TheSamba.com :: View topic

Tue Jan 28, 2014 7:23 am

I want to use my IDA weber for a blow through turbo set up. So far from MANY hours of searching, I can only find basic info. This is what I found...

1. Replace brass float with plastic float.
2. Replace needle valve with 3.2 glass ball needle valve.
3. Use turbo emulsion tubes.
4. Use 1:1 rising rate fuel pressure regulator (Like Mallory 4309)
5. And obviously, a hat/plenum on the top of the webers.

I already have the rising rate fuel pressure regulator and matching pump. And I made my intake plenum for the webers. But besides what I already listed, what has to be modified/changed on the weber to handle 10-14psi?

Tue Jan 28, 2014 8:19 pm

Anyone?

Tue Jan 28, 2014 10:08 pm

I'm surprised some of the turbo gurus haven't chimed in for you yet. Im blowing through EMPI 44 HPMX carbs with no changes except a bigger main jet. Granted I generally run only 5-8 PSI of boost, but thus far no problems with stock carbs other than a little lean at higher boost which can be solved by any combination of bigger mains, modulator rings, and turbo emulsion tubes. I do see a small amount of fuel leakage at times but nothing serious. It dries quickly. I know CBs Turbo Mania states otherwise but a search through here and Shoptalk will indicate plenty of folks doing it without problems, at least at lower boosts. If y'r looking to blow through 20 PSI that may be a different story.

Wed Jan 29, 2014 12:56 am

For a simple system with low boost (5-7 PSI) then you will need to adjust jetting and have a referenced fuel pressure regulator.

IMO the voo-doo stuff with seals and choke washers and the stupid looking emulsion tubes does not solve any of the real problems of running higher boost. The carb does not like high temperatures nor does it know how to adjust itself to higher density of intercooled air.

Wed Jan 29, 2014 1:01 am

sen2two wrote: what has to be modified/changed on the weber to handle 10-14psi?

Nothing has to be changed, but you'll need a bottle of aspirin a day to ward off the headaches caused when it doesn't run how you want it to. Fuel injection is the only real answer, but I'm sure that's not what you want to hear. Never is, then you get fuel injection and become one of us because you realize we were right all along.

Wed Jan 29, 2014 2:07 am

I don't like carbs, but have been involved with a few turbo engines running pressurized Solex, Weber and Dellorto carbs. They need the solid (plastic) floats, all vents on the pressure side, often bigger float valves, ( they can be bored out sometimes depending on design)pressure compensated fuel pump, and nothing else really.
I'd go for fuel injection, but carbs work just as good with a turbo as without.

Wed Jan 29, 2014 7:26 am

All my other cars are fuel injection. This car I am keeping old school as much as possible.

I am wondering how much boost can I get away with and not have to change to sealed throttle shafts.

Wed Jan 29, 2014 9:49 am

I ran my Solex turbo with about 15 psi without issues. A friend had around 20 psi on his Dellortos without problem. I think that worn shafts may be problematic, but then again- they cause trouble without turbo too.

Wed Jan 29, 2014 11:36 am

sen2two wrote: All my other cars are fuel injection. This car I am keeping old school as much as possible.

I am wondering how much boost can I get away with and not have to change to sealed throttle shafts.
The fuel that will leak from the throttle shafts is the least of your troubles. If you're already familiar with EFI, why not use the IDAs as throttle bodies and inject it? Still have the old-school look, but you can actually tune it. It's not magic, and carbs will work (sort of), but the path to the correct tune is very time consuming and can be more costly in both time and money than simply starting with EFI, and it will always have compromises involved. To me, not much about blowing through a pair of dual carbs says 'old-school'. An even simpler draw-thru setup is more 'old-school' in my opinion. A pair of IDAs on a big cc NA setup is 'old-school'. An EFI blow-thru setup is....smart :wink: . You can keep the rest of the car 'old-school'.

Otherwise, add a wideband O2 sensor setup to your current recipe along with a solid dose of patience and enjoy the almost endless jet swapping and float level adjusting and engine damaging you've got ahead of you with those IDAs.