Is the TB42 a good engine?

Hi all,

I have a TB42 (carby) in my GQ LWB which is a bit gutless in standard form like all GQ's I imagine, but I like it nonetheless.

I'm just wanting the opinion of mechanics or engine rebuilders or tuners on here about the reputation of the engine for making decent power, is it considered a good design?

Reason I'm asking is I'd like to invest some cash in the bottom end with some better conrods (Spool imports forged jobbies) a better cam (low-midrange torque) extractors, raised CR etc. I don't want to complicate things further with a turbo.

I also have a FB holden gasser project that I'm looking to stuff a big inline 6 into and I was wondering if the TB42 would be suitable for that as well seeing there are so many cheap engines out there at the moment. 265 hemis are hard to find and expensive etc. Is the engine considered too heavy for it's capacity for a light drag car?

Cheers for any help.

Tb42 is a basically a TD42 made for petrol. Everyone thinks that making more revs is the way to more power, but with the 4.2 it's the opposite. - it's like entering a clydesdale in the melbourne cup.
Lots of torque down low will give you power without wasting all that effort trying to scream like an overweight banshee through restricted inlet and exhaust ports/valves.
Compression ratio is a very lazy 8:1 for the older engines = E10 fuel will let you hit 10:1 without problems, and remember the bottom end is designed to handle at least 18:1 for diesel.
So the secret is to make a torquey low revver that pulls hard - like the clydesdale was bred to do.

Don't need to do anything to the bottom end - it's overdesigned to buggery.
Take 1.5mm off the deck to increase compression, put in a cam designed to make torque at a lower rpm (crow do a 1600 - 2600rpm "towing " cam)
VERY slight port work and improve the flow by reducing valve shrouding.
Extractors - EVERY extractor on the market has primarys that are too big (usually 40mm +)and too short. You need 37mm- no bigger, with as much length as possible back to a short secondary and 54mm main You will find the extractors are made for Diesel and petrol engines, and making big pipes means you don't need to bother with any carefull work - one look at how the extractors are made will confirm this. Big diameter pipes means loss of scavenge at low rpm, so you will actually LOSE power at low rpm fitting off the shelf extractors, just to gain a little at over 2600rpm where the standard cam tapers off.

If you want more power, whack a turbo in it.

Im gunna have to agree with mudski on this one.

Tb42 turbos when set up right are known to produce some decent numbers. (180 to 250rwkw) but obviously need some work done to them.

I have a mate who has a tb42 turbo in his winch comp truck and does well...

Personally and i dont wanna sound like a moron suggesting this but if you have no problem sticking to a petrol engine i would be choosing a 4 litre ford barra engine....

The are reliable as all hell. Produce silly amounts of torque... known to do 1 million plus kays in taxi engines and turbo ones as seen in an xr6 turbo are known for stupid horsepower applications...lets not also forget they are actually regarded as Australia's best ever engine ever made amd parts and aftermarket go fast bits are plenty....


The beauty of these engines is you can pick up an

Naturally asprirated $250 bucks

Lpg green rocker cover version $400 bucks

Ba to fg xr6 turbo variant from 1500 to 4000


A lot of people are prefering to buyNA engine's or lpg models as a cheap option... with just valve springs changed and supporting bolt on mods ie injectors fuel pump turbo tune etc they have been known to male 10 second passes with a completely stock wrecker motor from 250 bucks...

This is why i went for this option...

Best thing i did from my perspective...

I'm currently making 450rwhp
Attachment 79513

Shaved deck, cam, port , extractors on a tb42 for under $1.2k if you can use a spanner.
I'd love a hot to trot Barra, but It's worth more than my Gq.

Thanks heaps fellas- that’s given me plenty to think about!