4.6 plenum - max diameter?

[Seight-V8]

hello all,

So my next winter upgrade is a carbon plenum for my 4.6 v8 westfield.

currently it has a land rover thor throttle plate (70mm), but i much prefer the 4.6 throttle housing, as its better suited to my car layout.

As the thor has the throttle pot & linkage on the wrong side i need.

So i am thinking of cutting up a 4.6 plenum and mod to suit my needs...

But whats the max diameter the 4.6 sqaure type plenum throttle can be machined too.

Think about 70mm would be ok, currently is at 64mm.

thanks

scott

[kiwicar]

have a look on Eliot's website, I think he modifies them for 70mm throttle plates with a spot of tig weld in them.
Best regards
Mike

[Eliot]

I've taken a GEMs (black square one) out to 72mm. The main issue is a lack of meat underneath where the throttle heater goes. But the *only* gems one I have done seemed to be quite a reasonable casting.

[Seight-V8]

i think for what i need 70mm would be fine.

Gonna chop my plenum up first....

As i need to weld a flange to the end to mount it on to the carbon plenum some how.

Looks like i've got about 5mm per side...to make the diameter bigger.

So i could take it to 70mm internal and still have 2.5mm per side.

Will need to make a new throttle plate.

Hoping i can get it done at work.

cheers

scott

[Eliot]

Here's some sunday afternoon pondering I did a while ago on a scrap plenum..

[kiwicar]

Ah a man who "ponders" with a hacksaw, proper pondering!
Actually very interesting, the top of the trumpets are much closer to the underside of the plenum top than I thought they would be. I bet that distance has a big influance on the shape of the power curve you get with the standard injection. Also I suspect that trumpets that curve back on themselves at the top, rather than just ending at the horizontal with a sharp edge would flow alot more than standard ones.
Best regards
Mike

[Eliot]

Ah a man who "ponders" with a hacksaw, proper pondering!
Actually very interesting, the top of the trumpets are much closer to the underside of the plenum top than I thought they would be. I bet that distance has a big influance on the shape of the power curve you get with the standard injection. Also I suspect that trumpets that curve back on themselves at the top, rather than just ending at the horizontal with a sharp edge would flow alot more than standard ones.
Best regards
Mike

There was a rule of thumb (which i cant remember) that says you need a certain ratio of the diameter of the tube for clearance at the top.
On my mates one I done, we reduced the height of the tubes by 20mm as a reasonable compromise.

Edit - the rule of thumb is 1.3 times diameter - but that means lopping 53mm of the tubes, so I settled for 40mm off them.

[Seight-V8]

eliot,

What are those throttle bodies off in your picture no.3?

And what internal diameter are they???.

Might be useful for me.

cheers

scott

[Eliot]

Its early BMW I think. Around 60mm diameter.
Was inherited, so not sure of origins.