Exhaust Building & Questions

[tibbs.james 1]

Hi Guys

I have been doing some investigation on the forum & at the exhaust shop (Rangiora Exhaust Centre) but i want to see what other people have done with their exhausts.

Is 2.25 Inch a good diameter for a m20b20 that could possible be replaced by an m20b25 in the future ? I don't want to go so small that it won't breathe with a bigger engine in there.

but being a m20b20 for now it still has to work ok.

Is it worth using Mandrel bent "U" pipes or 180 deg pipes ?

@ $30 each i was going to use them to build my exhaust and do a tidy job, but does it actually make a diffierence being on a factory engine.

Backpressure > will a fairly standard muffler of matching inlet/outlet diameter work well ?

I was of the understanding that M20's like a bit of back pressure to work well and have good lower rpm pull

( spoke to ben @ the Rangiora Exhaust centre & he seemed to think a fairly standard 2.25 muffler they use on falcon or holden would work well for this, of the normal fairly restrictive quiet design)

I have plans here for building a copy of DELTA FLOW FLow Master muffler but i think that this would be too free flowing with only a Resonator in the middle, Is this correct ?

mid range pull at around 3000-4000 rpm is most important for me.

From another thread

From Gus

quote]i have used both a 2.5" and 2.25"..i had headers with the 2.5 and none with the 2.25...i have found the 2.25 to be faster..not as much lost torque. with the 2.5 i was waiting forever for power! both are from als mufflers with one resonator and one muffler. their work is great..just ring and book ya car in..great service.

the stock 325i dual pipe prob has just as good power...not a huge difference if there is anyway. some stock mufflers can sound super loud..not sure why though!

Has anybody else used a 2.25 on a 320i before ?

[Mike 1]

I was running a 2.25 on my 318i when it was N/A, reasonable improvement over stock from memory, nice noise (for a 4 cyl) too, quiet enough when cruising but louder when you floored. Can't see any reason why 2.25 wouldn't be great for a 320i

[bravo 35]

I have had the exact same experience as Gus with 2.5" single resonator and muffler done by Midas in Kerikeri by a mate who works there.

I've lost low down torque in exchange for more HP up top (but dyno). It is slower to 3500rpm, but then it really lets go and you feel a pretty hard shove in the back for an m20.

Mines the 2.5, but I would say that 2.25 would be fine for the 2l and perfect when you go to the 2.5.

I'm putting up with my 2.5" as it sounds sweet and I plan to add boost down the line when all my cash isn't going into my house renovations.

[tibbs.james 1]

3pedals

You seem to know all about this which is great,

In my Case I'm Planning a Facelift M20B20 with Factory Cast Manifold with a single 2.25" pipe into a single resonator then into a matching muffler.

Will it be worhwhile using mandrel bends, or will it be fine with just regular old crush bends ?

mandrel U bends are only $30 each , but since im not using a Exhaust Header at all will it make any diffierence ?

Keeping in mind later on when i swap to a B25 engine i suspect it will be fairly factory aside from maybe an ecu chip and a camshaft with a bit more lift and duration ( again still using a factory manifold )

[smiddy 76]

Hi there would be little point going to mandrel bends if you are not ging to do any thing with the manifolds , but having said that there is also little point chipping and doing cams if you are going to use standard manifolds.

You would get better results for less money by doing exhaust then headers and then chip , then if you decide to do cams any way at least you will get the full benefit of them.

Doing cams is one way to make the motor pump more , you can get the motor to pump more air by making the exhaust extract the burnt gases i.e. extractors, properly designed they will give the motor better flow and increase ability to pump more air.

Jimmey, PM me if you need headers!

[tibbs.james 1]

Well just playing around with autocad I sorted out how im going to build a collector, so i can merge the twin pipes into the single pipe shortly after the oxygen sensor. ( this is so i can keep my oxygen sensor and not have to have a new flange cut when there is already a pefectly good one there)

I plan on doing a full Autocad 3D model & Plans of this exhaust with all dimensions needed incase anybody else wants to know any dimensions, Or if they want to build one.

this pic here was just pissing around really.

If somebody Could give me some information on headers I could attempt to do a 3d model and create plans for building one.

Primary Length & Diameter ?

Secondary Length & diameter ?

Perhaps somebody has some good pictures Well Deisgned or L6 Headers ?

Thanks for the Offer Wayney, Im not ready for headers yet but it would be fun to mock some up on CAD.

Edited July 21, 2008 by Jimmy

[Mike 1]

I thought about doing mine in solid works but decided it was far too much effort working out space constraints, and even modelling the thing. Besides, I'd be very surprised if I could build the thing exactly how I'd modelled it. That said, it would give you an idea of what materials were needed, and any potential problems.

I just found it easier to sit the flanges where I wanted them and work my way out from each port. I did my wastepipe the same way, theres no way I oculd have accurately modelled my way between the block and around the steering column.

Edited July 21, 2008 by Mike

[smiddy 76]

Mike, please keep ear to ground, I have equal length SS short headers for M10, M40.

[westy 614]

Yeah its not terribly good sorry mate.

PM or email or something to try to get hold Andrew.

He has some really nice computer aided headers on his race car but to be honest they're well over the top for your needs.

The Gus car went very well, so what he says is a pretty good place to start.

Mandrel bends and the like are probably unnecessary for your needs.

[E30-323ti 66]

Here is a pick of the 'Burns' Y-collector.

From: Burns Stainless

Probably one of the best "off the shelf" suppliers.

I gather the intent of the pic/model posted above is something along these lines.

OT. Is that A2009? On Vista??

[tibbs.james 1]

Burns doesn't cut it for me has the same faults as jimmys modelling

Yo Fair Call, do you have an example of one that works properly?

Even if i take my car to an exhaust shop i don't think i could get one much better than the picture posted above.

Edit checked out the deisgn of some collectors on honda b18 engines, reading online a longer tapering collector is better for mid range torque. so i whipped up the image below on autocad.

Edited July 26, 2008 by Jimmy