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Author Topic: Exhaust under axle?  (Read 5100 times)

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Janspeedcapri

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Exhaust under axle?
« on: June 02, 2010, 22:38:40 PM »
I was thinking ways of reducing backpressure, to give my turbo every bit of help spooling up... They say bends in the exhaust don't help. I can't avoid a 75 degree bend on the back of the turbo to run the downpipe but how bout if I ran the rest of it straight-ish, under the axle rather than over it eliminating the nasty sever over axle 90-U-90 nightmare. If the last section with the backbox was joined with a flex pipe and bracketed onto the axle tube? It was rise and fall with the axle and the flexpipe would be like a uj wouldn't it? The flexpipe might need replacing more often than in normal use but if you postioned the exhaust components correctly it would all balance and swing nicely wouldn't it? anyone know if its been done on a capri (think I saw a stag like it once) and is it MOT-able like that?



Offline mk2 cossie

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Exhaust under axle?
« Reply #1 on: June 02, 2010, 22:53:52 PM »
theres no reason why not, but it would mean that the exhaust wouldnt have much clearance           As long as the section over the axle is made with mandrel bent pipe and not compression bent, the curves wont make any or very little difference to back pressure  

Janspeedcapri

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Exhaust under axle?
« Reply #2 on: June 03, 2010, 13:13:02 PM »
Quote from: mk2 cossie
theres no reason why not, but it would mean that the exhaust wouldnt have much clearance           As long as the section over the axle is made with mandrel bent pipe and not compression bent, the curves wont make any or very little difference to back pressure  

no less clearance really as it would hang (with a short hanger) from the tube so the exhaust need not be lower than the the diff casing. And form what Ive read, the bends in the over axel route do create backpressure, which slows down the turbo response/spool - maybe not appreciable with fast spooling, lagless little turbos but probably beneficial to me. Cheerrs

Offline cossiemk2

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Exhaust under axle?
« Reply #3 on: June 03, 2010, 14:44:09 PM »
Can't you have the exhaust coming out the side just in front of the wheel?

Or isn't that allowed in the UK?

Just 1 decent silencer will do the job anyway.

Offline capri v8 driver

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Exhaust under axle?
« Reply #4 on: June 03, 2010, 20:14:36 PM »
i did it with a capri mk3, but it hit the ground many times and after a while, it broke and i lost the mufflers.  

you can go over the axle, just use a bigger diameter bend (not the 40 or 45 mm pipe what ford uses) . but the bends that go over the axle are not 90 degrees. i use 4 ,  45 degree bends with straight pipe between the bends to make that pipe go over the axle.

or try what Jurgen already mentioned, a side pipe. but you still have to make a bend.

if the diameter off the pipe is big enough, backpressure in the bends is not really a issue.

greetz Paul.

Capri V8 Driver.

Janspeedcapri

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Exhaust under axle?
« Reply #5 on: June 03, 2010, 21:23:41 PM »
Quote from: capri v8 driver
it hit the ground many times and after a while, it broke...

I don't know why thats funny but it is  

I see what you mean bout the diameter f the overaxle bends... good point.

Jurgen, I'm not into the side pipe look tbh... do you think all I need is one silencer/backbox, thats It?
« Last Edit: June 03, 2010, 21:26:51 PM by Janspeedcapri »

Offline capri v8 driver

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Exhaust under axle?
« Reply #6 on: June 03, 2010, 21:52:40 PM »
Quote from: Janspeedcapri
Quote from: capri v8 driver
it hit the ground many times and after a while, it broke...

I don't know why thats funny but it is  


yong and wild
greetz Paul.

Capri V8 Driver.

Offline cossiemk2

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Exhaust under axle?
« Reply #7 on: June 03, 2010, 22:06:06 PM »
Quote from: Janspeedcapri
Jurgen, I'm not into the side pipe look tbh... do you think all I need is one silencer/backbox, thats It?

The pipe needn't be visible.

Cut it 2" short of the sill and paint it black.

Turbo's are very efficient at silencing the exhaust, I only have 1 silencer on my RST and that's plenty.

Twin turbo with 1 silencer either side??

Janspeedcapri

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Exhaust under axle?
« Reply #8 on: June 04, 2010, 00:03:04 AM »
No, single turbo, single pipe - I can't do the side exit near the back arch - I have arch spats going on that would get melted - it would have to exit about a foot along from thwe arch just before the sill part of the spat... thinks thats best and glad to hear bout the silencing affect of the turbo. I painted it black today - it looks mad  

zykotec

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Exhaust under axle?
« Reply #9 on: June 05, 2010, 18:06:58 PM »
The exhaust goes under the axle on Sierras, so I can't see why clearance is a problem (unless you have very small wheels with a low profile.)

Janspeedcapri

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Exhaust under axle?
« Reply #10 on: June 05, 2010, 19:31:48 PM »
Quote from: zykotec
The exhaust goes under the axle on Sierras, so I can't see why clearance is a problem (unless you have very small wheels with a low profile.)

jellies might look funny   but they do have irs. ...bastards

Offline mk2 cossie

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Exhaust under axle?
« Reply #11 on: June 05, 2010, 23:46:30 PM »
id go with what capri v8 driver said with the 45degree bends instead of the standard 90-u-90 set up.

that way theres more ground clearance, and less likely hood of being stopped by the BiB for having what may look like a dodgy exhaust

Offline cossiemk2

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Exhaust under axle?
« Reply #12 on: June 06, 2010, 01:07:56 AM »
Quote from: zykotec
The exhaust goes under the axle on Sierras, so I can't see why clearance is a problem (unless you have very small wheels with a low profile.)

