Downpipe: Does Size Matter?

I have been shopping for a downpipe for the past few weeks, I sort of have it narrowed down to the following:

Armytrix
Evolution Racewerks
Boost Logic
SSR

Price isn’t much of a concern, obviously the lower the better, but I would rather pay a little more and have a higher quality pipe than save a few bucks....

Anyway, I may be wrong, I have been emailing too many companies regarding their pipes, but I believe Evolution Racewerks is the only one that starts at 4.5” and then tapers down. The others are 4” and 3.5.”

So, is bigger better? If everything else was the same, would you get 4.5” pipe over a smaller one?

Thanks,

PS: With the SSR being on sale, it is pretty tempting.

No bigger isn’t better unless you plan on replacing stock exhaust. Think about it - having a larger taper than transitioned back to the smaller stock exhaust pipe makes no sense from a performance perspective because you are still limited to the smaller opening.

if you plan on replacing the factory exhaust with a full 4” or 4.5” then getting the larger downpipe would be worth it.

If not just get the Titan for $289 and be done with it. Save the money for more mods.

larrymz3 said:

No bigger isn’t better unless you plan on replacing stock exhaust. Think about it - having a larger taper than transitioned back to the smaller stock exhaust pipe makes no sense from a performance perspective because you are still limited to the smaller opening.

if you plan on replacing the factory exhaust with a full 4” or 4.5” then getting the larger downpipe would be worth it.

If not just get the Titan for $289 and be done with it. Save the money for more mods.

Click to expand...

Ditto

084runnerltd said:

I have been shopping for a downpipe for the past few weeks, I sort of have it narrowed down to the following:

Armytrix
Evolution Racewerks
Boost Logic
SSR

Price isn’t much of a concern, obviously the lower the better, but I would rather pay a little more and have a higher quality pipe than save a few bucks....

Anyway, I may be wrong, I have been emailing too many companies regarding their pipes, but I believe Evolution Racewerks is the only one that starts at 4.5” and then tapers down. The others are 4” and 3.5.”

So, is bigger better? If everything else was the same, would you get 4.5” pipe over a smaller one?

Thanks,

PS: With the SSR being on sale, it is pretty tempting.

Click to expand...

I just went through the same thing and decided on the euromotive performance DP. The video they created made sense with the smooth transition flow from large to small. Now will it really make a difference? Probably not since I'm keeping the exhaust stock or until I go titanium. But it doesn't hurt to try and it's not much more than the cheapest one on the market. I paid $339 plus $80 for the O2 spacer from them. So it ended up being the cheaper option anyways.

larrymz3 said:

No bigger isn’t better unless you plan on replacing stock exhaust. Think about it - having a larger taper than transitioned back to the smaller stock exhaust pipe makes no sense from a performance perspective because you are still limited to the smaller opening.

Click to expand...

This is not actually true, even though it seems like it makes sense. I've seen experiments where the only thing they change is downpipe size, and they get better and better performance the larger downpipe they used (even though it goes back to smaller exhaust after the downpipe). They even ended up trying something stupid like a 6 inch downpipe just to test it, and yeah that made even more torque than any of the others.

Speaking to a friend of mine who's an engineer at a race engine building shop, he says its the expansion from a small area (turbo exit) to a larger area (big downpipe) that is key as it helps pull the gas out of the turbine faster or something like that. It was a while ago since we talked about it so I can't remember exactly. All I remember is bigger downpipe is better and its also important that its a smooth transition between the smaller area and the larger area apparently.

Here's a post that references the experiment I was thinking of and also adds some more explanation:

ChrisD said:

Here's a post that references the experiment I was thinking of and also adds some more explanation:

Click to expand...

Wow this is a great post. Thank you for this information, exactly what I was looking for.

This was great ! exactly what i was looking for. I placed a pre-order for the LEM 5" catted DP.
Part of their monster series, so its a fat chubby 5". the above confirmed my assumptions.