Supercharged V8 fueled by LPG 2

[Carl12]

i am about to build a supercharged 308 and was going to dedicate it to LPG. The super charger will be a blow through setup so the LPG setup will be after it. I am using twin small roots blowers blowers from a toyota MR2. information i have found goes both ways some say supercahrgers can't be used on LPG some say they can. ANY help in this area would be much appreciated

 

[Fabrico]

LPG usually flows into an engine under low pressure. You will have to figure out out how to make it flow correctly regardless of intake boost pressure. Since you are going for much more power than usual, A/F ratio will also be more critical. It might be better to inject liquid instead of gas.

Why not LPG through the blower?

 

[kenre]

I believe the impco 425 gas carbs can be configured for blow through operation. one mod is to run a boost reference line to the convertor. Not sure of the boost pressure they can handle, although with 2 MR2 blowers on 308 cubes, you wont be pushing much pressure.

Ken

 

[franzh]

This is off topic as an engineering question, but basically, the 425 can be configured for blowthrough by compensating the pressure on the vaporizer. Its done all the time. The 425 assembly should be able to handle about 10-15 lbs boost.
A blow through system is not as easy to configure than a pull through, but on a Rootes system, a pull through works well. Also, there is no turbo lag.
Configuring a liquid injection system is a real engineering challenge and way out of bounds for a self built system.
Franz

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[mattsooty]

Why does it need to be a carb? I would advocate the use of an EFI system everytime (I don't get on with them nasty carb things) and Pre Compressor Injection does have a lot of pros when you dont have to worry about emissions regs etc...

I guarantee that an aftermarket controller could be easily configured to allow some rudimentary control of the system and all without the associcated headaches mentioned above. Infact I am quite convinced that it would make the whole job a lot easier & more elegant.

MS

 

[franzh]

No arguement from me on injection. The OP queried blowthrough which implied carburetion.
MAP compensated SEFI would work great, just source the injectors, controller, pressure reducers, program the pcm for the varying fuel densities and temps, calculate the corresponding ignition timing at NA/boost.
It is do-able, just takes some homework and a fresh mindset on different SI combustion principals than liquid fuel applications.
Franz

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[mattsooty]

Franzh, I detect a certain amount of resistance here....Infact I think that you may be making it a little more difficult than it is!

The first thing I would say is that you will have a problem with spark timing whatever system you use, it will never be optimum. Having said that, LPG is pretty knock resistant so you should be safe to play around a bit.

Find yourself an injector & setup that you can install before the compressors and ensure that it is specced for your application. ie LPG at atmospheric conditions. I am sure you can get a fuel system/regulator to deal with that, LPG isnt exactly an exotic fuel...

Obtain an aftermarket ecu/pcm that will operate with an SPI setup (should be millions about) and wire the thing up.

Guess at the spark tables, LPG is pretty safe so dont worry to much at part load, just be conservative at WOT points. To ensure safety fit & monitor a thermocouple in the exhaust manifold.

Try and get a wideband O2 sensor from somewhere to properly map the fuel tables.

Drive and map, drive & tweak until happy - using the above.

Your saving grace will be lack of knock sensitivity of LPG and also the fact that the rich misfire equivalency ratio is higher than gasoline.

As always, any questions then let me know.

MS

 

[patprimmer]

My previous post on this is missing. My sarcastic comment stemming from the lack of info in the OP must have struck a nerve.

I GUESS the 308 is an Australian Holden V8, even though the OP does not indicate that.

So I GUESS the information below might be of interest

Garry Willmington has some experience with suck through LPG conversions on Australian V8s and roots blowers.

As far as I know, he is in Luddenham near Sydney

Regards

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[franzh]

Matt:
No resistance, just trying to put it in perspective. You wouldnt believe how many people have contacted me at my real, bill paying job, asking if they can use gasoline injectors for LPG, run LPG liquid through gasoline fuel lines and rails and so on.

Sourcing an LPG capable injector can be a challenge but there has been some good development there and a greater supply then ever before. Keihn and Siemens are good sources, and suppliers in Italy always seem to be ahead of the rest of us in this field.

Using LPG as a fuel in the injected state requires a different mindset than with gasoline, plugging things in like injector lead-time, pulsewidth, doublehits, lean and rich modes under boost, cold start enrichment, and so on.

In almost all cases, its not a simple plug and play, but with very careful matching of injector flow rates and pressures, an OEM PCM can work well. I like the Ford EEC-5 with the TWEECER, but have used the Motec, Electromotive, and other industrial controllers in the lab.
Franz

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[Carl12]

thanks for all your help so far. yes the 308 is an australian V8. i don't know alot about LPG and the installers over here in New Zealand all say it is to hard to setup. So it looks like the easy way is to use a 425 assembly over the injection. And the hard thing is to find an installer that knows what he is doing. Might source the parts needed myself.

 

[rdd48856]

Here in Europe converting supercharged/turbocharged gasoline engines to LPG is an everyday job(a few weeks ago a BMW M5 8 cylinder with 400HP or an Impreza with 260HP) both on sequential gaseous LPG injection or sequential liquid LPG injection. You just need the gasoline ECU programmed, since the LPG ECU works on a master-slave mode.

 

[cammax]

Well, I have built many custom engines / control systems
for high end performance. I would suggest using a fully tunable DFI controller such as:

http://force-efi.com/dfi.htm

its not the best but it is very user freindly and has enough flexability for your purpose, First find an injector/injectors that will meet your needs.
I would also recommend using liqiud injection after the supercharger to take advantage of the evaporation cooling effect.