My 4 litre six pot taxi is going to be up for a head gasket replacement soon and I mainly use it on LPG, only on petrol once a week for a few mins to keep the injectors alive.

I'm under the impression the AU gasket is slightly thinner and will increase the static CR too. Since LPG has a considerably higher MON and RON than regular ULP, will the engine benefit from having the head shaved to bring the CR up around 0.3-0.6 ish?

What is the CR increase from merely switching to the AU gasket without modifying anything else?

Naturally I dont want to shave the head excessively which will result in messing up the squish area and combustion chamber, are these problems worth considering when wishing to increase the CR such a small amount?

Lastly, I'm intending on keeping everything else stock - I want to increase the CR mainly to improve fuel economy of the guzzler. Is there any other advice that can be given?

Cheers

id say the shave would be well worth it to keep them the same...i dont think there are a lot of diffderences between the two engins tho. If it were me id just put the AU head gasket on it n leave it...

if u get problems maybe shave it but you can always shave it again later but you cant add more to it!

My oppinion is do it once do it properly. What your symptoms so far as to why you need to change the head gasket? If it is leaking coolant between number 2 & 5 then you will probably need to deck the head again any way to get it true again, they dont take off much when they deck it though. JMM sell these funky dory head gaskets that are 0.020" thinner, and they are about $100

yes sahve the head a small amount it will be good forlpg then u may need to run PULP but meh!

make sure you have the head checked
hell while it is out get the ports matched at the same time makea good improvement in flow etc

Thanks for the replies everyone.

Engine is stock 9:1 compression ratio isn't it?

What is the exact CR increase by doing nothing other than using an AU steel gasket in place of the regular gasket?

What is an ideal CR to increase the engine to, purely for running LPG.

I understand that PULP would be required after the CR increase to prevent detonation, thats fine. The amount of times annually this vehicle sees the petrol tank opened would be easily counted with three fingers and you'd still have a spare