And the all around technical question for today is... Why is dual exuast a bad thing on 4cyl engines... No im not looking to do a dual setup on my sentra im just wondering.

So someone please explain to me the theory behind this, i have head from many that it is a bad idea. Now my question stems from the Dodge R/T's with the dual. I also noticed the Audi A4 1.8T has a dual setup, now i was under the impression that a 1.8L is a little small for a 6cyl and its a 4cyl why the dual exuast. You get the idea.

Just trying to learn a little more about the theory behind the performance. :D

I'm not sure it's a bad idea, but you would add unnecessary weight. I'm also not sure where you'd route it, FWIW.

think back pressure. too much is bad, too little is just as bad from a power stand point. the A4 has dual exhaust prolly 'cause of the turbo. as for the R/T's, i think it's just two outlets out of a single muffler. AFAIK, that's not a true dual exhaust.

Originally posted by Stiletto
as for the R/T's, i think it's just two outlets out of a single muffler. AFAIK, that's not a true dual exhaust.

The R/T exhaust is a single muffler with dual outlets. I used to have a 95 Neon with the same exhaust (before chrysler realized it looked good on the car) and it sounded really good. It was a little heavier than the stock muffler, but it was also stainless steel and also had huge 4" tips which carried a lot of weight. The sound that comes out of them is very deep and music to ones ears as compared to other aftermarket 4cyl. exhausts that sound like someone stuck a live cat in the muffler. According to the butt dyno it felt like it gave it better throttle response and better exhaust scavenging at high RPMs. As for being compared to a aftermarket single tip exhaust, I would say virtually the same performance benefit comes out of both (2-4 HP gains).

On a side note, Neons came with 2.25" exhaust piping all the way to the muffler. This made cat-back mufflers useless on that car unless it was running boost, and making exhaust upgrades easier and cheaper than many imports that come with tiny exhaust piping that must be replaced.

Well that's my .02 cents.

You can not have a true dual exhaust on an inline 4 cylinder engine, as there is only one bank of cylinders.

You must have a V-formation engine (V6, V8) to do true dual exhaust. One header, one pipe, one muffler/cat, one tailpipe -- per bank of cylinders is what true dual exhaust is. (Although you *could* split up the cylinders on an I-6, but I digress).

What you *can* have with an inline 4 cylinder is dual outlet exhaust. Simply put, splitting into two exit pipes from the muffler.

Why you'd want to do this, I have no idea. Does nothing. Nada. Zero. It looks cool to some people, but this ain't the Altima bling-bling crowd here. :D

yeah, exactly what serprise said. you need to have two separate exhaust manifolds to make use of a dual exhaust. a perfect example of silly dual exhaust design is the acura 3.2 TL and the accord v6's - from behind, you can clearly see where the piping splits to two separate exhaust cans. looks cool as heck, but worthless, AND it makes it just that much more expensive to modify! of course, for the purist, the added weight would be a waste as well.

I do not know what design they used (y-pipe, etc.), but the Sport Compact Car 200SX project car had a dual outlet setup installed. IMHO I thought it looked good and not 'bling' 'bling'. Only thing was, the picture in the mag showed the car with dual mufflers, but they never mentioned anything about the install or that they even did that. :confused:

My only thought about this is that you would have to use a much smaller pipe diameter at the split. For example, if you went with a 2.5" cat-back, you would then use two 1.25" pipes at the split back to the mufflers on each side.

Supposedly the 2000-2001 Sentra SE's (sr20de) had a dual tip muffler that only would have one tip open at low revs and at a certain point(by pressure maybe?) would open the second tip up for more flow thru.....

i don't know if they used the same muffler on the se-r's(2002+) but they do look similar...

Useless info to add to the discussion:

Many aftermarket exhausts for dual exhaust cars have a cross pipe that links the two sections. This (I believe) is to help smooth out the exhaust pulses and help "pull" the air out of the cylinders with the momentum of the exhaust gases before it. So then when you add in that cross pipe, do you no longer have a true dual exahust? :D

I'm pretty sure that dual exhausts on FWD (transverse engine mounting) and 4-cylinder cars is just for styling purposes only.

Originally posted by Xsanity
Supposedly the 2000-2001 Sentra SE's (sr20de) had a dual tip muffler that only would have one tip open at low revs and at a certain point(by pressure maybe?) would open the second tip up for more flow thru.....

i don't know if they used the same muffler on the se-r's(2002+) but they do look similar...

yes, a idea gleaned from the maxima was the:

http://www.nissandriven.com/m/cma/i/m2/m2_per_si15_varmuffler.jpg

Variable-Capacity Muffler

Delivers wide-open power-boosting exhaust flow without blowing Maxima's quiet, stealthy cover. A special valve stays closed when revs are low (e.g., when you're sitting at a stop light), and opens when engine speeds rise to allow for maximum flow and full-tilt horsepower.

Originally posted by Driven97
This (I believe) is to help smooth out the exhaust pulses and help "pull" the air out of the cylinders with the momentum of the exhaust gases before it.


That is called scavenging. I believe you can more effectively control that with good header(s).

Also, the 2nd gen RX-7's featured a dual muffler exhaust. The motor only had 2 exhaust ports, with a 2 pipe header, going to one center pipe and a bunch of cats, then splitting with a 'Y' pipe to 2 mufflers. Many owners said "sayonara" to the 2nd muffler and put a nice aftermarket one on there. Just testimony to the added weight thing that true enthusiasts care about :)

Originally posted by SERprise In WV
You can not have a true dual exhaust on an inline 4 cylinder engine, as there is only one bank of cylinders.

You must have a V-formation engine (V6, V8) to do true dual exhaust. :D

Hmmm; I don't see why you couldn't make a 4 into 2 into 2 set-up -- as long as the exhaust gases from one pair never co-mingle with the other, I'd presume it would meet any definition of "dual". OTOH, based on the other considerations, why one would want to, either.

Originally posted by Tigermiata

OTOH, based on the other considerations, why one would want to, either.

Exactly. :)

-GP-

Originally posted by SERprise In WV


Exactly. :)

-GP-

Then if you had one exhaust coming out under each door (sidepipe style!) It would sound -really- wierd. Like a wierd two cylinder?

Also- scavenging! that's the word I was looking for. I had reversion stuck in my head yesterday and couldn't shake it. Reversion is going to wrong way, right?

Originally posted by SERprise In WV


Exactly. :)

-GP-

Toyota did it. We get 20 valve 1600 Levin/Corolla coupes here with dual exhausts. Never actually looked at the header to see how they did it but it is definitely a dual as exhausts exit on both left and right hand sides of the car... looking for a pic now...
here is the car.....you ever see these?
http://cars.byweb.co.nz/thumbs/tn000243.jpg

Thats it. Toyota produced several worldwide models with the 4A-GZE supercharged 20v motor and dual exhausts. Another one we can get here in NZ in the link below. I guess like the 20v thing that it was never shown to provide benefits that offset cost/weight considerations... or the back pressure thing.
These go pretty well though for 1600's.....

http://www.4agze.com/visitors/visitors_080.htm

Fake dual exhaust = rice LIERS

sorry...more ClubSi lingo.... :)