Is 3" single better than 2.5" dual?

[mustange70]

I just got a new exhaust installed on my pickup, i got a 3" inch pipe straight from the header into a 3" y-pipe that is located at the back of the cab, then for a muffler i got a dyno max superturbo, from there it goes over the axle and dumps behind the passenger rear tire with a 18" 3.5" tip. Now i had the option of going with a 2.5" dual system but i liked the 3" system better for the sake it was a lot cleaner underneath. Would the duals have been better?

[WhëëlMå1]

No. The single 3" should provide the same, if not more power than the duals on a "normal" vehicles. Now, if you were running a 600hp 460, that would be a different story. The duals would be far superior to a single.


Rich

[There Goes The Neighborhood]

A pipe with 1 inch greater diameter flows twice as much. So, if you go from dual 2.5 to a single, you'd be better off with a 3.5 for max power, 3 inch is better for TQ.

[stevef100s]

It sounds like you have a straight 6. Am I right? If that is so, the 3" single may be a little big. If you have a small block v-8, the 3" would provide better torques at lower rpm's, or if you carry a load or tow a lot. If you mainly drive at higher rpm's, like with highway driving and such, then duals are the way to go. With a straight six, the only way duals would be a benefit, is if you had headers with two outlets, and then I would only run 2.25" at the largest. Running a single exhaust into a Y into duals doesn't do much for anything other then the sound.

[Icicle]

So if I get the jist of this conversation (not to hijacka thread) A small block v-8 (a 302 for example) would breathe best as a low torque truck motor with a 3" single exhaust...right?

[stevef100s]

Correct Icicle. It's mainly about exhaust velocity. At lower rpm's, the single 3" sytem will maintain better velocity then with duals. There's also a little thermodynamics involved.

[mustange70]

Thanks everyone, from what has been said it seems that i choose the right exhaust for my pickup. I just wish it was a little louder.

By the way the motor in my pickup is a 350hp 351Windsor, it's built to run in the lower rpms, and if i would have put in some slower gears (its got 3:1's) it would be able to keep up with a camero SS.

[DanZ]

I am also interested in the sizing of the 302 single exhaust.

I have been to a few shops to price cat back systems and the most experienced guy said that 3" pipe was too big for the 5.0 and that I would lose low end torque. He said he has had people come back because they were unhappy with the 3" size and they changed to 2.5". The other shops seem to think that 3" is the way to go.

I measured my pipe dia's and found the ypipes from the manifolds to be 2.25", then it is almost 3" between the cats, and then it necks down to 2.25 after the 2nd cat and then 2.25 out from the muffler.

So I thought 3" out from the back of the 2nd cat would be best. Especially since there is a total of 4.5" in dia when you combine both pipes of the ypipe.
Now I'm a little concerned about choosing between 2.5 and 3.0". I like having torque for around town but I want h.p. when pulling my boat.

Will either of these sizes make a difference?

BTW: I plan on going with the FM 40 series muffler.

[DanZ]

The other thing I meant to ask is whether mandrel bent pipe is really that important. For some reason all the shops I talked to have mandrel bent tubing in 3" only - not for the 2.5"

Any opinions?

[dk5122]

Originally Posted by mustange70

Thanks everyone, from what has been said it seems that i choose the right exhaust for my pickup. I just wish it was a little louder.

By the way the motor in my pickup is a 350hp 351Windsor, it's built to run in the lower rpms, and if i would have put in some slower gears (its got 3:1's) it would be able to keep up with a camero SS.

Would the duals have been better? Now knowing you have 350hp I would have run true 2.5" duals with a crossover pipe............Your first post says header which makes it sound like a six cyl. Later

[dk5122]

DanZ, you will be fine running a single 3" with your 302. My buddy has a six and runs a 3" single after the cats. He tows alot and said overall power has increased. It also sounds alot better. Get the mandrel bent pipes.

[DanZ]

Thanks DK,
I was thinking 3" would be ok but that guy at the muffler shop made me wonder....

Even better since the 3" will be mandrel bent.