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PostPosted: Fri Oct 23, 2015 8:10 am 
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It isn't, not if you do it properly.......

https://www.youtube.com/watch?v=orP1E-OKI9k

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PostPosted: Fri Oct 23, 2015 8:34 am 
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Never noticed a loss of performance. But I have noticed you need more fuel to equal the same.
I'd love to actually get it on the rollers to see the difference between the two.

But I imagine it all depends on the ECU and how they compensate.


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PostPosted: Fri Oct 23, 2015 9:02 am 
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As a one off blown conversion you don't know how much power would have been produced on petrol.

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PostPosted: Fri Oct 23, 2015 9:42 am 
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Hi,

I have a 3.8 MkII Jaguar and put it on the rollers a few years ago, on petrol then on lpg, it lost one bhp on LPG.

Brian


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PostPosted: Fri Oct 23, 2015 10:45 am 
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The point is that there are so many people that come on here who have been sold an inadequate system that isn't calibrated properly who have been told to expect less power when running on LPG. These are the ones who switch to petrol for 'enthusiastic' driving because they don't have a similar level of power available on gas (like the guy on here recently with an XK8 that was set to switch to petrol at anything over 2,500rpm!). Why would you want to use the expensive stuff when you are using the most? I like that fact that I can thrash the goolies out of my Range Rover with the Sport button almost permanently pushed in (or I can now my rebuilt engine has nicely bedded in) knowing that I may be down to 13 mpg but it'll still only cost me £35 to fill the tank.
Sir Henry wrote:
As a one off blown conversion you don't know how much power would have been produced on petrol.
Probably a lot less as it would have to run less boost and ignition advance because of the lower Octane rating of petrol. It won't be the same for all cars admittedly. Most these days use a knock sensor to back the ignition timing off as soon as pre-ignition starts to happen. How much will they advance it if there is no pre-ignition will depend on the individual ECU. But it does mean that you can tune an engine to produce more power on LPG than petrol if you want to. Robert proved what can be achieved here viewtopic.php?f=32&t=8781 and I doubt he was running LPG because it was cheaper......

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Fri Oct 23, 2015 8:37 pm 
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I'm not going to argue... but we canna change the laws of physics... Calorific value and stochiometric ratio (intake charge needs more air..) work slightly against us on the one hand. On the other hand, the ability to easily adjust high load fuelling, auto ignition advance features on some vehicles, knock sensing boost control on some blown vehicles, work in our favour. Individual engine designs respond differently but as a rule of thumb you shouldn't notice a difference in power to drive the vehicle.

Simon

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PostPosted: Sat Oct 24, 2015 8:47 am 
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On a mixer system and a normally exasperated engine you do loose some power. Generally because of the physical restriction of the mixer. I reckon that's where this originates from initially.
As said. A gas injection system. Properly set up should show no difference in bhp output.


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PostPosted: Sat Oct 24, 2015 9:32 am 
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Tubbs wrote:
On a mixer system and a normally exasperated engine you do loose some power. Generally because of the physical restriction of the mixer.
Very true but only once you get to the point where the throttle opening is larger than the diameter of the mixer, at smaller throttle openings, there's no difference. It does show to all those that have been told by an installer that it's normal to get less power (and to get the MIL coming on all the time) that it isn't.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Sun Oct 25, 2015 9:24 am 
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I had one in from "best LPG conversion in birmingham' last week. They told the customer that the mil light being on was normal and 'expected' lol.
Fuel trim bank 1.


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PostPosted: Sun Oct 25, 2015 9:38 am 
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Tubbs wrote:
They told the customer that the mil light being on was normal and 'expected' lol.
Well it is when they fit identical components to everything and can't be arsed or don't know how to calibrate it properly. Normal and expected but only when you have a conversion done by a cowboy outfit.......

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Sun Oct 25, 2015 11:03 am 
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When I commented that their atrocious spelling, punctuation and grammar might spill over into safety and/or fitting I was slapped down. Things seem a bit different now.

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PostPosted: Sun Oct 25, 2015 7:17 pm 
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Sir Henry wrote:
As a one off blown conversion you don't know how much power would have been produced on petrol.

