LPG Discussion Forum

alright peeps,

I have a Merc 230 Supercharged running about 200 brake with a max of 7 psi from the charger.

I have a dream 21 lpg system

I can get a smaller puller which ups the boost buy 2 -3 psi

But the pulley is designed to be used in conjunction with the later OBD2 type ecu which can be remapped but as I have a early car which has a OBD1 ecu which is not mappable and can only be "chipped" and the "Chip" is no longer available or prohibitively expensive

So what I was thinking of doing is getting the pulley fitted and then using the LPG to up the fuelling to match the increased air intake ??

Is this possible as I have not got a clue about these things !!

Cheers

Brett

What you are doing is effectively increasing the compression ratio by increasing the boost. Normally this could result in pre-ignition so would need either the ignition timing altering or running a higher octane fuel (such as 101 Octane Avgas). However, as Propane has an Octane figure of 112 RON, then pre-ignition won't occur unless you increase the compression ratio by an enormous amount. Autogas sold in the UK is as near as makes no difference 100% Propane but in some European countries it is a mix of Propane and Butane in a ratio of anywhere between 90/10 and 50/50. Butane has a lower octane rating, around 95 RON, so will drop the overall rating but even at 50/50, you've still got a significant increase.

A car set up for the max on LPG can run more ignition advance as well as higher compression ratios and can be made to produce more power than on petrol. The downside is that you can't go too wild as it still has to be capable of running on petrol during the warm up phase.