LPG Injector Sizing / Power Rating

[V8RX7]

Hi I'm hoping someone might be able to help.

I had a 215bhp Forester which had a BRC LPG kit fitted before I bought it, it was slightly less powerful on LPG than petrol but ok.

I've now had it remapped and Dyno'd at 270bhp and the LPG can't keep up and is running lean.

My issue is that the current Orange injector are rated as 48bhp/cylinder (192bhp) I was advised by an LPG installer to change these to the largest (BRC) size which are Yellow and rated at 54bhp (216bhp)

I can't seem to find out how these ratings are calculated - I'm wondering if they are at say 80% duty and the installers run them closer to 100% or do they run them at higher pressures ?

It seems a bit pointless paying £300 for injectors that are only rated 6 / 24 bhp higher.

[paintman]

I - and others - have found these to be helpful:
http://www.tinleytech.co.uk/

[stevieturbo]

V8RX7 said:

Hi I'm hoping someone might be able to help.

I had a 215bhp Forester which had a BRC LPG kit fitted before I bought it, it was slightly less powerful on LPG than petrol but ok.

I've now had it remapped and Dyno'd at 270bhp and the LPG can't keep up and is running lean.

My issue is that the current Orange injector are rated as 48bhp/cylinder (192bhp) I was advised by an LPG installer to change these to the largest (BRC) size which are Yellow and rated at 54bhp (216bhp)

I can't seem to find out how these ratings are calculated - I'm wondering if they are at say 80% duty and the installers run them closer to 100% or do they run them at higher pressures ?

It seems a bit pointless paying £300 for injectors that are only rated 6 / 24 bhp higher.

A lot of the regulators are only capable of around 300hp too, so make sure it's up to the job.

I've seen a few Subaru turbo engines blown up by local installers who havent a clue what they're doing.


You're other option if the ecu can handle the extra current ok, is to double up on the injectors and run 2 in parallel to each cylinder.

But again, make sure the regulator can handle the flow required.

[chuntington101]

Off topic but what pressure do LPG systems run at?

[stevieturbo]

chuntington101 said:

Off topic but what pressure do LPG systems run at?

Not honestly sure...

Up to the regulator probably fairly high so as to maintain a liquid state.

After that a lot less as it's in gaseous state, but to inject into a boosted engine, obviously it will still need to be a lot higher than boost pressure used.

[V8RX7]

I'll try giving Tinley a call but I pulled the Inj sizes from his site.

My regulator is rated to 268bhp - which seems close enough.

[chuntington101]

stevieturbo said:

chuntington101 said:

Off topic but what pressure do LPG systems run at?

Not honestly sure...

Up to the regulator probably fairly high so as to maintain a liquid state.

After that a lot less as it's in gaseous state, but to inject into a boosted engine, obviously it will still need to be a lot higher than boost pressure used.

So why don't people use these for injecting N2O? That way you can regulate the flow right down to 0.

[stevieturbo]

V8RX7 said:

I'll try giving Tinley a call but I pulled the Inj sizes from his site.

My regulator is rated to 268bhp - which seems close enough.

I sure as hell wouldnt want to be running my engine anywhere near close to the regulators limit.
I'd be wanting around 20-30% safety margin

chuntington101 said:

So why don't people use these for injecting N2O? That way you can regulate the flow right down to 0.

The "regulator" is purely to let the liquid turn into gas, so it can be injected. Technically regulator is probably a defunct term for it.

You always want to inject liquid nitrous into the engine, and solenoids will regulate this flow.

Same as ultimately gas solenoids regulate fuel flow in LPG, and fuel solenoids regulate fuel flow with petrol.

[Quinny]

I wouldn't take much notice of vaporiser power ratings.... The one on my hemi is rated at 400bhp... The hemi is around 330 bhp.........but the 400 bhp vapouriser, can't supply enough gas under heavy load..... I need 2 vapourisers...1 for each bank.

[V8RX7]

Oh.

I thought it would be more like construction where a 2 ton rated beam can hold in excess of 4 ton.

The local LPG guy said he's run 300bhp through my type of regulator.

[BritishRacinGrin]

My understanding is that they can extend the duration of the injection on each cycle but doing so often introduces an inherent inefficiency because the piston is obviously not decending in it's bore at a constant speed. Getting it wrong can result in fuel gas getting left over in the inlet manifold which isn't ideal.

[stevieturbo]

BritishRacinGrin said:

My understanding is that they can extend the duration of the injection on each cycle but doing so often introduces an inherent inefficiency because the piston is obviously not decending in it's bore at a constant speed. Getting it wrong can result in fuel gas getting left over in the inlet manifold which isn't ideal.

You cannot extend injection period longer than 100% duty, nor would you want to run it that high

When you need bigger injectors, then you need bigger injectors.

Likewise with the vaporiser/regulator. It must have adequate flow under all operating conditions...and then some

[V8RX7]

stevieturbo said:

You cannot extend injection period longer than 100% duty

nor would you want to run it that high

Agreed

Why ? I've heard this many times yet I've run petrol injectors at 100% duty on my supercharged MX5 for thousands of miles including track days without an issue.

[stevieturbo]

V8RX7 said:

Agreed

Why ? I've heard this many times yet I've run petrol injectors at 100% duty on my supercharged MX5 for thousands of miles including track days without an issue.

Fuel is metered by pulsing the injectors, not by relying on them when they are approaching or held fully open.
They are not designed to be run in that manner.

Hence it is recognised everywhere that they should not be, it is "bad". That isnt to say many do and no ill effects occur though.

But no tuner or sensible person would willingly or knowingly run them at 100% for extended periods as you basically lose all ability to regulate fuel flow into the engine at that point.

[V8RX7]

Update:

I called Tinley Tech to ask whether I could fit the Hana A+ injectors are they are cheap and good and are the largest available - apparently they are a copy of the Keihin used by Prins - they said yes as the impedance was the same.

Unfortunately they were wrong - the basic Hanas are 1.9ohm but the larger A+ are 1.3ohm (as are the Keihin)

However I went to a recommended LPG installer in Stoke (a 60 mile drive) and he found that:

A Bristol LPG "specialist" had electronically disconnected the MAP sensor and removed the replaceable element BRC filter and fitted a cheap one.

He reconnected the MAP and raised the gas pressure from 1500 to 1800 and then "tuned it" which seems very basic and relies upon the fact that LPG has a far higher octane rating than petrol - however it seems to have worked as it now runs as well on gas as LPG - although I will be monitoring the fuel trim and installing an AFR gauge