Advice on LPG Impco setup

[hogster]

I've finally been given the thumbs up from Motor Vehicle Registry on my build, "in principle".

As far as the Impco setup is concerned, I want to run a dual quad inlet manifold and two Impco 425's, for my warmed up 302 windsor.

Is any one else running something close.

I need help on the throttle body sizes (base plates) I understand holley base plates required, but is a particular part better than others???

Photos of setups or instructions would be great.

Regards to all from the North.

Thanks, Hogster.

[Aussie Mike]

I don't think it matters too much what size baseplate you use. The CA425 operates on vacume much like a CD stromberg. It has a diaphram that pulls a slide up allowing air to flow through. In the bottom of the slide is a cone shaped knob that meters how much gas is let through. A screw in the side of unit moves a plate back and forth to restrict the size of the opening and set your overall mixture. There's a seperate idle mixture circuit on the side which lets you set your idle mixture.

I believe there are a couple of different slides with different shaped end cones to give a couple of jetting options much like different needles for the jets in a SU or Stromberg carb.

A CA425 will only flow 425CFM wide open so the base plate probably doesn't matter too much. Smaller butterflys will give you a bit more throttle sensitivity. The mixer bolts directly to any of the Holley square bore base plates. I believe the 465 and 600 both have the same size butterflys under there.

I built one for my F100 years ago and just picked up an old Holley from a swap meet for $25. Take a vernier caliper with you to check the sizes of the butterflys if you are looking for a matching pair.

Most of the donor carbs that you will find at swap meets etc are Vac secondary but it's pretty straight forward to make them mechanical. A bit of welding on the linkage and an extra spring for the secondaries.

Cheers

[Kanga]

Hello, I run a single 425 on my F100, however I used a Rochester carb base plate and impco make an adapter plate to bolt the carb to the base plate. the Rochester has mechanical secondaries which are bigger than the primaries. With everything its all in the tunning, I think that at best the 425 is rated at about 300 hp Max

steve

[Gav]

I have a mate who has removed a twin gas carb setup from his 350 Chev in a boat. He may be interested in selling the complete setup to you, get back to me if you are keen.
Gav

[hogster]

Yes Gav, I would be interested in a complete setup.

Thanks for the advice Mike and Steve. I fear that if it wasn't for the people like me being your wastegate from time to time, your brains will probably explode.

Thanks again
Hogster

[Gav]

Hogster,
Sorry for the delay but I had a bit of trouble getting in touch with the owner.
The system is a gas research twin gas carb arangement that has only done around 200hrs work.
One carb is a 400cfm unit and the secondry is 440cfm.
They are made to suit a spread bore manifold. The owner has everything, an 'end fill' 90ltr useable tank, 300mm round and 1500 long. It may not fit as it was made to fit behind the boats rear seat. The tachometric switch for the ignition and gas saftey shut off valves for tank and engine bay. The converter and all linkages and hoses. He also has extra jets and gas detection switchs that where in the bilge. you might want them for in the boot, or probably the bin.

Anyway he wants $1900 for the lot.
Give me a ring on 0407 110 641 if you are still keen.