Propane (LPG) Conversion!

[niky]

Had a chance to put the car up on the dyno the other day and finish off our LPG (propane) conversion. I've got a sequential gas injection kit installed with a 36 liter tank where the spare used to be.

The kit is computer-controlled, and is run by a pretty basic air-fuel computer that intercepts the stock ECU signals and runs a set of propane injectors based on those signals.

At first, we tried to tune it with the Unichip piggyback. But Ferman (the tuner-guy) soon found out that the car ran perfectly fine on exactly the same advance and fuel maps as on gasoline. Car made 5-10 hp less on propane than on gas.

Then he borrowed the tuning-computer of the propane installer (Greenfuel, Philippines) for another run on the dyno, and this is what we got:



Dyno on gasoline is higher than previously partially because the weather is nicer, the dyno is better ventilated and because we lengthened the intake tube to get the filter out of the turbulent air behind the radiator (AFRs changed when we did this, and we actually gained power... apparently, these engines hate short short-rams, and the longer the tube, the more power, even if it isn't a CAI).

As you can see, it's around +2 to +3 hp at low rpms, and -2 to -3 hp at high rpms, except at redline, where it's -7 or so. This is probably because we have the propane kit nearly maxed out at redline.

Take note, this is a Dastek... it should read between 5-10 hp higher than a Dynojet... but still... I'm happy about the numbers.

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Current mods: K&N filter, custom intake tube, filter behind left headlight, coolant bottle relocated by battery, Liang-Fei 4-2-1 headers, 2.375" resonator, 2.5" exhaust and muffler (catless), Integral Stage II cams and a port and polish.

Current power:

151.9 whp @ 6500 rpm (gas)
144.2 whp @ 6500 rpm (lpg)

145.1 whp @ 6000 rpm (gas)
142.8 whp @ 6000 rpm (lpg)

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Not that I'm in the race, but since this car runs on either gasoline or LPG and not both at the same time, I'm still qualified in the NA race, right?

 

[twilightprotege]

lpg requires more timing - try that and you should get up to the same if not more power than pump fuel. lpg has an octane of like 110 or something i think?

 

[LordWorm]

lpg requires more timing - try that and you should get up to the same if not more power than pump fuel. lpg has an octane of like 110 or something i think?

it may, but petrol has more stored chemical energy...i.e. petrol releases more energy when burnt. I'd suggest that the petrol configuration should make more power, all things being equal.....

and niky, you still qualify...yes

 

[twilightprotege]

i still qualify with n2o my engine is still NA

 

[niky]

Nah... LordWorm stated that it must use one fuel at a time... :lol:

We tried extra timing... but there's a practical limit to the amount of timing you can add. With the car at a relatively low 9.7:1 compression and with oversized cams, there's not much hope of taking advantage of the 110 octane rating... like I said, Ferman tried tuning for LPG from scratch, but it turns out the timing advance we had for gasoline was enough... so we just tweaked with the fuel maps.

I'm thinking, though... prices for FS-ZEs here are pretty cheap... maybe when the engine starts eating oil excessively, I can probably rebuild it with higher compression pistons and see what we can get out of it.

 

[LordWorm]

i still qualify with n2o my engine is still NA

n2o is not NA, no matter how you look at it.

 

[twilightprotege]

but i am using 1 fuel at a time...i'm just adding additional oxygen and nitrogen

 

[LordWorm]

THE RULES
#1 - Open to all mazda NA piston powered vehicles. No power adders. No Wankels.

point 1) nitrous oxide is not NA
point 2) nitrous oxide is a power adder

no dice mate

 

[Shane5425]

propane at a 1.87 a gallon, but what type of fuel efficiency does it get?

 

[niky]

No idea yet. Still testing. Had to have the idle fixed. Car dies on LPG at idle due to my absolutely huge cams (and it dips below 500 rpm, too, on gasoline), so we had to add timing to get it stable.

From what I can see, fuel economy is just as good (or bad, depending on how you look at it) on LPG as it is with gasoline. Will still have to trace the wiring and look for issues with the intercept for the injectors (there's a gasoline injector auto-cut-off) and make sure that the gasoline injectors are getting a strong enough signal.

It's an interestingly sophisticated system, all things considered. My piggyback controller cost me about $600, while the LPG kit, including the LPG piggyback controller cost about $800.

The system automatically switches between gas and LPG on the fly, transparently (at least at low rpms/load... sometimes bucks if you try to switch at midrange rpms under load due to closed-loop adjustment). The LPG computer has a function comparing gasoline injector duty cycle and LPG injector duty cycle, allows you to baseline LPG injectors on that, and then has a separate map for fine-tuning the LPG injectors, much like you'd get with any piggyback/standalone... the map divided by load/throttle and rpms.

It also has an overboost function that overdrives the LPG injectors for higher load duty at high rpms. The operational range of the injectors in standard trim seems to be only half that of the gasoline injectors... we had to lower overboost from a "standard" 4000 rpm to 3000 rpm to cure a 10hp dip there. This factor probably explains the dip in power at redline. Might be that we're exceeding the operational abilities of this fuel rail at redline, which is why the dip is bigger.

And to keep the stock fuel injectors from gumming up from disuse, it cycles the gasoline injectors on once every few minutes (this still isn't dual-fueling... this pumping won't show on the dyno).

Thinking about using that facility to boost the fuel charge at high load at high rpm with gasoline, to gain back some of that power... or more... with the right mix of LPG and gasoline, we should actually have more power at high rpms than with gasoline alone (maybe a 3-5 hp bump). But then that would be cheating... (cryhard)

 

[jeffmsp]

old thread from 2008 but worth reading.

very surprised the stock fuel system stays running during propane operation i would think the energy being wasted from driving the fuel pump is good enough reason to turn it off and then if you want to clean out the injectors do it manually when you feel like it.

 

[niky]

The problem is, most people don't take the time to run their stock gasoline system. They turn on the car and switch right away. It's not good for the injectors.

Hell... I actually had to replace my fuel pump assembly (not the pump) because I didn't bother to add gas to the tank every now and then, which meant that ethanol fumes in the tank ate into the rubber gaskets.

At 120k kms now. System still runs okay. Only issue I've had from this is a half-melted spark plug from when my gasoline pump went dry, and the car ran too lean on gasoline...