Rev calc's for Bundy with 34's Q.

[sudso]

Hi, I'm after the formula for working out rpm calculations for my Bundera, RJ70.
I know the diff ratio's are 4.88 and the tyres are 34" JT's.

I'm putting a 350 chev in with a turbo350 auto so steep hills are obviously going to be an issue with the auto. I'll probably have to get a torque convertor that locks up at lower revs and a mate is going to put a manual valve body in for me.

Also does anyone know what the low range gearing is in Bundera's so I can work out what revs I'll be doing when crawling etc.
2.7:1 sounds familiar but I'm not sure, I may need lower gearing in low range.
cheers

[HotFourOk]

Taken from marks4wd:

"RJ70 Bundera Information:
Manufacture Date; November 1984 through to October 1985
Engine; 4-cylinder 2.4 litre 22R, petrol engine.
Transfer Case; The transfer case is the same as the Toyota Land Cruiser split transfer case and is part time 4WD with a 34mm idler shaft and a low range ratio of 2.276:1.

Differential; The differential ring and pinion tooth count is 43/10 giving a ratio of 4.3:1.

Manufacture Date; October 1985 through to August 1992
Engine; 4-cylinder 2.4 litre 22R, petrol engine.

Transfer Case; The transfer case is the same as the Toyota Land Cruiser split transfer case and is part time 4WD with a 38mm idler shaft and a low range ratio of 2.276:1.

Differential; The differential ring and pinion tooth count is 41/9 giving a ratio of 4.55:1."

Its the LJ70 Bundera's which have a differential ring and pinion tooth count of 39/8, giving a ratio of 4.88:1

[dumbdunce]

I know the diff ratio's are 4.88 and the tyres are 34" JT's.

if it's an RJ70 then it will have 4.3 or 4.6 diffs

I'm putting a 350 chev in with a turbo350 auto so steep hills are obviously going to be an issue with the auto.

up hills or down hills? the only issue you're likely to have is that it might rev too high on the freeway, but if you have 4.3's, and 34" tyres, it will be ok. what hill issues were you anticipating??

I'll probably have to get a torque convertor that locks up at lower revs and a mate is going to put a manual valve body in for me.

neither is necessary. you're talking about stall speed for the converter, not lockup, and the stall speed should be to match the engine, not the vehicle so much. what makes you think a manual valve body is going ot be a worthwhile addition?

Also does anyone know what the low range gearing is in Bundera's so I can work out what revs I'll be doing when crawling etc.
2.7:1 sounds familiar but I'm not sure, I may need lower gearing in low range.

it's 2.27:1, far from needing lower low range gears, you'll probably find that you never need low range again. you get torque multiplication in the torque converter (unless you go stupid and get a very low rpm stall converter - but why??), and sticking with the 4 cylinder gearing will give fantastic low range poerformace from a big motor.

it also has to be asked - why a 350? a 5 litre or even a 3.8 litre V6 will give perfectly adequate on and off road performace with less fuel useage and less weight penalty. even a very mild 350 will have you snapping CV's, diffs and axles pretty easily if you're not very very careful.

cheers
DD

[sudso]

Guy I bought it off says it has 4.88 diff gearing, spose I'll have to take one off and count the teeth to be sure.

Reason for manual valve body and low stall is that the T350 auto's apparently have a habit of changing into 2nd even when the shifter is in 1st position. Dont want it doing that down a steep slippery slope, want it to have decent engine braking when going real slow.
Bro in law is also giving me a B&M shifter

Reason for the 350 chev is I already have one sitting here, was going to put in my HK, a complete stock runner (unleaded with carby) and the auto as well. Plan to dual fuel it too for cheaper running.
Yeah your'e right, a smaller V8 or a V6 would be ample but it saves me buying one if I use the one I got. Good for towing too.


cheers.

[-Scott-]

I know (from experience ) the 700's in the VS/VT would change into 2nd even when held in 1st, but I have no idea if earlier trannies do that.

There was a topic on here some time back about enabling the lockup converter for engine braking. From memory, it was primarily Rover trans. I don't know if the TH350 can adapt to a suitable converter?

Scott

[cloughy]

I know (from experience ) the 700's in the VS/VT would change into 2nd even when held in 1st, but I have no idea if earlier trannies do that.

