13 replies to this topic

[Bazcad]

Hi all, have started the build process on my LX. Going well on rust repairs but still need to find a rear LHS door. I’ve got an SS Ute that I’m using for the donor engine/auto combo and looking an ordering the 9” true trak thru CRS.
Got a few questions :
What ratio to run and what the expected rpm at 100km/h
Diff Width I need to fit 17x10” rims. (17x8” on front)
Will the standard 1440 accommodate and if so what back space to suit flares.
This will be a cruiser that will be driven most weekends. Most likely with the Mrs and kids but still want it to launch without revving it’s nuts off at 100.
Your advice would be most appreciated.
Melbourne, Northern Suburbs.
Cheers.

[Bigfella237]

G'day Barry,

 

What is the exact size of the rear tyres? (eg. 265/50R15 etc.) Overall diameter needed for calcs.

 

What is the ratio of the highest gear (overdrive) in the transmission? Or at least the TRANS code off the donor car's build plate and I'll try and look it up.

 

I'd take a guess that you're looking for something around 3.5:1 or 3.7:1, but it depends on what type of driving you'll be doing? If you do a lot of freeway work then maybe something a little higher, but if you "live life a quarter-mile at a time" then a lower ratio might be more suitable?

[Bazcad]

G’day Bigfella,
Thanks for your reply.
I think for now I will work with the 265/50/R15 that have a diameter of 625.2mm. The 17” equivalent is 265/40/R17 which has a diameter of 627.2mm. I’ve made some inquiries about 17” rims/tyres and availability.

The transmission is the 4L60E with Trans code M30.
From what I’ve read ratio’s are :
1st 3.059
2nd 1.625
3rd 1.000
4th 0.696
I’ve got a VCM 480 cam to go in the LS1 with a 2800 stall converter when the time comes.
I plan on driving the car as many weekends as I can with the Mrs and 3 kids so mainly 80/100 zones. I would like it to launch when its just me but understand theirs a compromise for cruising at a reasonable rpm. Guess I’m looking for best of both worlds.

Thanks for your input. I’m a bit of a Nooby, my first build.
Cheers.

[Heath]

Something around 3.9's or 3.7's would be in the ballpark.

3.9's are a slightly better holeshot and 3.7's would give you a touch less exhaust noise on the highway. 

 

A ~1300kg Torana with a 6.0L motor will get up and boogie fairly well irrespective of the gears you choose.

 

With flares, you don't need to shorten your diff unless you want to get seriously baller spec wheels. If you want to run cookie-cutter off the shelf wheels like like 0 offset 10"s then to fill the guards you'll actually probably benefit from a longer diff, like a VL Commodore length for example.

Edited by Heath, 08 February 2021 - 10:40 AM.

[Bazcad]

Thanks Heath, from what I’m reading and replies I’m leaning towards 3.7
As for length of diff ???? I’m waiting on some info re wheels and tyres I like but would love to get it nutted so I can order.
I’m guessing I need to take a few flare to flare dimensions and work back based on back space etc
And unfortunately I couldn’t get my hands on the 6.0 at the time, 5.7 for me 😉

[neglectedtorana]

Mine is manual but I have 225/50-16 631mm and a 3.7 diff with .75 5th gear and .5 6th gear and on the freeway I enjoy 5th a lot and find 6th a little too tall for enjoyable acceleration

I also comfortably take off in 2nd so 3.7 would be fine for me and it is only a small difference to 3.9 so whichever you choose won't be a mistake

It will still go well with 3.7 and might be easier on the family

[Heath]

Thanks Heath, from what I’m reading and replies I’m leaning towards 3.7
As for length of diff ???? I’m waiting on some info re wheels and tyres I like but would love to get it nutted so I can order.
I’m guessing I need to take a few flare to flare dimensions and work back based on back space etc
And unfortunately I couldn’t get my hands on the 6.0 at the time, 5.7 for me

I would think 3.7 is fine. I didn't mean precisely 6.0L, we're talking ballparks here. These cars have a good power to weight ratio once we do all this shit to them.

 

I personally would buy the wheels you want, cut the shit out of your guards, fit your flares, put your wheels where you want them, and then measure the distance between the hub faces and order your diff accordingly.

 

For wheel size, you can find examples of what other people have on their cars and they'll proudly talk about how their combos don't rub... cool. But most flares cars barely even use the flares. They sit up with a 4WD ride height and they have flares that are so empty you can stick your fist between the fibreglass and the top of the tyre, bump-stops that never seat beacuse the tyres touch the steel bodywork on the inside before the suspension reaches full bump, etc.

