Alternative fuel (LPG) L6 Intake Manifold Choices

[DAW]

I'm kicking around the idea of adapting an L6 to run on LPG. For reasons of my own I'll be using LPG and not CNG so the choice of fuel isn't the subject of the thread; only the distribution of LPG to an L6.

 

I'd like to do the conversion itself as simply and cost-effectively as possibe. The engine is a 10:1 2.8L with a beefy bottom-end and an N42 head. It is na at present with a basically stock L28E efi set up from a '76 280Z (some minor enrichenning tweaks to the system; but stock components). If it runs well on LPG with the 10:1 cr, then I may add a stock L28ET turbo system (and run low-pressure turbo) to extract more energy from the LPG fuel.

 

The question I'm posing here is the choice between two very different intake manifold/fuel delivery approaches: 1) the efi manifold with LPG distributed through the injectors; and 2) a single 2-barrel downdraft L6 (JDM) manifold with a progressive secondary carb (Weber 32/36) with the typical LPG carb-adapting set up.

 

The single carb manifold's unique factor has appeal, but the efi manifold is on there already and if it would distribute fuel better, I'd stay with the efi.

 

I'm assuming that a LPG/air mixture won't have the same degree of atomization/variable distribution that a gasoline/air has and one of my questions re the manifold is what effect, if any, the plenum size and runner configurations might have with LPG that may be different than a gasoline engine.

 

The single carb manifold basically has no plenum and is a 1-into-2-into-3 arrangement (cyls 1-3/4-6); while the efi manifold is a large plenum 1-into-6 arrangement with single-plate throttle body.

 

I'm wondering how the manifolds would differ in driveability and performance using LPG. Would the carb manifold give better throttle response? Obviously, with gasoline/air, the better flow of the efi manifold at mid to high rpm would be the better choice; but how would the smaller volume single carb manifold perform with LPG/air (especially when forced induction is applied)? Should I consider a 4-barrel Holley manifold? If I go with the single carb manifold should I run a mechanical secondary 2-barrel or adapt a large single barrel carb or a single throttle plate to the manifold? Maybe the long runner/large single plenum manifold adapted from an LD28 would work better than the L28E intake?

 

The single carb manifold was on a JDM L26, and the 2.8L displacement might be sucking on a straw through it (even with forced induction). The single carb manifold might be better-suited to conversion of a L24 to LPG rather than a 2.8L.

 

This car will be street-driven and efficiency and driveability are more important factors here than is all out performance at the expense of efficiency. BTW, the car is A/T (I don't know if that matters or not re manner of LPG fuel distribution or driveability using LPG).

DAW

[Tony D]

I'd go with Multiport EFI. I have been in LPG powered ZX's in Europe (Megasquirt Driven!) and they performed flawlessly even in cold weather.

 

My experience with vaporiser carbs has not been as good.

 

If you had some really good friends in Japan, you could have them look up the old Taxicab LPG fuel systems for the L-Engines. They were everywhere and like you said, used a downdraft carburettor style setup.

 

But the newer EFI multiport technology is better IMO, as it will allow you to go with a spare 'cheater' tank of gasoline to get you to your next fillup should you need to do it. And if you are REMOTELY considering a Turbo, then don't bother with the vaporiser carb setup, multiport FI is the only way to go---all components are available to easily change the turbo system to work with the EFI plenum...whereas the carb setup would be a suck-through nightmare conversion with much wailing nad gnashing of teeth.

 

The ZX I was in overseas could flip a switch and select fuel sources: Gasoline running on the stock ECM, or LPG run by a Megasquirt Piggybacked onto the harness through the same injectors. I took some photos, but who knows where they are now...and likely they are 6000 miles away at this point in time.

 

"I'm on the road to Morocco..."

[DAW]

Tony D, Thank you so much for responding to my post. You just saved me a lot of grief.

 

I do like the idea of the JDM taxi LPG L6 fuel supply/vaporizer set-up, if nothing more than to convert initially to LPG (the engine I'm converting is already 10:1 as-is). [it's my '82 Maxima that I'd be doing this to and maybe they used Maximas for taxis in Japan?] To keep things more simple, I didn't mention it's my Maxima or that it's a LD28 that I converted from diesel to gas by adapting an N42 head, which is where the 10:1 comes from. I just use this car as a rolling test bench for some of my hair-brained (or is it hare-brained?) ideas. It has headers, stock '75 L28E cam and it runs very well on gasoline.

 

For an MPI delivery system I'd like to keep it on a tight budget, but I guess I can buy Megasquirt. Any idea if I could modify/recalibrate one of my spare L28 ECU's for LPG so that I could mount that LPG ECU next to the gas one and just swap the large main efi connector from one ECU to the other when using either gas or LPG?

 

On the dual fuel (LPG or gasoline) set-up, where or how are the two fuels chosen and fed to the fuel rail? A manual valve? Solenoid-valves? How would LPG pressure regulation be done?

 

Thanks again Tony.

DAW