[BavarianBullet]

Originally Posted by GreenPlease

Has anyone considered a carbon fiber cat-back exhaust? I did a but found nothing. I have to think that there is potential for ~70lbs of weight saving by switching from SS to CF.

Anyone know the limits of the resin used for CF? I want to say 350C....

Thoughts?

Carbon is quite heat resistant and making CF takes some significant heat. However, CF cloth before impregnated with resin is like fiberglass cloth. The resin and CF together make a tough part.

So while carbon fibers made into a part would take a lot of heat, the resin would not and therefore you could never use it as a high temperature component.

This link details some OEM for CF that claims some people have stuck it on mufflers with adhesive but not made exhaust using only CF: http://www.protechcomposite.com/serv...FQyfnAodjGnG6Q

Titanium is the same strength as steel at 60% of the weight I believe. It's also notoriously difficult to work with and has bad wear resistance.

[GreenPlease]

Thanks for all the input guys! Esp Jp!

[darkphantom]

If i'm reading this right, higher temps = elasticity o_o...=not good

Carbon heated in the range of 1500-2000 °C (carbonization) exhibits the highest tensile strength (820,000 psi or 5,650 MPa or 5,650 N/mm²), while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity (77,000,000 psi or 531 GPa or 531 kN/mm²).

[LateralG]

Originally Posted by BavarianBullet

Carbon is quite heat resistant and making CF takes some significant heat. However, CF cloth before impregnated with resin is like fiberglass cloth. The resin and CF together make a tough part.

So while carbon fibers made into a part would take a lot of heat, the resin would not and therefore you could never use it as a high temperature component.

This link details some OEM for CF that claims some people have stuck it on mufflers with adhesive but not made exhaust using only CF: http://www.protechcomposite.com/serv...FQyfnAodjGnG6Q

Titanium is the same strength as steel at 60% of the weight I believe. It's also notoriously difficult to work with and has bad wear resistance.

what he said. and..
FRP = Fiber Reinforced PLASTIC. plastic it is.

[NM_BMW]

Originally Posted by BavarianBullet

Carbon is quite heat resistant and making CF takes some significant heat. However, CF cloth before impregnated with resin is like fiberglass cloth. The resin and CF together make a tough part.

So while carbon fibers made into a part would take a lot of heat, the resin would not and therefore you could never use it as a high temperature component.

This link details some OEM for CF that claims some people have stuck it on mufflers with adhesive but not made exhaust using only CF: http://www.protechcomposite.com/serv...FQyfnAodjGnG6Q

Titanium is the same strength as steel at 60% of the weight I believe. It's also notoriously difficult to work with and has bad wear resistance.

+1 I know there are mufflers that are actually CF parts. The HKS exhaust for the Evo is all Ti except the muffler is CF. Now if it is a wrapped muffler in CF idk...

I do know that they make CF mufflers for street bikes with Ti piping. Problem a lot of us riders that have had them run into heat problems. Everyday driving, sure no problem, but once you expose the exhaust to long periods of heat the CF would start to crack or come apart at the seams. Looks good, but Ti would be the way to go in this instance. BTW I swapped my CF pipe with a Ti after a few hard canyon carvings.

[94JZA80]

Originally Posted by BoostedBMW

+1... we are talking about an exhaust that would most likely weigh less than 15lbs (dual mufflers for the 335) if it were made out of titanium. This car is a pig to begin with so to have to go through all of the trouble of making a custom CF exhaust (I have never heard of this to be honest) seems like it wouldn't be worth the trouble. BTW, what happens when a rock hits the undersite of your CF exhaust? I know that the CF diffuser on my s2000 took a whole month to crack.

In any case, does anyone even produce a full Ti exhaust yet for this car? I can't remember if it was JIC or some other JDM brand that I think produced one.

Originally Posted by thegeneral101

i agree with you, the cost would not "outweigh" the benefits

+1

carbon fiber is strong but brittle, hence the reason it cracks so easily. and the cost for sure would outweigh the benefit. think about it - suppose someone brings the weight of his 335i's cat-back exhaust from 70-lbs down to 20-lbs by going from the stock cat-back to a full titanium cat-back. it is expensive enough to go to titanium, but it would cost far more to do it with carbon fiber b/c 1) its never been done before (and so you'll have to spend quite a bit of $ on R&D, not just production), and 2) there's more labor involved in producing a full carbon fiber exhaust (assuming the general procedure you proposed is possible in the first place). so what's the point in further reducing the weight of your cat-back exhaust if it already only weighs 20-lbs?..especially if it can't be done for cheap?

while Al is lighter than Ti according to the periodic table, i never see aluminum exhaust systems. why? my guess is that it bends, creases, and pinches too easily - and so a minor bump or large rock might pinch off the exhaust to the point where flow is dangerously low. i don't think it has anything to do with temperatures since blocks are sometimes made of aluminum, and the highest temperatures occur inside the block. regardless, your answer for the lightest exhaust systems are going to be made of titanium.


