73mm Plenum

Wotland · Post by **Wotland** » Mon Feb 02, 2009 10:08 am

After to have developped 71mm plenum I just finished my first 73mm plenum . Early plenum waren made on milling machine but I developped an special tool to hold correctly the plenum and made the conversion on an lathe.
After boring the plenum need to be sleeved.
By comparaison an standard 65mm plenum and 73mm plenum

ArneV8 · Post by **ArneV8** » Mon Feb 02, 2009 2:18 pm

Hmm, nice work!

When can you do mine?

Eliot · Post by **Eliot** » Mon Feb 02, 2009 5:15 pm

ArneV8 wrote:Hmm, nice work!

When can you do mine?

I will have some available soon.
The problem is that the castings are very poor and once you get out to the 71mm+ range, the wall underneath the throttle gets very thin or even breaks through. Sleeving is a solution, but too much effort for me personally.

You can see that this one has slightly broken through:
http://www.mez.co.uk/dcam/DSCF2567.JPG

Wotland · Post by **Wotland** » Mon Feb 02, 2009 6:10 pm

The 73mm conversion is made in 3 steps :
1) plenum bored
2) aluminium liner installed
3) plenum bored to final size

Sleeving is the only solution I found for 73mm conversion simply because during first step I break though the plenum heater and idle port every time.

Arne I am happy to see I am not the only belgian member

Post by **katanaman** » Mon Feb 02, 2009 7:19 pm

nice work, would it not be possible to tig it up first and then machine it down? Seems like a lot of extra work having to sleeve it.

Eliot · Post by **Eliot** » Mon Feb 02, 2009 8:32 pm

katanaman wrote:nice work, would it not be possible to tig it up first and then machine it down? Seems like a lot of extra work having to sleeve it.

I did try welding one up and I wont show you the results - although that was one that had broke through already. I might have a go at pre-welding one whilst its still thick.
The other area to keep an eye on is the idle/co2 grub screw - at 72mm it just starts to break through also.

mooose · Post by **mooose** » Sat Feb 14, 2009 11:24 pm

Has anyone tried welding a larger throttle body on to a normal plenum top ?
Can it be done ?

ian.stewart · Post by **ian.stewart** » Sat Feb 14, 2009 11:35 pm

I did a similar thing with a TB from a 3.0 Opel Monza/senator, that one unbolts from the plenum and I think its 70 or 72mm, then I bored it out, and hand cut a new buterfly, which was a real PIA to fit, It was on my original v8 in my hot rod, but the home made plenum was too tall for the cortina, hence the TBs the Opal TB is now fitted toa Audi turbo powered skoda.

Eliot · Post by **Eliot** » Sun Feb 15, 2009 8:53 am

mooose wrote:Has anyone tried welding a larger throttle body on to a normal plenum top ?
Can it be done ?

Take a look through my manifold archive for some examples:
http://www.mez.co.uk/ms12.html

To put this all into context, my mate pulled 280 bhp on the std 65mm plenum on a 5L engine - so dont get too hung up on thottle size. We did replace it with a 72mm one later, but haven't dyno'd it since.

Wotland · Post by **Wotland** » Sun Feb 15, 2009 12:17 pm

If you are not happy with an single 72mm throttle plenum.... you can always try the Twin 72mm throttle plenum

Picture from an SD1 forum.

Eliot · Post by **Eliot** » Sun Feb 15, 2009 3:59 pm

Blimey - even the dual 65's are plenty - especially if you are drawing that through the original air flow meter.

Post by **Coops** » Sun Feb 15, 2009 9:34 pm

OOOOOOOOOOOOO i like that,
any mods needed to the twin plen casting?

Eliot · Post by **Eliot** » Sun Feb 15, 2009 10:15 pm

thev8kid wrote:OOOOOOOOOOOOO i like that,
any mods needed to the twin plen casting?

You're kidding right? - the 65mm plates are plenty unless you are packing well over 500 bhp

kiwicar · Post by **kiwicar** » Mon Feb 16, 2009 9:53 am

If you chopped the top off one twin plenum top and welded another one on top you would have 4 65mm TBs, now that would look very cool

Mike