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Been getting some custom quotes on some custom exhaust work for the 6, finally got it u on a lift and had a chance to walk around the bottom of the car. The V6 basically has a 2.25 coming into the resonator and a 2.0'' back to the rear y-pipe and exhaust. My tenative plan was to do a 2.5 from the resonator to the y-pipe, and a 2.25'' y-pipe to some magnaflows. This guy seems to know his stuff, I had a chance to look at his work on other vehicles and it looks pretty quality. The quote I got was about $500 including tax and muffler tips, however, this guy doesn't do mandrel bends, but they don't look crushed either, is there something in between? How much of a diff does mandrel make? Can you get a consistent diameter with out mandrel? Going to get a few more quotes tomorrow, so any advice would be appreciated.
 

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Reading Topic: Custom Exhaust

Unless your on a circle track 99% of your time, a mandrel bent exhaust system won't make that much of a difference. It will allow it to flow better and flowing better is best, but like I said, on a street application the difference will be minimal.

Whenever I do an exhaust system, I usually keep the same diameter pipe from the headers to the tips. This way the exhaust gas does not have to compress or expand, thus slowing it down, when it changes pipe sizes.
 

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Replying to Topic 'Custom Exhaust'

QUOTE
Originally posted by Brillo


            Been getting some custom quotes on some custom exhaust work for the 6, finally got it u on a lift and had a chance to walk around the bottom of the car. The V6 basically has a 2.25 coming into the resonator and a 2.0'' back to the rear y-pipe and exhaust. My tenative plan was to do a 2.5 from the resonator to the y-pipe, and a 2.25'' y-pipe to some magnaflows. This guy seems to know his stuff, I had a chance to look at his work on other vehicles and it looks pretty quality. The quote I got was about $500 including tax and muffler tips, however, this guy doesn't do mandrel bends, but they don't look crushed either, is there something in between? How much of a diff does mandrel make? Can you get a consistent diameter with out mandrel? Going to get a few more quotes tomorrow, so any advice would be appreciated.[/b]
I haven't seen the exhaust from underneath a 6. But if what you are saying is true, the stock has to be a good deal restrictive, especially with the 2.0" pipe.

I would say get a 2.5" in/out resonator (high flow of course) into the y pipe into the two magnaflows. If you have 2.5" in / 2.25" out, wouldn't that be creating an unnecessary bottleneck? Either that or have a single in / dual out resonator (if you can get one) that has 2.5" in / dual 2.0/2.25" out (effectively creating 4.0-4.5" out). The stock configuration doesn't utilize dual mufflers or does it? Again, I haven't seen it. Doesn't make sense to have 2.0" bottleneck to y-pipe to dual mufflers because your not utlilizing the increased diameter of dual mufflers.

There are some people I know who live and die by mandrel bends. But these are on true drag cars running insane boost. Brillo, I don't think there is an in between. He might just be taking already mandrel bent exhaust pipes as templates and welding them together. Mandrel machines are rather expensive from what I heard.
 

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Replying to Topic 'Custom Exhaust'

Why not do up a custom True dual exaust setup...with some awesome sounding Dynomax Ultraflow mufflers, my whole system was less than $220. I used mandrel bends and flexpipes from summitracing and I got the straight pipe from jc whitney.

Here's some pictures of the nicest setup I've seen to give you some ideas:
http://home.kc.rr.com/newshore/Cars/Exhaust.html

For performance, this is definately the best route to take.
 

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Reading Topic: Custom Exhaust

Yes, Demon's setup is dope!

Did you do the welds yourself. Did Demon? It doesn't sound like this gentleman has that capability.
 

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I hope we all realize that an exhaust system which is to big for the engine isn't a performance increase, but a decrease... Since your car is naturaly aspirated you wouldn't want to just slap on a dual 2.5" system. You still want some pressure in your system to help evacuate the spent gases from the combustion chamber. If you have a two indipendant exhaust syetms for each of the three cylinders you wouldn't need that big of a pipe dia.

