FFIM Long runner fabrication question

[C.44]

Hey guys, i've decided to build my own long runner ffim. Buying a ffim from anyone in the USA isn't really an option because shipping a core to the USA from germany and shipping the completed ffim back here would be plain absurd. As there have quite a few ppl to build a ffim this way i thought i'd ask a question here that's been bothering me for a while now.

I have cut the orinal plenum from the intake manifold so i only have a set of runners with attached to the flange left. Now for the new plenum (100mm/4" aluminum tube) to fit nicely i need to make the runners slightly curved/hollow. To illustrate what i mean look at the picture below.

if saif want's me to remove this picture (it's his) then i will and add a mspaint drawing

How would i best go about this without resorting to a mill (which i don't have and i can't get anyone to use for me - asked maybe 6 - 7 shops so far) or taking an anglegrinder to it.

Any ideas ?

 

[IJ.]

I used to make mine like that and would slice the 4" length ways so you have 2x U shaped pieces, cut the holes for the runners finish weld them radius the entries then weld the "lid" on.

 

[C.44]

But how would you know where to cut the holes in the 4" U piece then ? Not one of the runners is actual perpendicular to the pipe so the further i want to move the pipe over the runners the bigger i need to make the holes in the pipe. Problem is that it will fit then but i will have horrible big holes in the end making it very hard to get a nice weld.

 

[HommerSimpson]

But how would you know where to cut the holes in the 4" U piece then ? Not one of the runners is actual perpendicular to the pipe so the further i want to move the pipe over the runners the bigger i need to make the holes in the pipe. Problem is that it will fit then but i will have horrible big holes in the end making it very hard to get a nice weld.

I Just bought a upper intake to fab my own ffim... but i plan on eather buying this off summit and use just the top part or making my own... Or hopefully find one used...

http://store.summitracing.com/partdetail.asp?part=hly-7540

 

[C.44]

Well the plenum itself isn't really the problem, a 4" pipe with flange on the front and a cap on the rear and you're set. It's the damn holes i'm worried about. I first figured i'd make the plenum fit on the runners and then mark the runners outline onto the plenum. Then it would be easy to get a very tight fit hole.

But getting the runners to fit nice is going to be a real bitch so i'm open for all other options. Cutting holes in the plenum first and radiussing the runners after that is one option. I'm just curious as how to go about marking the holes on the plenum without so i can get it to fit nice and don't get gaps that i need to fix afterwards.

 

[HommerSimpson]

Well the plenum itself isn't really the problem, a 4" pipe with flange on the front and a cap on the rear and you're set. It's the damn holes i'm worried about. I first figured i'd make the plenum fit on the runners and then mark the runners outline onto the plenum. Then it would be easy to get a very tight fit hole.

But getting the runners to fit nice is going to be a real bitch so i'm open for all other options. Cutting holes in the plenum first and radiussing the runners after that is one option. I'm just curious as how to go about marking the holes on the plenum without so i can get it to fit nice and don't get gaps that i need to fix afterwards.

Well... stupid idea maybe... 4 inch pipe with sand paper glued to it.. after you take a grinder and get a ruff curve.?
Never had to round pipe like that... was wondering myself.. i have seen that pic you posted couple of times and wondered how they got like that...

 

[C.44]

Well i just took a shower and had some time to think it over once more. Then it dawned on me... TEMPLATES. I think i'll try to fab up a paper template that fits where the plenum should meet the runners. Then i'll transfer said template onto the pipe and mark the pieces that need to be removed.

Hopefully i can fit the pipe (u piece) onto the runners then and sand off all excesses from the runners. Then i'l take it apart again to give it a good sanding, maybe even polish it, and then weld the first piece of the plenum to the runners. Should work... i think

Anyway, thanks Ian for kicking me in the right direction

The idea of sticking sandpaper to the pipe and just try to sand it down seems possible too. But considering i have sanded down half my car... i'll try making a template first lol

 

[HommerSimpson]

Well i just took a shower and had some time to think it over once more. Then it dawned on me... TEMPLATES. I think i'll try to fab up a paper template that fits where the plenum should meet the runners. Then i'll transfer said template onto the pipe and mark the pieces that need to be removed.

Hopefully i can fit the pipe (u piece) onto the runners then and sand off all excesses from the runners. Then i'l take it apart again to give it a good sanding, maybe even polish it, and then weld the first piece of the plenum to the runners. Should work... i think

Anyway, thanks Ian for kicking me in the right direction

The idea of sticking sandpaper to the pipe and just try to sand it down seems possible too. But considering i have sanded down half my car... i'll try making a template first lol

well what i was thinking was drill in vise and then just a braket at other end to support drum... it would atleast get them all evenly sanded... but yea paper templet to...

