Weber 40IDF Carb Mods

Racer Chris · Post by **Racer Chris** » Wed Dec 08, 2004 8:00 pm

What do you think? Can we cram enough air through here to support 180hp at 8K rpm?
I can open up the primary vents a little more still.

There's not much left of the original secondary venturi.

OriginalCustoms · Post by **OriginalCustoms** » Wed Dec 08, 2004 8:25 pm

Just a little grinder happy.

Looks massive!

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Dec 08, 2004 8:25 pm

I just hope that little piece of the secondary vent don't snap off and find its way in the cylinder...

We'll test it with Dells and P11s as well on the dyno... I'd say the dells will make more power..

Post by **sparkmaster1** » Wed Dec 08, 2004 8:35 pm

I'd recommned the CB Update kit. It gets rid of that Secondary Venturi. I could send you pics of a some on 44's if you'd like. Tim

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Dec 08, 2004 9:10 pm

Not allowed in F production... The carbs must retain the stock method of fuel delivery.

This class is VERY specific and at the runoffs they'll tear you down if you hit the podium...

Thats where Chris will be in 2005 after he gets MassIVe power...

Everything has to be flawless with these engines and built definitively to the rule book or your really racing for nothing.. The labor that goes into one of these is insane..

There is one on the dyno now thats taken us almost two weeks just to assemble... It actually races against Chris and thats going to be very interesting- Very!

Racer Chris · Post by **Racer Chris** » Wed Dec 08, 2004 10:33 pm

That's a long 4-40 set screw holding the vent in place. I completely eliminated the outer support.
I haven't done it yet, but I am going to use a tiny piece of brass tubing between the body
and the vent (epoxied into the vent side) to help seal the fuel passage.
It should also add a little support to help keep the venturi in place.

I expect the Solexes will make a little more because of the additional diameter above the primary,
but I'm doing everything I can to close the gap.
I bet it's down to less than 2hp at peak, and negligible below that.

I am also modifying PMO Weber intake manifolds to be the exact same length as
the Solex manifolds, which may mean longer V-stacks will help.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Wed Dec 08, 2004 10:45 pm

We'll test all sorts of stacks. I just sent to the UK for 4 more lengths of 40mm stacks for testing..

In my previous tests Dells have made more power than even the P11s.. Maybe its just because I am so much better at tuning them than anything else.

The dyno will tell us.. We may have to rebuild it after the dyno session though

Racer Chris · Post by **Racer Chris** » Wed Dec 08, 2004 10:55 pm

Actually, peak won't mean squat to me on the track anyway. I'm looking for pull out of the corners.
The entire system being designed around one race track: Mid-Ohio.

As long as everything stays inside while on the dyno a rebuild will be a piece of cake.

Racer Chris · Post by **Racer Chris** » Thu Dec 09, 2004 6:55 am

Here's a comparison between the stock secondary and my modified units.

________UNMODIFIED ___vs. ___WHAT I HAVE USED BEFORE (unfinished) ___vs. ___MY LATEST INSPIRATION

Racer Chris · Post by **Racer Chris** » Thu Dec 09, 2004 6:14 pm

Here's a pic of a modified manifold next to one as received, and a top view of the modified one.
I will have to re-flatten the carb mating surface to be certain of no leaks.
I made a fixture to do this mod accurately and repeatably.

turboteener · Post by **turboteener** » Thu Dec 09, 2004 10:33 pm

Chris
You would have been better off leaving the wing on. It will have less drag than the little round screw.

Cd of round tube: .60
Cd of streamlined tube: .06

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu Dec 09, 2004 10:36 pm

It does have a pretty nice airfoil shape, it may have sped the air up off its trailing edge. I never thought of that one.. Good point Brett..

Racer Chris · Post by **Racer Chris** » Fri Dec 10, 2004 4:56 am

turboteener wrote: Cd of round tube: .60
Cd of streamlined tube: .06

I was going to check with my dad, who has a PhD in aeronautics before I finalized this,
but I figured that with the smaller frontal area (about 25%) I would be better off with the screw,
and I can go even smaller in dia safely I think.

Do you have an accurate estimate of the Mach numbers found in there at high engine rpm?

If I thought I could airfoil the screw and index it properly I would.

There are some other advantages to leaving the wing in place, but contouring it is a lot of work.

Maybe I can come up with a thin sheath for the screw using brass tubing that is airfoil shaped.
I'll have to check at the hobby shop.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Fri Dec 10, 2004 7:45 am

Chris,
I just got off the dyno.......

Good news for next year !!!!!!!!

You'll figure out what I'm talking about.........

Racer Chris · Post by **Racer Chris** » Fri Dec 10, 2004 8:12 am

It took me about 2 seconds Jake!

BTW, I'm shipping some more parts to you today: oil pump, oil filter & fittings, Mallory, pressure relief valve, case hardware, cam bearings, etc.