Single fuel LPG injection conversion

[Conza]

A while ago was at the pump, guy next to me in his HSV was filling up on gas, hmm.

ME: "Gas?", GUY: "Yes, more octane ~110, also cheaper".

That's the summarised conversation, so I'm wondering, I know some of us will have converted to the old/new LPG, probably most of those on a 'duel' fuel system (retain petrol tank).
What I want to do, if possible, is keep my old petrol tank, remove it, and replace it with another tank in the same shape/size/position (even if only roughly) designed to hold LPG, and have that as the only tank.

I basically only want more power, I know that economy will be less and more, because per km I'll use more gas than petrol, but gas is cheaper, so still better off. I also want to keep my old tank so if I went to sell it the new buyer could easily go back to petrol again.

Is this a common thing to do?

 

[Dennisch]

You'll lose power when converting to LPG.

The higher octane number basically means it can handle higher compression, so if you just swap fuel, and don't change anything to the engine nothing happens except the money stays longer in your wallet.

I have LPG on my V8, just like everyone here in the Netherlands with an old American car. And I notice that I have a lot more power when driving on gasoline instead of LPG.

 

[Slash]

Higher octane means it can handle higer compression but it also takes longer to burn and it has more of a complete burn than a lower octane, essentially giving more power. But that depends on the setup and if it's built to run on on that type of octane.

I had an old engine that ran on 117, and it made lots of power. But it was built to run on it. If I put 117 in an engine that I have now, it wouldn't even start.


I personally don't know a lot about LPG conversions though. I wouldn't do it if it was me.

 

[Dennisch]

Every normal petrol street engine can run on LPG, as long as it is an engine which doesn't need lead anymore. Easy install on a carb engine, bit more hassle on a fuel injected engine.

The easiest way to get more power out of a LPG conversion would be higher compression and longer duration of the spark.

 

[Slash]

Every normal petrol street engine can run on LPG, as long as it is an engine which doesn't need lead anymore. Easy install on a carb engine, bit more hassle on a fuel injected engine.

The easiest way to get more power out of a LPG conversion would be higher compression and longer duration of the spark.

That would lead to a head change though, which can cost serious money depending on the engine you are converting over, at least for power. Same with the ignition system.


So if an engine that originally ran with lead, and now has valve seats that were hardend, it would run? Pretty sure that's a yes but not sure.

 

[Dennisch]

So if an engine that originally ran with lead, and now has valve seats that were hardend, it would run? Pretty sure that's a yes but not sure.

Yes. Any hardened engine would happily run on LPG.

 

[Slash]

Yes. Any hardened engine would happily run on LPG.

That's what I figured. Thanks 👍

 

[Conza]

Hmm, interesting conversation, thank you gents.

Uhh, yes, higher octane I suppose past what my ecu can handle (which is probably between 91-98), will be meaningless I suppose, unless I then chip the car to run on 110/117, the best fuel I could run, sustainably, on an LPG injection system.

For example, I'm pretty sure I tried using 98 a couple of times over 95 (the minimum my car requires), but instead of feeling more powerful and or lasting longer, it may've left a little less muck in the engine, but overall I think it would've adjusted it so it didn't knock, or whatever, and that was it, so I switched back to 98, thought I'd save the 4-5 bucks a fill when it had little/no benefit.

Neither of you have done this though? Or not recently/to a small car?

It's for a vaguely modern engine, its the Peugeot pictured basically, a 16v 2 litre i4 engine, which produced 135PS from the factory, who knows how much of that is left, its serviced regularly, every 6,000miles/10,000kms (its kms but 6k miles is a close approx), revs happily, all is well.

If it does require a head replacement, I might look into getting the GTi6/S16 head, which I hear has sharper cams, but I figure it wouldn't be too camy, who knows.

If I replaced the head (since I'd be doing that anyway), and then, had a chip to help the engine run on higher octane, would this make for a much more powerful and frugal car?

 

[Slash]

117 was $9 a gallon in the 1990's. I think last time I checked it was up to around $15 a gallon.

What is the car you drive? I wouldn't pick an octane too high because if you do it could cause all sorts of problems ie not starting, flooding the engine with unburnt fuel, error codes on the ECU and the check engine light on.

I haven't done it personally and from my personal standpoint I never thought it was really common. But I think for it to be beneficial you'll need to put some engine work in before it really pays itself back in the long run.




Just saw you had your car listed. I wouldn't do it to be honest. More money than its worth before it becomes beneficial. If you get another head it would have to create a higher compression in which you can change octance and have it work well.