 

[C.44]

well what i was thinking was drill in vise and then just a braket at other end to support drum... it would atleast get them all evenly sanded... but yea paper templet to...

That would actually be a good idea, but you'd have to find a way to center the drum/plenum/pipe on the drill and the supportbracket. Otherwise it will wobble and give you a very uneven result.

 

[Rennat]

i was going to say you could put the pipe on top of the plenum, and then spray paint the underneath where they meet. And if theres a small enough gap then it would tell you where to cut roughly...

this is why you see some weld a flat piece of aluminum to the top part, and then weld the tube onto that.

 

[C.44]

i was going to say you could put the pipe on top of the plenum, and then spray paint the underneath where they meet. And if theres a small enough gap then it would tell you where to cut roughly...

this is why you see some weld a flat piece of aluminum to the top part, and then weld the tube onto that.

Spraypaint would be one option, but only if you are using a flat surface and and using runners that are perpendicular to the plenum. The further you move the plenum over the runners, the wider the area that runners cover gets. So in the end to make the runners go inside the plenum you'd have to gut the original holes even bigger and that would leave you with a huge gap. Which will be a real PITA to close.

On the other hand, i did almost resort to just buying a flat piece of alu and go that route, but i'm stubborn and have my mind set on a circulair plenum. If i'm going to put a flat piece onto the runners i might aswell build myself a shortrunner rightaway lol.

 

[williamb82]

or do what some people do, weld a flat plate to it then smooth the entries like a ventrui then weld the pipe to that? heres a folder full of diff intake pics i have saved over the years.

http://s5.photobucket.com/albums/y155/williamb82/intakepics/

 

[C.44]

or do what some people do, weld a flat plate to it then smooth the entries like a ventrui then weld the pipe to that? heres a folder full of diff intake pics i have saved over the years.

http://s5.photobucket.com/albums/y155/williamb82/intakepics/

I'm about to start on the template (will probably do 2 or 3 to see which one would work best) but i really want a completely round plenum. But i will be smoothing the entries like you said. That's quite possible the thing i like the most on custom ffim's so it'd be stupid not to do it on my own ffim lol.

Thanks for the link btw, lot's of good pictures, very inspiring.

 

[IJ.]

I used to use a Marker to trace around the runners then cut the holes out roughly with a hole saw and blend with the Die Grinder and a carbide bit.

I found it's MUCH easier to use a flat floor though say 3" wide by the length of the runners then cut a strip out of the 4" pipe to match.

 

[C.44]

Yeah i think it'd be much easier indeed. But like i said... i'm friggin' stubborn about this. I want it round lol. Tracing lines as we speak lol...

 

[IJ.]

You can't avoid the Gaps then
(easy enough to fill with the TIG then grind em smooth and lay a finish bead over the top)

 

[C.44]

Well i'm trying to avoid it as much as possible. Cutting up paper for both set of double runners and for both single runners. Then i'm going to fit them together so that they match lengthwise and then trace onto a bigger piece of paper to get a one piece template. Then i'll trace it onto the pipe and hopefully i can convince > the tube to fit at once lol.

I do think i'll clean the runners before whacking the tube into place though. When it fits i can weld it rightaway without having to remove it and whack it into place once more.

 

[IJ.]

Trust me you CAN'T avoid it due to the angles on the end runners.

You can either have minimal gaps inside or outside it's your choice.
(I found outside gaps were easier to deal with)

 

[C.44]

Trust me you CAN'T avoid it due to the angles on the end runners.

You can either have minimal gaps inside or outside it's your choice.
(I found outside gaps were easier to deal with)

Well i have my paper template ready, i started with halves for each of the four "sets" of runners. Then i put one side together, then the other and finally put every thing together as a whole. Took two new A4 pieces of paper and traced that templated onto that one. Cut the holes out and they fit pretty good around the runners. Ofcourse i will need to do a lot of trimming before it fits nicely but it's a whole lot easier then just sanding away hoping that one day it will actually fit...

Anyway, i'll use a drill with a "milling" bit to get all the holes opened (unless someone has another suggestion instead of a "millingbit") and try to get every thing to line up nicely

 

[HommerSimpson]

I demand Pictures!!!!!!!!!!!!!!!... HEHEHE can you take pics for us please ?