There was a topic on here some time back about enabling the lockup converter for engine braking. From memory, it was primarily Rover trans. I don't know if the TH350 can adapt to a suitable converter?

Scott

That's cause there elctronically controlled and prevents you hitting the rev limiter, but hits the limiter in 2nd 3rd 4th

A B&M shifter is no reason for a fully manualised valve body, all it is is a T bar shifter in wanky form but easy to install cause its cable

[lay80n]

I know (from experience ) the 700's in the VS/VT would change into 2nd even when held in 1st, but I have no idea if earlier trannies do that.

There was a topic on here some time back about enabling the lockup converter for engine braking. From memory, it was primarily Rover trans. I don't know if the TH350 can adapt to a suitable converter?

Scott

That's cause there elctronically controlled and prevents you hitting the rev limiter, but hits the limiter in 2nd 3rd 4th

A B&M shifter is no reason for a fully manualised valve body, all it is is a T bar shifter in wanky form but easy to install cause its cable

A B&M ratchet shifter is not useless if its used in its proper application - to ratchet through gears in manualised auto's. The ability to ratchet up gears is pretty handy in a drag car, but in a standard VS V6 commadore will full sick chromies, yeah there is the deffinate wank factor. A ratchet shifter coupled with a worked and manualised auto would not be that bad. Have seen this setup in a few yank rigs that worked well.
Layto....

[sudso]

A B&M shifter is no reason for a fully manualised valve body, all it is is a T bar shifter in wanky form but easy to install cause its cable

yeah but he's giving it to me for free and I dont have a shifter for it yet
nothing to do with manual valving it.

if it's an RJ70 then it will have 4.3 or 4.6 diffs

yep, they are 4.56 (4.6?)

[Hoppy11]

http://www.4lo.com/calc/gearratio.htm

Hoppy

[sudso]

http://www.4lo.com/calc/gearratio.htm

Hoppy

Well that makes it easy now dont it? Thanks Hoppy, that link should be a sticky!

So with my current gearing, tyres etc: 4.56 diffs, 2.27 low range, T350 1st. gear-2.52, 34"tyres:

1000rpm = 3.9mph and a 26.09% crawl ratio, hmmm pretty ordinary

with Marks Adaptors 3.05 Gearmaster low range:
1000rpm = 2.9mph and a 35.05% crawl ratio, better but still ordinary

with Trail Tamer 4.0 low:
1000rpm = 2.2mph and a 45.96 crawl ratio, good

with Trail Tamer 4.7 low:
1000rpm = 1.9mph and a 54.01 crawl ratio, cool

with Trail Tamer 5.0 low:
1000rpm = 1.8 and a 57.46 crawl ratio, not much in it from the previous

Funds for this at the moment =

[dumbdunce]

So with my current gearing, tyres etc: 4.56 diffs, 2.27 low range, T350 1st. gear-2.52, 34"tyres:

1000rpm = 3.9mph and a 26.09% crawl ratio, hmmm pretty ordinary

those numbers don't really mean anything!

remember that you are more than doubling your available torque at low rpm with a massive engine capacity increase, and your torque converter will about double the flywheel torque in high slip (ie crawling) conditions. the off road performance will be fantastic with stock gearing - you will find the problems occur at the other side - on the highway it will be revving way too high and you'll be begging for bigger tyres or taller diffs.

[sudso]

It wont be revving too high on the highway cos I am looking at only lowering the low range gears for better engine braking down tricky steep declines.
The high range gearing will remain stock, eg: if high range ratio is 0.8:1, the diffs are 4.56 and the tyres are 33", at 110kph the rpm is 2400

If the high range is 1:1 then the rpm's at 110 are 3000.

Not sure if the Bundy's are 1:1 high range, has the cruiser style split transfer.

[dumbdunce]

It wont be revving too high on the highway cos I am looking at only lowering the low range gears for better engine braking down tricky steep declines.
The high range gearing will remain stock, eg: if high range ratio is 0.8:1, the diffs are 4.56 and the tyres are 33", at 110kph the rpm is 2400

If the high range is 1:1 then the rpm's at 110 are 3000.

