Weber downdraft results
Turbo Mini Forums

I am running a blow-through Weber downdraft. I went with this because I was avoiding becoming an SU needle surgeon.

It has been an interesting road. I now own an extensive collection of carburetors and jets.

Here's where I wound up, and now I'm convinced it is working about as well as it can:

Weber 38 DGES with the gear linkage removed so it runs on only one venturi. Previously had 32/36 DGV, but went away from it due to large hesitation when the second venturi opened up.
The simultaneous-opening 38 was too much when both venturies opened. Not enough velocity on this engine.

I have the accelerator pump jet set up to only squirt into the active venturi. The Pierce manifold is not my favorite. It seems to swallow the pump shot as internal wall wetting and go lean, and then the engine goes rich as the shot evaporates into the air stream.

Jetting is as follows: 40 idle jet, 110 main jet, air bleed plugged off. This gives 12.2:1 AFR at 8psi boost, and reasonable cruise mixtures.

1275 with Back Door Turbo

One more thing:
I have a wideband O2 setup on the car, which lets me see when the mixture is not right. It seems off fairly often. A Megasquirt project is next.

1275 with Back Door Turbo

Any pics of the setup?
And did you have trouble getting that lot down the back of the engine?
Also what turbo is it?

Warning:Stig in Training

I have some pics but can't post right now. Will be offline about three weeks coming up.
No trouble putting the downdraft setup on the back of the engine - it's a pretty common setup on NA cars, and mine has no turbo in the engine compartment.
The turbo is a Garrett GT15. My turbo is mounted in the rear near the rear bumper, so I have more room at the back of the engine.
If you search for rear turbo you'll find some pics.

1275 with Back Door Turbo