As for pipe bends the least restrictive type would be with a mandrel. Any ridges inside a pipe will cause the flow to become unstable and generate an increase in back pressure.
 

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Originally posted by GreenNuggsDid you do the welds yourself.[/b]
Isn't welded yet...Just clamped. When the engine swap is finished up, we're gonna drive it to the nearest exhaust shop and get it welded.
 

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Originally posted by Commuta_BusaI hope we all realize that an exhaust system which is to big for the engine isn't a performance increase, but a decrease... Since your car is naturaly aspirated you wouldn't want to just slap on a dual 2.5" system. You still want some pressure in your system to help evacuate the spent gases from the combustion chamber. If you have a two indipendant exhaust syetms for each of the three cylinders you wouldn't need that big of a pipe dia.[/b]
Most people when going with the true duals on contours go with 2" or 2.25"...2.5" would be too big. But the duals definately make a large difference, I'll try to dig up some dyno sheets.
 

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Reading Topic: Custom Exhaust

hmmmmmmmmmmm. i was also considering Custom Exhaust. how much would a Custom True Dual Exhaust run?
 

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QUOTE
Originally posted by WhoDiddy


            hmmmmmmmmmmm. i was also considering Custom Exhaust. how much would a Custom True Dual Exhaust run?[/b]
The one we pieced together for my brother's car was:

QTY 3.......2-1/4"OD Tailpipe Tubing.....$15.99 ea.
QTY 2.......Dynomax Ultraflow Welded 2-1/4"....$65.95-$25 rebate ea.
Assorted mandrel bends, flex pipe, hangers, and clamps ~$120
------------------------------------------------------------------------------
Total: $250....(plus a case of beer to get a friend to weld it :cheers )
 

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Backpressure is bad for perfomance period. Flow is key. I'll explain later why a different diameter piping for different engines is crucial for optimum flow. Maybe DuratecPerformance can explain. Got to go...time to party.

QUOTE
Originally posted by Commuta_Busa


            I hope we all realize that an exhaust system which is to big for the engine isn't a performance increase, but a decrease... Since your car is naturaly aspirated you wouldn't want to just slap on a dual 2.5" system. You still want some pressure in your system to help evacuate the spent gases from the combustion chamber. If you have a two indipendant exhaust syetms for each of the three cylinders you wouldn't need that big of a pipe dia.  [/b]
 

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hmmm... I wonder why race cars don't just run a big 5 inch dia pipe for an exhaust... I wonder why they would want any pressure in their exhaust systems?? wow F1 could gain alot of HP? lbs-ft? if they went with a big coffee can sized exhaust????
 

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Originally posted by Commuta_Busa


            hmmm... I wonder why race cars don't just run a big 5 inch dia pipe for an exhaust... I wonder why they would want any pressure in their exhaust systems?? wow F1 could gain alot of HP? lbs-ft? if they went with a big coffee can sized exhaust????[/b]
To quote a couple of posts by a Ford powertrain design engineer...

QUOTE
but what about the 'back pressure' you asked!!!!!...doesn't make a lot of sense for an engine...which is a 'heat pump'.....to have high back pressure does it!!....or F1's, or NASCAR, or dragsters or...well you catch the drift......backpressure is a no no...  When the exhaust valve opens the cylinder pressure is around 60-70 psi and the velocity around 350 feet/per sec...sounds a great idea to slow it down and choke it off!!![/b]
QUOTE
Dont get me cranked on back pressure..its an OLD WIVES TAIL...BS,RUBBISH...if it made power we would all fit 1" exhaust pipes!!!!!....fit a pressure gage on the exhaust manifold,fit a smaller more restrictive system ,dyno it and watch the power go DOWN!!![/b]
 

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ok, so the guy being quoted talks about sticking a tiny pipe, which I agree is bad. but why not just stick a straight 6" dump pipe from the collecter to the exhaust tip? Isn't there a balance between backpressure and velocity? you mean if I stick a big pipe on it the velocity will increase?!?!? I would think the highest velocity with the lowest backpressure would be ideal... maybe I'm wrong..... I think I can pickup some 6" tubes from the tractor truck supply store... now I'll have so much more hp than the guys running a 2.5" exhaust system!
 

