Supercharged 318Ti Exhaust Noise Problem

[Geoff Hoad]

My 318Ti has a Rotrex Supercharger and puts out about 210 hp, 170 hp at the rear wheels. Exhaust was recently replaced with a less restrictive custom free flow system (as the old one had rusted out). The results, well the engine is breathing a lot better, acceleration is more noticeable and here's the BUT! The sodding thing is far too loud for an old fart like me and resonates badly at low revs. since its my daily driver, its driving me up the wall. The only advice I have had which makes sense is to get the exhaust of either a 323Ti or a Z3 2.8 and have it modified to fit. Has anyone had the same experience and can anyone offer any advice? Signed, deaf and desparate, Sydney, Australia.

[96cali]

Supersprint makes an all stainless and another aluminized steel cat back system for the 318ti. It is widely regarded as closest to stock in noise level but does actually increase HP slightly. Another popular exhaust is Stromung but is considerably louder. Not sure of availability in Australia but here in the US BMP sells SS and understeer sells Stromung. I advise you to contact the manufacturers to find someone closer to you for ditribution.

[angel318ti]

+1 for the supersprint. I love the low rumble but its not loud at all. it gives it that "performance sound"

[Geoff Hoad]

Appreciate the suggestions. My question however is, will a stock exhaust system take an increase of around 50% in horsepower> Onbe manufacturer in Europe I contacted said no. But I see a number of people with supercharged cars still running with stock or aftermarket exhaust systems.

[pnosker]

Sorry for the late answer, but yes it will.

[Geoff Hoad]

Thanks.

[greenie]

I had the single-outlet Supersprint that tested so well on my car until recently. It is relatively quiet. After about 9 years, it developed a rust hole, so I replaced it with a dual pipe all-stainless Supersprint system. It is quite a bit louder than the old system, probably because it has one muffler pot
instead of 2 and is used on both 4 and 6 cylinder models. The single outlet system has been discontinued but is still readily available. I discovered that the 2-pipe DTM model would fit in a 323ti valence without cutting, so that's what I have.

Milton Horst
Seattle, WA USA
'96 318ti Boston Green Sport

[Geoff Hoad]

I saw that exhaust in the Supersprint lineup and thought that of all the options available, it looked the best. Unfortunately, Supersprint exhausts here in Australia are horribly overpriced, the cat back section for instance is nearly two grand and the cat section is much cheaper at a grand and a half! Upon the recommendation of my local shop I am getting a custom exhaust system made to my specification at a race workshop. Seen their work and its very good.

The lessons here for anyone with a supercharged 318Ti are that a stock exhaust will work ok but it seems to be ebtter that where it is interchangeable with say a 323Ti, the flow though characteristics are going to be a lot better. One thing I will do is have the car dynoed after its all back in and see what output the car is mking.

Thanks to all of you for your contributions and help.

[marko]

what size diameter is the tubing??

I got a DASC-ed ti & have just yesterday received a Stromung 2.5 diameter SS exhaust (was supposed to be 2.25 - but thats a too long & too convoluded of a story for this thread )...
may concern is similar (though I have not installed it yet) I feel I may have bitten off more than I can chew, in terms of noise (while trying to maximize on power)..

anyway, more importantly.. @ which (diameter) point does an exhaust become too big, and starts actually loosing power (due to not enough back pressure - is that even possible)??

lastly, any thoughts on the flat spot (clearance issue)?? should be of no consequence, but who knows... pix below!

Originally Posted by Geoff Hoad

My 318Ti has a Rotrex Supercharger and puts out about 210 hp, 170 hp at the rear wheels. Exhaust was recently replaced with a less restrictive custom free flow system (as the old one had rusted out). The results, well the engine is breathing a lot better, acceleration is more noticeable and here's the BUT! The sodding thing is far too loud for an old fart like me and resonates badly at low revs. since its my daily driver, its driving me up the wall. The only advice I have had which makes sense is to get the exhaust of either a 323Ti or a Z3 2.8 and have it modified to fit. Has anyone had the same experience and can anyone offer any advice? Signed, deaf and desparate, Sydney, Australia.