That is true and there's not much point in denying or ignoring it - I have mentioned calorific value and laws of physics. Any difference in power, though, shouldn't be enough to change the driver experience, seat of the pants should feel the same, hardly a difference in acceleration, probably no difference in top speed. This is an LPG only vehicle, so might not be capable of running same compression with same boost if it did have a petrol fuel system - LPG has better anti knock properties (higher octane rating) so engine may have been designed with LPG in mind. Vehicles we convert run standard petrol compression ratio and generally use a few% more LPG than petrol due to the lower calorific value, also reflected (usually to a lesser degree) in oeak power output. Probably won't impress anyone clued up saying otherwise...
Gilbertd wrote:
Tubbs wrote:
They told the customer that the mil light being on was normal and 'expected' lol.
Well it is when they fit identical components to everything and can't be arsed or don't know how to calibrate it properly. Normal and expected but only when you have a conversion done by a cowboy outfit.......
Agreed and seen on a regular basis, some of these outfits don't bother to even fit appropriate size nozzles in injectors.. Sorted loads like that and with other mapping / inappropriate component issues. Only so much that Stag reducer / injectors or Alaska reducer and V30 injectors are capable of. When we see multiplers of 1.6 at idle we know there is going to be a problem with fuel trims at some point.

Simon

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PostPosted: Mon Oct 26, 2015 10:24 am 
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Although yes it does have a lower energy density doesn't it just compensate by having injected more generally?
Hence the drop in MPG vs petrol.

Then valves get a bit hotter due to it being a dry fuel. Not much though.

But to be honest I've never noticed a drop in power. If anything I get to use the full rev's more becasue I'm not worried about using up the fuel as its 40p a litre anyway.

Average mpg on petrol 32
Average on lpg 25.5

That's more than a normal amount. But I drive however I want now. I drive quicker. I use more of the revs. I don't worry about it as its cheap.

Horses for Courses though...


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PostPosted: Mon Oct 26, 2015 12:36 pm 
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The only time I've notice power being down on mine is when the spark plugs just got renewed or a small vac leak from a broken clip on the brake vacuum line I spotted by chance, Fixing that made a hell of a difference on both Petrol and LPG, only cost 15p for a new jubilee clip. Down side MPG has gone down.

Just wish 40p/l lpg was available further outside the Birmingham area.


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PostPosted: Wed Oct 28, 2015 8:58 am 
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Doesn't calorific value depend upon whether you're talking per unit volume or per unit mass (Kcal/litre or Kcal/Kg) ?

I think (but correct me if I'm wrong) that volumetrically lpg has a lower value than petrol, but by mass it is slightly higher (petrol is a bit heavier per litre which tips it the other way).

So IF that's right then all this talk of lpg being lower in calories is probably just because we are accustomed to talking about fuel in litres (since that's how we buy it) rather than in Kgs. And that makes a nice easy (lazy?) way for customers to have a power loss explained in terms of calorific value. That is until you get a customer who is a chemist and therefore automatically looks at it in terms of power per Kg of fuel and says "but hang on, petrol should be the one with less power!"

So the relevance of calorific value per litre is in terms of miles per gallon (ie. relative economy) rather than relative available power which is all about the way the motor is set up to use the fuel/air mixture.

Take a methanol dragster for example (and why wouldn't you?) - methanol is somewhere approaching half the calorific value of petrol (I think), but the motors are set up to run a mixture of about 7:1 (or something like that) and I think it's fair to assume that you will never hear a methanol engined dragster builder telling his customer "of course you will notice a slight drop in performance" - LOL

BTW methanol has an octane rating somewhere about 130 I think.

Anyway as I say there are some "ifs" in there which I'm not 100% sure about, so correct me if you think I'm talking gibberish.


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PostPosted: Wed Oct 28, 2015 9:57 am 
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The other thing to take into account is that with LPG we are injecting a vapour compared with petrol where it relies on the injectors turning a liquid into small droplets. This, in many cases, results in more complete combustion. When I went for my MoT test, out of interest, I asked if they could check the emissions on both fuels. The unburnt HC figure was considerably lower on LPG than on petrol. This shows more complete combustion although I will admit it could also be influenced by the petrol injectors being a little gummed up through lack of use.

As I said previously, whether you get the same, slightly more or slightly less power on LPG will depend on the configuration of the petrol ECU. If it can run more advance than the Octane rating of petrol allows, then it will benefit on LPG but if the maximum advance is pegged to suit 95 Octane petrol then it won't.

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'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.


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PostPosted: Thu Oct 29, 2015 10:20 am 
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We haven't mentioned ethanol in petrol yet, this lowers the calorific value of pump fuel, we cannot buy petrol without ethanol at any forecourt these days.

Simon

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Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
Mid Yorkshire
2 miles A1, 8 miles M62,
http://www.Lpgc.co.uk
Twitter https://twitter.com/AutogasSimon
07816237240


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PostPosted: Thu Dec 10, 2015 10:49 am 
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my NA astra lost around 5-10 bhp.
the impreza is about the same realy

i think its enterly down to the ECU. if it makes no adjustments power goes down. if it adjusts well then power gose up


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PostPosted: Wed Mar 09, 2016 10:26 am 
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i would say there is a loss of power when you go up hills on gas..had this problem with all my vans


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