Dual exhaust must mix

[vettedog72]

Some where I read the TR6's MUST have a common (mixing area) point in the exhaust or a loss of power will occur. Some systems don't have a cross over or X pipe provided. If you have one of these dual systems what are you doing to get the advanctage of mixing the duals?

 

[Yellowdog]

As I understand the theories of gas flow and engine output, the 'mixing' of the dual exhausts is to allow the system to pressure balance itself. If running true separate dual exhausts, a pressure differential can buildup back through the valve train from one group of cylinders to another, thus hurting total performance.

The stock dual pipe exhaust on the later cars has a hole between the outlets in the cast iron manifold to allow this balancing. This works with the stock exhaust and aftermarket add-ons.

There has been considerable discussion on this and other boards about headers, collectors, 6:3:1 systems, 6:3:2 systems, backflow pressures and tuning headers for equal length from the exhaust valve to the collector. Do a quick search and you will learn more than you ever wanted to know about exhausts.

Back in the late '60's I was introduced to the concept of balancing the exhaust on my big block MOPARS. By simply adding an x-pipe we were able to pick up a minimum of 6-8% hp at the rear wheels on the dyno. I never thought it looked as clean as dual pipes mirrored along the frame rails, but it you go with what works.

 

[DART]

My SP250 (V8) had the crossover pipe originally, and the CO (as opposed to PO) eliminated it for reasons unremembered. Seeing your post, during the current rebuild it will reappear. And as I remember, it also made the exhaust note much sweeter.

 

[Guest]

I had the split manifold on my TR6 as OE an indeed it does have a large hole to connect the two systems. I recently opted for the Falcon split header (two piece, 6-3-2) and can tell you that there is virtually no way to add a crossover on this system that would work. The two collector pipes exit at different levels and at different angles so that getting the "H" piece to insert would be virtually impossible, unless you were to assemble then bolt up the header to the head last. Too, you would slightly be violating the principle of measuring the distance from the valves, but that is probably nitpicking. The fact that I run true duals, no crossover, gives me a lower exhaust note, more rumble and the resultant "pop" when I decelerate, none of which I find objectionable. Sounds like a TR6. I especially like the little rasp that I get on long, hard acceleration and a lazy shift when the engine throttles down a bit. Sounds bad to me. Strangely, my 70 454 Vette didn't have a crossover from the factory when I bought it new. One, there was absolutely no room for one.
My observations.

Bill

 

[vettedog72]

I'm looking for a publication by one of the old TR6 racing groups. Booklet published power changes (as measured on a dyno) with certain specified mod's. As I recall head mods including porting, polishing, some (then exotic) valve cuts, cams, and exhaust. The team was looking for the "tuned" exhaust including length of pipes and hp vs. backpressure. I recall a summary statement about one of the most important things for exhaust as it relates to power is to have the pipes mix.

My 72 454 vette has side pipes with long headers, a real spider web guarding anything you might need to repair. No cross over on my highly modified, nothing original nor stock, vette either.

With as much power as your TR6 has a few more hp vs. the sound you want is an enviable option. Besides, I doubt that the team that wrote the book ever tried those foot wide rectangular exhaust tips; may be they make up for a crossover. Still I remember a dyno test with the stock muffler giving more performance than open pipes and the team giving the credit to the cross over in the stock muffler.

Does any body have this booklet?

 

[vagt6]

Probably some of the best exhaust system research on these engines (Triumph 2000/2500 cc) was conducted by Kas Kastner when he was in charge of the Triumph factory race effort. Kastner found that the most efficient exhaust pipe diameter was a single, 2 1/2 inch (or was it 2 1/4?) pipe, run as straight as poss to the rear of the car.

Dave Vizazd's article is also very good. I suggest you grab a copy of Kastner's most recent book, it's indispensible for modding these engines.

 

[vettedog72]

What did the cover of Kastner's publication look like (black and white, color, size, anything would help). It will help me find my copy.

Also, what is Kastner's most recent book as I would like to read it.

 

[vagt6]

Here you go, I think it was published in 2003 or 2004:
https://www.google.com/search?ie=UTF-8&oe=UTF-8&sourceid=gd&q="Kas+Kastner"

 

[Rabid_Dolphin]

[ QUOTE ]
I had the split manifold on my TR6 as OE an indeed it does have a large hole to connect the two systems. I recently opted for the Falcon split header (two piece, 6-3-2) and can tell you that there is virtually no way to add a crossover on this system that would work. The two collector pipes exit at different levels and at different angles so that getting the "H" piece to insert would be virtually impossible, unless you were to assemble then bolt up the header to the head last. Too, you would slightly be violating the principle of measuring the distance from the valves, but that is probably nitpicking. The fact that I run true duals, no crossover, gives me a lower exhaust note, more rumble and the resultant "pop" when I decelerate, none of which I find objectionable. Sounds like a TR6. I especially like the little rasp that I get on long, hard acceleration and a lazy shift when the engine throttles down a bit. Sounds bad to me. Strangely, my 70 454 Vette didn't have a crossover from the factory when I bought it new. One, there was absolutely no room for one.
My observations.

Bill

[/ QUOTE ]
While an Xpipe setup should yield THE most power from any dual bank engine, I'm not positive the results are directly applicable to straight configurations. I think the hole in the OE manifold would take care of balancing the pulses and maximizing scavenging, but we ultimately want that effect WITH the beneficial flow of a header. Theoretically, we want to place an X somewhere in the system after the header. We want to do this without making one exhaust pipe longer than the other. To be honest, I'm not sure that the Xpipe's benefit would over come the sacrifices in exhaust flow created by the pipe contortions necessary to put the X in the exhaust tubing while keeping the pipes of equal length. Oh Bill, Our Vette doesn't have a crossover pipe either. Side pipes are funny that way. /ubbthreads/images/graemlins/thumbsup.gif

 

[MNColin]

I bought a complete st/st Exhust system from Rimmer brothers in the UK.
I was looking for a System that met all the requirements of the above and found this one.

6 into 3 and then into 1 at the manifold. Then a large single bore splits into two after the transmission mount and exits at both sides of the car.
It looks great, however it's not fully installed yet as I'm still in the middle of my resto.

https://www.rimmerbros.co.uk/cgi-bin/rimmer?tr6/exhaust#Exhaust%20System%20(Sports)

I chose System B, Shipping was'nt to expensive, I could of waited untill they have a sale as they somtimes give free shipping.

Regards Colin

 

[jeff3113]

Interesting discussion. Been on my mind since I finshed the V8 install.

I saw a similar article years ago about the increase using the crossover pipe. In that example it was an H-pipe configuration. Seems to me it had something to do with wanting equal back pressure. I recall the dyno was measureably higher using the crosssover.
I'm running dual 2 1/4 straight pipes and there sure can't be alot of pressure in the 6 feet it runs. The mufflers are even larger...
That all said,,,,I was considering putting in an H pipe if I could find reason to do all that extra work....
Jeff3113