Gq 4.2 Petrol performance

[Mrme4u]

Hi there I am restoring my GQ but want to improve the performance of the engine.

Which mods are worthwile doing

[Bigcol]

fuel injection
extractors
2.5" exhaust
smaller tyres
electronic ignition
no roof rack
no bull bar
road terrain tyres


the list is quite endless

[Arfa Brayne]

It might be easier to advise you if you can give us an idea of what patrol you are driving.
What engine does it have?
What gearbox does it have?

There are quite a few things possible, as BigCol said, but.......... "how long is a piece of string ? " Need a bit more info.

[taslucas]

It might be easier to advise you if you can give us an idea of what patrol you are driving.
What engine does it have?
What gearbox does it have?

There are quite a few things possible, as BigCol said, but.......... "how long is a piece of string ? " Need a bit more info.
Isn't all that in the thread title? A petrol 4.2 litre gq.

>>>tappin from tassie

[Arfa Brayne]

Isn't all that in the thread title? A petrol 4.2 litre gq.

>>>tappin from tassie

Duh - OK , Didn't see that, still used to dealing with mitsubishi owners.

Personal opinion is the best mods are not the "bolt on" kind
Bolt on mods are like accelerating harder because the handbrake is dragging. The following mods "release the handbrake" of the mass produced engine design.

Top end - match the manifolds, tidy and flow the ports. Reduce valve margins and shrouding. If you are going to fit extractors (which is a good bolt on), regrind the cam profile as the exhaust valve opens too early with standard cam and extractors.
Take 50 thou (1.1mm) off the head to increase compression ratio from 8.5 to 9.7:1 (still runs unleaded), or 1.6mm if you want to run LPG and Premium.
Bottom end - balance the rods and pistons to make the motor run "sweet" at higher revs.

These mods increase the efficiency of your engine = more horsepower for less fuel consumption.
After that, breathing is the biggest limitation of the Tb4.2
A 65mm exhaust is as big as you need - over that and you'll reduce bottom end torque. Use a "pong box" and decent muffler to avoid exhaust drone.
The standard carb and (clean) air filter breathe quite well, although the efi manifold gives better "ram" effect. Cold air intake via a decent snorkle is a tiny improvement as long as the snorkle doesn't restrict the air inlet or mess up the LPG mixer ratios.

[billyj]

or just go a turbo. you can get away with about 7-8 psi without an intercooler if tuned properly and running premium fuel, much better power and torque everywhere