Cheap exhaust alternatives?
Discussion
I hoping ask the knowledgeable people here a few things that have been bothering me with regard to exhausts.
Why I have always wondered why exhausts are so expensive, especially if I am looking for an after market exhaust that is essentially just a metal tube with a bend in the middle?
why does no one make generic exhaust pipe sections that could fit together like Scalextric track? E.g. I’ll fit a 140cm straight to a gentle bend to a 100cm straight to a… Is this not a good idea?
Could I not just get a bit of metal pipe bend it and clamp it to my headers?
Why I have always wondered why exhausts are so expensive, especially if I am looking for an after market exhaust that is essentially just a metal tube with a bend in the middle?
why does no one make generic exhaust pipe sections that could fit together like Scalextric track? E.g. I’ll fit a 140cm straight to a gentle bend to a 100cm straight to a… Is this not a good idea?
Could I not just get a bit of metal pipe bend it and clamp it to my headers?
robseagul said:
Hello there.
You could just bolt pipe straight to you manifold however as engines need back pressure to work peformance would suffer.
A lot of r&d goes into exhaust systems therfore they cost...rob
I think you mean "A lot of r&d goes into OEM exhaust systems therfore they cost". A lot of aftermarket systems appear to have bugger all R&D, I mean some pattern parts dont even fit never mind do a good job!You could just bolt pipe straight to you manifold however as engines need back pressure to work peformance would suffer.
A lot of r&d goes into exhaust systems therfore they cost...rob
philo said:
Say if I took a scaffolding pipe with a 1.5” inner diameter and slapped it onto my headers, (to complex to replace those).
Would the narrow pipe provide enough back pressure? What about in a turbo car?
My understanding with a Turbo car is ...The turbo provides the back pressure and after the turbo you want the biggest piece of pipe you can find really.Would the narrow pipe provide enough back pressure? What about in a turbo car?
ks. No engine wants backpressure.
only two strokes need back pressure,if only i had a pound for everytime this old chestnut came up 
Hello there guys i just came accross this and what do you know ...
The general rules for exhaust and downpipe sizing for a turbo car is pretty simple.. The bigger the better.
Some may think that a small turbo doesn't need a large downpipe or exhaust.. That is completely opposite of reality. With a small turbo, the pressure levels between the engine and the turbo is high, obviously due to small turbine and smaller turbocharger needing to wind itself up to 16-18 PSI of boost or higher to create any significant power. When the pressure between the turbo and the engine is high, it requires even more exhaust flow AFTER the turbine wheel. That means when you decide to run a small turbocharger at its limits, which often means lots of boost (high intake manifold pressure) and a turbine near choke line on the turbine flow maps, it is in more desperate need of a larger exhaust downstream of the turbine wheel (Downpipe/cat/exhaust/muffler) versus a larger turbocharger.
Forget about "HP" numbers.. 200 HP, 300 HP, 500 HP, these numbers are just rough figures to go with. Real exhaust sizing is determined by turbine flow vs compressor flow, exhaust manifold back pressure between engine and turbo, and back pressure after the turbine exit. I don't have the actual formula on hand to calculate pressure differential between the engine, pre- and post-turbo, but generally, each PSI of exhaust back pressure backtracking against the turbine exit equates to about 4-5 times the amount of exhaust back pressure upstream (between engine and turbo). So with a smaller turbo, it usually runs at high boost (high intake manifold pressure), which in turn elevates the exhaust back pressure between the engine and turbo already... That means any noticeable restriction AFTER the turbine exit (downpipe/exhaust/muffler) will create an exponential increase of exhaust pressure upstream between the engine/turbo, thus, choking the engine, killing performance, high EGT's and more likely to detonate. Picture the turbo's turbine side as an air pump that is designed to "suck" in exhaust flow with its blade direction, turbine housing design and passages meant to push exhaust "out" of the turbo. It's main job is to absorb the exhaust energy and flow, and then dump it out of the turbine exit, just like a vacuum cleaner! If you have a restriction at the vacuum's suction side, say you are vacuuming your carpet or something, it still manages to have its sucking power. The moment you put your hand and block off the vacuum's exit/exhaust port, it becomes useless. Same theory actually.
A more real life example would be.... Well, smaller turbos need a lot of PSI, therefore, also create a lot of exhaust back pressures for the same given HP of compressor flow as mentioned earlier. So when you have a large turbo with a huge turbine (ie: GT35R), if you run this GT35R at 300 WHP @ 12 psi for example, it actually requires a smaller downpipe and exhaust than a 19T pushing the same WHP @ 18 PSI. The GT35R has a much lower exhaust back pressure between the engine and turbo from the start, therefore, it can operate flawlessly with a smaller exhaust.
