Hq Ratios

[Owen04]

Hey Guys,

I've got a 74 Hq One Tonner which has a 308, M21, with a 4.11 diff. Looking at changing diff ratio to something more suitable for highway driving for lower rpm at high speeds but whislt still having decent acceleration down low. Any suggestions or other alternatives would be appreciated.

Cheers

 

[losh1971]

Back in the day the popular gears were 3.08 in HQ-HZ and Torana's LH-LX. The V8 came out with something pretty tall (2.92 maybe) I remember the 308 was pretty sluggish with standard gears and that my 202 LX with 3.08 pulled as hard or harder than a stock 308 Kingswood.

These days that might be considered too tall?

 

[Smitty]

Hey Guys,

I've got a 74 Hq One Tonner which has a 308, M21, with a 4.11 diff. Looking at changing diff ratio to something more suitable for highway driving for lower rpm at high speeds but whislt still having decent acceleration down low. Any suggestions or other alternatives would be appreciated.

Cheers

you don't have a HQ diff if the ratio is 4.11...

HQ Tonners used 4.44 and 3.55 (FWIW, 4.11 is a Ford 9inch ratio)

re your question though... what size wheels are you running?
14s? 15s?
with either size, try for about a 3.5 ratio. Not silly crazy on the highway (like the 4.44)
but still with a good acceleration

 

[Bigfella237]

Yeah, agree with losh. From personal experience, a 3.08:1 is too tall for an M21 with modern sized wheel/tyres. That combo may be alright if you're only doing highway work but it's too hard on the clutch in stop/go traffic.

As Smitty alluded to, what ratios are available to you depends on which diff you have?

 

[the_boozer]

3.36:1 or 3.25:1 if its nine inch

 

[Bigfella237]

If you post the exact size of your rear tyres (for example: 265/50R15) then I can run some numbers through the calculator and give you some cruising RPMs @ different speeds?

 

[Owen04]

you don't have a HQ diff if the ratio is 4.11...

HQ Tonners used 4.44 and 3.55 (FWIW, 4.11 is a Ford 9inch ratio)

re your question though... what size wheels are you running?
14s? 15s?
with either size, try for about a 3.5 ratio. Not silly crazy on the highway (like the 4.44)
but still with a good acceleration

I was told when i purchased it is was 4.11, however i dont know for sure, im running 14s. Thanks for the info

 

[Owen04]

If you post the exact size of your rear tyres (for example: 265/50R15) then I can run some numbers through the calculator and give you some cruising RPMs @ different speeds?

235/60R14. Cheers

 

[the_boozer]

this might amuse you
https://www.blocklayer.com/rpm-gear
the cheats way to get tire diameter 638mm https://tiresize.com/tyre-size-calculator/

 

[Owen04]

I was told when i purchased it is was 4.11, however i dont know for sure, it is a 10 bolt so it could have a 4.44 as im around 3000 doing 80km/h, im running 14s. Thanks for the info