Maniflow 2 1/4" System

[Henry 1.9GTi 36]

flow of air out the exhaust determined by density, area of pipe, and speed of the gas.

 

You can't move the gas faster than speed of sound. But it is spupirsing how rapidly the speed of sound increases with temperature. Obviosuly with a stupidly small exhust gas speed will reacspeed of sound and thats it then no more gas is gonna come out. If pressure generated by the piston pumping the air out = back pressure then there is no flow. So piston has to overcome this pressure before useful work is done.

 

Anyway I have nothing useful to say about whether to buy a particular exhuast lol . Miles does a good price on a maniflow equivalent though.

 

"An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work"" Taken from http://www.rbracing-rsr.com/exhausttech.htm

 

interesting read.

Edited March 19, 2009 by Henry 1.9GTi

[Cameron 16]

Well I've only been there 8 months so I'm no expert, ivv been recommended by one of the guys (who is) that I need a 2 1/4" system for my 205 and that will be good for anything I wanted to do.

[edbar 6]

Thought that would be enough for anything my 8v could throw at it. So as the post has gone on a tangent now, think i will possibly go for the ashley for now and if i get a "better" system and proper two stage 4-2-1 later when i have more funds and decided whether to stay 8v or go 16v.

[edbar 6]

Any other suggestions are welcome though.

Edited March 19, 2009 by edbar

[GTI6BOY 29]

The supercharger boys are running 400bhp threw a 2 1/4 system

 

I was running 200bhp NA with a 2 1/4 system but on the standard mani and exhaust you wont get much more the 230bhp.

 

To run 275bhp i must have a straight mani and 2 1/2 system...NA tho remember.

[Cloverleaf 1]

You going for the 2 1/4" competition system mate? I'd be interested to know how loud it is cause I was thinking of that for my 309 but it needs to be track friendly.

[welshpug 1,670]

competition systems if designed for track or rally race cars tend to be within the MSA noise regs, so wouldn't be anything to worry about if your engine is what the exhaust was designed for (a higher output will produce more noise...)

[edbar 6]

Going to speak to ashley today to see what db they think they're at with their system.

[whizzer71 0]

I had an Ashley system on my last 205 with Gti6 power and that was way too rawcus !,started off quiet but got louder and louder it ended up being way too horrendous !

 

[Cameron 16]

That would probably be because they use cheap packing materials!

[andychalmers 0]

I have a Suzuki Swift S1400 rally car now, BTB custom made the manifold & exhaust. This was done 3 yrs ago & still it cost £2300 fitted, it took them 35hrs to make it plus £650 materials

Excellent quality, I personally would'nt have paid that but the last owner did so happy days lol.

[Sandy 191]

The cam profile, ports and exhaust manifold are the most critical exhaust issues, but I'm not giving details of that away! System wise on N/A engines I use 2" up to around 185bhp, 2.25" up to around 240bhp and 2.5" up to around 290bhp. I don't think back pressure for its own sake is a good thing, but tuning the system diameter, boxes and lengths can greatly influence the engine's delivery.

I can give you plenty exceptions that defy the "rules" though, I've had over 200bhp on the 106 2" "Pugsport" system, which I'm told isn't possible and my the Accord TypeR 2.2 collector is 42mm internal diameter, which works with 209bhp on the standard engine and around 235bhp on my TB'd one in the 309; clearly it was restricting the latter though.

Some literature will tell you that flow rate increases at the rate of radius to the power of 4. Tests I've witnessed however at stable temperatures, indicate a closer correlation of flow to the sectional area. With exhausts, the quality of the bends are a big issue, they are invariably where systems really differ.

Edited March 24, 2009 by Sandy

[Cameron 16]

I have a Suzuki Swift S1400 rally car now, BTB custom made the manifold & exhaust. This was done 3 yrs ago & still it cost £2300 fitted, it took them 35hrs to make it plus £650 materials

Excellent quality, I personally would'nt have paid that but the last owner did so happy days lol.

 

Yeah the one-offs get expensive!

[Cameron 16]

flow of air out the exhaust determined by density, area of pipe, and speed of the gas.

 

You can't move the gas faster than speed of sound. But it is spupirsing how rapidly the speed of sound increases with temperature. Obviosuly with a stupidly small exhust gas speed will reacspeed of sound and thats it then no more gas is gonna come out. If pressure generated by the piston pumping the air out = back pressure then there is no flow. So piston has to overcome this pressure before useful work is done.

 

Sorry to drag this thread up again, but my recent work has brought me back to this post and I feel I should clear it up.

 

It isn't actually the gas that travels at the speed of sound, it is the pressure wave caused by the opening exhaust valve. The gas actually travels at a far lower speed.

 

That is all.

[Rippthrough 98]

Sandy's rule of thumb is pretty similar to my own, the buggy is putting nearly 270bhp through a 2.5" system (with 2.25" baffles!), the Fouquet puts 380bhp through a 3" system, and Kershaws 206 is putting the same power through a 2.75" Tony Law exhaust.....