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obround tube?
RazMan - 21/8/10 at 04:43 PM

I am looking for some obround metal tube for my weird and (hopefully) wonderful throttle body project. I need 35mm x 80mm id - where on earth can I find some??

SeaBass - 21/8/10 at 04:59 PM

78 x 39 any good?

http://www.hubbardsmetalwork.co.uk/eliptec/sizes-specification.php

interestedparty - 21/8/10 at 05:00 PM

How about making some GRP ones? It's something I've been thinking about, seems perfectly feasible, probably do the manifold flange in it too.

austin man - 21/8/10 at 05:11 PM

If your doing GRP I would recommend that you strengthen the inside, I have seen this done withoutstrengthening and the airbox started to colapse on hard acceleration. It looked like a beating heart when being revved

matt_gsxr - 21/8/10 at 05:13 PM

obround:
A shape consisting of two semicircles connected by parallel lines tangent to their endpoints.

Always nice to learn a new word.

Re GRP throttle bodies. What about heat soak? I guess they would be air cooled when running, but when you stop... I guess its only 100deg C, but they might go a bit floppy.

Matt

RazMan - 21/8/10 at 05:21 PM

quote:
Originally posted by SeaBass
78 x 39 any good?


Looks pretty close !!

Actually I was thinking about GRP too, but by the time I've made the buck I might as well make a one-off (six off actually) from alloy. I need to blend a pair of 35mm ports (obround shape) into a conventional 55mm dia inlet trumpet, so I was thinking about taking a length of obround alloy tube and basically bending one end into a round shape, then attaching a conventional 55mm dia trumpet.

Am I on the right track or is there an easier way?

[Edited on 21-8-10 by RazMan]

907 - 21/8/10 at 06:15 PM

IMHO the other way round Raz.


This may give you ideas.
Cheers,
Paul G

Press tool
Press tool

RazMan - 21/8/10 at 06:57 PM

Cheers Paul, I guess it might be easier to get some 55mm id alloy tube and beat the cra ......er ... gently persuade it into an obround shape

However I was thinking how awkward an obround would be to hammer out 6 times - at least I could ram a cone into the end to make an easier circle - Mind you, that's a very neat job you've done there :

Is there a particular type of alloy that would tend to reform easily?

[Edited on 21-8-10 by RazMan]

907 - 21/8/10 at 08:22 PM

Enough of this "beat the crap".

Finesse man, Finesse. Use a 12 tonne jack in a press frame.


If you must use a cone then press the second stage into the round end and form the trumpet.

90% of the time goes on making the formers BTW.

Material.
I find it's best to roll half hard ally sheet to form the pipe.
(Anneal areas you wish to stretch)

Cheers
Paul G

MikeR - 21/8/10 at 08:50 PM

If you want to make one out of GRP can i suggest that you speak to the rather talented Clairetoo - she's made a few bits out of carbon for her engine and others.

RazMan - 21/8/10 at 11:13 PM

Thanks for the tip Paul, I am not sure if I am going alloy, GRP or carbon at the moment, but someone's going to get a phone call one way or another

Still waiting for prices on the other ITB mods at the moment so my quest continues .....

interestedparty - 22/8/10 at 05:13 AM

quote:
Originally posted by matt_gsxr

Re GRP throttle bodies. What about heat soak? I guess they would be air cooled when running, but when you stop... I guess its only 100deg C, but they might go a bit floppy.



Mondeos and I expect many other cars have plastic inlet manifolds.

But in any case, GRP it thermosetting so although it will burn if it gets hot enough, it doesnt go 'floppy' like ABS etc would

Richard Quinn - 22/8/10 at 10:16 AM

I did a similar exercise, but not quite so extreme, a few years back. I did it the other way round as per Paul's suggestion (albeit with less finesse and craftsmanship) and I managed to get the "obround" (today's new word for what I previous referred to as the "flattened bit") pretty much there using a large bench vice.

[Edited on 22/8/10 by Richard Quinn]