BoostedBMW: i'm not aware if JIC offers any products for the 335i, but i can tell you that their quality is second to none. i replaced the stock exhaust on my Supra with a JIC Bullet full titanium cat-back exhaust, and while i don't recall how much the stock system weighed (probably in the neighborhood of 50+ lbs), the JIC only weighed 11-lbs. (that includes everything after the downpipe). the welds are flawless...in fact you can see them here (i took the pic a few weeks after the install):

[IMG][/IMG]

[94JZA80]

Originally Posted by Humtek

+1 I know there are mufflers that are actually CF parts. The HKS exhaust for the Evo is all Ti except the muffler is CF. Now if it is a wrapped muffler in CF idk...

i'm pretty sure that HKS's Carbon Ti exhaust is just a titanium canister wrapped in CF. also, i think just the canister and tip are titanium, while the rest is stainless steel. there aren't many full-Ti exhausts out there, even for the JDM crowd.

[bdkevoIX]

Originally Posted by 94JZA80

i'm pretty sure that HKS's Carbon Ti exhaust is just a titanium canister wrapped in CF. also, i think just the canister and tip are titanium, while the rest is stainless steel. there aren't many full-Ti exhausts out there, even for the JDM crowd.

this is correct.

HKS Carbon Ti is only titanium "TIP". The rest is stainless steel and muffler is wrapped around with CF. It looks good but not as good as other genuine titanium parts like Greddy Ti,JIC Ti, etc.

[1clean335i]

Originally Posted by 94JZA80

BoostedBMW: i'm not aware if JIC offers any products for the 335i, but i can tell you that their quality is second to none.

They have exhausts for the 335i but its just 2 mufflers. And theres also a strut bar available

[94JZA80]

Originally Posted by 1clean335i

They have exhausts for the 335i but its just 2 mufflers. And theres also a strut bar available

what's up Chino. i almost opted for JIC's FLT-A2 coilovers b/c i've heard so many great things about them, but went with something else in the end just to try something new and different. JIC also makes coilovers for euro cars (i specifically know of Porsche applications, but there could be others) under the brand name "JIC CROSS Suspension"...and while i don't know much about it, i'm sure you'll find some feedback on them over at 6speedonline.com (a big Porsche community).

[GreenPlease]

while carbon fiber heated from 2500 to 3000 °C (graphitizing) exhibits a higher modulus of elasticity

I doubt highly doubt that such temperatures are ever seen in an exhaust system as, in general, combustion regimes try to avoid going over 1500C (2800F) to prevent NOx formation. I would imagine that temperatures after the CAT are below 1000C. It wouldn't be too hard to find this out for someone with a temperature probe and some time.

FWIW CF would probably be cheaper than Ti as Ti needs to be welded in a vacuum to avoid... I don't know. Its in this article. Read it last night. If I remember it had to do with corrosion. So, from this standpoint, it would seem that CF would be significantly less labor and $ intensive to produce.

Aluminum exhausts seem to have mixed results. Some have had great results, others have reported deterioration due to sulfur in the exhaust stream (per some JDM forums).

it would cost far more to do it with carbon fiber b/c 1) its never been done before (and so you'll have to spend quite a bit of $ on R&D, not just production)

Where's the fun in spending $ on R&D when you can just build one and see if it works?

[cazisk]

I think if you want weight savings go for titanium.

I remember helping my friend install his trust titanium cat back exhaust on an evo 9, man that thing felt like it was plastic, it was so light. It did increase the sound by alot though compared to his previous exhaust (non stock).

I have enquired for titanum exhaust for e92 and it would cost about 6 grand for a full (from turbo back) titanium exhaust from dixis.

[aut0sh0cker]

Originally Posted by GreenPlease

I doubt highly doubt that such temperatures are ever seen in an exhaust system as, in general, combustion regimes try to avoid going over 1500C (2800F) to prevent NOx formation. I would imagine that temperatures after the CAT are below 1000C. It wouldn't be too hard to find this out for someone with a temperature probe and some time.

