Roy928tt

I had always wanted to build a Twin Turbo V8 "supercar", having bought my '79 5 spd a few years ago I felt I had a starting point to work from.

It kept me amused for those years with a constant string of issues and failures, but these only endeared the car to me, as I discovered the depth and quality of the engineering wrapped in the enigmatic styling. Finally as the price of petrol climbed toward $2/ litre last year, I settled on a course of action.

I would convert my 928 to run on LPG (liquified petroleum gas) as I knew that this would provide me with a cheap and high octane fuel supply that has easy boost enrichment when I add the turbos. Australian government policy also added another convincing factor, they paid for the conversion !

I elected to go with a straight gas system based around Impco components, this stuff is stone old but it is simple, reliable and responds to boost perfectly.

So I stripped out all of the petrol fuel system, tank, pumps, filters, hoses&pipes, CIS unit and ultimately the inlet manifold was replaced with one from a 4.7. I simply plugged the injecton holes with little freeze plugs.

I fabricated a manifold to carry the pair of Impco 425 mixers, mounted the fuel locks and gas converters in the space freed up by removing the windsreen washer bottle and inoperative cruise control actuator, plumbed it all up, the gas converters require warm coolant to prevent them freezing, to facilitate this I made a new header tank with returns for these coolant hoses and for coolant hoses for the water cooled turbos. The supply for these was taken from the coolant gallery on the rear of the LH cyl head. While busy fabricating I also made covers for the gas mixers that I could fit air cleaners to but later would accept boost.

I had always wanted to fit the gas tank where the original fuel tank had been, but no one in Australia could make one short enough to fit so i had to fit it behind the rear seats, which also meant that the spare tyre was a delete option.

I had the stock distributor regraphed to a more suitable advance curve for gas and turbos, this will be further refined when the time comes to start aiming for more power!

Imagine my satisfaction, when after so much toil, it came to finally start the car it simply burst into life and sat there idling as if it nothing was more natural.....

Driving the car, it had lost a little power just off idle, but for the rest of the rev range it was just sweet, noticebly smoother than the CIS. I feel that I had made the right decision to fit 2 X 425 mixers to allow plenty of flow, up in the rev range, and when I fill it up at the service station, I just grin like a loony.

Obviously the way I went about this conversion is not for everyone, but LPG brought the answer to me, for my car, it made it nicer to drive, primarily due to the reduced cost of fuel but also the smoothness. Suddenly I found myself making long detours to seek out driving roads on my way from A to B. That lasted till the registration ran out and the lure of TURBOS demanded that my928 make itself comfortable on the hoist again............

But thats another story.....

Cheers Roy

Roy928tt

further photos

Sailmed

Ingenious - what kind of mileage do you get and what size tank?
I can see pulling in for a six pack....

of 20 pounders....

belgiumbarry

hey that's great job Roy

same in Belgium, LPG is much cheaper... I have a SRT10 which i bought with a LPG installation in it ( 2 vaporising units and 10 injectors just near the fuel ones ) ... run great but not max power ( think the evaporators cannot deliver the needed max flow ... ) Meanwhile i mounted a Roe Racing twin screw blower on it and forgot the LPG story... it's not a daily and Blower + LPG would again have cost extra equipment...

just a remark : does it start easy direct on LPG ? our systems use fuel and switch automatic to LPG once at a certain temperature... ???

Fabio421

Cool project. Do you have a dyno yet? How many psi of boost are you running?

Alot of cars in S. America have both gasoline and LP gas systems fitted. This way they can buy which ever is cheaper.

DR

VERY Impressive and ingenious Project, Congrats!!

Tony

Cool.. these kind of projects are great!
The knock rating on LP gas is quite high if i recall?...104 or more?

Jim bailey - 928 International

Looks like if you cut away the battery box and relocate the battery the LP tank could fit ! That would be much cleaner looking and put the weight of the tank and fuel down lower.

Roy928tt

Thanks for the kind remarks guys,

I dont really know what milage it gets, the odometer is broken! the tank size is 53 useable litres, LPG tanks have a 80% fill limiter. I should have gone for a larger tank, I was concerned tht it would inpinge on the rear view mirror, view, but as Norbert discovered that is not as extensive as you might think. As in Belgium LPG is half the price of petrol currently around 50 c /litre.

No in the as built configuration It didn't start well, it would crank over quite a while before starting, this was caused by the distance from the convertor to the mixer, around 1.2 meters!

I expressly did not want to cut the body, so sadly the gas tank had to go behind the seats,I'm sure if one was prepared to move the battery a tank could be fitted under there.

I believe the octane rating of gas is above 100 just what it is I don't know and have never found a definite figure that I would quote with confidence.

Boost and Horsepower ? Patience my son, That is another story......

belgiumbarry

the tank in the SRT10 was in the bed... 230 liters... , useable 170 liters ...

928 Bro

I like LP do to the engine lasting longer because it is a clean burn. But you do lost HP and it burns it faster then gas. I ran it in a 250 ford and I could start it on gas(alway started fine) and there I would switch to LP. COOL Project

turbobrat930

Well Roy, I really like how you have fabbed this up yourself BIG props for you!!! Would love to see you final plans.. IE: how much boost you plan on running? What type of engine management? and get that dodometer working...we need MPG!!!!! GREAT JOB!!!

Lance J

its not old yet but bump...........

Roy928tt

Yes LPG is a clean burning fuel, it produces 20% less CO2 than petrol and in the case of my car I've gone from a very dirty polluter, a non cat. car running on unleaded, to low CO2 emission LPG. It tends to wear engines less because a rich mixture will not wash the cylinder walls nor contaminate the engine oil, on the flip side it is very dry, can be hard on valve guides, and valve seats if they are soft.

Sorry what means "its not old yet but bump" ?

I'll try to kick off the Turbo thread tomorrow.

Cheers Roy

Darklands

I have a 928 S3 on LPG too.

The main problem with LPG is the hotter burning.Like Roy wrote,the valveseats and valves must be hard enough.The most japanese cars have too weak valves.
One litre LPG has 80-85% the energy of gasoline so your engine needs 10-20% more LPG.It has 110 octan,so pinging is unlikely.

My tank is 80l behind the rearseats.I can drive 360 km with one load.5 l is the rest in the tank so maximum fillage is 63 l.
Roy use an old system.My prinssystem is sequentiell and the gas comes right before the intakevalve in the intake.

Here some pictures.