3.55 lsd out of Tonner

[Vombil]

He used the wrong gearbox. To successfully run a 278 rear with an Aussie you need an M22, if your engine is a V8 then you swap the input shaft in the M22 for the input shaft from a V8 M15. This will give you a first gear ratio of 10.39:1 with the 2.78 diff. This combination will also give a 2100-2200 rpm cruise at 100km in 4th, comparing this with an M20 with a 3.55 diff giving a 10.83 overall ratio you can see that the M22 and 2.78 diff is a good choice as long as you don't want to be a boy racer. The beauty of this combination really comes into its own behind a 308 as the extra torque of the bigger engine masks the wide ratios and gives great take off and cruise. I am going to run a Falcon T5 with the 3.50 first gear behind my 253 with a 3.08 diff, this will give me a 10.78 first with an 1800-1900 rpm cruise at 100km with the standard 0.78 over drive.

just flick the 253 for a 308 and then you can keep it all aussie with m21. the T5 a bit of a drama with tunnel, clutch, cross member and tail shaft?

[Dick61]

just flick the 253 for a 308 and then you can keep it all aussie with m21. the T5 a bit of a drama with tunnel, clutch, cross member and tail shaft?

The whole idea is to get away from the aussie box, the T5 in standard form will take 300hp and can be beefed up to take 500hp, the tunnel isn't a problem if you change the rear housing for a Mustang one which moves the shifter box about 50mm forward so the stick comes out the original hole. The M21 isn't a nice box to use for the street, the close ratios and high 1st gear make it a pain in the botty to use with a higher ratio diff and used with a lower ratio it has great acceleration but revs it tits off at highway speeds. The T5 coupled to a 3.08 diff has a lower 1st gear ratio than any M20 aussie/diff combo except the M20/3.55. The T5 shift is much smoother than the aussie and doesn't wear like it does either, if my ute was a genuine Sandman then it would be a different story, the work needed at the moment is not beyond me so taking it slow I'll hopefully end up with a great looking replica. I also prefer the 253 over the 308 as I have always found it to be a sweeter running motor.

[Beachy]

I had a wb with a m20 and 2.78 it was fine I reckon a 3.55 would be good 3550 rev at 120 kph would give the 253 a bit of go I have had all the diff ratios and reckon there is not much difference in fuel economy

[Big Rob]

My HZ is 253/M20/3.55 and does (with 245/60 14" T/A's) 100km/h at 3000 RPM in top gear. It does feel like it's revving a bit high, but it's also keeping the 253 around it's useful rev range so you can overtake if required.
Because of where I live, most of my driving is in 100 km/h zones and it'd probably be a bit better with a 3.36, but I bet it would be great in the city the way it is.