FWIW CF would probably be cheaper than Ti as Ti needs to be welded in a vacuum to avoid... I don't know. Its in this article. Read it last night. If I remember it had to do with corrosion. So, from this standpoint, it would seem that CF would be significantly less labor and $ intensive to produce.

Aluminum exhausts seem to have mixed results. Some have had great results, others have reported deterioration due to sulfur in the exhaust stream (per some JDM forums).



Where's the fun in spending $ on R&D when you can just build one and see if it works?

Correct! Ti welding requires an environment of either a vacuum or some inert gas (argon is common). Hence, even the welding process is expensive and time consuming.

[BavarianBullet]

And another odd point with CF is that there is apparently a "worldwide shortage" that's been going on for at least 2 years. Supposedly it's because Boeing (dreamliner), Airbus and number of smaller defense contractors are using all that can be made and then some. So it's um, pricey.

[Cloud9blue]

Originally Posted by GreenPlease

@Amir87

Titanium cat-back? I'd think that would actually be heavy... strong, but heavy. Aluminum's number on the periodic table is 13, Ti's is 22.

The exhaust isn't a load bearing structure, so as long as it can hold up to the pressure and heat of the exhaust gas (and occasional shock) you should be able to make it out of whatever is lightest.

titanium has lighter density than aluminum due to atomic packing structure.

[NM_BMW]

Originally Posted by BavarianBullet

And another odd point with CF is that there is apparently a "worldwide shortage" that's been going on for at least 2 years. Supposedly it's because Boeing (dreamliner), Airbus and number of smaller defense contractors are using all that can be made and then some. So it's um, pricey.

LOL Boeing is the cause. My good friend is project manager for avionics and fuel systems for the new 787 dreamliner and he laughs all the time how all the CF in the world has been sucked up by Boeing to build their CF plane.

[baron]

Carbon fiber is impregnated in a epoxy resin that would sure to deform after passing hot exhaust gases. It is used as a high tensile strength lightweight material and not intended for high temperature applications.

[darkphantom]

so, in conclusion, CF exhaust is not the way to go. Ti all the way or bust!

/thead

[GreenPlease]

so, in conclusion, CF exhaust is not the way to go. Ti all the way or bust!

I wonder, though, if there isn't a better material out there, like some sort of plastic that can take the heat and doesn't weigh much. Considering that it might get hit by a stray rock or something, I would think that plastic with a little bit of give in it would actually have better longevity than steel/stainless/titanium.

[94JZA80]

Originally Posted by GreenPlease

Where's the fun in spending $ on R&D when you can just build one and see if it works?

point taken. but, despite the fact that exhaust design is a pretty simple and straightforward, you never know what problem(s) you might run into while trying to develop an all-CF exuahst that's never been done before on a car. and so it may not be the smartest thing to just fabricate a mock-up first thing and see if it works. and god only knows how many times one will have to go through the trial and error process to get it right (or very possibly finding out that it isn't doable at all, which i highly suspect). so it kinda seems like "building one and seeing if it works" is part of the R&D process anyways...

Originally Posted by darkphantom

so, in conclusion, CF exhaust is not the way to go. Ti all the way or bust!

/thead

essentially, yes.

Originally Posted by GreenPlease

I wonder, though, if there isn't a better material out there, like some sort of plastic that can take the heat and doesn't weigh much. Considering that it might get hit by a stray rock or something, I would think that plastic with a little bit of give in it would actually have better longevity than steel/stainless/titanium.

here's the catch: full titanium exhaust systems typically reduce the weight of the exhaust system by over 50% anyways. the weight of mine was reduced significantly more than that - if you recall above, i said that my exhaust went from 50+lbs to 11lbs. by switching to a full titanium system. in addition, there are a million other ways to reduce the weight of your car without spending a fortune. so really it becomes a matter of price : performance. while titanium exhaust systems are far from cheap, they apparently reflect a price to performance ratio acceptable by a large enough market of enthusiasts to justify their production. to try and find a better/lighter/more suitable material than titanium and study its physical properties in depth will cost lots of $, and will only reduce weight marginally (b/c titanium exhaust are already so light). hence the law of diminishing returns comes into play, and you're spending significant amounts of money just to shed a few marginal pounds (i.e. price : performance will suck unless someone succeeds in developing and mass producing such a product).