running a turbo on LPG
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tallmat
New member
Give the guy a break - he may have been asking with genuine intent, thinking that the higher octane rating would boost performance.
The ever wise Stuart has, as usual, made the most sensible comments.
To quote from a research website:
"Another loss off volumetric efficiency and power is related to alternative fuel conversion hardware itself. Most engines converted to burn LPG or CNG suffer an additional 10-20 % power loss due to obstruction of air flow"
(http://www.naftc.wvu.edu/technical/indepth/LPG/LPG.html)
Incidentally Tankman you're showing as a non member too!
(A quick e-mail to club office will recitfy).
regards
The ever wise Stuart has, as usual, made the most sensible comments.
To quote from a research website:
"Another loss off volumetric efficiency and power is related to alternative fuel conversion hardware itself. Most engines converted to burn LPG or CNG suffer an additional 10-20 % power loss due to obstruction of air flow"
(http://www.naftc.wvu.edu/technical/indepth/LPG/LPG.html)
Incidentally Tankman you're showing as a non member too!
(A quick e-mail to club office will recitfy).
regards
garyw
Moderator
I'm certainly not going to knock the guy for asking the question, it was recently asked on another roadster forum I visit. His thoughts were the same as in LPG does in fact have a higher octane rating so in principle theres more burn, but I think the physics are a little different.
Maybe a diesel conversion would be a better idea
garyw
Maybe a diesel conversion would be a better idea
garyw
Guest
New member
I thought that the energy density of LPG would be lower than for petrol, but I don't have time to look. I know that you get less power after conversions, but I don't really know why. I guess you need to optimise the basic design for the different fuel.
The diesel option is not quite so daft. After the initial coughing, spluttering and outrage, if you think about it it is not quite so daft. Just to be clear, I do not in any way want to advocate a diesel TT, but...
Porsche adopt a low rev limit for the TT and optimise the turbos to deliver maximum boost from low revs.
The car is set up for maxumim torque, with outright power being secondary. Torque = acceleration, power = top speed.
If you were to lower the rev limit to 5000 (from 6750), then I reckon you could get a 3.6 litre twin turbo diesel with more torque than the current car. Change the ratios to preserve the same top end, and I suspect the performance would not be so different. The bottom end of the turbo is quite strong, although the gearbox may need to be uprated.
However, it would not sound right and would not smell right.
What would be more interesting, would be to convert it to run on aviation fuel (especially if you can get it tax free, like the airlines).
The diesel option is not quite so daft. After the initial coughing, spluttering and outrage, if you think about it it is not quite so daft. Just to be clear, I do not in any way want to advocate a diesel TT, but...
Porsche adopt a low rev limit for the TT and optimise the turbos to deliver maximum boost from low revs.
The car is set up for maxumim torque, with outright power being secondary. Torque = acceleration, power = top speed.
If you were to lower the rev limit to 5000 (from 6750), then I reckon you could get a 3.6 litre twin turbo diesel with more torque than the current car. Change the ratios to preserve the same top end, and I suspect the performance would not be so different. The bottom end of the turbo is quite strong, although the gearbox may need to be uprated.
However, it would not sound right and would not smell right.
What would be more interesting, would be to convert it to run on aviation fuel (especially if you can get it tax free, like the airlines).
Guest
New member
We should not be narrow minded.
Whilst a year ago I was dead set against all such contrivances, progress is progress, and anything which is better should not be dismissed just on the grounds of "we've always done it that way".
If you gave me something that would do 300,000 miles before being overhauled, was as quick or quicker than the current car, and got 10% better fuel economy, then I might consider it. The key is the performance. If there is some other solution (or even hybrid) that is goes, stops, corners as well or better, then you can't just reject it out of hand.
However, just to restate the case, I do not think these criteria are yet met, so I do not see a requirement to deviate from the current Optimax diet.
Whilst a year ago I was dead set against all such contrivances, progress is progress, and anything which is better should not be dismissed just on the grounds of "we've always done it that way".
If you gave me something that would do 300,000 miles before being overhauled, was as quick or quicker than the current car, and got 10% better fuel economy, then I might consider it. The key is the performance. If there is some other solution (or even hybrid) that is goes, stops, corners as well or better, then you can't just reject it out of hand.
However, just to restate the case, I do not think these criteria are yet met, so I do not see a requirement to deviate from the current Optimax diet.
vitesse
Active member
If you ever want a great day out,Phil Price's Rally school in mid Wales is well worth the money;the point? all the cars run on LPG including MK2 Escorts(for the actual rally driving training) a Cosworth turbo Escort and a hackRally escort MK3.Phil says they all suffer a reduced power output and the turbo car needed a special gas regulator setup.He said then that it costs £1200approx with benefits ;lower emmissions,cleaner engine,less oil changes(all attractive to his form of business) and of course massive cost savings.
But on a Porsche?
But on a Porsche?
tallmat
New member
Stuart's comments on diesel may yet come to bear....
Until the recently launched Gti, the fastest Golf was the 150 turbo diesel.
Same for BMW 330 (the d compared to the i).
