was the exhaust the same size as the collector outlet? I am dying to know this answer.

A tube chassis racecar.....who wants that junk......everybody got a car you gotta drag around on a trailer everywhere you go with it.


David

 

I vote for equal length collectors as well.

There is good power to be made in the collector area. Most performance headers
will have meticulous attention to detail in their merge collectors.

look down the throat of your collector and hope to see four smooth entries
from the primaries into an unshrouded collector.

You'll also find that any tapers, bends, or reflective surfaces should occur
after the optimum collector length if at all possible.

One last tip: Don't forget the offset of the cylinder banks. Do not subtract/
add this length too early in the system. Make up the difference in length
after the catalytics, or just before the mufflers to keep tuning balanced.