plenum design

[SirYun]

Hi Guy,

I'm puzzeling how to get additional induction lenght in the limited amount of space available under the front of a ''classic'' mini bonnet.


in case you where wondering: the intakes are at the front as
the head is a BMW part (K1100 4V..like most all 4v head looks like a scaled down BDA) which is fitted to the original but modified A-series engine .

using four seperate throttle bodies in fron of a injector mount adaptor.

the BMW engineers (who in general tend to know a bit or two about engines) used quite a long intake of about 27 CM, however the conversion kits tend to use short bell mouths.

I have thought up a variant of the design that BMW used with a twist..


but when i had drawn it out it looks oddly similar to the flat plane intake you designed for the racing FIRE engine.. but where the DCOE sits there is a radiused intake and the throttle bodies (and injectors) are on the head.

the butterflies could be moved away from the injectors without much trouble but I am not shure if they designed the port taking into account the flow vectoring during part throttle ( and i'm unlikely ever to find out).

[Guy Croft]

Looks fine that idea, love the sketch, very arty!

For what it's worth, you get better power (for sure, proven over and over on dyno test of GC equipped Vauxhall XE units) from injecting onto the throttle plate. It's obvious that the turbulence helps atomise and mix the fuel.

The effective intake runner length in your setup will be the chord length (ie: the length along the pipe centre axis) from valve head to end of pipe in plenum. Make sure the the pipe ends are radiused where they enter the plenum.

Rather than a rampipe on the plenum, better to run the large pipe (I'd use about 3" dia) from the plenum to a large turbo type remote filter sealed off from the engine bay feed that with another large diameter pipe from a scoop (tapered intake duct) at the front of the vehicle. You could equally as well put a large slab K&N in the plenum itself; this is what Chad Eayton-Williams, founder and former owner of the Monte Hospital did for the twin sidedraft setup on the Lancia Montecarlo at my suggestion and a very good job he did.

GC