D2 V8 LPG compression ratio

[2door_rrc]

hi im the process of rebuilding my d2's 4.0 v8.
it runs mainly on lpg via a injection system and i wondering is it worth rasing the cr to 9.35 over the std 8.35 ??
the engine is already getting a crow cam port and polish and of couse a port mach and it already has extractors and a hi flow exhaust. so is it worth the extra $$$$?
thanks

[bee utey]

Seeing as the later D2s run the higher compression it should be easy to source the pistons for a high comp rebuild. Running the high comp will definitely be worth it, to the tune of around 10% increase in efficiency.

[plus 30]

Hello all this is my first post.
My experience from running gas on a Holden V8 is that gas is a higher octane fuel than petrol therefore requires higher compression to have correct efficiency. ( 10: 1 )

Running both petrol and gas negates the power benifits of gas, it is much better to run straight gas, you can remove your petrol fuel tank and use the space for something else.
Gas supply centres are/or were printed in booklets like the Klenheat one, so there is no excuse for not knowing wher the nearest gas is located.
Therefpre it is the same as petrol in that respect, just check your gas gauge, like is required for petrol. Offroad will require more planning though.

The compression for gas needs to be around 10:1 and you need to get a dedicated gas cam too, ( you didn't say what you were using, Crow do a gas cam too ) don't worry about fitting a petrol fuel cam or again your are not maximising the increased power of gas.
Lumpy cams with valve overlap significantly reduce engine performance at low revs, so if you use it as a 4WD I don't think that this would be a good Idea for you.
If your supplier tells you that gas cams are not required, then he is just taking your money, and cannot be bothered to phone Crow for a gas cam, make sure you get the cam card with your engine so you can be more sure what you are getting.
The distributor requires recalibrating to match gas also, and of course electronic HEI ignition is best for igniting what is a dryer fuel.

The exhaust will run hotter too so that needs to be able to handle hotter temperatures, as do the spark plug leads.

There is also a dedicated oil for gas engines which is best to use.

My advise is convert your engine to run on straight gas and don't compromise the benifits of gas, and then find that you have a loss of power.
If you set it up correctly you should get more power on gas than petrol, and not less as many experience with ad on gas/petrol systems.
You have the opertunity to do it correctly so make the most of it!

plus 30

[101RRS]

If you want to travel around this country you definitely do not want a gas only vehicle - likewise often garages that do have gas are not always open, have restricted hours or run out as soon as a shipment arrives.

There are a lot of benefits using gas in remote areas (two fuels if there is an issue with one) but there are also issues with availability. Try leaving Bourke with a full tank of gas and head further west into SA and up into Qld and see how far you get.

Unless you stay on the main roads, then dual fuel is a must.

Garry

[Outback 1]

If you want to travel around this country you definitely do not want a gas only vehicle - likewise often garages that do have gas are not always open, have restricted hours or run out as soon as a shipment arrives.

There are a lot of benefits using gas in remote areas (two fuels if there is an issue with one) but there are also issues with availability. Try leaving Bourke with a full tank of gas and head further west into SA and up into Qld and see hoe far you get.

Unless you stay on the main roads, then dual fuel is a must.

Garry

FULLY AGREE DUAL FUEL IS A MUST !!!!!:wasntme::angel:

[bee utey]

FULLY AGREE DUAL FUEL IS A MUST !!!!!:wasntme::angel:
Agreed #2

For a bush vehicle dual fuel is faar better than straight gas. With good availability of high octane petrol you can have high compression and dual fuel too. With a D2 with knock sensors and gas injection you'd be mad to go straight gas in any case. It self tunes to a reasonable degree for both fuels.

A D2 is nothing like an old holden engine.:)

[Battler]

IMHO definitely worth increasing the compression ratio for LPG. I have a 4.6 D2 duel fuel and I got the compression up by shaving the heads, tin head gaskets (had to machine down the inlet manifold). Not exactly sure what the compression ratio is but it doesn't like any petrol below 98. Nice increase in power.

[2door_rrc]

yes defiantly staying with the dual fuel as i have done a lot of bush driving and plan to do a lot more.
and i have talked to the machine shop that has my engine bits, they want to raise the cr to 10.1.
i know that will go very well with gas but will it run on the pump petrol lol and how forgiving are the knock sensors ??
im in half a mind to tell them to leave it around 9.5 but idk
and the crow cam im thinking of using is part no 371613 ???

[ozscott]

I used crow stage 2 cam. Mine was already a high comp LR motor. Port .matching and clean up. High flow cats and mufler and stock else including LR stocker leads. Gas plugs though. Lpg injection is sweet.

Always dual fuel for a tourer, especially a 4wd. Apart from range there are some things that will cause far less probs on petrol until fixed than lpg - eg vacuum or spark issues.

Cheers

[Pedro_The_Swift]

I dont know I'd spend any money on a 4l without putting tophats on it,, running at 10-1(a good idea by the way--) will only make "things" happen so much sooner--

[ozscott]

Depends on engine. Mine had done 200, 000 including plenty of heavy towing and the block and liners were perfect...so Ieft pots alone. If they hadn't moved by then they shouldn't. Not all moved.

Cheers