Vapor injection on older motor

[Dan350]

Friends, can a vapor injection system be fitted to a gen 1 small block chevy for a dedicated propane only motor? I know that the ECUs are normally used as a piggy back to the gasoline ECUs but are there any stand alone units available for a setup such as this? I started thinking about this when i saw that my carbureted intake manifold had bosses that i can drill for injectors. fabrication would be pretty easy. Are there very many advantages over a carbureted setup as far as long term fuel efficiency and reliability? I suspect that the cost would be substantially more than an impco 425 / model E setup but what would something like this set me back? Is it also true that the injectors used in the prinns or BRC or landi renzo are good for about 50hp each? That way i would be good for about 400hp and i could use 1 convertor per bank of cylinders. Any thoughts?

[storm]

There is a company in Western Australia that makes a dedicated ECU to run Prins injectors. Google ProFire Engine Management and you'll find them.
Keihin makes injectors for Prins (and I think BRC as well). There are 6 different injectors based on their flow rates and they are identified by a dot of various colours to signify what injectors are what flow rate. Only the largest injector can flow up to 50 HP.

[kuchen]

I used a Megasquirt MS2extra to drive Keihin Injectors (Prins) in my Citroen 2CV Project car. It is driven daily for half a year now without any issues. I altered the code to use the 2 spare analog inputs to compensate for fuel pressure and temperature, though. If you keep the LPG absolute pressure as constant as possible, eg. by using a 2 stage converter like the OMVL (do not connect to Map) plus installing an in line thermostat, you may be able to use the Ms2 out of the box.

[storm]

Kuchen I'd be interested in what you done with the Megasquirt if you care to share more details.

[kuchen]

in the MS2extra code, there is a function called flex-fuel that is intended to read out a alcohol-content sensor and correct the fuel injection times accordingly.
I rewrote this function completely to read the fuel temperature and pressure using a combined MAP & LPG/CNG pressure and temperature sensor supplied with the AC Stag 300 sequential LPG injection kits.
The fluid dynamics behind all this is called "choked flow of a compressible fluid through an orifice" https://en.wikipedia.org/wiki/Choked_flow

Choked flow of propane vapour through an injector happens when the upstream pressure from the regulator is more than 1.7 times as high as the downstream pressure in the manifold. On an NA engine with manifold abs pressure of 1 bar at WOT, the LPG supply pressure should be more than 1.7 bar abs.

At the end of the fuel calculations, the MS2 code multiplies the fuel injection time with a factor in % that is supplied by the flex fuel function.
With choked flow and all, this factor is (p_ref/p_gas)*sqrt(t_gas/t_ref) with
p_ref: the reference absolute pressure, the supply pressure at normal operating conditions
t_ref: the gas temperature under normal operation conditions in Kelvin
t_gas: the actual measured LPG temp. in Kelvin
p_gas: the actual measured LPG absolute pressure

so for instance when actual conditions equal the normal operation conditions, the correction is 100%, if the pressure rises by 25%, the injection time is shortened by 25%.

[storm]

Excellent info, thanks Kuchen.

[kikkegek]

can you expain some more why you ad to alter the code?

And why and what thermostat did you use?

[kikkegek]

can you expain some more why you ad to alter the code?

And why and what thermostat did you use?

[kuchen]

I altered the code as I am not using a thermostat and the single-stage, air-heated CNG Regulator does not keep the temperature and pressure constant enough. So I just had to implement a pressure compensation as described above.
Furthermore this is a dual-fuel CNG/LPG setup so depending on the fuel used, the function also compensates for the different heat contents.

On Impco setups, I use the inline thermostat sold by altfuel in Chicago.
In this case an auxiliary water circuit consisting of copper tube wound around the exhaust, Mercedes Auxiliary water pump and Aprilla expansion tank heats up the LPG regulator
Vehicle:

Regulators:

Water heater

[kikkegek]

he thanks for the info man.

so if I were to fit it on my chevy small block, the megasquirt would be plug n play with a regeular converter and vapor injectors?

no altered code neccesary

[fpvmustang]

I run ms3 with fuel pressure and temp compensation.
it's standard now no special code needed. they also added a second accel enrichment and warm up for dual fuel vehicles.

[kikkegek]

cool...I got a un-assembled MS3 laying around. are you using the MS3X board tfor sequentiaL INJECTION?

[fpvmustang]

I'm using the main inj drivers. I tried the ms3x with resistors and wasn't getting the response. It worked I should go try it again.
But 4cyl I'm semi sequential never set up cam sensor. had other stuff to play with mostly vgt turbo. 30 psi boost

[kikkegek]

what is a VGT turbo?

and your running 30psi?.... rock n roll man

[fpvmustang]

hit 33 psi boost today on lpg
I don't dare run that much boost on pump gas.
vgt is variable geometry turbo i run a he351ve off a 6.7 cummins.
https://www.youtube.com/watch?v=NXAx6KC0ixA