siamese plenum

[Markh]

Anyone here tried fitting a plenum set up like this to a chimaera, looks a neat solution I thought


http://images.google.co.uk/imgres?imgurl=http://ww...

[450Nick]

From what I've heard it's not as easy as it looks... Someone tried this and actually lost horsepower, turned out to be a problem of air interference in the middle of the chamber where air was rushing from both sides and creating strange vortices and areas of low pressure around the plenum. Not sure of the specifics though. You would also have to think about adding a second air flow meter and induction pipework if running the standard ECU. You're better off going with a bigger bore plenum or a multi-throttle setup such as the ACT triple plenum etc IMHO

[Markh]

Cheers Nick, I thought it seemed too easy, it dose look a neat solution. I already have a large throttle body (aftermarket ECU etc) so it looks like I'm back to 8 singles again

Thanks mark

[trackcar]

Ive heard it said that these style plenums have problems, but i just don't see why. Admitted i havent tested back to back so I don't know for sure, but I just can't work out how they can possibly be worse than a normal single side entry plenum.

[V8 GRF]

Not having any REAL knowledge about this I'm just wondering if the two different airflows clash as they come in and cause some sort of disturbance to the air supply? Just a thought.

[450Nick]

No nor can I really... I'm sure there was a thread on here at some point about them because I remember someone did a test of standard vs siamese vs that SD1 plenum with the twin throttles on the same side (standard throttles). IIRC they came out SD1 twin side throttles on top, standard in second and siamese in third. Do a search, I'm sure it wasn't that long ago!

[neal1980]

Would there not be room inside to seperate them so your effectively get 2 plenums one for each side of the engine. I happen to have 2 but again have never got around to doing this.

I have heard about the airflow clashing situation before.

Neal

[ihatesissycars]

Hey Mark, Phil who built that plenum did it as its a cheap way to get a second throttle body in the intake. Its just two plenums cut n shut together.

Rover did do a similar thing before deciding on on the twin plenum system with both tb's on one side.

Eta it did give a sizable improvement on Phils engine which is a 5.0 griff long engine.

Edited by ihatesissycars on Wednesday 1st October 15:50

[spend]

I knew we discussed this a while ago...

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Posh Fiats do exactly as you say Neal:

but they do have a strange firing order

[350Matt]

They also have a separate plenum for each bank and each throttle so its not the same.

My first job was at TWR engines who developed the twin plenum for rover, I was told that they tried the throttle on either side / siamese set-up and lost power over the std throttle.
They didn't go too deeply into it but moved onto the side by side set-up which was eventually homologated.

Potentially you might be able to make it work by adding some sort of internal turning vane or splitter.

Although to be honest the std inlet manifold is rubbish, you're better off throwing the entire centre vee in the bin and fitting / making something else if you already prepared to go this far.

Matt

[GreenV8S]

350Matt said:

Although to be honest the std inlet manifold is rubbish, you're better off throwing the entire centre vee in the bin and fitting / making something else if you already prepared to go this far.