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