Twin plenum? Worth it or not......

Lewis · Post by **Lewis** » Wed Jan 10, 2007 10:47 pm

Hello all,

After browsing thev8kid's excellent Capri site I've become increasingly drawn to the prospect of fitting a twin plenum to my 3.5EFi....it'd just look great under the bonnet!

Are there actually any gains to be had with a TP or is it down to a combination of things rather than just the extra hole for a bit more air to flow through?

Is there anything else that goes with the TP hood or could I just fit the plenum and appropriate hoses?

I understand they're a bit rare thesedays - what could I expect to pay for one?

Full of questions aren't I

Looks jolly tight in there actually....

I might be converting to MS soon so could ditch the flapper...that'd free it up a bit

Thanks all,
Lewis

Post by **katanaman** » Wed Jan 10, 2007 11:22 pm

depends what power you want if its 300+ bhp then its worth it if less then no its just eye candy IMHO. The kit is now old and worn and parts are hard to come by for them as Tony will testify.

Post by **Coops** » Wed Jan 10, 2007 11:36 pm

yup if it breaks, you get it made now for a price and not buy off the shelf

kokkolanpoika · Post by **kokkolanpoika** » Thu Jan 11, 2007 9:34 am

1x std 65mm Throtle flows about 280-300hp on V8
1x 71mm Throtle flows about +400Hp
2X 65mm(twin plenum) flows i think +550hp.

You need bigger throtle if you want to make over 300hp.
But 2x65mm is quite big for 300hp. But i think it work. Throtle responce is quicker in twin plenum, but low rpm behaviour is quite agressive, because 2x65mm throtles give you 2 time more air than 1x65mm @ low rpm.
(Excample: i dont know how mutch 300hp engine need air, but i estimate some numbers? your engine need i think about 140cfm air if it makes about say 300hp?
And those twin plenum flows i think over 250-300cfm?)
You need good heads if you want to make lot of power, this throtle is not the limiting part.

This 71mm throtle is good for any tuned rover v8.

One question. Why use twin plenum if use std Y- pipe/adaptor?
Not sure, but i think this Y-pipe bore is near of std 65mm?

chodjinn · Post by **chodjinn** » Thu Jan 11, 2007 11:12 am

I saw a few of these on the eBay over xmas, they go for quite a bit of cash though (£300+)

You could always get two standard plenums and do a cut+shut job, bit cheaper, unusual, more spares, but more work!

Lewis · Post by **Lewis** » Thu Jan 11, 2007 11:18 am

Like Mr Ringwood's?

I have the facilities to do that....

chodjinn · Post by **chodjinn** » Thu Jan 11, 2007 11:22 am

aye that's the stuff mate! I'd love to do it with my motor, but impractical what with the twin turbos and intercooler

Lewis · Post by **Lewis** » Thu Jan 11, 2007 1:22 pm

daxtojeiro · Post by **daxtojeiro** » Sat Jan 13, 2007 12:35 am

If you want a twin intake then do the siamese setup, obviously you cant run the Lucas with it but then I guess youve already dumped that, as the AFM will remove any gains a twin plenum setup wll bring anyhow. The reason I recommend the siamese is price, it cost me £25 for the welding, the plenums were freely sent to me, but even if you bought them they are very very cheap on EBay. All you have to do is get them cut and welded where as a twin plenum setup seems to go for silly money,
Phil

JSF55 · Post by **JSF55** » Sat Jan 13, 2007 8:58 am

I take it with this set uo you would need a linkage between both intakes to control the throttle ? how critical would the linkage have to be? would 2 cables to the accelerator pedal work? any pictures? john

Eliot · Post by **Eliot** » Sat Jan 13, 2007 9:01 am

hey phil how did you cut the plenums? -

daxtojeiro · Post by **daxtojeiro** » Sat Jan 13, 2007 8:39 pm

Hi there,
I cut them in a bandsaw at work, simply bolted it down and cut them. I didnt cut them down the middle, as I wanted to keep the flat part that the Idle valve sits on at the rear, rather than half at the front and half at the back.

I bolted the 2 bits to an old trumpet base and got it welded up. Then a lot of fileing, polishing, etc!!

The throttle linkage between the 2 makes absolutely no difference as the plenum is shared between the 2, I have mine so the original side opens up for about 20% of the way before the next one starts to open. This is done with 2 throttle cables, both attached to the throttle pedal. Simply make one a little slacker than the other, that way you dont loose any drivability at low throttle openings. Ive driven an ACT triple plenum and that was a complete nightmare in town had to slip the clutch all the time, where as this setup is superb! Throttle responce is very much improved too

Phil

Lewis · Post by **Lewis** » Sat Jan 13, 2007 8:54 pm

Awesome stuff! Definitely something I might consider.

Thankyou for the information and pictures!

Wotland · Post by **Wotland** » Mon Jan 15, 2007 9:13 am

Hi There,
May be something more suitable for your application. Triumph Rover Spares (Londsale - Australia) offers an twin 57mm throttle bodies converstion for $775AUD. This kit is based on Jenvey throttle body.

Cheer.

ihatesissycars · Post by **ihatesissycars** » Mon Jan 15, 2007 9:32 am

That is pretty much identical to my ACT twin plenum which uses the same bodies but on a carbon plenum top.