That is why you often hear factory turbo cars running their factory turbos near the limits gaining so much spool, power and response from large downpipes and exhaust. Such examples would be DSM's (Eagle Talons/Mitsu Eclipses), all Subarus, and actually almost every turbo car out there that has bolt-on upgrades to "max out" the stock turbo(s).
Larger turbos on the other hand, makes you wonder why a 600-800 WHP Supra can still run the same friggin 3" downpipe and exhaust and still have no problems because we all know Supra run ridiculously large turbines.
So a good guideline is, take a look at the turbo you are running and how close you are to maxing out the turbo. But in almost all cases, the bigger is better, but now knowing that a smaller turbo running at full tilt requires even more exhaust flow, it gets you thinking when you make your next downpipe/exhaust purchase
Go 3" or larger, or go home! No and's if's or but's if you are looking for performance. You can easily build a 3" exhaust that is quiet by running the correct muffler and a decent resonator.
I have found however that on open pipes the tick over can be poor and have allways fitted a restricter of some sort to improve this.
The general rules for exhaust and downpipe sizing for a turbo car is pretty simple.. The bigger the better.
Some may think that a small turbo doesn't need a large downpipe or exhaust.. That is completely opposite of reality. With a small turbo, the pressure levels between the engine and the turbo is high, obviously due to small turbine and smaller turbocharger needing to wind itself up to 16-18 PSI of boost or higher to create any significant power. When the pressure between the turbo and the engine is high, it requires even more exhaust flow AFTER the turbine wheel. That means when you decide to run a small turbocharger at its limits, which often means lots of boost (high intake manifold pressure) and a turbine near choke line on the turbine flow maps, it is in more desperate need of a larger exhaust downstream of the turbine wheel (Downpipe/cat/exhaust/muffler) versus a larger turbocharger.
Forget about "HP" numbers.. 200 HP, 300 HP, 500 HP, these numbers are just rough figures to go with. Real exhaust sizing is determined by turbine flow vs compressor flow, exhaust manifold back pressure between engine and turbo, and back pressure after the turbine exit. I don't have the actual formula on hand to calculate pressure differential between the engine, pre- and post-turbo, but generally, each PSI of exhaust back pressure backtracking against the turbine exit equates to about 4-5 times the amount of exhaust back pressure upstream (between engine and turbo). So with a smaller turbo, it usually runs at high boost (high intake manifold pressure), which in turn elevates the exhaust back pressure between the engine and turbo already... That means any noticeable restriction AFTER the turbine exit (downpipe/exhaust/muffler) will create an exponential increase of exhaust pressure upstream between the engine/turbo, thus, choking the engine, killing performance, high EGT's and more likely to detonate. Picture the turbo's turbine side as an air pump that is designed to "suck" in exhaust flow with its blade direction, turbine housing design and passages meant to push exhaust "out" of the turbo. It's main job is to absorb the exhaust energy and flow, and then dump it out of the turbine exit, just like a vacuum cleaner! If you have a restriction at the vacuum's suction side, say you are vacuuming your carpet or something, it still manages to have its sucking power. The moment you put your hand and block off the vacuum's exit/exhaust port, it becomes useless. Same theory actually.
A more real life example would be.... Well, smaller turbos need a lot of PSI, therefore, also create a lot of exhaust back pressures for the same given HP of compressor flow as mentioned earlier. So when you have a large turbo with a huge turbine (ie: GT35R), if you run this GT35R at 300 WHP @ 12 psi for example, it actually requires a smaller downpipe and exhaust than a 19T pushing the same WHP @ 18 PSI. The GT35R has a much lower exhaust back pressure between the engine and turbo from the start, therefore, it can operate flawlessly with a smaller exhaust.
That is why you often hear factory turbo cars running their factory turbos near the limits gaining so much spool, power and response from large downpipes and exhaust. Such examples would be DSM's (Eagle Talons/Mitsu Eclipses), all Subarus, and actually almost every turbo car out there that has bolt-on upgrades to "max out" the stock turbo(s).
Larger turbos on the other hand, makes you wonder why a 600-800 WHP Supra can still run the same friggin 3" downpipe and exhaust and still have no problems because we all know Supra run ridiculously large turbines.
So a good guideline is, take a look at the turbo you are running and how close you are to maxing out the turbo. But in almost all cases, the bigger is better, but now knowing that a smaller turbo running at full tilt requires even more exhaust flow, it gets you thinking when you make your next downpipe/exhaust purchase
Go 3" or larger, or go home! No and's if's or but's if you are looking for performance. You can easily build a 3" exhaust that is quiet by running the correct muffler and a decent resonator.
I have found however that on open pipes the tick over can be poor and have allways fitted a restricter of some sort to improve this.
You are "Tony the Tiger" from the Volvospeed forums AICMFP
http://volvospeed.com/vs_forum/lofiversion/index.p...
http://volvospeed.com/vs_forum/lofiversion/index.p...
Edited by Podie on Monday 3rd November 13:38
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff