Twin Plenums

[matt-man]

Hi all,

As my car is out being fixed and not with me for a while, all i can do is think of things to change in the future!

Found on the mega squirt pages, that there was a twin plenum for the rover V8...

Does this give noticible difference (if you can find one that is..!)

[Number 7]

They were used on the SD1 racers in the '80's, still sometimes come up for sale, but from what I recall, the twin throttle mechanism is difficult to set up properly. ACT do twin and triple versions in CF. Most people looking for increased flow (including me) go for a 72mm throttle disc conversion. Much cheaper and is certainly good for engines generating 300 bhp. The ultimate of course is individual throttle bodies.

7.

[pwd95]

concurr with that. They go for silly money on ebay sometimes.
They tried them on the SEAC racer too by the looks

http://www.theseacpages.co.uk/album/gallery/images...

[C O Jones]

Chatting with Chris Schirle once at a TVR Club meet, he told me that the SD1 Twin Plenum installations didn't do much below around 7000 revs. They were only put into road cars to allow them to be used to good effect on the racers (Saloon Car championships?).

So if you have an engine that is capable of this sort of revs and you will use it regularly then the Twin Plenum may not be for you.

But they do look good under the bonnet don't they!

Russ

[pacman1]

I wondered about this as a future potential mod and have taken quite a liking to sax player's Stag (check out his recent posts). However, it appears the twin plenum doesn't give much of an increase in performance on its own, but certainly helps the engine to breath better. A performance exhaust will give you a more of an increase in power, although I'm not sure how that would work on a wedge, given the angles it goes through at the rear.

[Waynester]

Wedge exhausts are strangled by the manifolds too, very little space.
Griffs & chimps do better numbers with their better designs.

I have the cf ACT plenum, I must admit the twin and triples look mighty fine!

[pwd95]

Talk of the Devil.....

ebay

[350zwelgje]

Seemed the twin-plenum vitesses for the road (a number to be able to race with this modification) were running very lean and the throttle mechanism as mentioned is prone to wear and not easy to fix). So it is a low number of sd1s produced with limited benefits (other then rarity, but making them special) and other solutions are more easily available, working well with corrected fueling/mapping and could be more cost effective. As always: decisions, decisions....

Rob

[adam quantrill]

Number 7 said:

Most people looking for increased flow (including me) go for a 72mm throttle disc conversion.

Hmm, sounds interesting - with mine the throttle body is separate to the plenum, is it just a question of machining out for a larger disc? Do you also whittle the spindle that the disc sits on a bit to streamline it?

[Wedg1e]

This was my version... shame I lost enthusiasm and sold it



That's the largest hole that will fit between the top and bottom walls of the narrow part of the tract.



Mind you, I still have a few spare plenum tops and I know a Jag breakers...

Edited by Wedg1e on Friday 30th April 00:58

[adam quantrill]

Gotcha - on the 400SX the throttle body has been sawed off already, and is before the supercharger.

I'll take a look at the existing diameter but I suspect it's the same one, so what is your larger one off? A jag?

If I needed to swap them over it should be really quite simple.

[rev-erend]

Waynester said:

Wedge exhausts are strangled by the manifolds too, very little space.
Griffs & chimps do better numbers with their better designs.

I think it's only the 5 litre engines when put into a wedge that have a real restriction. Mind you - the very acute bends on the rear pipes and the linking of pipes 5 and 7 do not help it to be as efficient as it could be.

I think the 73mm plenum and 45mm inlets are all you need on any wedge from 4.0 to 4.5.

[wedgienauld]

.. don,t forget the original twin plenum engine in the SD1 was not just the plenum and intake it was also fitted with Volvo rocker gear. I bought a complete engine from a breakers - and had a look, sure enough... Intended to fit it into my Range Rover - but ended up selling it to a guy who said he was going to fit it into a Triumph Stag ...

Edited by wedgienauld on Friday 30th April 09:07

[Meatball]

Ive got one on my Chim it was/is a bugger to get running right, i had to have most of the throttle linkage re made. The trumpet base is only 42mm too so if your running larger ports on your inlet manifold more works needed.