The mk3 1.9L TD power-quest

**GoLfMan** · 25-10-2010, 05:45 PM

Originally Posted by gldgti

you have no beard, so this doesnt make any sense to me.

Beards FTW!

***edit - actually, you might have a beard, i havnt seen you since the nationals that time....

Im rocking stubble, close enough

**gldgti** · 26-10-2010, 06:08 PM

I'm finally getting around to my new manifold design....

should look nice curved over the valve cover... It will clear the factory oil separator on the right and there ought to be plenty enough room to get the oil filler cap off and fill using my normal slanted funnell.

its a bit of fun anyway.

Best part is I can use my geometry to make a dxf with all the parts on it, and get them lasercut. Then I just have to weld them all together

**Gigitt** · 26-10-2010, 06:43 PM

That's looking good... I have been watching you build thread for a while.

Can I ask why the double plenum?

**gldgti** · 26-10-2010, 08:05 PM

Basically.... if I'm to be bothered to make a manifold, it might as well be a double plenum one

. I also figure down the track, when I have to rebuild this engine (its only on 256,000km at he moment, but I do a lot of km and I plan to keep the car for a long while) - with a fresh bottom end and some porting there's no reason for me not to push past 30psi. Once you get up in this region, its more important to have good flow distribution between the cylinders - makes it less likely to burn pistons 1 and 4, or bend conrods 2 and 3.

**Preen59** · 26-10-2010, 09:57 PM

Interesting..

**Greg Roles** · 27-10-2010, 08:50 AM

Geezuz that's serious stuff! Awesome!!

Any reason for the smaller slot between the initial round plenum and the box?? Seems to be the point of restriction in an awesome design!

Oh and please put bellmouths on top of those individual runners!

**gldgti** · 27-10-2010, 05:55 PM

you got it Greg, those will be bellmouths, but i couldnt be bothered doing it on the model (which is really just for me to check sizing and get geometry to have the flat sections lasercut).

The slot has a cross sectional area 80% of the area of the inlet pipe (2.5"). This is necessary with the double plenum in order for it work properly (the slot area should be equal to or a little less than the area of the inlet) so that all of the flow doesnt end up at the cylinder furthest away from the inlet pipe (due to the momentum of the gas). When the slot area is smaller, the primary plenum "pressurises" compared to the secondary, so that flow into the secondary is more balanced.

Imagine a vertical cylinder, with some holes drilled down its length, and the bottom end capped. If you pour water into the cylinder at the same rate at which it can exit (as the water is incompressible) then the holes at hte bottom of the cylinder will flow more water than the onces at the top. Now imagine instead that you pressurise the cylinder by trying to add more water than will flow out of the holes - the jets of water at the top will be almost as powerful as those at the bottom.

It should still flow far better than what I have now - the smallest part of the stock inlet manifold is equal to about a 1/3/4" (1550mm^2)circle, whereas the slot area is more like equal to a 2.25" (2565mm^2).

**Greg Roles** · 27-10-2010, 08:20 PM

I bow to the plenum master....carry on!

**gldgti** · 13-01-2011, 08:50 PM

A little update...

Been real busy at work and in wedding preps during the past little while so the manifold project hasnt moved much - however - this evening I decided to try a little tweaking and turned the fuelling up a little more. I fully expected a bit more smoke for not much gain but a funny thing has happenned...

Before the tweak, taking off in traffic, being off boost, I could soot out the back pretty badly, up hill or similarly because i would have to give it quite a lot of pedal to get moving at low revs. But - with the increased fuelling, it seems to be helping the spool up quite a lot - and as such, I can take off more easily and with less soot! Big bonus for me really, because smoking in traffic is the whole reason I hadnt turned the fuel up since refitting the big merc turbo. The further bonus is that the car is much faster through the rev range. This makes 2 fuelling increases after I had the car dyno'd last, and given the feel of the thing, I reckon quite a lot more power.

Happy days