LPG

[barks944]

So its actually 103 octane and the reason you get less HP in most systems is because it requires a different ignition map to petrol as it has a different burn rate. So you should actually get more power with LPG than petrol when a car is mapped for it. As I soon might have the capability to run multiple fuel/ignition maps this looks like a very tempting option. Add the fact its so cheap and you have a pretty great fuel source for a turbocharged motor. I guess the issue is where to put the tank. Having it in the cabin, which seems almost unavoidable in the 944 seems a bit risky should you have a crash. Maybe a tank in the area of the rear seats would be feasible and reasonably protected from crash damage.

 

[DavidL]

I run LPG on my old rangie.
Your tanks only fill to 80% so where space is an issue it can be a problem.
Availability is also an issue - you always need to be aware of how much fuel you have and how far you are from the nearest gas station.
I still have a 35 litre petrol tank but at a proper 18 mpg I don't tend to use much petrol!

 

[JamesO]

Was tempted by LPG myself at one point but I quite like to be able to use the channel tunnel and they don't allow it. Also with limited mileage its just not worth it.
That and the loss of storage space, unless a terroidal(spelling?) tank will fit in the in the spare wheel well. Would also be concerned that in a rear impact its first in the firing line. Also its a lot of weight in a bad place.

 

[ukmastiff]

Tref came round my house in a 944 with an LPG tank behind the front seats. I belive he is a bit of an engy wizz and was in the process of converting the car himself but I may be wrong on that bit. It went right accross the back seats and 'looked' bigger than some doughnut tanks that I've seen in cars.

Regards Mas

 

[944 man]

The GTS had its tank where the spare wheel well is found on more road-focussed cars, so Porsche seemed to think that it was reasonably safe there...

For 103RON (to burn as efficiently as it is able, even with a special ignition map) youre going to need a higher compression ratio: I think...

 

[sawood12]

I've asked this before about E85, but why? Why go to all the inconvenience to benefit only about 10 - 15% of your driving time? You are only going to get the benefit of the 103 octane on the occasions you're running at full throttle going like a scalded cat. Unless it is for a track car where you're on WOT for alot of the time you're just driving in traffic for 90% of your time with the odd short blast at WOT for a short time till you hit the speed limit (of course!). I've said it before on the thread on E85. In my view for those 10% of occasions your booting the car then NOS is a far more elegant and efficient option, the tank takes up less space in the car than an LPG tank, you're not limited to a handful of petrol stations around the country so long journeys are not turned into a logistical nightmare, and the super cooling effect of the NOS will give you even more benefit (well over E85 at least - you will get some of this effect with LPG, but not as much as the gas is not at as high pressure).

 

[zcacogp]

Yes, I think the theory is that you could do a LOT better with LPG than with petrol, but your engine would cost a lot to convert to do this (higher CR, greater ignition advance - beyond that which most cars can achieve) and would then not be able to run on petrol. You would end up with something that, if it runs out of LPG, couldn't drive and would need to be towed to the nearest LPG-supplier to drive again. For most people, this is too compromised a machine.

BUT, I have toyed with the idea of building something like this, partially for the giggles, partially to see what could be done. The higher octane would lend itself well to forced-induction and you could make something stunning. Scott, yes it would have advantages when giving it some beans, but it would also have much more mid-range torque, and hence be much easier to drive in 'normal' conditions.

The other thing is that an engine properly tuned for LPG would return much better MPG.

Tref is your man for these sort of details. An engineer indeed. I too have seen his semi-built LPG S2, and the tank (in the back seats) is VAST! I don't know how he is getting on with it (it was very much a work in progress when I saw it, over a year ago) but I will be very interested to see the end result.


Oli.

 

[barks944]

Don't forget about the cost benefit. I plan to rebuild my turbo and use it for a long time thus a lot of miles and a big fuel bill. So not only is it a much cheaper fuel, but I can run higher boost pressure and or more ignition advance as well......

What about liquid phase injection? That has the additional benefit of what is very similar to water injection in that the LPG vaporises in the manifold and massively cools the air charge. Sounds nice.