Header & exhaust design - now with video!

[falcon fanatic]

Okay hardcores, here's the deal:

I've been studying up on header and exhaust design, and having had more than 25 years of occasional successes taking David Vizard's advice I tend to lean towards what he says. Going by Vizards calculations in his latest book, and the dimensions of my Clifford dual out header (which only has primaries) I get the following:

(Vizard suggests a multiplier of 1.68 from primaries to secondaries for a street engine)

* Primaries are 1.5" diameter and average out to 21" in length measured from the exhaust valve.
* That means my secondaries ought to be 1.5 x 1.68 = 2.5", and about the same length as the primaries.
* That means my exhaust should be 2.5 x 1.68 = 4" (!!!) and about 36" long, dumping into a roughly 300 ci termination box (and then out to whatever will flow adequately)

Well, those are the numbers according to his latest book, although it focuses on 4:1 headers so the extra step (tri-Y) is probably throwing me off. My gut tells me 4" is insanely huge for a 6000 max rpm motor, so THIS is my actual plan:
*Secondaries at 2.25" and 21" long
*y-adapter 2.25 to 2.5" for 36" into the termination box.

The question is, should the 36" length really be 3" instead of 2.5"? I know 3" seems really big, but plenty of 302 V-8 run that size and bigger with only 152ci per bank, so... Nevertheless, I think I'll err on the side of small and make my pipe 2.5" into a single-in/dual-out box (Flowmaster or Jones most likely) and then 2" dual out to the back through some Porter mufflers.

As a point of comparison, my current exhaust dumps the header outs into a 2" to 2" y adapter with only 8" of length and then steps up to a 2.25" exhaust about 45" long to a turbo muffler. Pretty ugly. I wonder why my new awesome engine didn't make the power I expected. So, I'm going to hand make this intermediate section and have it ceramic coated to match my header. Should be pretty sweet and certainly a better match for my high-revving engine.

 

[falcon fanatic]

In that case I guess I'm on the right track

 

[MustangSix]

The problem I see with most exhaust calculations is that they are optimized at a single rpm. You can calculate what the optimal pipe size and length are for maximum power, but in reality how often do you hit that?

The other thing is that inline sixes and V8's don't have the same exhaust issues to deal with. 90 degree v8's typically have irregular exhaust pulses from bank to bank. They need to be sized and tuned to account for back-to-back firing orders on two cylinders that have a peculiar effect on how you have to size the collector. That's why tri-Y setups can be effective on a V8; they capitalize on that irregular exhaust beat to help improve torque.

But an inline six, split 123 - 456, has a regular beat, from one bank to the other. As it fires, 1-5-3-6-2-4, the exhaust beats go out one bank, then the other.

Rather than a large collector, it might be better to have a long downpipe on each bank to maximize velocity. Take a look at what AJ6 Engineering does for the Jag inline sixes and V12's (two inline sixes, essentially). http://www.jagweb.com/aj6eng/exhaust1.php BMW does something similar on their inlines.

Coming off of each bank, a long exhaust downpipe that eventually merges into a Y- might be more effective than a large collector that looks like what you typically see on a V8. It should maintain a lot of velocity thru the system over a broader rpm range and should maximize torque.

 

[Invectivus]

I wonder if it wouldn't be a possibility to design a variable length exhaust system to broaden the RPM range tuning. I realize it would be problematic, as pushed air creates high pressure zones that increase friction and inhibit airflow much more than vacuum drawn air does, as well as a variable length runner assembly similar to the aussie intake would most likely create a large hot spot mass off the side of the block.

A slide pipe would work, but the torque required to overcome metal friction and carbon buildup would be prohibitive, and the control mechanism would be a pain. It would have to be hydraulic, heavy, and probably too slow to act on time to RPM variance.

 

[MustangSix]

Trombone?

There's another thread here that also discusses Vizard's ideas and perhaps a resonator box to connect the two outlets would be a power adder. The closest thing to that I've seen is the Y-pipe on a BMW and on Bill's (WSA111) car.

I just like the way an E-type sounds though.....

 

[StrangeRanger]

You can get multiple tuning points with a stepped primary tube, a pair of 3 into 1 primaries and a pair of 2 into 1 collectors

 

[Invectivus]

i thought by default with irregular runners than only 1 cyl out of 3 woud be optimally tuned and the other 2 not.

 

[StrangeRanger]

True but in the systems being discussed, there's no need for the runners to be different lengths

 

[falcon fanatic]

Actually, all my primaries are different lengths, I just averaged them to come up with a secondary length. Apparently equal length primaries is not all that important as long as they are close; smooth routing is more important. I agree with your observations Mustangsix, and those jag exhausts are stylin' 8) It's pretty much identical to what I am planning, although I was going to make shorter secondaries into the y-pipe. However, theoretically I'll get a broader torque band if I make them longer, so I suppose I could run dual until I get to my Pulse Wave Termination Box [using a single in/ dual out Flowmaster clone (Lawson industries, check them out!)] and out to a pair of round mufflers squeezed in between my springs and my gas tank. Just like the jag system.

 

[MustangSix]

Probably going to sound pretty good, too.

 

[falcon fanatic]

Yes, if I ever get to actually drive my car again...

Hope to be done with the rust repair by October so that I can send her off to the body shop. MIght build the pipes first, though, so that I can have them ceramic coated while I finish up the body.

 

[falcon fanatic]

Finally getting close to done. Here is a writeup on the exhaust center section I created. Mustangsix, you'll like it as it is very similar to that jag exhaust you like. I'm even going to finish it off with dual tube mufflers, probably porters depending on how loud it is in the current configuration;

http://falconfanatic.blogspot.com/2012/ ... ng-in.html

 

[falcon fanatic]

Allright, installed the center section with the chamber muffler and fired it up and it sounds awesome. Like a big v-8 with flowmasters. Too loud, of course, but a great tone which should be perfect after I install the mufflers. Idle seems smoother than before and it revs lighting quick. Can't wait to drive it. Will post video with sound tomorrow.

 

[falcon fanatic]

http://falconfanatic.blogspot.com/

 

[bubba22349]

It has a real nice sound Are planing any types of power tests or Dyno runs to compare to your old setup?

 

[tri-power 250]

That sounds great! Are you finishing the exhaust off by running the pipes over the rear axle and exiting under the bumper?

 

[falcon fanatic]

yes, tri-power. I'll have dual outs through a pair of mufflers. Probably something straight through like porters. I'd like it to be throaty, but quiet.

Bubba, I never finished tuning the engine with the old setup, so I can't do any comparative tests. I do plan on driving the sh*t out of it, though, and since I've had the car for ten years that should be comparison enough!

 

[bubba22349]

Yeah I would say you will probably feel something.

 

[woodbutcher]

Very NICE.Sounds healthy,but not obtrusive.
Good luck.Have fun.Be safe.
Leo

 

[64 200 ranchero]

i like this idea, i think im going to try something like this, its alot like how i have my exhaust now, i have dual out headers going through a Y pipe then to a cherry bomb extreme with dual outs, but the exhaust pipes are 3" OD, too big for my setup, it was sold to me as a compleate unit, im going to get a set of the new stainless headers and build somthing like this, but with a flowmaster 44 and have it dump out before the rear end.

Awsome idea falcon fanatic