Thursday, July 22, 2010 - 03:01 pm, by: Mark Donovan(Mark_donovan)
in response to Mikes suggestion of getting aluminium clad piping, this is what my V8 mechanic had to say:
"Aliclad exhaust tube means that the exhaust will not be mandrel bent like ours, as you cannot buy aliclad mandrel bends so it would be a press-bent system like most exhaust shops do. This means the bends are restrictive as the bending process crushes the tube. We sand blast our systems and either have them HPC coated or painted with high temp exhaust paint. Also note with aliclad whereever it is welded is not aliclad anymore and will rust. "
Thursday, July 22, 2010 - 09:09 pm, by: Adam Lonergan(Alchemistal)
Ken, you could write a thesis on the calculations involved and still not come up with a commonly accepted answer. Based on my knowledge the paramount issue would be pipe internal diameter, then the angle of the bend, then the reduced diameter of the bend, then the length of straight pipe before the bend, then the angle and restriction of the bend prior to the bend in question, then the length of straight pipe after the bend. This assumes nothing unusual like bends greater than 90° and reductions in diameter of more than 15% etc. Probably easily a dozen more things to consider that don't immediately come to mind, and completely ignores the flow rate and temperature of the exhaust gas which you could reasonably assume are fixed for any comparison.
From my understanding press bending also tends to leave the inside of the pipe less smooth than it originally was and this would also have some impact (more on the outside of the bend and less on the inside of the bend), but how much impact is hard to know.
Friday, July 23, 2010 - 01:18 am, by: Aiden Cheese(Chillpen)
Ken Yo wrote on Thursday, July 22, 2010 - 07:51 pm:
Hope you don't mind me asking how is it too nasty? I've got Press bent on mine :-(
Good post up there by Ken Yo.
Here's the short and long of it (and most of it is a grey area for exact numbers). - Mandrel bent is obviously going to have the same diameter all the way through. - Press bent is going to have bends with restrictive corners. - Mandrel is more expensive - Press bent is cheap
So from that people would generally ask "Is it worth getting for cheaper a larger press bent system over a mandrel bent system?". That starts getting tricky.
In another thread I calculated the diameter of a press bent bend versus the equivalent size of a mandrel bend (so if you went press bent because you were in the sticks and wanted an exhaust) and naturally it depends on the size.
So exhaust flow is two dimensional in a specific point in the exhaust (the point being that third dimension). In other words you can work out that a 3" mandrel exhaust system will have an area of 3.14159*1.5^2 = 7.06 square inches. A press bent basically turns the circle into an oval. how "oval" the oval is is dependant on the angle of the bend. The sharper, the more oval it gets (and less it flows. So instead lets say the bend has squished the exhaust from being a 3" to being about a 2" top to bottom and 3" wide. That calculates an area of only 4.71 square inches! That's nearly half.
But because of how much an extra inch can add to a exhaust if you went a 4" press bent system which might be comparable to the price of a 3" mandrel bent system you would get 8.35 square inches if it was squished to only being 4" wide and 2.66" tall. That would in theory at that point irrespective of the rest of the system flow more than a 3" mandrel bent system.
But then comes the other speculation: pressure. Because air works like liquid, it actually causes pressure to build and relax. Especially in turbo systems this is important, but basically it's like this:
The air flows through very freely out your exhaust vents given all the room in the world and then comes to it's first corner and slows down and builds up pressure at the point before the curve! Then it actually speeds up as it squeezes through and enters a low pressure zone and chills out moving slower again.
How that affects the performance of the car? No idea personally. But that's the facts as I understand them today.
Anyway - mandrel bent systems are much higher quality of bends and have no disadvantages. But if you want to compare the types then that's the considerations you'll want to put in when comparing them. But from my basic and rudimentary calculations (not based on real bends) you can understand that at least if you have to consider a press bent system, that's what is going to happen and if you believe the bends they make are quite squashed, then you'll want to go a full inch larger from 3" if you want similar flow rates at the point of the bends.
