I'm making a 100 degree elbow adapter for an Accel Pro ram base, and I've run into an issue. The tubing came in at a smaller size than I was expecting, and due to that and that the tubing is smaller in ID near the bend its going to be too small where I plan to attach my throttle body plate. I was going to form the end into an oval shape (using a TPI TB), and then have it all welded up. I used the piece I cut off from one side to oval that and test fit, and its too small to cover the holes in the TB plate side.

So, I have a couple choices. I can form the end into an oval, and attempt to stretch the tubing using the end of the jaws on my bench vise so that its big enough (near as I can tell from experimenting, this isnt going to work out real well) or I can use something like an exhaust pipe expander to stretch out the currently 3.8" ID tubing to about 4.1" ID, or thereabouts. I dont really want to spend a lot of money on a single use tool either, and I'd rather do it myself than take it somewhere that can probably do this in about 2 seconds with the proper tooling. I went to China Tools... err, I mean Harbor Freight Tools, and the largest size exhaust pipe expander they sell (or anyone for that matter) will only go to 3.25". The tubing is fairly thin wall, its 0.080" or less, so it seems to deform and stretch fairly easy. I was thinking of using some 4" ABS pipe cut into pieces and glued onto the pipe expander and see how far that gets me. I think it might just work. I dont think its actually going to take all that much force to expand this thin wall AL tubing but probably more than even a hardwood could handle. I think the ABS might be up to the task.

Anyone have a better idea? The end can be tapered for all I care and actually that would probably be better, just as long as the very end is about 4.1" or so and it has at least 1" of taper or close, thats good enough. I'm attaching a picture of what I have so far.



My other thought was to have the guy that welds this up add a lot of extra material near the offending areas on the TB plate and just grind away till I'm happy, but I'd rather not do that. I may have to if nothing else works, but I'd like to leave that as a last resort.

I talked with someone about this tonight, he suggested a lengthwise cut (that would be perpendicular to the end) and weld in a 'pie' shaped piece. I'm considering that, I would just like to keep the amount of fabbing to a minimum since I am not welding this together myself.

 

A pie cut is what I would suggest also, you'll need to add about 3/8" just to get the diameter .1" larger.

A tubing stretcher would work but I've never seen one over 3"

If you're good with a hammer, you could probably stretch it out by hammering, but most people wouldn't manage it without hammering a bunch of "eyebrows" into it and making it look like crap. Best chance to do it cleanly is to use something with a soft, rounded face and anneal the aluminum before you hammer on it

 

is there an exhaust shop around that you could swing by and see if they have an expander for 4"? its worth a shot. It is aluminum tubing though, it may breakup if you try to streach it too much. How thick is it?

 

Its about 0.080" or around 5/64", not the oops typo 0.80 I posted above.

I'll have another piece to experiment with once I cut off the end going to the TB plate. I did use the vise on the other leftover piece and while I did increase the circumference, it was not near enough and did more damage to the shape than I really want. The piece came polished and I can see when its starting to stretch, the finish goes dull. So far no signs of tearing apart. I may just break one to see how far I can go with it.

I can call a guy I know that runs a muffler shop, see what he has laying around. He may have something, he assembles and welds up headers for a large manufacturer and has a lot of related tooling. Maybe he has something in a size larger than 1.5-2"

 

i tried streaching a piece of tubing with the bench vise a while back and it didnt work out so well, kinda mutilated the pipe, had better luck with a hammer and a anvil, stretch and reshape things a bit. Wouldnt work all that well on aluminum though.

 

Well... the vise is not going to work. It gave up before I could break the experiment piece. Didnt break it, but I'm not going to try that again. Its not really designed to pull apart, only clamp things together. Heh.

I did get it almost big enough though, and its not showing any signs of failing so I'm 99% sure I can stretch it to size if I had an appropriate tool to do so. Its close enough now that I could have it welded with maybe a slightly larger fillet and do a quick sanding roll job to clean up the transition.

 

it's much easier with steel... but to do it with aluminum you really want to anneal it till it's soft enough to bend with your hands (working it, time or reheating and slow cooling will re-harden it) and then use wood for both the anvil and mallet, you won't butcher it up as bad. It can be done, but if you don't have the right touch you'll just make it into an ugly lump

 

a method that I have seen used with success is to form the shape you want for the taper then gt it wedged into the end of the tubing and get yourself a heat source a hammer and an afternoon to waste. Its a pretty simple process, just keep everything hot and slowly pound the buck into the pipe and it will slowly shape it. For aluminum you could use a nice hardwood for the buck.

 

Why don't you just run an LSx throttle body, and forget all this ovaling madness to get a twin bore working?

This is the one I built in 2008

http://members.cisdi.com/~anesthes/s...complete/2.JPG


-- Joe

 

I dont really feel like spending a bunch of money on a TB and adapting it to work with TPI, thats why. I almost forgot, I also have another part going on there in the future that is oval in shape to attach to the TPI TB and that would just mean more fab work later as well. This is actually the cheaper/easier route. I only have about $45 invested so far.