As for your last sentence/question, in short, yes it would. But that mainly depends on the head. A higher octane alone won't really net you a *ton of power by itself. A better head can really increase power output without changing octane and you wouldn't need to spend more money on fuel.

 

[Conza]

Yes, see your first paragraph, I'm hoping, could be addressed by an ecu upgrade, a chip if you will.

No idea if 117 is too high, maybe 100/105, idk what these ecus cater for, its running at 95 at the moment, and 98 requires no ecu change, but again no performance/economy improvements (that I noticed on a few tanks).

Hmm, I love all of this compression/new head stuff, I'm going to see if I can find out what I'm at, what I could get to. I have a game that you build car engines in and it has all of these parameters, so I sort of understand where you're coming from.

TBE

Compression
Peugeot 306 N5/Mk3 2.0 XT - ??

Peugeot 306 N5/Mk3 2.0 GTi6/S16 - 10.4

Peugeot 306 N5/Mk3 2.0 Cab - 11

Peugeot 306 N5/Mk3 2.0 XSi (97) - 10.4

Not the 'exact' car, but I believe this one in bold (and first link below) to be the correct engine, otherwise it's this engine, which is a little lower, but I have a feeling it isn't since it 'feels' older, and my car was right at the eol for its model. The third link is the GTi6, also 10.4, which I find odd, and it may be my engine is at 10.4... then again that cab, they might've updated the compression for other reasons, like higher octane fuel usage, and therefore cleaner burning and economy results.

http://www.cars-data.com/en/peugeot-306-cabriolet-20-16v-135hp-21817/specs.html
http://www.cars-data.com/en/peugeot-306-xsi-20-16v-135hp-21940/specs.html
http://www.cars-data.com/en/peugeot-306-gti-16v-167hp-21941/specs.html

 

[Slash]

117 is like really really high, even beyond what NASCAR uses, which I believe they use 106 or something like that.


If anything I'd ran at most 98. You may be able to get away with a head swap without using higher octance fuel. A lot of older Fords respond well to head changes and still run great with 87.

 

[niky]

Dirty little secret: If you get an electronic injection conversion kit, you can retune it on the dyno for more power. Only change needed is colder plugs.

If you've got control over spark advance, you can make as much power as on gas, or more, and minimize fuel economy differences.

Not because LPG is better, though. But because typical factory EFI maps suck like hell. If the stock gas maps are really bad, you can even get better economy.

Removing your tank is impractical. Non-cylindrical LPG tanks are hideously expensive. Most practical for a small car is the toroidal tank that replaces your spare tire.

 

[Conza]

haha, 87, and premium 93, you poor guys over there, mind you, we're not that far ahead at only 98, wish we all could have access to 100.

My point mainly is, if I do this, I want to know that I can go to Shell/BP, and just fill it up using the gas they have, and if it's a higher octane, that I could get more out of an engine that's designed to run on gas, and specifically at a certain octane, ect.

Dirty little secret: If you get an electronic injection conversion kit, you can retune it on the dyno for more power. Only change needed is colder plugs.

If you've got control over spark advance, you can make as much power as on gas, or more, and minimize fuel economy differences.

Not because LPG is better, though. But because typical factory EFI maps suck like hell. If the stock gas maps are really bad, you can even get better economy.

Removing your tank is impractical. Non-cylindrical LPG tanks are hideously expensive. Most practical for a small car is the toroidal tank that replaces your spare tire.

Yes, really really really, do not want to replace the spare tyre, or drill holes in my body work, blah blah blah, would rather remove the tank, even if it's too replace it with an almost same size cylindrical version (obviously losing 5-10 litres of that were the case).

When you say more expensive, what's the ball park we're talking here? $100s of dollars or $1000s of dollars for a 'square'ish LPG tank?

 

[Slash]

Dirty little secret: If you get an electronic injection conversion kit, you can retune it on the dyno for more power. Only change needed is colder plugs.

Thanks for that, I had no idea.

@Conza

Here in New York (as far as I know), anything over 96/97 you have to go to the airport to get. Even finding that is tough. Most pumps in my area carry only 87, 91, and 93.

 

[niky]

Yes, really really really, do not want to replace the spare tyre, or drill holes in my body work, blah blah blah, would rather remove the tank, even if it's too replace it with an almost same size cylindrical version (obviously losing 5-10 litres of that were the case).