[Geoff Hoad]

From talking to a lot of people, BMW, aftermarket exhaust manufacturers and custom shops, these cars have a 2.25" stock pipe. However, aftermarket units usually have two types, a 2.25" for stock replacements and a 2.50" pipe for those who have modified engines (that's us)! The main idea is to have a larger pipe and same size mufflers (or as close to) as stock to improve flow though, maintain the correct back pressure and enable the engine to get the exhaust gasses out as fast as possible. What tends to happen when you increase the flow through with the same size muffler is that you also increase the volume and vibration. In tuned aftermarket products like yours this should be a louder sportier sound than stock. But when custom shops build 2.5" and then go for smaller muffler like mine presently has, then you get a much louder exhasut with greater resonance. I would have no problems with the Stromung. It will be louder and sportier but from what I have heard, this should not be unpleasant! Once you go beyond 2.5" for our cars and engine capacities (even when they are supercharged) then the back pressure drops and the exhaust is less efficient. That flat spot is not going to be a problem. It provides extra clearance under the rear axle and is perfectly normal. This looks like a nice exhasut. Very straight so that there are no bends to slow down and restrict exhaust gasses. I had a good look at the specifications for Stromung and if I could have got one in Australia I would have bought one. Their SS models such as you have are perfect for our application.

Interestingly, my new exhaust goes on today. It will have a 2.25" pipe but will have a dedicated flow through cat and larger than stock mufflers. My criteria are a quiet sportier sound and I am reassured tht is what I will get. Let's see. I wil report later!

[marko]

good luck & do report please... my exhaust will go on weekend after next & I'll do as well. cheers..

Originally Posted by Geoff Hoad

From talking to a lot of people, BMW, aftermarket exhaust manufacturers and custom shops, these cars have a 2.25" stock pipe. However, aftermarket units usually have two types, a 2.25" for stock replacements and a 2.50" pipe for those who have modified engines (that's us)! The main idea is to have a larger pipe and same size mufflers (or as close to) as stock to improve flow though, maintain the correct back pressure and enable the engine to get the exhaust gasses out as fast as possible. What tends to happen when you increase the flow through with the same size muffler is that you also increase the volume and vibration. In tuned aftermarket products like yours this should be a louder sportier sound than stock. But when custom shops build 2.5" and then go for smaller muffler like mine presently has, then you get a much louder exhasut with greater resonance. I would have no problems with the Stromung. It will be louder and sportier but from what I have heard, this should not be unpleasant! Once you go beyond 2.5" for our cars and engine capacities (even when they are supercharged) then the back pressure drops and the exhaust is less efficient. That flat spot is not going to be a problem. It provides extra clearance under the rear axle and is perfectly normal. This looks like a nice exhasut. Very straight so that there are no bends to slow down and restrict exhaust gasses. I had a good look at the specifications for Stromung and if I could have got one in Australia I would have bought one. Their SS models such as you have are perfect for our application.

Interestingly, my new exhaust goes on today. It will have a 2.25" pipe but will have a dedicated flow through cat and larger than stock mufflers. My criteria are a quiet sportier sound and I am reassured tht is what I will get. Let's see. I wil report later!

[rik89]

whats the report?
i've just bought a ss stainless with two tail pipes for my m44(stock exept for green filter)
which im fittin this coming weekend, will hopefully give a nice low sporty note,
what sort of power gains(if any) will it give?

[rik89]

oh by the way sorry for reviving an old thread XD

[Geoff Hoad]

Although the through flow of the custom exhaust was excellent, the resonance was not controlled enough to make it worth living with. Junked it and replaced it with a stock cat back. May have lost a few horsepower but really didn't notice it as it is supercharged.

If I were to put another cat back exhaust on I would go for a Supersprint or similar. Would expect any decent cat back to give about 5 hp on a non-supercharged (i.e. stock) car and if you add a cold air intake that will climb to about 8hp.

[rik89]

excellent, well in 9 months I shall be dropping a 2.5L m50 in and turboing that, so I hope the supersprint won't be too restrictive, like the sound of 8hp tho
i'll let you know how i find the exhaust anyway