Teaser exhaust prototype

[MTD]

Mmmmmm, shiny.

[BluMeanie]

Nice welds. Axle-back?

[GreyGhost12]

Nice welds. Axle-back?

Yeah, nice clean TIG welds... However, too bad the pipes are incorrectly mounted and restrict flow potential.

[MTD]

Catback prototype. Testing for fit and sound.

Those are just the tail pipes. I can't see them mattering much. I will mention it.

[GreyGhost12]

Catback prototype. Testing for fit and sound.

Those are just the tail pipes. I can't see them mattering much. I will mention it.

I understand they are "just tail pipes" but that is the incorrect way to make a performance exhaust. In all fairness 99.X% of non-custom OTC "performance exhausts" are made incorrectly this way. The pipe down stream should always fit OVER the previous component/pipe. This will create an anti-reversion step. The pipe can be easily swaged to fit over. If it's stuffed inside, flow restricting however small at that point is still happening. I'm just sayin'...

I estimate a minimum 4-7hp gain (in some cases a fair amount more) can be realized if these measures are taking throughout the exhaust system starting at the head.

To me that's nothing to sneeze at.

[gt800]

Ghost is right. Exhaust should always fit over from piece to piece regardless of what piece or where. I dont know about gains but its just the proper way.

[MTD]

I'm not 100% sure what you guys mean "fit over". Can you clarify?

[GreyGhost12]

I'm not 100% sure what you guys mean "fit over". Can you clarify?

MTD: If you look at your pic closely, you can see how the tail pipes fit "in" the muffler. The pipe should in fact be 1/8" larger OD than the exit of the muffler in order to "fit over" it rather than slip inside it.

[MTD]

So the tail pipes should be slightly larger in o/d then? Muffler being male and pipes being female I guess?

I'll be driving around with it for at least a week. It sounds good. Slightly louder under normal throttle, very stock sounding and a bit more under more aggressive driving. Wife and I both agreed it could make a bit more sound, but I told it should break in and get louder. Might try a version with no muffler at all, just the resonator.

[GreyGhost12]

So the tail pipes should be slightly larger in o/d then? Muffler being male and pipes being female I guess?

That is correct. Exhaust flows similarly to intake with a boundary layer on the pipe wall. If the exhaust flow hits the 1/16" negative step of the pipe that is inserted in the rear of the resonator or muffler, it gets turbulent and tries to turn around on itself, go back up the pipe, and thereby restricts the flow. There are naturally exhaust pulses that travel up and down the exhaust pipe. If the steps are always in the correct orientation, once the pulses pass these correct steps, it's almost impossible for them to back-flow up the exhaust and contaminate the fresh A/F mixture being introduced into the combustion chambers or slow the flow down. This in turn increases mpg's, power, and transient response.

[MTD]

Makes perfect sense. Even the v-bands being used are neat. Ive never seen them used and didnt really know what they were lol.

[MTD]

And a crappy video I did today
http://smg.beta.photobucket.com/user/DumbasSi/media/A075B604-BF91-413C-B73A-7330C095CA3D-52903-00000607505F7498.mp4.html

[weirtech]

That is correct. Exhaust flows similarly to intake with a boundary layer on the pipe wall. If the exhaust flow hits the 1/16" negative step of the pipe that is inserted in the rear of the resonator or muffler, it gets turbulent and tries to turn around on itself, go back up the pipe, and thereby restricts the flow. There are naturally exhaust pulses that travel up and down the exhaust pipe. If the steps are always in the correct orientation, once the pulses pass these correct steps, it's almost impossible for them to back-flow up the exhaust and contaminate the fresh A/F mixture being introduced into the combustion chambers or slow the flow down. This in turn increases mpg's, power, and transient response.

please do not take this the wrong way, but you are providing misinformation... what you are saying might be true for a n/a application, but for a turbo application it is not the case. anti-reversion is a non issue due to the fact that there is a turbine wheel in the exhaust flow path preventing pulses from travelling back through it. infact the turbo creates a huge retriction in exhaust flow. that is why you get turbo lag on turbos that are sized too large. they do not build enough boost to overcome the flow restriction until they reach a higher rpm when the engine is pumping more air through it. there is a tremendous amount of back pressure between the exhaust valves and the turbine housing. that is part of the reason why in high hp applications you see so much heat in the ehxuast manifold and not further down stream the exhaust system. as the exhaust leaves the turbine it cools down rapidly which also slows it down. by the time it reaches the back end of the exhaust small details like you suggest are not nearly as significant in effecting performance.

as for the slip fit of the muffler, you will be hard pressed to find production mufflers or exhausts that are designed and built the way you suggest. if you want to get really picky about it, you should not have any change in diameter at any joint. a v-band does this. it matches perfectly from pipe to pipe. where you have weld joints with no flange they would be better off if they were butt welded instead of stepped. most people are not willing to pay the cost for such attention to detail. just look at any mass produced exhaust for about any car. most manufacturers use cheaper material, cheaper design and make compromises to make money. to think that the exhaust flow is going to be significantly effected at the entry and exit of a muffler is plain silly. the muffler itself creates far more exhaust turbulence than the pipe joint at the end of it. that is what it is designed to do!

