Exhaust flow technology
08-02-2006, 03:22 PM
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Exhaust flow technology
OK... First, after seeing how people got angry when I questioned an Amuse exhaust in another thread, let me post my credentials as a motor builder:
I worked at a local machine shop called Auto Sports Center for 5 years. We had a full Winona Van Norman machine shop that we had purchased from Lamborghini. It included a flowbench operated by an ex-Keith Craft Racing fabricator. I have seen a bunch of heads on a flow bench so I have some idea of what flows and what doesnt.
That said, I dont know everything, so enlighten me as to this:
Why are some high dollar titanium exhausts angle cut and then welded with sharp angles? This CANNOT flow as well as a mandrel bent pipe. This is a recent pic form the Gallery forum to show what I mean.
Can titanium even be mandrel bent... if not, that probably explains it. However, that would mean that a mandrel bent stainless system would perform better than a Ti setup that is twice the price!!!
Just trying to find the truth.
I worked at a local machine shop called Auto Sports Center for 5 years. We had a full Winona Van Norman machine shop that we had purchased from Lamborghini. It included a flowbench operated by an ex-Keith Craft Racing fabricator. I have seen a bunch of heads on a flow bench so I have some idea of what flows and what doesnt.
That said, I dont know everything, so enlighten me as to this:
Why are some high dollar titanium exhausts angle cut and then welded with sharp angles? This CANNOT flow as well as a mandrel bent pipe. This is a recent pic form the Gallery forum to show what I mean.
Can titanium even be mandrel bent... if not, that probably explains it. However, that would mean that a mandrel bent stainless system would perform better than a Ti setup that is twice the price!!!
Just trying to find the truth.
08-02-2006, 03:32 PM
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generally, titanium cannot be bent.
the general rule is that bending titanium is harder than welding it, which is plenty difficult.
however, i have seen titanium stock being sold that can be bent but it is not available in any diameter suited for an exhaust.
and you're right, a mandrel bent system will hold it's diamter throughout the length of the exhaust, and flow better than the cut and weld systems.
the general rule is that bending titanium is harder than welding it, which is plenty difficult.
however, i have seen titanium stock being sold that can be bent but it is not available in any diameter suited for an exhaust.
and you're right, a mandrel bent system will hold it's diamter throughout the length of the exhaust, and flow better than the cut and weld systems.
08-02-2006, 03:32 PM
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pie slices do not flow as well as mandrel bends from what a few Mech. E's have explained to me.
Titanium can be mandrel bent but not as well and I haven't seen any titanium tight radius U's probably because they'd crack.
Titanium can be mandrel bent but not as well and I haven't seen any titanium tight radius U's probably because they'd crack.
08-02-2006, 04:18 PM
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Thats what I suspected.
That leads to the next logical question... why buy a titanium exhaust system that doesnt flow as well as a stainless system that is half the price.
I understand that Ti might weight a little less than Stainless, but we are talking about less than 10 lbs on a complete exhaust system. You would save more weight by taking out carpet or the spare tire.
Why buy a more expensive exhaust that doesnt flow as well as a cheaper stainless version?
That leads to the next logical question... why buy a titanium exhaust system that doesnt flow as well as a stainless system that is half the price.
I understand that Ti might weight a little less than Stainless, but we are talking about less than 10 lbs on a complete exhaust system. You would save more weight by taking out carpet or the spare tire.
Why buy a more expensive exhaust that doesnt flow as well as a cheaper stainless version?
08-02-2006, 04:21 PM
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Originally Posted by TJF,Aug 2 2006, 05:18 PM
Thats what I suspected.
That leads to the next logical question... why buy a titanium exhaust system that doesnt flow as well as a stainless system that is half the price.
I understand that Ti might weight a little less than Stainless, but we are talking about less than 10 lbs on a complete exhaust system. You would save more weight by taking out carpet or the spare tire.
Why buy a more expensive exhaust that doesnt flow as well as a cheaper stainless version?
That leads to the next logical question... why buy a titanium exhaust system that doesnt flow as well as a stainless system that is half the price.
