Dual Exhaust Thoughts

[Beodude123]

The dual exhaust thread got me thinking about how air moves and fluid dynamics. The move from 2 valves per cylinder to 4 per cylinder greatly increased the efficiency of engines. Air flows better through two separate holes than a single of the same area.

So here is what I was thinking. Take a ZXTuner header, and disconnect the bottom half. Fabricate up a new bottom half, but don't connect the two pipes together. Then you could run the exhaust wherever you wanted. If you had two 2" pipes, it would work out fairly close to having a 2.5". The two separate pipes should keep your air flowing faster at most engine speeds due to the split air flow. The two 2" pipes would be able to flow more air than the single 2.5", just based on area alone. I wonder how it would work out on the car.....

This is all theory though. What do you guys think?

[random_hero]

.....ricer.




j/k:)

[pissdrunx16]

this is the only way it would make n e sense to me!!!!

[ZX2 Sleeper]

True dual would mean you would need another cat. resonator and such. Im sorry for ruining your parade.

[pissdrunx16]

yez it would but if you plan on doing this... I hope you thought more ahead than that!!!

[Beodude123]

I never said I would be doing it. Just discussing mostly.

Come on guys, you think I don't know you would need more than one resonator and muffler? Please.

[Beodude123]

.....ricer.




j/k:)

Don't hate, because you know I'm right.

[Twiggy2cents]

True dual would mean you would need another cat. resonator and such. Im sorry for ruining your parade.

the end of the first header in a two piece header collects into two pipes it would be very easy to change that so they never collect

[Beodude123]

Plus, it would be a piece of cake to shorten the pipes. You could put the pipes out each side right after the first hanger, and put a resonator in there before that. The shorter exhaust would give you one hell of a top end to boot!

[swedevil]

I measured the cut outs for this on my side skirts the other day. I was thinking the same thing. I have ZXTuner header and was under there looking at it (was going to take a pic of the duals I'm running and started thinking about how that would work. I got it priced at the local shop and they said it would only be $125, so I'm thinking I may try it!

[mechtech]

It should have a unique sound, and probably real cool.

[Beodude123]

It would be loud as hell, that's for sure.

If you had the pipe that short, would you really need flex pipe? It would only have one hangar connected, so it would be able to swing fairly easily.

[Beodude123]

It's too bad I just spent $400 on a new exhaust.... I kind of want to give this a try. I think it would sound pretty good.

[pdwighty]

how would you get such short pipes inspected with the ammount of noise they would be putting out.... expecially on a four cylinder. I say IF you could make it work, have an increase of power, and still be quite enough to get away with (at speed limit speed), I would get it done.

[powder]

I've wanted to do this for a few years now. I don't have an escort anymore though.

[Blue ZX2]

Sounds like a bad idea to me. I am not hating just hear me out

1- Your engine needs back pressure
2- If you do not have any it can cause issues such as burning your valves out
3- If you do split this there is no where to rout the tubes, unless you want them hanging out the bottom looking like shit. or you can some how manage to get them both in the old exhaust tunnel
4- Rest assured it will sound like poop and most def like a Honda civic with a 16" outlet fart can.
5- You will lose power, yet again back to the back pressure issue.

Sure it might be cool, to have a one off thing... but in the end, a waste of time and more than likely a horrid noise that will sound so terrible you will go on a grandma killing spree only to slit your wrists in a large pool of aids and feel good about letting yourself die.

[WdcRobertL]

A motor needs proper exhaust scavaging, not necessarily backpressue.

In practice, a dual exaust doesn't work quite as well as you think it might, unless you pulse tune the thing, and have balance tubes or something.

It's possible to go very in-depth with fluid dynamics here, but basically, dual exhaust on a single-bank motor doesn't work very well, unless you are tuning for maximum flow.
An excellent example would be the 1000HP Ecotech Drag motor.
Dual exaust, IMHO, Doesn't even work very well on motors with Dual-Banks.
I have a 1984 300ZX N/A with a Nismo header, that the banks do not join until just before the Cat.
I have a cutout before the Cat, two actually, one off each branch of the header.
It does provide a slight HP increase at 6,000-7,000RPM, but below that the banks are unbalanced. not something I thought about before I had it done, but it doesn't run quite right below 5K or so.
I lose Max power if I close them, but the area under the curve is much more consistent.

My wife has a 95 Mustang GT 5.0, that has dual exhaust with no X-pipe, crossover, or balance tube, and the thing lopes like crazy at idle, is mean at 2-3K, but then just runs out of steam at anything above 4,000 RPM.
and sounds like a Civic to boot.

I could go into so much more detail, but they are far more knowledgeable people on this subject, and several web sites with massive amounts of information.
And hey, I could be very wrong, but this is what i've experienced.

[powder]

A motor does not need back pressure. Look up the definition of back pressure and you will agree with that.

[Blue ZX2]

Yeah, proper exhaust scavaging is related to back pressure in different areas of the exhaust, I didn't feel it useful to get that in depth about this monstrosity of an idea.

[SDreamz]

Sounds like a bad idea to me. I am not hating just hear me out

1- Your engine needs back pressure
2- If you do not have any it can cause issues such as burning your valves out
3- If you do split this there is no where to rout the tubes, unless you want them hanging out the bottom looking like shit. or you can some how manage to get them both in the old exhaust tunnel
4- Rest assured it will sound like poop and most def like a Honda civic with a 16" outlet fart can.
5- You will lose power, yet again back to the back pressure issue.

Sure it might be cool, to have a one off thing... but in the end, a waste of time and more than likely a horrid noise that will sound so terrible you will go on a grandma killing spree only to slit your wrists in a large pool of aids and feel good about letting yourself die.