When you say more expensive, what's the ball park we're talking here? $100s of dollars or $1000s of dollars for a 'square'ish LPG tank?

Don't know yet. Haven't ever seen a square tank "in the wild." And square is much different from your stock tank, which is wide and flat. LPG requires pressurized tanks, and it's exceedingly difficult to make pressurized tanks in such irregular shapes. I doubt it'd fit such a small car, not without some of that cutting and clearancing you don't want to do.

Replacing a full-sized spare with a toroidal tank is not a big deal. That's what most of us who need the trunk space do, then we simply buy the appropriate space saver spare and plop it down in the trunk. A space saver doesn't impair carrying capacity all that much. If it bothers you, go for the fix-a-flat kit, instead. A toroidal tank costs only a bit more than the steampunk-ish cylindrical ones.

-

If you want best performance, you want SGI. With SGI, removing the gas tank is horribly impractical, because SGI kits run like garbage when they're cold, so you need to start on gas. You can disconnect the gasoline system if you get an old-school venturi (in essence, a very crude carburetor) kit. And some venturi kits come with O2 intercepts, so they can adjust, somewhat broadly, to your needs, but not as well as SGI, and fuel economy really sucks.

The benefit of venturis is you can cold start on LPG (no need to keep a gas tank) and the up-front cost and maintenance are cheap.

 

[Bopop4]

haha, 87, and premium 93, you poor guys over there, mind you, we're not that far ahead at only 98, wish we all could have access to 100.

Our octane rating system is different, our 93 is like your 98.

(I have a Spanish bike, and I was worried because it needs 98, but then I researched and found out that I could run 91 and be fine.)

Edit: Apparently you can get 101.5 RON/94 AKI in Canada.

 

[Conza]

@Conza

Here in New York (as far as I know), anything over 96/97 you have to go to the airport to get. Even finding that is tough. Most pumps in my area carry only 87, 91, and 93.

Ah, see that's what I found when I drove around Nth & Sth Carolina too, pre-pay is a must, gas is extremely cheap, and lasts for extremely little time, not identical car comparisons, but 14.5 gallons (roughly 55 litres) got me... I think it was 260 miles, travelling at 65/75mph. So that's on 93, and it was in a horrible rental Nissan Versa 'sedan'. On 95 here, my car returns 375/400miles on the same tank, and that's including lots of round town driving, maybe 35mph average - was totally gob smacked! Needed two tanks just to cross the border! (wow that only comes in at 29mpg? gezuz! still better than 18 I guess).

If we all had 100 that'd be better, a little late in the life cycle of gasoline/petrol to do much about it now though.

Which brings me back to LPG. With a petrol car that I love, I either, continue on petrol, maybe/maybe not tune it (don't see any economy/cost savings there, potentially no gains either), or switch it to something that's quite popular here, LPG, and if I get more power to boot, win win.

LPG costs (checked today) 67c per litre, its 75% as efficient, so its basically the same as 90c on petrol, compared to $1.50, or 60% better.

With no performance gains, depending on the installation costs, that could pay for itself quite quickly. If it included performance gains, in my opinion, that pays for itself instantly.

 

[Dennisch]

Oh and LPG loves to be supercharged into an engine. Loves it.

 

[Slash]

Ah, see that's what I found when I drove around Nth & Sth Carolina too, pre-pay is a must, gas is extremely cheap, and lasts for extremely little time, not identical car comparisons, but 14.5 gallons (roughly 55 litres) got me... I think it was 260 miles, travelling at 65/75mph. So that's on 93, and it was in a horrible rental Nissan Versa 'sedan'. On 95 here, my car returns 375/400miles on the same tank, and that's including lots of round town driving, maybe 35mph average - was totally gob smacked! Needed two tanks just to cross the border! (wow that only comes in at 29mpg? gezuz! still better than 18 I guess).

If we all had 100 that'd be better, a little late in the life cycle of gasoline/petrol to do much about it now though.

Which brings me back to LPG. With a petrol car that I love, I either, continue on petrol, maybe/maybe not tune it (don't see any economy/cost savings there, potentially no gains either), or switch it to something that's quite popular here, LPG, and if I get more power to boot, win win.

LPG costs (checked today) 67c per litre, its 75% as efficient, so its basically the same as 90c on petrol, compared to $1.50, or 60% better.

With no performance gains, depending on the installation costs, that could pay for itself quite quickly. If it included performance gains, in my opinion, that pays for itself instantly.

Yeah gas is really expensive in NY but its going down.