dual exhasut

[PapaCreech]

Is there a safe way to run dual exhaust on a stock 78 280 2+2?

i know i could just drive to the shop but sometime i think those guys are out for cash and i dotn want to get dangerous know what im saying?

im worried about gettin it to close to the gast tank and/or fuel lines but dearly want a dual exhasut 280

thanks

ron

[Bartman]

Sure, you can install duals on your car. If you want both to be on the same side, you don't need to make any modifications to your car. If you want one on each side, then you'll have to change your fuel tank.

[katman]

And keep in mind that you will probably lose horsepower doing so...

[PapaCreech]

thaks for the info guys

C-cut

ron

[Danno74Z]

Kateman,

 

Why do you say you loose HP is this your opinion or fact? If done correctly, I don't see why you would loose HP?

 

Thanks

Danno74Z

[ezzzzzzz]

Poor exhaust scavenging will result in lower hp. The exhaust pulse rate is effectively cut in half with split exhaust. I'd at least run a crossover pipe if I split the exhaust. You could run a proper exhaust and Y it at the rear for the look.

[AK-Z]

Actually in my MSA catelog I saw a (not dual exhaust) but exhaust system with dual tail pipes (quad tips). It looked like a standard exhaust layout but had another pipe (after the muffler) bend to the right side and beld out. So it looked something like this

 

||

||

| |

| | <-- muffler

| |________________

| |-------------------

| | <-- tip---------->| |

 

 

something like that but the muffler had one inlet and 2 outlets.

 

edit: my visual got a little scewed after posting but you can see what I was trying to show.

[Ed260Z]

They also sell a "Twice Pipe"

 

The winning Rally car from the 70's ran a dual exhaust set up with a muffler in the middle. The muffler had 2 inlets and 2 outlets, and the tips where centered in the rear of the car.

[katman]

Kateman' date='

 

Why do you say you loose HP is this your opinion or fact? If done correctly, I don't see why you would loose HP?

 

Thanks

Danno74Z[/quote']

We tried it on stockish motors and we lost hp over single exhausts on the dyno. So, fact.

[Bartman]

We tried it on stockish motors and we lost hp over single exhausts on the dyno. So, fact.

I'm sorry, but I can't buy your experience with duals and then call it "fact". Dual exhaust has been used for years to increase horsepower, and "if done correctly" I still think that it does. There are many factors that need to be considered in determining the proper size and routing of both single and dual exhaust. I agree that scavenging is important in exhaust, but you can still use scavenging with duals. In general I think the best system is duals with an 'x' pipe.

 

For those that want to learn more about the physics of exhaust here's a link to a thread that contains some real "facts".

http://forums.hybridz.org/showthread.php?t=98786

[johnc]

Keith is referring to L6 engines.

 

Dual exhausts have been used for years mostly because light weight exhaust tubing sizes over 2.5" OD were extremely expensive and mandrel bends in those sizes were difficult to find, at least until the mid 1970s.

 

A single exhaust (even on a V8 engine) can produce more torque and horsepower then a dual exhaust. Most Trans Am cars run 180 degree headers and a merge into a 5" exhasut system. Unfortunately, all street and most race cars have packaging issues which preclude a properly designed single exhaust. Those Trans Am cars have the header collectors and exhaust taking over the entire passenger seat area.

 

Another example was the development effort Guy Ankney put into making a fast B Stock Nissan 350Z. All the dual exhausts (including a complete custom system) he tried showed little (if any) horsepower or torque gains. When he had a custom single 3" exhaust build with a properly designed 2 into 1 merge collector he saw a multi-digit percentage torque increase across the rpm band with a corresponding horsepower increase.

 

And, yet another example was the exhaust I built for Dave Schotz's T2 Camaro. 2.5" primaries, X pipe, and a merge collector into a 3" exhaust. He saw a 14% increase in torque when that exhaust replaced his previous 2.5" with X pipe and dual 2.5" out the back.

 

Also, an X Pipe simulates a single exhaust with a merge collector. Its basically the same as 2.5" tubing feeding into a proper merge collector and a 4" exhaust from the collector back. But again, packaging issues with tubing over 3" precludes most folks from running a good single exhaust on a V8 powered vehicle.

[Ed260Z]

It seems that on a N/A engine you want to keep some pressure in the exhaust system, to increase it's power. But does this hold true for Turbo applications? More specifically Twin Turbo'ed cars.

 

A turbo wants 0 pressure in the pipes, so that it can flow as quickly as possible. So in the case of a TT application it seems to me that 2 pipes would be better than. Also when you take into account that a overly large pipe will not flow as quickly as a properly sized pipe. Ideally a TT motor making around 600HP wants a pipe that's 4-4.5", which is to big to fit under my Z. Now two 2.25" pipes (one for each turbo) will be easier to fit under the car. And with a smaller diameter it should have a much higher exhaust velocity.

 

I'm no expert on the subject, and this more of a long winded question w/ explanation of my reasoning behind it. If I'm wrong please correct me.

[JMortensen]

2 2.25" tubes will have nowhere near the flow capacity of one 4.5" pipe. Not even close. Here's a simple way to show you why. Draw a 4.5" circle. Then draw 2 2.25" circles next to each other inside the 4.5" circle. SURPRISE!!! I'm just SWAGGING here, but I'd guess you'd need dual 3 or dual 3.5" pipes to flow the same as a 4.5" pipe.

[JMortensen]

Just did the math. Two 3.25" circles have pretty close to the same surface area as one 4.5" (within 4 sq in). So dual 3.25's would be the way to go if 4.5" was what a formula said you should have.

[Ed260Z]

I was doing some more reading on this great thread listed above http://forums.hybridz.org/showthread.php?t=98786, and I saw a link to a co that makes oval tubing. That looks like a great solution to my clearance problem, but I would like to get a Dual look at the end.

[Bartman]

And' date=' yet another example was the exhaust I built for Dave Schotz's T2 Camaro. 2.5" primaries, X pipe, and a merge collector into a 3" exhaust. He saw a 14% increase in torque when that exhaust replaced his previous 2.5" with X pipe and dual 2.5" out the back.

[/quote']Thanks for the very informative post.

 

The snipet from your post above intrigues me. Do you have any idea what could make a single 3" perform better than dual 2.5" with an X pipe? It makes it seem like more performance and race cars should be using a single. Even to this day I think most "performance" cars use duals including Ferrari's, Vette's, Stang's, etc. Even tuned cars from Rousch, Saleen, etc; also stick with duals. Aftermarket companies such as Borla and Monza generally use duals. I don't think that packaging is the answer because the instance you used above wouldn't affect packaging that much (especially if you used oval pipe on the single). Maybe the market demands duals whether they perform better or not (sounds better)?

 

Given roughly the same size and routing I have a hard time understanding how the single could be better.

[johnc]

Packaging that 3" exhaust under Dave's Camaro was very difficult. It was very tight over the the axle because the panhard rod mount takes up some of the available space. He previously had dual 2.5" pipes over the axle going through the same spot and they fit much better because one of the pipes was routed to a different side of the mount. With a 3" pipe I had to route it outboard of the mount and I needed a very specific bend (5.5" CLR) to keep from hitting the mount, floor pan, and fuel tank.

 

 

I know the exhaust pictured above looks very simple, but it took a while to get that simplicity.

 

I'm not an engine guy so I can't give many intelligent reasons why X works better then Y. I do spend a lot of time talking with engine builders about exhaust systems. I've also spent some time talking with fabricators like Andy Bondio who builds a number of the Trans AM team racing exhausts.

 

The engine builders like to have the exhaust work with the entire engine as a "system" from the throat of the carburator/throttle body to the exhaust tip. Often when I ask about header primary tube length I'm given a measurement to build to that goes from the exhaust valve seat to the point where the primary tube necks down into the collector.

 

So, I guess I can't really answer "why" a single exhaust seems to work better then a dual. And I do know that there are lots of racing examples where duals are used when there are no rule or packaging restrictions. My only thinking there is that the engine builders are looking for ultimate horsepower and very high rpms (F1, ALMS LMP, etc.)

[Bartman]

I should have used you to do my exhaust.

 

What's really interesting to me with that exhaust you did for the Camaro is the merge. You actually kept it dual in and out an 'X' pipe and then merged it into one downstream. Maybe it's scavenging twice?

 

Either way, nice system and you can't complain about the results.

[johnc]

You actually kept it dual in and out an 'X' pipe and then merged it into one downstream.

 

This was by customer choice. I recommended no X pipe and a longer merge collector with a 14 degree cone transition from 2.75" to the 3" tail pipe (notice, no muffler on this system). But, the existing exhaust already had an X pipe and Dave wanted to re-use it. It worked well but I've always wondered if it would have worked better with a coned merge collector and no X pipe.

[racerx260]

They Used Dual Exhausts On The Early 240 Rally Cars. They Ran Side By Side Right Under The Gas Tank And Out The Back. They Used An Extended Megaphone That Was Like 18 '' Long. A Slow Gradual Taper.they Used Two Small Diamiter Pipes To Prevent Loosing Exhaust Scavaging And Tourqe.there Are Old Photos Around Showing Them.