[Grimace]

are any exhausts being made full 3"? with no cats? as well as true 3" downpipes with no cats? i live in nebraska and lets just say we dont know what emission laws even are in this state. Just wondering if anyone can help.

[335iheLLraiseR]

contact VIP Tuning, i think they said it was 3.5 though.

[Grimace]

hmmm 3.5" really seems like overkill on the small turbos. especially not pushing THAT much boost.

[335iheLLraiseR]

tell them that.

[Grimace]

i dont need to tell anyone anything. it was an opinion.

[335iheLLraiseR]

i was being sarcastic.

[Grimace]

stoopid internetz.

[335iheLLraiseR]

most are 2.5", that i have seen.

[Grimace]

yeah ive done some research id just like a full 3" if im gonna get the 3" DP

[Gen_E92]

anything more than 2.5'' is overkill unless you have turbo upgrade. 335i use dual exhaust so obviously 3'' is not just 3'' like on Evo's/Sti's which use single turbo and single exhaust...

[Grimace]

yeah thats true also. i just got out of the single turbo honda scene so some of my knowledge from that just carried over.

[335iheLLraiseR]

also, if your intentions are based on downpipes, all the ones currently available taper to 2.5", unless you go custom of course.

[Grimace]

yeah i made a post about true 3" dp. but they havent gotten back to me yet

[Lane]

Any tapering in the early stages such as in the DPs is bad. However, since also 2.5" flows enough, it doesn't matter much. There is nothing wrong with 3". It fits. Go with 3", but you need to have it custom made.

The reason of the DPs tapering down to 2.5" is that the stock DP tapers down and DP manufacturers wnat their products to fit to all the catbacks in the market. However, Riss Racing has told they were considering having full 3" if there were demand enough. However, having all the catbacks smaller diameter to be fitted to the tapered DPs, adn therefor having all the DPs tapered, I think there is a circle that the catbacks and DPs have used to meet at the de facto standard diameter initiated by the original stock system.

You would need to go full custom, which is a good alterative anyway, since you can select whatever sound and configuration you prefer.

[jbuds335xi]

I believe the Borla is 3' all the way through, and I think they have secondary cat deletes.

[judec]

there were tests about a year ago with 3" dual setups. Results:
1. absolute overkill for stock turbos
2. serious fitment issues, there is not enough space for 3" dual systems under the car
3. because of 2. there is not much possibility to play with exhaust geometry so it droned like crazy
4. it was loud like hell but I suppose this fact won't bother some of U.

Still want one?

PS: the VIP 3.5" is a single pipe conversion prototype setup.

[335i4u2nv]

get it! make it 4 inch and out the sides!

[Lane]

Originally Posted by judec

there were tests about a year ago with 3" dual setups. Results:
1. absolute overkill for stock turbos
2. serious fitment issues, there is not enough space for 3" dual systems under the car
3. because of 2. there is not much possibility to play with exhaust geometry so it droned like crazy
4. it was loud like hell but I suppose this fact won't bother some of U.

Still want one?

PS: the VIP 3.5" is a single pipe conversion prototype setup.

Can you point out who made these tests and where I can find them?
The testing does not sound very reliable because first they stated that there is not enough space and however, they were able to install it...
Regarding the noise issues, it depends on the mufflers, resonators and catalysators used - not that much wether the diameter is 2.5 vs 3 inches.

[Tortfeasor 335xi]

Originally Posted by Lane

Can you point out who made these tests and where I can find them?
The testing does not sound very reliable because first they stated that there is not enough space and however, they were able to install it...
Regarding the noise issues, it depends on the mufflers, resonators and catalysators used - not that much wether the diameter is 2.5 vs 3 inches.

+1 a link would be appreciated. Though I know in the world of mustangs that 2.5" was not a restriction till you were making in the 500+ hp range. Though its different for turbos as they spool due to pressure differences pre and post impeller. Presumably the shortest pipe with the largest diameter will have the greatest pressure differential and thus best spool characteristics. But without hard data its hard to say if 2.5" is enough of a restriction to really matter.

[judec]

Originally Posted by Lane

Can you point out who made these tests and where I can find them?
The testing does not sound very reliable because first they stated that there is not enough space and however, they were able to install it...
Regarding the noise issues, it depends on the mufflers, resonators and catalysators used - not that much wether the diameter is 2.5 vs 3 inches.

I can't. As I said it was one year ago and I dont care enough to search.

If I say there is not enough space, there is possibly not enough space to fit it confortably or fit it w/o touching the chassis or each other and plenty other reasons. But they were able to install it, test it, then throw it away - that's what U will possibly end up doing too, but just keep going on, a first hand experience is always better.

And regarding the noice issues - U are right, but not 100% - first of all I dont think U intend to use cats (or even resonators), second there will be possibly no place to put resonators in reasonable places, third the mufflers are not a universal cure. Especially if U intend to put on 3" exhaust for performance purposes (unsubstantiated) it would be stupid to apply restrictive components to deaden sound and drone. A high-perf flow-through muffler wont help much.

[Lane]

I have had multiple turbo cars with one big 3" muffler at the very end of the exhaust. 3" mufflers flow so well that you don't need to skimp on their muffling abilities. The sound has been reasonable. Now having 2 small turbos instead of 1 big one silences the sound to begin with, and doubling the number of mufflers I would guess we end up with a BMW quality sound level - i.e. not too loud. You are right, I think I should try it out myself.

[Gen_E92]

2.5'' is definitely enough w/o a doubt. Just think how those Evo's/Sti's have one much bigger turbo and 3'' is good enough for them, and now we have two much smaller turbos and 2.5'' exhaust coming out from each of them.