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6 inch tubes after the "right" header isnt a bad idea actually. Just make sure it tapers nicely to 6 inches or it will create a lot of turbulance. 2.5 might be optimum...so you may not see much of a gain.

Go to section 3. “The Back Pressure Myth”
http://borg20012.tripod.com/service_sectione.htm

Other posts about back pressure myths.
http://www.hondalife.com/articles/backpressure.htm
http://honda-tech.com/zerothread?id=242473

This one is about the Formula 1 exhausts.
http://www.f1technical.net/articles.php?id=6

Look at the size of the primaries. Looks at least 3 inches. The exhaust pipe looks 4 or 5 inches. That’s the whole exhaust system for today’s Formula 1 racecars...just header, collector, and a short exhaust pipe to the atmosphere. These engines spin at 18000rpm’s producing about 850HP. All from 3liters.
http://www.carsfromitaly.com/paris02/ferra...1_engine_w6.jpg

The primaries of the Mclaren F1 BMW 6.1 Liter V12 are of smaller diameter. This provides optimum flow and scavenging at lower rpm’s. Max HP for the BMW V12 is [email protected]’s in road trim(4 high flow cats and a huge muffler, which isn’t shown in the picture).
http://www.geocities.com/MotorCity/Flats/1...engine_full.jpg

“The F50 uses a stainless steel exhaust system insulated with "six in two in one" mixing junctions on each bank, with a dual entrance into the silencer built by ANSA. A throttle valve driven by the Motronic control unit makes available two exhaust system lengths. One tuned for best torque values and the other for better performance at top speed and full load, by reducing back pressure on the exhaust.”
http://www.f50.com/f501997/engine/




QUOTE
Originally posted by Commuta_Busa


            ok, so the guy being quoted talks about sticking a tiny pipe, which I agree is bad. but why not just stick a straight 6" dump pipe from the collecter to the exhaust tip? Isn't there a balance between backpressure and velocity? you mean if I stick a big pipe on it the velocity will increase?!?!?  I would think the highest velocity with the lowest backpressure would be ideal... maybe I'm wrong..... I think I can pickup some 6" tubes from the tractor truck supply store... now I'll have so much more hp than the guys running a 2.5" exhaust system![/b]
 

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i got a deal that will beat your prices and they are boltons all the ifo is under engine/drivetrain, its a topic called who wants bolt on racing mufflers check it out there is a url to his web site and see some pics of my car whith them on it
 

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I wonder why an engine without any exhaust (=no back pressure) doesn't perform as well as an engine WITH the appropriate size and length exhaust system. hhmmmm NO backpressure...bad performance...SOME back pressure better performance.... to much back pressure... bad performance....

or we could rephrase this in terms of exhaust gas velocity.....
 

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SO your honda source supports my statement.... biggest is NOT always better...


III. Backpressure and velocity

Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?

I often wonder how the myth "Hondas need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).

VI. Conclusion.

SO it turns out that Hondas don't need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.
 

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QUOTE
Originally posted by Commuta_Busa


            I wonder why an engine without any exhaust (=no back pressure) doesn't perform as well as an engine WITH the appropriate size and length exhaust system. hhmmmm NO backpressure...bad performance...SOME back pressure better performance.... to much back pressure... bad performance....  

or we could rephrase this in terms of exhaust gas velocity.....[/b]
An engine with right headers will actually create a low-pressure area near the exhaust valve. So a header that is tuned right will scavenge exhaust out more than an engine w/o one. Also, headers take advantage of the sound waves to evacuate the exhaust gases.
 
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