Enlarging stock intake manifold plenum

[Poopie]

I'm still mocking things up for my avant. I'm stinking about slicing the stock aeb manifold open and tig welding in a strip of aluminum to add volume. Has anyone had before and after experiences with this homebrew mani? Did you throttle response lag noticeably more?

Any one know the stock plenum volume? I'm guessing the target volume is 3.5-3.6L from what I'm reading.

[Crispy222]

You could cut everything after the runners/flange and start from there.

Example:

[Poopie]

did you see a noticeable gain? once my car is running well enough for me to start tweaking things i think i will go that route and add a large throttle body. what did you go with?

[Crispy222]

Throttle body from an AHA v6 manual transmission (B5 Passat or A4)

[Poopie]

you got a nice set up. what alt/bracket set up is that? did you remove the viscous clutch fan?

[M-Hood]

I'm still mocking things up for my avant. I'm stinking about slicing the stock aeb manifold open and tig welding in a strip of aluminum to add volume. Has anyone had before and after experiences with this homebrew mani? Did you throttle response lag noticeably more?

Any one know the stock plenum volume? I'm guessing the target volume is 3.5-3.6L from what I'm reading.

Actually I have seen that done many times including LucasGT and BillyT with his transverse 1.8t.

You can see it on Billy's site for his GTI
http://www.18turbo.com/billytmk4gti.html


Basically what ABD does for their manifold.

[Poopie]

thanks. looks like he added about an inch and a half strip. I'll give that a try

[Crispy222]

you got a nice set up. what alt/bracket set up is that? did you remove the viscous clutch fan?

That isn't mine. Its a 06A block w/ AEB head. Its just an example of what can be made. I still run the stock AEB manifold on my 058 block/ AEB head. I ported the opening and made an adaptor plate for a v6 tb.

did you see a noticeable gain? once my car is running well enough for me to start tweaking things i think i will go that route and add a large throttle body. what did you go with?

The whole idea of adding volume to the intake manifold is to create a larger reservoir for charged/compressed air (potential energy). Thus it is waiting behind the valves to enter the cylinder rather than as a flow that has to enter the intake through the TB, distribute in the plenum, down the runner, and into the cylinder (all kinectic). This is the scenario prior to the turbocharger producing position pressure. Or more air flow through the compressor than what you flow through the engine.

You may know this already.

[Crispy222]

You can see it on Billy's site for his GTI
http://www.18turbo.com/billytmk4gti.html

WOW, how old is that page?

[M-Hood]

WOW, how old is that page?

Very old. lol

[Dan[FN]6262]

You want the plenum to be 100% the displacement of the engine, no more than 150%. Intake manifold design for a boosted engine is different than a Naturally Aspirated engine.

[Wet0willy01]

You could cut everything after the runners/flange and start from there.

Example:

Where is your alternator pulley?

[Wet0willy01]

[SleeperAvant]

Where is your alternator pulley?

You tell us

[M-Hood]

You want the plenum to be 100% the displacement of the engine, no more than 150%. Intake manifold design for a boosted engine is different than a Naturally Aspirated engine.

Increased plenum for increased displacement. This gave me a gain of around 70awhp.

[ZimbutheMonkey]

You want the plenum to be 100% the displacement of the engine, no more than 150%. Intake manifold design for a boosted engine is different than a Naturally Aspirated engine.

So does anyone know offhand what the size of the stock manifold is? Welding a strip in would be fairly cheap, however I don't know how much displacement it would add and if it would be worth it.


EDIT: You know, for the time it would take and the minimal cost, I think I may take the plunge on this one. What I like about it is that you're not enlarging the plenum outward. In other words, you're adding volume in line with the plane that the air is already running through to get to the runners. Intuitively, it seems that would help maintain intake velocity. Anyone with an engineering background (or otherwise) care to weigh in on that thought?