I recently took the family car, Audi A8, for a service and (no doubt with sales pitch in mind) they lent me their demonstrator diesel A8. Compred to my V8 4.2 it has staggering torque and towering poke all round.
Just don't have the caravan to maximise that tow-car potential.....
It's not long before there's a Cayenne diesel. In 10 years time will we care if the 911 has spark plugs or not?
Well, I will, but it's food for thought.
Until the recently launched Gti, the fastest Golf was the 150 turbo diesel.
Same for BMW 330 (the d compared to the i).
I recently took the family car, Audi A8, for a service and (no doubt with sales pitch in mind) they lent me their demonstrator diesel A8. Compred to my V8 4.2 it has staggering torque and towering poke all round.
Just don't have the caravan to maximise that tow-car potential.....
It's not long before there's a Cayenne diesel. In 10 years time will we care if the 911 has spark plugs or not?
Well, I will, but it's food for thought.
Guest
New member
For the normally aspirated cars, and in particular the GT3, where a free revving engine with power at the top end is a key part of the cars character, the diesel option is not really applicable.
But because Porsche use turbos that deliver high levels of boost at low revs and maximum torque low down, the characteristics are not so clearly different. This was their approach to the turbo racing cars as well.
I would rather the TT revved higher. Maybe once its all out of warranty I'll fit some titanium con-rods and raise the rev limit. 8000 rpm, foot on the floor with 1 bar boost, all that induction roar and a bit more noise from the exhaust would be fantastic. Then the diesel comparison would be less appropriate.
I'm just waiting for the oil to start running out, so I can start up a sugar plantation and produce methanol. I'd rather run the car on that and I can be become rich (plus may bottle some and sell it for drinking, for a bit of extra cash on the side).
But because Porsche use turbos that deliver high levels of boost at low revs and maximum torque low down, the characteristics are not so clearly different. This was their approach to the turbo racing cars as well.
I would rather the TT revved higher. Maybe once its all out of warranty I'll fit some titanium con-rods and raise the rev limit. 8000 rpm, foot on the floor with 1 bar boost, all that induction roar and a bit more noise from the exhaust would be fantastic. Then the diesel comparison would be less appropriate.
I'm just waiting for the oil to start running out, so I can start up a sugar plantation and produce methanol. I'd rather run the car on that and I can be become rich (plus may bottle some and sell it for drinking, for a bit of extra cash on the side).
Guest
New member
tankman the whole point of asking this question is to see if lpg does genuinely give extra power you need to chill out and maybe try and help
i use only super unleaded/optimax couldnt careless if my turbo gave me 6 to the gallon i still wouldnt sell it. Optimax has an octane rating of around 97 if the lpg has a higher octane rating then maybe it is better for decreasing detonation and increasing power, will never know if you dont ask!
i use only super unleaded/optimax couldnt careless if my turbo gave me 6 to the gallon i still wouldnt sell it. Optimax has an octane rating of around 97 if the lpg has a higher octane rating then maybe it is better for decreasing detonation and increasing power, will never know if you dont ask!
Diver944
Active member
Shortly after I bought my S2 I started commuting 20k miles a year so I did look at this very conversion. The S2 averages 30mpg but I thought LPG fuel at half the price would be nice (and therefore equivalent to 60mpg). A local company has a good reputation with converting Land Rover/ Range Rover. However the problems would be:
1. Where to put the tank? The spare wheel well was not large enough to be worthwhile
2. They did quote a 10% power drop
3. The age of the car would not qualify for government subsidy
The final nail on the coffin was the sucking of breath through his teeth and the shaking of head which was immediately followed by the 'Porsche premium' pound signs in his eyes. I walked away.
1. Where to put the tank? The spare wheel well was not large enough to be worthwhile
2. They did quote a 10% power drop
3. The age of the car would not qualify for government subsidy
The final nail on the coffin was the sucking of breath through his teeth and the shaking of head which was immediately followed by the 'Porsche premium' pound signs in his eyes. I walked away.
Guest
New member
Funnily enough, I have the new Mark V Golf GT TDI as a daily driver.
I used to be a complete diesel cynic until recently but now find myself a convert []
The new golf has plenty of torque, 45 mpg and handles like a dream. It is also cheap as chips.
Now, when i look at real performance diesels e.g. BMW 535D sport, i find myself wondering why I would choose a petrol model in the future []
I await some abuse!
I used to be a complete diesel cynic until recently but now find myself a convert [
]The new golf has plenty of torque, 45 mpg and handles like a dream. It is also cheap as chips.
Now, when i look at real performance diesels e.g. BMW 535D sport, i find myself wondering why I would choose a petrol model in the future [
] I await some abuse!
Michael Downing
New member
Last time I changed the daily driver I looked at the 330Cd and the 330Ci. On paper there was no question - the d please.
Until I drove it, that is; it was singularly unrewarding. Perhaps I am a petrolhead through and through, but the gearchange was more difficult to time and the response seemed flatter. (note: seemed).
If I had been after an auto then the diesel would have been a no-brainer. But in a manual coupe the diesel took all the feedback and satisfaction out. We came back to the dealership, got in a Ci, and within a few minutes my mind was made up.
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