Remap & extra power, whats involved while running LPG?

[reggieroo]

Ok at the moment My Audi S6 is pretty standard with just an exhaust & performance air filter, standard figures are 340bhp so maybe a little more with the exhaust & air filter but who knows if it's lost any power of the years. I will know when it gets put on the rolling road, going to get it checked on both petrol & LPG to see how much difference in power there is between the two fuel systems. I'm looking at taking it to an Audi tuning specialist to have it remapped, been told an extra 25bhp is possible with a remap & with the air filter & exhaust it would be nice to get 375bhp.

What I'm wondering is do you need to do anything to the LPG system for the extra power? What happens when you remap the petrol ECU, also what about the slightly better economy you get after a remap, will that still be the same on LPG. Do you need to add bigger LPG injectors or get the LPG ECU remapped also?

The system I have is a Prins kit, don't know much more than that about it.

[Speedy999]

I would think that you probably have the best Prins components available already fitted with the car being 340BHP as standard. That could depend on the age of the Prins system though.

Just get the LPG system remapped after the upgrades and see how it goes.

Personally I would want proof that any claimed HP increase is actually achieved by getting a dyno before and after the mods/remap.

[john_d]

you will likely need to drill out you injectors/get bigger ones & possibly urn up the vap, all depends on what you end up with.

[reggieroo]

It will be put on the dyno as that is part of the remap so I will see what power it produces before & after. Will also be able to see the difference on LPG also. I have read somewhere that the LPG ECU takes the signal from the petrol ECU & adjusts as it needs to, is this correct? From what I can see with paperwork that came with the car etc the Prins kit is about 4 years old.

[sijones]

you will likely need to drill out you injectors/get bigger ones & possibly urn up the vap, all depends on what you end up with.

I think it's only valtek rails that you drill nozzles, the rest are usually purchased at the required size or they have reducers that screw in on the rail, with like small medium and take them out gives you 3mm.

The LPG ecu will adjust to the petrol ecu, you'll just have to do the remap and then see how it runs, if it goes lean, then you'll have to get someone who has the prins kit to see what adjustments are necessary.

[reggieroo]

The LPG ecu will adjust to the petrol ecu, you'll just have to do the remap and then see how it runs, if it goes lean, then you'll have to get someone who has the prins kit to see what adjustments are necessary.

How will I know if it runs lean? What I don't want to do is get the remap done then find out I have a problem, wouldn't it damage the engine if it runs lean for instance?

[sijones]

Watch the fuel trims on the petrol ecu, and lambda... the guy's remapping it will have the tool to monitor it, once they have done the remap, ask them to watch the trims while on gas doing the rolling road run.

[Gilbertd]

and, to finish off what Simon is saying, if the short term fuel trims start to go up while it is running on gas then the gas system needs re-calibrating to put more gas in.

[rossko]

I think I'd take a slightly different view ; if the trims used to be matched between petrol and gas (check before the work) then they will be afterwards, in a slave gas system. If the trims start creeping up on gas, it is because you have now hit a throughput limitation, and no recalibration will really fix that.

However, if you were to run into a limitation it will almost certainly be apparent under high throttle, where it's not running closed-loop and trims are irrelevant anyway. It's a case of observing lambda outputs under load, as already suggested you get the tuners to do.

Please do not ever drill anything with Prins injectors, you'd totally scrap them. You need to buy the right size, you could identify what you have now by looking for the coloured spots on the labels - probably yellow or brown.

[reggieroo]

What are the trims? The injectors have a yellow dot on them & say class 2 & I wouldn't drill them as I'm not an expert, I'd leave that sort of thing to someone who knows what they are doing.

[rossko]

We're talking about the fuelling trims in the petrol system; all modern engine management self-adjusts (trims) fuelling accuracy under normal loads. It is possible to observe how much it is adjusting using an OBD diagnostic connection. That self-adjusting is still active when you run gas instead of petrol. In a perfect gas install, there will be no difference in the degree of self-adjustment between one fuel or the other. Large differences are a clue that something is amiss.

Really it would be wise to check this degree of matching before your work. The tuner will be able to do that if they understand what's needed.

That would enable re-checking of the matching after the work. But that's not the whole story, the most likely problem area will be at high load, where the self-adjusting mechanism doesn't work. So the tuner needs to check lambda readings there too.

Your yellow-spots should be good for 50bhp per cylinder, but I would expect a single vaporiser/reducer to be running out of puff somewhere about there. You may or may not need to upgrade that.
Other potential bottlenecks are tanks, valves and pipework, but as its a modest bhp increase try it and see.