Need help fabricating exhaust manifolds

[aerosam]

Hi guys,

One of the last big jobs on my to do list is to fab the exhaust manifolds, so far i have welded the exhaust flanges on to 10" lengths of 2" dia, 3mm wall pipe.

At the moment I have 4 straight pipes sticking out of either side of the engine. I planned to join them all together by welding in another length of 2" pipe across the open ends, but that means I have to cut 4 2" holes in it to allow them to fit snugly, how do i do that?

The rest of the exhausts should be fairly straightforward, it's just the manifolds I'm struggling with. I'd love to be able to buy a pair of ready made mainfolds, but they just dont exists for my engine (BMW M60 V8) and i can't afford to have bespoke ones made for me either.

[Talonmotorsport]

It will certainly breathe easy if your using 2" tube as the primeries. You could use a bi-metal 2"-50mm hole saw in a pillar drill held by a very good vice thats clamped down. Run the drill at it's slowest speed and cool it down half way through with some water. Do not try and use a pistol drill you WILL end up hurting your self. Another way would be to cut a 2" hole in a piece of paper and use as a template to draw around and chain drill the tube and file to fit.

[ozzy1]

If u can get someone to put it on a mill and machine the holes in it would be the best or if doing it yourself i would do as talon says and chain drill it and finish it off with a dremel .By far the safest bet.

[Davey]

2" sounds a bit big for primaries and 3mm wall is a lot heavier than it needs to be. If you put a secondary tube across the ends of your four straight pipes you won't do your engine's gas flow wcharacteristics any favours. There is a good reason why tubular manifolds are made of smoothly swept bends. You can buy a variety of bends in SS tube for sensible money, all you need then is a TIG welder to glue them all together.

D.

[aerosam]

Thanks guys, some great ideas there. I'll have a chat with the guys in the milling shop in work, otherwise I'll get a holesaw for my pillar drill.

I wish I had the skill to make a full set of tubular manifolds out of SS, i realy do.

[davidimurray]

Aerosam - the setup you are proposing is less than ideal to be honest with you. If you can, individual runners with much longer primary lengths will be better. Have you calculated your pipe diameters, not sure on your engine size, but too big is as bad as too small as it reduces the exhaust gas velocity. Hope you don't mind me commenting. If you want some info on exhaust design and calculations drop me a PM with your email address and I will forward it to you.

Cheers

Dave

[aerosam]

Hi David,

the engine is a 3.0L V8 so each manifold is flowing exhaust gases for 1.5L of engine.

I'd love to be able to make something more suitable but I don't have the skill necessary to do it myself, nor the funds available to pay somebody else to do it for me.

I'll send you a PM shortly.

[aerosam]

forgot to mention, the reason I'm using 2" dia pipe is because that's what was on the donor.

the BMW manifolds looked very constrictive as they all bent sharply down to follow the contour of the engine to allow it to fit in the engine bay of the 5 series. Some were even very squashed across the cross section as the crossed over eachother.

I just want something to get it going for now, and maybe upgrade when funds allow.

[raceral]

I am not sure if you are finished your exhaust or not, but thought I would post a few photos of what I did, it might help or be of value to someone later down the road.
In the case of my V6 I picked up a header gasket and made a template out of 3/8 steel for some header flanges. I cut the circles out with a hole saw on my drill press and hacksawed/filed the rest into shape.
I then welded up some tubes using 1.5 inch tubing, in my case I had some .083 dom tubing and I also am fortunate to have a tube bender. Though you can buy bends.
I then just tacked welded the tubes together bringing it all into a 3 into 1 collector, from there I necked down to 2 inch and using a V clamp exited the body to the muffler which is a reverse flow round tube.
In my case I didn't exit the body with individual tubes because I will be running clamshells and didn't know if having the exhaust exiting right underneath might affect them or the paint.

The drivers side took about three days to do because of clearing the steering column and such, but the passenger side was much easier as it took about 6 hours to do.

It is not a difficult task I would recommend to anyone to try to do their own if possible. Even if you can buy a complete exhaust it is not cheap.
Doing it myself cost me about 150 dollars or roughly 60 0r 70 pounds.

Al

[davidimurray]

Lovely looking exhaust there raceral. Did you buy your collectors in? So far the cheapest 4-1 I have found in the uk is about £50-£60 which seems ridiculous for a bit of pressed stainless!