It's a Capri with live axle!

Not much room to play with.

zykotec

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Exhaust under axle?
« Reply #13 on: June 06, 2010, 11:52:29 AM »
Quote from: Janspeedcapri
Quote from: zykotec
The exhaust goes under the axle on Sierras, so I can't see why clearance is a problem (unless you have very small wheels with a low profile.)

jellies might look funny   but they do have irs. ...bastards  
Well, with the irs comes huge a-arms, and a diff that layes quite close to the ground, so the exhaust actually goes down towards the ground and up after the axle. 


But, about back pressure, the back pressure is usually less the further back you get, as the exhaust looses heat and speed on the way, so the axle bends usually won't rob much horsepower


Janspeedcapri

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Exhaust under axle?
« Reply #14 on: June 06, 2010, 16:13:10 PM »
O.k, everyone seems to agree, bad idea  

Now, are we all agreed that there is no need or benefit in splitting the exhaust into twin pipes? ...with a single turbo that is.  the bloke from caprisport was trying to tell me that it needs to split as early as possible for best flow but I can't see it -  but whats the truth?

Offline mk2 cossie

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Exhaust under axle?
« Reply #15 on: June 06, 2010, 19:07:29 PM »
i wouldnt have thought it would make that much difference where the system is split. i take it you mean so that you can have twin pipes out the back like the v6 capris normally have?

id imagine a nice sized box in the middle/centre of the car, then split from that to each side for the tailpipes. mate worked for Piper Cams and they found that silencers in the middle worked better at reducing exhaust boom and still made a decent amount of racket when booted  


Offline capri v8 driver

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Exhaust under axle?
« Reply #16 on: June 06, 2010, 19:38:15 PM »
i dont think it has a real performance advantage, its more a practical advantage.

in the case off a capri v6, you can reuse most off the twin exhaust, you only need new downpipes from the turbo. you can use 2 smaller pipe insteed off 1 big pipe.

greetz Paul.

Capri V8 Driver.

Janspeedcapri

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Exhaust under axle?
« Reply #17 on: June 06, 2010, 19:56:24 PM »
Quote from: mk2 cossie
i wouldnt have thought it would make that much difference where the system is split. i take it you mean so that you can have twin pipes out the back like the v6 capris normally have?

id imagine a nice sized box in the middle/centre of the car, then split from that to each side for the tailpipes. mate worked for Piper Cams and they found that silencers in the middle worked better at reducing exhaust boom and still made a decent amount of racket when booted

I'm not hung up on the look of twin pipes so if I can avoid the extra cost and weight, I'd rather keep it single all the way. It was only that one bloke who insisted that splitting to twin pipes was essential, infact noone else has even suggested it. - I didn't beleive it then and I not heard anyone agree.
I like simplicity, so if one box will do the job, then thats great, this will be one cheap exhaust system.

The turbo has a 2.5 inch exhaust but Ive read on scooby forums that you want a downpipe that smoothly opens up - say to 3" before the bend at the footwell. Then, with what Pauls suggest, I should increase the diameter again after the box to say 3.5" for the bends over the axel. I like the idea of no heavy silencers rear of the axel for weight distributiuion...

Was thinking that a single pipe (rather than 2) would mean I can bend the pipe in much wider arc by bending the pipe over the axel diagonaly - see what I mean? so the turbo, down pipe and box are on the left side and the over axel bend crosses the pipe over to the right side... anyone done this?

Janspeedcapri

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Exhaust under axle?
« Reply #18 on: June 06, 2010, 20:27:27 PM »
Quote from: capri v8 driver
you can reuse most off the twin exhaust,

yeah right - I'll do that, and re-use me scabby old fuel lines too  


Offline capri v8 driver

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Exhaust under axle?
« Reply #19 on: June 07, 2010, 08:09:46 AM »
Quote from: Janspeedcapri
Quote from: capri v8 driver
you can reuse most off the twin exhaust,

yeah right - I'll do that, and re-use me scabby old fuel lines too

maybe you already have a nice stainless twin exhaust  

most turbo kits for the capri reuse the stock twin exhaust.
greetz Paul.

Capri V8 Driver.

Offline ibrooks

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Exhaust under axle?
« Reply #20 on: June 07, 2010, 10:55:11 AM »
Splitting the pipe also allows you to use smaller silencers if ground clearance is an issue. Quite few of the competition Minis do this. They run a 3-into-1 manifold and then run a single big pipe down the tunnel with no silencer like a road car would have as there is no room (not a big tunnel and mega low  ground clearance). Then at the rear subframe the pipe splits and runs into two small silencers tucked up into the gap in the middle of the subframe with twin tailpipes ducking under the rear crossmember of the subframe to stick out under the rear valance. The idea is that you can get as much flow and the same amount of silencing from two small silencers as you can from one big one.

Think of them a bit like resistors where two in parallel gives a different effect to the same two in series.

Iain

 

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