Is true dual exhaust overrated for perfomance
#1
Drifting
Thread Starter
Is true dual exhaust overrated for perfomance
I have been doing a lot of reading on different car forums trying to decide on exhaust options. I know there are some good vendors here that sell kits but I do not want to spend $2500 on exhaust to update the entire factory exhaust. I am thinking of going to a single 3 in. mandrel bent exhaust coming off of a Y just after the cats. I will be using pre- bent 8 in. offset pipes from flowmaster to do the routing. My local shop will weld the pieces together after I get the correct layout. The car will remain mostly stock except for the exhaust. A big advantage in going with the single is weight and cost savings, but will it hurt performance? I have learned it should flow as well as 2.5 duels so I do not think it will. So here is the big question, will a single 3 in. exhaust have any negative effect on the x-pipe gains upstream? Below is a link to a flowmaster Y that I would use to go to the single 3 in. pipe after the cats. The Flowmaster guy told me that the scavenging effects of this Y have proven to be remarkable. Who knows but it sounded good. After the Y" I will be installing one flowmaster muffler in the original resonator location. Any thoughts?
http://www.flowmastermufflers.com/sh...=&orig=Y250300
http://www.flowmastermufflers.com/sh...=&orig=Y250300
#4
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
I would never say that dual exhaust is overrated. There are single exhaust systems that yield the same gains as dual.
I can compare a car that does have a single 3" exhaust that makes over 370 HP and that is a 208 chassis CLK55 AMG. It has a 5.4L V8 and a single pipe exhaust that still makes more power than our newest 928, the GTS. Of course the piping is all mandrel bent, which would significantly help flow.
According to Louie Ott's research and judging by his dyno graphs, there is only a 7-10 HP difference between a single and dual setup all depending on pipe size with the 3.5" single pipe losing torque and a 3" pipe maintaining the factory curve but less HP than a dual 2.5" exhaust (only 10HP which could be picked up somewhere else like Roger's EIS intake.) Had I known about Louie's page sooner, I probably would have opted for a 2.5" to 3" merge collector and kept it single all the way back. I also keep getting burned by the passenger side muffler when checking the ATF. A 10 horsepower difference cannot be felt anyways in your butt dyno.
If you decide to go 3" single pipe, get rid of your factory's dual cats. Adding a Y-pipe afterwards will introduce too much scavenging and you will experience horsepower loss. Other than that, stick with an x-pipe and 2.5" dual pipes.
Below is also a chart that will give you a general idea of how pipe sizes relate to engine displacement and horsepower:
I can compare a car that does have a single 3" exhaust that makes over 370 HP and that is a 208 chassis CLK55 AMG. It has a 5.4L V8 and a single pipe exhaust that still makes more power than our newest 928, the GTS. Of course the piping is all mandrel bent, which would significantly help flow.
According to Louie Ott's research and judging by his dyno graphs, there is only a 7-10 HP difference between a single and dual setup all depending on pipe size with the 3.5" single pipe losing torque and a 3" pipe maintaining the factory curve but less HP than a dual 2.5" exhaust (only 10HP which could be picked up somewhere else like Roger's EIS intake.) Had I known about Louie's page sooner, I probably would have opted for a 2.5" to 3" merge collector and kept it single all the way back. I also keep getting burned by the passenger side muffler when checking the ATF. A 10 horsepower difference cannot be felt anyways in your butt dyno.
If you decide to go 3" single pipe, get rid of your factory's dual cats. Adding a Y-pipe afterwards will introduce too much scavenging and you will experience horsepower loss. Other than that, stick with an x-pipe and 2.5" dual pipes.
Below is also a chart that will give you a general idea of how pipe sizes relate to engine displacement and horsepower:
Last edited by Mongo; 03-01-2011 at 12:33 PM.
#6
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
4" is way too big on a street 928 with a 5.0L unless it's supercharged. I would say 3.5" is better if a large pipe is needed.
The trick is to keep the exhaust gasses hot so that they are passed through the pipes faster. If the pipe is too big, the exhaust will cool becoming more dense and may result in loss of torque in low and mid-range. It's all about balance.
The trick is to keep the exhaust gasses hot so that they are passed through the pipes faster. If the pipe is too big, the exhaust will cool becoming more dense and may result in loss of torque in low and mid-range. It's all about balance.
#7
Rennlist Member
Good Point. My reference is my '82 Auto, where I put in an LS6 that is making about 420 flywheel hp. With the 3 speed auto, it is really a great street car. Just need to put some stickier tires on now.
Also, where's the chart you mentioned?
Also, where's the chart you mentioned?
Trending Topics
#8
Drifting
Thread Starter
One big reason I would go with 3 in. is cost. I really like that new Flowmaster Y- pipe but I do not think they have it in 3.5 or 4. If I could find the pre-bent 3.5 in., (and a good Y in 3.5 in) I would look into going that route. There is just no one around here that does mandrel bending, so for best value for the buck I think I will need to stay with the 3 in. Flowmaster line.
#9
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
If you can't see it, click this link. It is in my Rennlist album.
https://rennlist.com/forums/members/...eter-table.jpg
https://rennlist.com/forums/members/...eter-table.jpg
#10
Rennlist Member
One big reason I would go with 3 in. is cost. I really like that new Flowmaster Y- pipe but I do not think they have it in 3.5 or 4. If I could find the pre-bent 3.5 in., (and a good Y in 3.5 in) I would look into going that route. There is just no one around here that does mandrel bending, so for best value for the buck I think I will need to stay with the 3 in. Flowmaster line.
Burns Stainless and Stainless Works
#11
Race Car
Originally Posted by Mongo;8343054
According to Louie Ott's research and judging by his dyno graphs, there is only a 7-10 HP difference between a single and dual setup all depending on pipe size with the 3.5" single pipe losing torque...
snip
[img
According to Louie Ott's research and judging by his dyno graphs, there is only a 7-10 HP difference between a single and dual setup all depending on pipe size with the 3.5" single pipe losing torque...
snip
[img
https://rennlist.com/forums/members/mongo-albums-other-picture9152-exhaust-diameter-table.jpg[/img]
I guess the backpressure helps.
Michael
#12
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
One big reason I would go with 3 in. is cost. I really like that new Flowmaster Y- pipe but I do not think they have it in 3.5 or 4. If I could find the pre-bent 3.5 in., (and a good Y in 3.5 in) I would look into going that route. There is just no one around here that does mandrel bending, so for best value for the buck I think I will need to stay with the 3 in. Flowmaster line.
What is your displacement though? If you are not running a stock S4 or GTS motor, you need at least 3.5".
Last edited by Mongo; 03-01-2011 at 01:40 PM.
#13
Official Bay Area Patriot
Fuse 24 Assassin
Rennlist Member
Fuse 24 Assassin
Rennlist Member
I remember a thread a while back where Louie said a 3.5" pipe would reduce the torque output though, but yield more HP on the top end. It's a trade off depending on where and how you drive your car.
#14
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
The typical V-8 hotrod sound is the result of having two seperate exhaust systems, one for each bank. The uneven firing order where two cylinders on one bank fire one after the other is part of the rythmic pattern our ears and brain seem to LIKE. So I would say Yes dual exhausts are over rated BECAUSE we like how they SOUND.....and two exhaust tips look better than a single