What diff ratio?

**James** · 22-10-2013, 04:24 PM

I just fitted a 304 and 4 speed auto into my HZ wagon.

Just wondering opinions on best diff ratio to fit. It currently has a 2.78 which is way too high.

3.36 or 3.55?

**SANM4N** · 22-10-2013, 05:12 PM

id go 3.08 or 3.36 probably 3.36 i reckon that would go well with the 4 speed, have you kept the injection on it? did you modify your loom or did you buy one to just plug in?

**James** · 22-10-2013, 05:52 PM

Yeah mate I kept the injection and made my own harness.

**Valencia** · 22-10-2013, 06:58 PM

3.36 would be a good ratio in a wagon

**matt159** · 22-10-2013, 07:25 PM

I had my diff reconditioned and was advised that the 3.36 was going to be too low with the supra box I was fitting it behind. The shop recommended I went 3.08 ratio for added strength as the 3.36 teeth are thinner. Not sure if I was taken for by the sounds of it or if it's good advice. I guess the good news is I've got a set of 3.36 gears in a box somewhere if you decide that's the path you take and need a set

**HK1837** · 22-10-2013, 07:29 PM

What tyres? In a Commodore, Calais or Statesman the 304 and 4spd auto normally have 3.08 and 15" tyres.

**James** · 22-10-2013, 09:29 PM

It has 14" tyres.

**adam perth** · 22-10-2013, 11:12 PM

James I would go 3.55 if I were you . This will give you a 2.84 overall final drive in overdrive. 3.36 large Salisbury are getting difficult to find

**HK1837** · 23-10-2013, 08:42 AM

Originally Posted by James

It has 14" tyres.

What size though?
I would have thought a 14" tyre with 2.78 would be fine, if not 3.08, in something light like a HZ. Remember a HZ is significantly lighter than a Statesman or VT

**James** · 23-10-2013, 09:54 AM

245/60/14 on rear. With the 2.78 it's nearly like it's labouring in overdrive at 100kph. It sits about 1900rpm.
I do have a 3.08 diff to go in but not sure how much difference it would make.
I have been told the revs need to be up a bit higher for the lock up to work??