some FBend production plant mfg (Mechanical assembly) info I have might help
this for VK only... with VH starting this (and nothing on VC, HDT Commodore engines were done by them)



and after the 5,000 'performance equipment' engines were made (GMH ended up making apprx 15,000 in various forms)
some engines got all, some lost the lightened flywheel and windage tray, some got std valve heads, just a real mix...

A VH SS 4.2L had a M21 4sp box in them all ? i think they were all M21 and 3.08 ratio diff.
A mat was going to traid his VB 4.2L 4sp in on this VH SS 4.2L 4sp, we thought yep ! this will be great to trade up to, but it was gutless ! It had dual exhaust and the VB stock single rubbish exhaust.

I was totaly blowen away about how gutless the VH SS was, i believe the reason why is that the M21 ratios are crap for a 4.2L because they do not have enough torque to pull such ratios and a 3.08 ratio diff. the M20 ratios are much better for the little 4.2L and the 3.3L 6 cyl as 1st 2ed and 3rd are much lower ratios that help get it going and i believe that the 3.36 ratio is the best for a 4.2L as you will not get any better top end speed with a 3.08 nor a 2.78 ratio as they all only do arounf 180 to 185KM/H flat anyway.

A mate had a HQ 253 with M21 and a 2.78 diff it was gutless and 1st gear was so stupid high. I drove it and the gearing just did not inspire you at all ever.

I do not know about the stock VH 4.2L 4sp, i think they were trying to flog off the M21 as well with them ? it was an option on them.

A M21 is magic ratios in a 308 and a 3.08 diff is the magic ratio ! 3.36 is far to low for a 308 and crap top speed of 185 KM/H as you get valve bounce at 5000 RPM with a Red motor in top gear.

I believe that Red motors be it stock 6 cyl or V8's bothe valve bounce at 5000 in top gear, but you can go to 5500 RPM in the lower gears, for you do not hold such revs as long as in top gear, so i believe what happens is that the valve springs get a shimmy up ! and this type of crap can kick off at 4800 RMP for sure and it's this that give the valve colets a hiding and that's why you can drop a valve ? because the colets are floged out ?
Not to mention when the springs get into the shimmy stage then they produce more heat and to much heat flogs the springs out, then they become weak and they can start to valve bounce at 4500 RPM, i have driven crap 202's like that or did they drive with a buggered radiator for years, a lot of Joe average people back in the days drove around in cars like that. many would not replace a radiator if their life depended on it ! It was like a badge of honnor to be like that back in the days ! they had a fix for it, just drive slower ! seriously that's what they would say, such stupid idiots !

Yes I thought 6 cyl blue could rev to 6500 RPM but i did not know if the Blue V8's did have stronger springs as well.

Std setting is 12 deg and you go to 18 deg, ok !

I know that 253's need a singel 2 1/4 free flow to exhaust or a stock dual exhaust is the trick to wake them up. but i was thinking why would anyone want to put a M21 behind a 253 regardless as it kills the perfomance. when overtaking at 100KM/H or 80KM/H the M20 3rd is much better perfomance than a M21 will do. not to mention 1st 2ed and 3rd with M21 make a 253 feel like a slug. I can not think of anything good about a 253 and a M21 at all.
Not to mention a M20 behind a 308 would be stupid as well, because in stock form you use the torque to do all the work and do not bother rev it over 4500 or it will not perform the best, that's why M21 is best in a 308.

The M22 is the most stupid ratio box of all, they are good for nothing !

The 4sp Box sag ratios behind the HT-G 253 is not the best ratio's as well but 3rd is fine.

I think that the 253 HT-G-Q could be revved out to 5300 RPM if you wanted to with a Auto and 2.78 diff but about 4800 best max to change gear with that. but i do not know about the HX-Z 253 as they got a stupid smaller camshaft grind. the 253 Blue Camshaft must of been changed to be able to rev to 6600 RPM ? I am sure that no stock red will go that high even if you put stronger springs in them. maybe the V4 carby helps them rev better as well.

M22 is 6cyl commercial only in HK, HT (2.85:1 1st Saginaw) and then from 1974 onwards (Aussie M22 wasn’t called M22 until 1974, it was just wide ratio M20 until then).

M21 Saginaw that came behind 253 in HT-HG was the same 1st gear ratio as M21 Aussie, ie 2.54:1. Just like HQ, in HT-HG a 253 manual was standard with a 3.08 rear axle except for cab-chassis got 3.55 unless it had C60 aircon (these had a 3.36). Not sure what you mean about 3rd, M21 Saginaw is 1.44, not much different to either M20 or M21 aussie which are respectively 1.51 and 1.38. Multiply all of those by the diff ratio you get 4.65 (M20), 4.45 (M21 Sag) or 4.25 (M21 Aussie) as the overall 3rd gear, not much difference. But that point is moot, as in HQ, if you optioned an M21 behind a 253 you also generally got a 3.36 rear axle like a 308 did. Stay with me, why did they do that? Work it out, here are the overall ratios:

3.05 x 3.08 = 9.39
2.54 x 3.36 = 8.53
Those above are 1st gear.