 

I know it might sound daunting, but I much prefer to do it "the hard way" and measure as you go.

Edited by Heath, 08 February 2021 - 02:26 PM.

[Bazcad]

Thanks guys. Solid advice.
I might need to find me a Melbourne, northern suburbs mentor 🤘🏻
Got some good photos and info from a fellow Torana nut at the cruise night last week. I was amazed that of all the cars the kids all knew a Torana when it idled past and they got excited. I was like a kid in a Lollie shop myself 🤣

[Bigfella237]

Sorry, I'm late to the party again...

 

I ran some calcs (all running in OD) and with a 3.25:1 diff ratio:

Tyre Size = 265/50R15
Tyre Revolutions = 492 per km
Gear Ratio = 0.70 : 1
Diff Ratio = 3.25 : 1
40 km/h = 746 RPM
60 km/h = 1119 RPM
80 km/h = 1492 RPM
100 km/h = 1865 RPM
110 km/h = 2052 RPM
120 km/h = 2239 RPM
140 km/h = 2612 RPM
160 km/h = 2985 RPM

 

And with a 3.55:1 diff ratio:

Tyre Size = 265/50R15
Tyre Revolutions = 492 per km
Gear Ratio = 0.70 : 1
Diff Ratio = 3.55 : 1
40 km/h = 815 RPM
60 km/h = 1223 RPM
80 km/h = 1630 RPM
100 km/h = 2038 RPM
110 km/h = 2241 RPM
120 km/h = 2445 RPM
140 km/h = 2853 RPM
160 km/h = 3260 RPM

 

And with a 3.70:1 diff ratio:

Tyre Size = 265/50R15
Tyre Revolutions = 492 per km
Gear Ratio = 0.70 : 1
Diff Ratio = 3.7 : 1
40 km/h = 850 RPM
60 km/h = 1274 RPM
80 km/h = 1699 RPM
100 km/h = 2124 RPM
110 km/h = 2336 RPM
120 km/h = 2549 RPM
140 km/h = 2973 RPM
160 km/h = 3398 RPM

 

And with a 3.90:1 diff ratio

Tyre Size = 265/50R15
Tyre Revolutions = 492 per km
Gear Ratio = 0.70 : 1
Diff Ratio = 3.9 : 1
40 km/h = 895 RPM
60 km/h = 1343 RPM
80 km/h = 1791 RPM
100 km/h = 2239 RPM
110 km/h = 2462 RPM
120 km/h = 2686 RPM
140 km/h = 3134 RPM
160 km/h = 3582 RPM

 

And with a 4.11:1 diff ratio:

Tyre Size = 265/50R15
Tyre Revolutions = 492 per km
Gear Ratio = 0.70 : 1
Diff Ratio = 4.11 : 1
40 km/h = 944 RPM
60 km/h = 1415 RPM
80 km/h = 1887 RPM
100 km/h = 2359 RPM
110 km/h = 2595 RPM
120 km/h = 2831 RPM
140 km/h = 3303 RPM
160 km/h = 3775 RPM

 

Please note that these RPM figures are only approximate and only with the torque converter locked-up, I can't account for the slippage of a high-stall converter.

 

Also note that with ratios down around 3.7 or lower, the ½ critical speed of a standard (green) V8 Torana driveshaft would be right around 100~110 km/h, which is not good. Remember to consult your driveshaft builder about this, you would need to go with a larger diameter shaft or possibly even a two-piece shaft with a centre bearing (which would require body mods).

 

[Bazcad]

Thank you so much for this info Bigfella.

[gtrboyy]

3.7 would be tallest gears I'd go & 3k stally smallest even for stock cam ls1.

 

Got 3.46 in manual vy sv8 with otr/tune/extractors etc etc...gears way too tall for dailty duties.Did long highway trip 6th gear@1500rpm yuck

 

Overdive & taller tyres will chop revs down on highway anyway...exhaust will annoy you more if it drones or too loud.

[DanWA]

I have 3.9 with T400 and 3800 stall and it isn't much of a Sunday car more of a 1/4 mile car

[WA1TNC]

G’day Bigfella,
Thanks for your reply.
I think for now I will work with the 265/50/R15 that have a diameter of 625.2mm. The 17” equivalent is 265/40/R17 which has a diameter of 627.2mm. I’ve made some inquiries about 17” rims/tyres and availability.

What are they & where are you getting these 265 40 17’s from & how much mate?

Cheers, Nig.

[yel327]

Bob Jane have heaps of different 255/40/17 listed but no 265.