I understand that Ti might weight a little less than Stainless, but we are talking about less than 10 lbs on a complete exhaust system. You would save more weight by taking out carpet or the spare tire.
Why buy a more expensive exhaust that doesnt flow as well as a cheaper stainless version?
08-02-2006, 04:23 PM
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Because people go ga-ga over JDM even if it's not functional or great. A lot of the stuff people purchase aren't that spectacular or even functional. It just makes them happy to have that stuff. Their money...just as long as people don't start associating me or my S2000 with theirs I'm fine (I'm talking about the people who rice out their cars).
08-03-2006, 05:30 AM
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Originally Posted by kane.s2k,Aug 2 2006, 04:23 PM
Because people go ga-ga over JDM even if it's not functional or great. A lot of the stuff people purchase aren't that spectacular or even functional. It just makes them happy to have that stuff. Their money...just as long as people don't start associating me or my S2000 with theirs I'm fine (I'm talking about the people who rice out their cars).
Bump this one up to spread some truth.
Next question: which popular S2000 exhausts are mandrel bent and which are angle welded???? Also, post up the diameter of each exhasut for comparison as well.
Amuse = welded
T1R = Mandrel
Mugen = Mandrel
Spugen = Mandrel
J's = ?
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08-03-2006, 08:31 AM
#9
Titanium has a little lower density than stainless, but that's not its true benefit:
Titanium has poor ductility (low elongation) and a lower modulus of elasticity, resulting in greater springback and significantly greater forming difficulty. And since you're trying to reduce the gauge, forming is even more difficult.
You have to realize that when making exhaust manifolds, Titanium is being compared with Type 309S Stainless, which is a very ductile stainless steel.
- It has better oxidation resistance, especially at high temperatures. So it won't "rust out" as quickly (actually, titanium oxidizes very easy, but it has a very tenacious oxide layer that resists further oxidation).
- Titanium has high strength at elevated temperatures. Coupled with its improved oxidation resistance, this means that exhaust systems can be produced at thinner gauges for weight reduction
Titanium has poor ductility (low elongation) and a lower modulus of elasticity, resulting in greater springback and significantly greater forming difficulty. And since you're trying to reduce the gauge, forming is even more difficult.
You have to realize that when making exhaust manifolds, Titanium is being compared with Type 309S Stainless, which is a very ductile stainless steel.
08-03-2006, 10:02 AM
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slalom44: Then it sounds like the only benefits of Titanium are
1) superior resistance to oxidation
2) reduced weight due to superior strength at high temp while at a low gauge thickness
these benefits come at the detriment of:
1) not being very elastic, which necessitates welded angles rather than radius bends, thereby restricting flow and performance
2) repairability: since it is difficult to weld
3) cost: as it is about 75-100% more expensive than a mandrel bent (and thereby superior performing) stainless system.
Since stainless will probably outlast most other parts on a car, the superior resistance to oxidation is invalid. I personally dont care if my exhaust lives 1000yrs. Stainless will easily go a couple hundred thousand miles.
The weight argument might mean something if you had a full race car looking to save every pound, but the 5-10 lbs difference between a Ti system and a stainless system hardly seems worth the price difference between the two. I would save a couple hundred bucks and take out my trunk carpeting for that much weight savings.
1) superior resistance to oxidation
2) reduced weight due to superior strength at high temp while at a low gauge thickness
these benefits come at the detriment of:
1) not being very elastic, which necessitates welded angles rather than radius bends, thereby restricting flow and performance
2) repairability: since it is difficult to weld
3) cost: as it is about 75-100% more expensive than a mandrel bent (and thereby superior performing) stainless system.
Since stainless will probably outlast most other parts on a car, the superior resistance to oxidation is invalid. I personally dont care if my exhaust lives 1000yrs. Stainless will easily go a couple hundred thousand miles.
The weight argument might mean something if you had a full race car looking to save every pound, but the 5-10 lbs difference between a Ti system and a stainless system hardly seems worth the price difference between the two. I would save a couple hundred bucks and take out my trunk carpeting for that much weight savings.