2.19 x 3.08 = 6.74
1.83 x 3.36 = 6.15
Those are 2nd gear

1.51 x 3.08 = 4.65
1.38 x 3.36 = 4.25
3rd gear.

As you can see they aren’t hugely different.

You have to look harder at the overall ratios. A prime example is people incorrectly claim that an LH L34 optioned with a 3.08 rear axle is faster than the standard one. That is 100% wrong, they are the same other than 4th gear, if you got a 3.08 rear axle you got a close ratio M21 too. Multiply out 1st, 2nd and 3rd gears of the two boxes with their respective diff ratios and they are all but identical.

I also had to edit and add that unlike HQ, in HT-HG if you optioned a 4spd on an otherwise standard V8 model you didn’t get a 3.36 as there were no V8 3.36 banjos, you had to have 3.08 and you couldn’t option a Salisbury. So a 253 M21 in a HT-HG was a far worse combination as 1st was very tall due to the 3.08 rear axle. Whereas in HQ it was normally 253, M21 and 3.36 which was far better through the gears, just less 4th gear.

Having said that, a HQ 253 with M21 and 3.36 would be fine if you got dual exhaust, and a few years later fitted a HJ 5.0L cam plus a 308’s Quadrant and intake. Then it’d be a neat little package and probably a 3-5mpg better than a 308.

Edited by user Thursday, 19 September 2024 10:40:13 PM(UTC)  | Reason: Not specified

yep.. to pretty much all that but 2 comments come to mind reading it...

Most remember the M22 was in the Holden One Tonner range and were commonly known as stump pullers!
and
there was another L34 M21 box available, homologated by Harry Firth (CAMS forms signed by Joe Whitesell or was it Joe Felice?)
... totally different ratios starting with a 2.32 1st gear (as against the std 2.54:1 fitted to both LH SLR5000 models)
these were never fitted to road cars ex the factory ... available only out of GMP&A at Dandenong

What you are saying their is 3.08 ratio diff and 14in wheels and 2.78 diff and 13in wheels are much and much the same ratios.

I had a L34 SL/R5000 with 3.08 LSD and 14in wheels. and I did put a 2.78 diff in it later on, it pulled that ratio fine with 235/60 x 14 tyres, but i liked the 3.08 ratio better tho even tho it valve bounced at 200KM/H so with 2.78 it would of gone faster, but i did not change the speedo gear in the box when doing so. but with the 3.08 diff if i dropped it back to 3rd at 100 KM/H it would hop like in the tail like jump jump jump jump as the tyres lost traction, so i would just use 4th mainly when over taking at 100KM/H it overtook real well regardless 650 DP Holley extractors dual exhaust but 308H Engine number just a stock reco HG motor i would say. It had L31 on the plate and a center console tho. I bought it in 1990. and i had a 308 Sandman 4sp Van as well at the same time, but i liked the Van better as it sat on the road better at over 180KM/H to 200KM/H all good but the Torana had wind noise and floated about and rear brakes would lock up like a bastard when diving on them 200k or so, you had to be carful of that. but the lightness of the Torana power to weight was king !

I took big bro out for a fang in the Torana with 2.78 and he had just been out fanging a VN SS 5SP and he spun out directly saying the Torana would kill the SS Commodore.

But i sold the Torana in 1992 as i had a Kawasaki ZX10 Ninja, best thing i ever did, saved a lot of money with the bike, with a 240KM/H Crusing speed easy as comfortable as and you can wash away 140KM/H in no time back to 100 most people do not have a clue ! it's save as, just do not push yourself and you can ride 500km trip and get off feeling fresh as.
I road some old type 750 for 90km on the HWY and i was roo tead as the wind wanted to blow ya off the bike no end and at only 180KM/H you were working it hard time struggle. i had to lay down for a bit when i got to my mates place.

When you have driven something real good you know ! I look at GT-HO Falcons and fear them as total rubbish to drive, they are a death trap at speeds above 180KM/H Seriously ! it's the rear springs they are total shit ! all the way to XD.

That is probably true but not what I was saying at all.

Yes but 3.36 5.0L is restricted to 185 KM/H on a stock engine as it's valve bounce at 185 KM/H in fact.
A good 5.0L can float along with ease at 180 KM/H with a 3.08 diff x 14 wheels. you are still in the primarys at 180 KM/H and still good on fuel not to worry you are chewing fuel, it's a sweat spot that you can run on all day long.
But a 4.2L can cruse along at 150 KM/H as that's the sweet spot good on fuel etc all day long.
But a 3.3L red with 3.55 or 3.36 what is the sweet spot to sit on and not chew fuel ? 120KM/H ? maybe 130KM/H.

I never had to replace any clutch ever in my 308 with the 3.08 diff ratio and i drag raced and flogged that car hard not to mention load it up for every week for work, no tow bar on it tho.

I had a New VS ser 3 ute getrag 5sp and 3.08 diff, 160.000 KM up with original clutch, and every week i would load that up with sand and cement bags over the limit, sure the getrag box has a lower 1st gear than a M21 box. had it on the race track a few times as well.

what sort of f*cken idiot wants to drive a HZ at 185 k's they were all over the road by 160k's.

They sit on the road just fine at 180 nothing to it all day long bro but over that and it takes more work to sit back with ease ?