as for the 4-7hp gain you claim there is to be found by building the ehxuast this way, i would very much like to see results from a test proving this in this application, or a similar power TURBO application. i'd be surprised if you get more than a half hp gain. this type of manufacturing detail is really only taken advantage by race teams. no one driving a vt is going to be willing to pay what it costs to build an exhaust that will be built with such detail that it will out perform everything else available. these are -200hp street cars, not +800hp f1 cars. if you realy want to get technical you should consider extrude honing the entire exhaust while it is assembled.

aaron

[weirtech]

oh, btw, those are not autogenous welds. that is never a good idea on anything that will see repeated heat cycles. the weld would not last very long at all.

aaron

[GreyGhost12]

^^ Perhaps you should take this discussion to John Grudynski, David Vizard, or Larry Widmer and you'll find out a thing or two about a thing or two in regards to exhaust flow whether it's N/A or FI.

It is the sum of all the little things that add up to the big-picture of gains or losses no matter a street car or race car.

As I have already stated, 99.X% of after market exhausts are incorrectly built. While they work, they are not maximized. I'm simply trying to help MTD to have a maximized exhaust.

For the record, my 4-7+ HP gain was from the 4-2-1 header/merge collector all the way to the tip of the exhaust in my "other 10k rpm N/A 4-banger".

[Memphis]

I would pay for a properly done exhaust. I am a very picky person when it comes to things done right.

[GreyGhost12]

I would pay for a properly done exhaust. I am a very picky person when it comes to things done right.

I modified my Magnaflow 15060 to match my tastes on my NAV.

The custom stainless steel cat + cat-back exhaust I built to perfectly match up to my Hytech header for my "other car" would have cost well over $1500 if I had to buy it, but only cost me about $500 in parts. The labor was free since it was done after hours at work. That included a 300 cell high flow cat, WBO2 bung, primary O2 bung, post cat O2 bung, laser cut flanges, 2 resonators, a muffler, hangers, aluminum gaskets, back-purged TIG welding, swaged pipe fittings, and a total of 7 anti-reversions step...

There was/is nothing on the market anywhere near it and I wanted to best... So I built it...

[weirtech]

^^ Perhaps you should take this discussion to John Grudynski, David Vizard, or Larry Widmer and you'll find out a thing or two about a thing or two in regards to exhaust flow whether it's N/A or FI.

It is the sum of all the little things that add up to the big-picture of gains or losses no matter a street car or race car.

As I have already stated, 99.X% of after market exhausts are incorrectly built. While they work, they are not maximized. I'm simply trying to help MTD to have a maximized exhaust.

For the record, my 4-7+ HP gain was from the 4-2-1 header/merge collector all the way to the tip of the exhaust in my "other 10k rpm N/A 4-banger".

there are lots of smart people in this world. what makes one person smart than another is not measureable. an engineer with 50 years under his belt has no more knowledge than the next guy if he has never applied it. knowledge is valuable, but cannot be compared to first hand experience. reading what someone else does is swell, but doing it yourself will always help you attain a deeper understanding in life.

as for what is correct and what isn't is a matter of opinion. that is why everyone does things differently. when you use someone else's opinion as your own, your opinion has no true value, you are just transcribing what they have said. experience will always outweigh knowledge. no one owns knowledge. as valuable as others' experience is, i don't feel a need to drop names to make my case. i will take my first hand experience over what is written on the internet any day of the week.

comparing your relatively stock vt to a 10k rpm n/a race car is not valid at all. they are completely different cars. n/a and turbo exhausts are completely different animals and cannot be treated the same. re-read my initial post and provide some factual results with the vt as an application instead of making claims based on a completely different car or what someone else has said. i would be very much surprised if a dyno test showed any gain at all. a muffler's purpose is to deaden exhaust sound. it does this by interrupting exhaust flow. the flow will be more effected by the perforated tube inside the muffler than a 1/16" step at the exit.

aaron

[weirtech]

an anti-reversion step is not the same thing (nor does it perform the same) as a proper anti-reversion chamber such as hytech uses on their race headers. they may have introduced this idea to the honda performance aftermarket, but they are certainly not the first to use the anti-reversion chambers in exhaust systems.

aaron

[GreyGhost12]

I "dropped names" because those 3 are known as some of the best of the best in this industry. They have all been around a lot longer than I have and have done far my R&D than I have. With that said, I have followed their teachings (as well as teachings from others and my own R&D) and have come to my own versions of things that work very well.

I agree that turbo exhaust is different than N/A exhaust but they both function upon very similar principals. Also for the record, my 13.5:1 10k rpm engine runs on pump gas and is in a daily summer driver, not a race car. And it's a heck of a hoot to drive!

I agree an anti-reversion step isn't the same thing as an anti-reversion chamber, but again, they work on similar principles and help aid exhaust flow and free up lost power when properly implimented.