I don't know if this was supposed to be a joke, but this is just all wrong. Once and for all, your engine does not need backpressure. What you need is the right diameter piping to suit your application. The biggest way people go wrong is trying to put too big of piping for the exhaust. When the engine can't flow enough to use the bigger piping, you lose velocity (which is also related to a temperature loss). This is not representative of backpressure in any way. An ideal engine would have absolutely no backpressure. This includes friction, as well as, bends in the fluid flow.

To the OP, I'm interested to see how this turns out.

[ilarson007]

Well, hopefully the motorsports engineering that i want to go into will teach me all about this stuff. Than I can try it.

[Beodude123]

The only way you would burn valves is if you ran open port. Just having an exhaust manifold the length of the ZXTuner will do the trick of keeping your valves from dying. I know what effect exhaust tubing has on your power curve from first hand experience, so I know how it affects the power curve. My RS2000 was open exhaust right after the cat. It had no bottom end, but it pulled like crazy up top.

Routing the tubes wouldn't be all that hard, since you would be able to fit two smaller pipes in there more than likely. Obviously I haven't measured, since I'm nowhere near my Z. I don't really plan on doing this any time soon... Just putting out ideas to get some juices flowing.



I just hate it when people talk about back pressure, especially when they say you need it.

[Beodude123]

In practice, a dual exaust doesn't work quite as well as you think it might, unless you pulse tune the thing, and have balance tubes or something.

It's possible to go very in-depth with fluid dynamics here, but basically, dual exhaust on a single-bank motor doesn't work very well, unless you are tuning for maximum flow.

I'm not a pro with fluid dynamics by any means, but I know enough to get myself in trouble. Why would it be any different on the exhaust piping than the intake and exhaust ports? Either way you are trying to move a volume of air through a space. Maybe I'm not getting something though. So feel free to get a bit more into it. That's what the purpose of this thread is!

[powder]

Yeah, proper exhaust scavaging is related to back pressure in different areas of the exhaust, I didn't feel it useful to get that in depth about this monstrosity of an idea.

Scavenging and back pressure aren't even related.

Back pressure is when you're getting resistance in the exhaust system and it's not flowing properly.

Scavenging is when the pulsations from your valves releasing exhaust creates a vacuum effect thus making your exhaust flow the way it should be.

[powder]

I'm not a pro with fluid dynamics by any means, but I know enough to get myself in trouble. Why would it be any different on the exhaust piping than the intake and exhaust ports? Either way you are trying to move a volume of air through a space. Maybe I'm not getting something though. So feel free to get a bit more into it. That's what the purpose of this thread is!

Ultimately it's a good idea but you would def need an x pipe and maybe even smaller diameter tubing than 2". 1.5" maybe.

[Beodude123]

Two 2" pipes would give about 6" total area, while a 2.5" pipe gives about 5". I think a built up Zetec with cams and head work would be able to fill that up pretty well. I have a FRIM and an extra head sitting at home, so it would be something I could consider. I should be pushing enough air with both cams and everything else in there.

I would be tuning more for top end power with a setup like this. For some reason, I like to have that good top end, even if I have to sacrifice a bit of the bottom.

[ilarson007]

Two 2" pipes would give about 6" total area, while a 2.5" pipe gives about 5".

Explain?

[Beodude123]

Pi * R^2 gives area. 3.14 * 1.25^2.

3.14*1.56= 4.8.

For two 2" pipes, it would be
3.14*1^2, which equals 3.14. Two separate pipes with 3 inches of area would give you a total of 6.

[SDreamz]

Explain?
Assuming the cross-sectional area to be a circle; Area=pi*radius^2.

If d=2in, then r=1in. For two 2in pipes, Total Area=2* pi * (1^2) = 6.283 in^2

If d=2.5in, then r=1.25in. For one 2.5in pipe, Total Area= pi * (1.25^2) = 4.908 in^2.


Edit: He beat me to it, oh well.

[zx2cambo]

duals usually look dump on smaller cars but ive seen some decent looking ones. also i dont know how much hp gain youll get out of it but the theory of it sounds correct.

[Beodude123]

It could be a decent amount. If I had the exit right in front of the back tires, the exhaust system as a whole would be a lot shorter. When you shorten the exhaust, you will make your power curve teeter totter. The bottom end will drop off a little bit, but you will have a lot more power after torque peak, and it will carry past peak HP a lot longer. Couple that with the better flow of the two separate tubes, and I bet it would give a good amount of gain.


If I was ever to do this, it would be after I build up my head and stuff. Doing this with just bolt ons and such would be a waste of time pretty much.

[Beodude123]

Ultimately it's a good idea but you would def need an x pipe and maybe even smaller diameter tubing than 2". 1.5" maybe.

That's one thing I was thinking about... I don't know if there is a single car with separate banked cylinders that didn't join them together at some point. This would be more for driveability more than anything else I think.

Like I said before, this would be a pretty extreme exhaust setup.

[zx2cambo]

ya....as long as you dont run it all ricey i dont see why this isnt a good idea. you should do it then show a before and after photos and dyno charts.

[Beodude123]

I doubt I would do dynos. I still haven't even put it on the dyno yet. I don't really care what my numbers are. They are probably somewhere around 140 whp...

What do you mean by run it all ricey? I'm all about quality now man. I'm done with half ass stuff on my car. Quality work is what I do now. I would definitely post up lots of pics though.

[zx2cambo]

well...if you do it at least tell us if you felt a decent difference in the butt dyno.

[Beodude123]

I would probably measure the size of the start of the secondaries on the header, and go with a pipe size similar to that.