If you read around the place there's lots of places which dyno a 3" mandrel vs a 3" press and find the HP % difference etc. It's not negligible. But the two prices aren't really comparable. I believe personally that it'd be fairer to compare the two similar cost solutions.
Anyway I'll let that sit, a lot of people are very passionate about this topic and don't like to think that press bent has any application in life but the truth is it's still used all the time so it's good not to be blind to it, or so I think.
Tuesday, July 27, 2010 - 11:12 pm, by: Trent Linnell(Tlinnell)
My baby went in today to have my "mess" of an exhaust fixed.
2 years ago I got a quote from Ringwood Performance Exhaust to get a 2.25inch Cat Back Exhaust with a X-Balance Pipe. Went I went to pick up the car, nothing was said to me and I assumed it was completed to my request.
I had the car up on the Hoist a few months ago. I had a look at the exhaust and found out that, for compliance, my car had a Center Catalytic Converter put in place of the factory Resonator. It is my understanding that this was done by some importers to reduce the emissions levels, to comply the car.
So anyways, I booked my car into another exhaust company to have my "chop job" fixed. She is getting a full 2.25inch Mandrel Bent Straight Through Exhaust with no balance pipe into the current Straight Through Mufflers and 3" Tips.
Depending on how loud it comes out, we might have to make some adjustments but we'll see how it goes.
Wednesday, July 28, 2010 - 07:58 am, by: Trent Linnell(Tlinnell)
Yeah Ken I will. I have made a video of my current set up and I will make a new one tonight when I get the car back. I'm hoping it will sound good and perform better.... Fingers Crossed!
Wednesday, July 28, 2010 - 08:37 am, by: Matt Shields(Smokeyvip)
just as an FYI: having had a true dual 2.25" straight thru to rear mufflers setup, and then getting a balance pipe put in about a month later - i can honestly say that with the balance pipe it:
a) sounds better at idle and at full throttle
b) is significantly quieter
c) performs a lot stronger in the low and midrange.
only area that the true dual beat it was in sound at slow speed acceleration, say, around a carpark or taking off from the lights - made my balls tingle! but every other aspect, balance pipe beats it.
Wednesday, July 28, 2010 - 03:15 pm, by: Mike Beck(Gold_40gt)
For my second E36 V8's exhaust I will have a vacuum actuated valve section in the middle of the H pipe balancer so when I want true dual I have it Closed, and when its open I have it balanced with an H. Easy enough to accomplish, that way I would get the best of both worlds.
I must reiterate, the only way a true dual setup sounds it's best is when the rear mufflers have a single entry and dual split, it means you will have 4 tail pipes though, but solved by running two wide oval tips.
Wednesday, July 28, 2010 - 05:40 pm, by: Trent Linnell(Tlinnell)
Well the exhaust is done... I am still not too sure about it. But I think it will grow on me. Hey Matt how much did it cost you to out the Balance Pipe in after wards and which one did you go with (ie, X-Pipe or H-Pipe).
Thursday, July 29, 2010 - 03:04 pm, by: Matt Shields(Smokeyvip)
cost me 20 bucks to get the balance pipe put in, it's just an H-pipe.
an x-pipe would have been 100 bucks, and on the advice of the exhaust shop, not worth the spend.
i just did it without at first to see what it sounded like, as i knew that true dual would have been the more extreme sound, and it takes 15mins to whack a balance pipe in if i didnt like it - which is what i did.
here is a pic, note - this is BEFORE the balance pipe:
Thursday, July 29, 2010 - 07:39 pm, by: Trent Linnell(Tlinnell)
Well after driving my car around for 2 days now, I think I might be inclined to get the balance pipe put in..... Hey mate, where abouts in Vic are you located?? Maybe if it's ok with you, I could meet up with you in the next few weeks to her your car vs mine.
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