Cammed straight LPG setup

[XFChris 126]

I bought a car early this year with a rebuilt EFI crossflow, running a Dynotec stage 2 cam (CM251) 214/214 @0.050 , 112 LSA,  2000-4800rpm. It's got a D head that has apparently been worked to suit LPG and the cam. The mixer is a Impco 200, convertor a LG B2  from memory.

Since buying the car, I've put in a electronic dizzy that was recurved to suit the car, swapped out the stock exhaust for a 2.25" freeflowing system plus pacemakers.

In the new year, ill hopefully get a 2nd lpg tank put in for extra range, convert the car from auto to manual, and do a proper CAI, using a shielded pod or a factory EFI airbox if I can make it fit. Then get the LPG system tuned.

Can anyone who is well clued up about LPG tell me if the Impco 200 mixer is up to the task of running my car well, or should I be looking at something else to get better efficiency? As it is now, it drives well under part load, but seems a bit underwhelming at WOT.

[gerg 10,871]

200 is way too small for your needs. That size would be suited to a dead stock 250 at best, but ideally a light commercial under 3 litres. I'd be looking upwards of a 300 to get any kind of performance out of your setup. If you can stretch to a GRA mixer to use with the EFI manifold, that would be the easiest solution, not necessarily the best though. The EFI runners would choke the engine at higher RPMs. Remember gas takes up 20% more volume in the inlet compared to air alone. Otherwise a 4-barrel carby manifold with a 425 would be more than adequate.

[XFChris 126]

200 is way too small for your needs. That size would be suited to a dead stock 250 at best, but ideally a light commercial under 3 litres. I'd be looking upwards of a 300 to get any kind of performance out of your setup. If you can stretch to a GRA mixer to use with the EFI manifold, that would be the easiest solution, not necessarily the best though. The EFI runners would choke the engine at higher RPMs. Remember gas takes up 20% more volume in the inlet compared to air alone. Otherwise a 4-barrel carby manifold with a 425 would be more than adequate.

 

 

I have heard of, and seen Impco 300A mixers used on crossies, it looks like they are made for a dual fuel setup. with some sort of push/pull operated diaphram. 

 

I've heard of someone getting good gains with a impco 425, who ran the same cam as me, but I wonder if it will use much more gas while driving sedately?

 

I may also turbo the car in future.

[deankxf 20,278]

425 would be My choice, on the efi manifold should be good , 225 would be an improvement over the 200, they shouldnt use more gas if tuned right.

My XG XR6 has a impco 200 on it.. goes well, but i bet its restricted.. i have an impco 425 to fit one day.. and a 225 .. but it works(so don't touch it?)

[gerg 10,871]

I havent seen a 425 sideways mounted on a throttle body, or even in an inline setup with adaptors, etc. might have bonnet clearance issues being such a chunky mixer.

[deankxf 20,278]

hard to see in that pic, but Mark's XH had a 425 on with a hat on it with side entry(mixer mounted sideways )
they would be good on a 4 barrel manifold also, probably easier to set up

 

[gerg 10,871]

Spose when there's a will there's a way

[adrianphu123 73]

425 is made to be mounted to a Holley 4 barrel baseplate, but you'll need a 4 barrel manifold to go with it. A 200 is easily mounted to a EFI manifold, since the inlet and outlet are at 90 degrees. WIth a 225, the inlets and outlets are inline, so unless you can fit an elbow between the mixer and shock tower, you'll run into packaging issues.

 

I'd say fit the manual gearbox first, then think about diff gears. Check whats in it now, then aim for a 3.23 or 3.27 diff.

[deankxf 20,278]

gas research on efi manifold..


impco 225 with hot air intake...(could run a longer tube and mount air filter in front of the radiator or other side of engine like the turbo setup)



impco 225 (with turbo) on efi manifold

 

impco 425(with hat and turbo on 4 barrel manifold)

 

[gerg 10,871]

I had a Nolff's NCA 300 on my Cortina which was basically an Impco 300 anyway and it was a great carby. It was mounted on a Redline 2-barrel manifold which in retrospect I think was the main limitation of the setup.

[XFChris 126]

Looks like I'll eventually have to chase a impco 425 setup.

 

A 225 probably wouldn't have much gain over a 200, though I'd give it a go if i found one dirt cheap.

 

 

 

425 is made to be mounted to a Holley 4 barrel baseplate, but you'll need a 4 barrel manifold to go with it. A 200 is easily mounted to a EFI manifold, since the inlet and outlet are at 90 degrees. WIth a 225, the inlets and outlets are inline, so unless you can fit an elbow between the mixer and shock tower, you'll run into packaging issues.

 

I'd say fit the manual gearbox first, then think about diff gears. Check whats in it now, then aim for a 3.23 or 3.27 diff.

 

I dare say it has a 2.77 diff in it now, does a crack above 70 in 1st, and sits at around 2200 at 100kmh in 3rd.  I know the autos are a power robber of sorts, but with the info given in this thread, a mixer change could help greatly.