You may have seen I'm developing a 8v inlet manifold, I want to enlarge the runners, any ideas? I was thinking a large carbide burr on a flexible drive bit I can find one big enough! Open to suggestions
How much do you need to enlarge them? If it's just a MM or so and a general clean up, how about a flap wheel? If it's lots, cut them up, bore them out, weld them back up, or just graft in pipe of the right ID and bend, as already suggested - tricky with Ally pipe though.
I want to make them as big as practical I dont really want to cut it up, any further than i have already. i can get then welding done by a mate but i dont want to be taking the p....
UNless you've got aline expensive CNC mill with maybe a FAROarm then you're not going to mill it out. As Mike said, a course flap wheel back and fourth or machine up some tube and have it mandral bent,
When building my 16V Syncro stainless manifold I've been using a tungsten carbide burr on an air die grinder to do complicated shapes and smooth out within the ports afterwards. How well you could uniformly open out the bores by hand I don't know; it'd probably be painful and take forever. I'd want to start with new fresh tubing. But I TIG weld. I appreciate that you don't want to give your mate too much welding to do though. But in the long run it might work out more economical to chuck him some extra coins towards time and argon and use new bits. It sounds like you want to use the nominal bore style fittings like I used, except in aluminium - if such a thing exists.
Why are you wanting to open them out Alan? Could extending the runners into the plenum help achieve the same thing by giving a volume increase? It would be a lot easier to make up some short stubs with a radius or bell mouth that could be tig welded onto the existing runners, then finished off with a die grinder to neaten the welds up. It looks like there is going to be tig welding needed to rebuild the plenum case so why not go for a completely new plenum to give you the volume and runner length you want. Or just get one of the numerous sets of ITBs you have hoarded put on it!!
thats the plan Dan, i want to turn some bell mouths on the lathe to suit the size of the runners then weld on a new larger plenum which looks like it could be made from a 120mm tube. i want to maximise the runner size as they cant be aslong as i would like for packaging reasons. the ITB's are a option, but not at this point, i use the car daily so the dicking around i would need to do to get the ITB's to fit in the engine bay along with all the other crap needed to get them to fit and work means its off the agenda for now, not forever tho, just for now, this manifold should be pretty much bolt on
bends in pipes are bad, you get all sorts of stagnation in flow around the curves radii which in turn leads to a reduction in performance. you'd be much better opting for a new flange, new straight pipes and an optimised plenum chamber. just so you know the dimensions (lengths) you need: working in an idealised straight line from the back of your inlet valve to the entrance of the inlet runner within the plenum you would need to achieve an ideal length of 294.1mm asuming an average operating air temp of 20oC. 294.1mm is assuming you want to hit the 3.5 order which would be absoloutly ideal if you were atempting to achieve the best pulse tuning results possible.... which you may as well do if your going to the effort.... and dont forget to use a progressive radii on the bell mouths for each runner inside the plenum. off the top of my head I cant remember what they are exactly but I could dig it out of my dissertation for you tomorrow if I remembr... might even have a cad file knocking about too!
Just remembered about this post in a thread a while back. Long runner for sure. Clearance with the rain tray area too but performance has to sacrifice something.. http://www.clubgti.com/forum/showpost.php?p=2109531&postcount=71