Not sure if the Bundy's are 1:1 high range, has the cruiser style split transfer.

yes the bundera transfer is 1:1 high range. 3000rpm is screaming its head off for a 350 - remember you have 4 cylinder gearing in the diffs and with standard gearing everywhere else the V8 will have to make 4 cylinder style revs to make it go that fast - you'll be pouring a lot of fuel through! a 350 will easily push a bundy along at 2000rpm or even less. 3000@110km/h is what my 1.8 litre pulsar does! to put that in 350 terms, that's under 1000rpm for the same volume air flow.

with such a big motor, even with average crawl ratio, even with the auto, even without manual lockup on the converter, it will have better engine braking than in stock form. Any descent steep enough to need really phenomenal engine braking is too steep for engine braking alone, not to mention too steep for a bundera. Keep it cheap and simple!

cheers

DD

[sudso]

Yeah the "KISS" principal is usually the best.

Did any of the split t cases have a 0.8 or less high range gearing?

[sudso]

3000rpm is screaming its head off for a 350

Thats what my 3.2 V6 Rodeo is doing at the state limit with 31/10.50's. In 5th gear!
So much more normal with the 33's on but.

[dumbdunce]

Did any of the split t cases have a 0.8 or less high range gearing?

no, all the factory high range gears are more or less 1:1, you need to go aftermarket to go higher. bigger tyres or taller diffs are your only real choice, the marks gears only give you 8% overdrive and bugger all extra low range underdrive.

these are some of the things that make a bundera a particularly crappy starting point for a conversion. no other tranfer will fit (no room), and the axles and diffs are the wrong ratio and too weak for big power - so if you do go down the 350 path, the crystal ball says there is an expensive 80 series axle converison front and rear in your near future. the axles themselves are pretty cheap but the chop and weld is not.

[sudso]

Any descent steep enough to need really phenomenal engine braking is too steep for engine braking alone, not to mention too steep for a bundera.

Wouldn't slower be better for a tippy Bundy though?

[+dj_hansen+]

In response to various tyre/rpm questions and for those that want to do precise comparisons charts and get really technical etc, here ya go.

Many of the tyre size/ rpm charts that can be found on the net can be useful for very basic comparison purpose, if your tyres do actually come close to sizes specified. But that is usually the problem as most rarely do so they can't really be used for precise calculations.

Also there is no way of knowing what "constant" they use. Tyre diameters indicated on these charts may also not be “loaded”. To make it worse not all manufacturers tyres have the same actual overall height or radius.

But further limitations are that realistically there are only specific ratios commonly available for the Toy anyway, ie 4.1, 4.3, 4.56 and 4.875, ie if you now have 4.56’s the only step available is the 4.875 irrespective of what a chart may determine.

So in our case it makes more sense to only use our given ratios to outline the various options and what is best for your plans and there are also other factors that you should take into account, especially when considering forking out the big dollars necessary for a complete ratio change or tyre change, ie body or suspension lifts etc and the first is to be sure the figures you have are accurate.

I have been using the loaded wheel radius for many years, ie from the ground to the centre of your wheel as your vehicle currently sits. This is the true height that will determine your vehicle speeds/rpm etc and not the overall measured static height.

A wheel rotates in a perfect circle as per its radius from the centre of the axle and not its static diameter as we all know there is a flat spot on the bottom, Very Happy , ie I don’t know about yours but my wheel rotates in a perfect circle from the axle centre, it doesn’t rotate like an egg to take account the constant flat spot on the bottom or the perfect circle at the top, Very Happy .

Therefore, doubling the LWR will also become your tyres true overall diameter, ie if your LWR is 15" and you then measure from the centre of the wheel to the top of the tyre you will find this section will be slightly more than 15". Therefore, the true loaded wheel diameter (LWD) of your tyre is double the LWR, which in this case is 30".

As an example my LWR is 15.25” and my “wheel” rotates in a perfect circle on the axle meaning I have an overall diameter of 30.5”, yet my tyre is marked as a 32”. Big difference.

Recently I found this site that also uses this method of calculation (finally) so this makes it a lot easier and quicker.

http://www.albinsgear.com.au/formulae.html

But here’s a written example.

You need to know the diff ratio to get the overall gear ratio you want to use, which is the diff ratio multiplied by the gear ratio.

Speed has to be in mph in the written formula Very Happy but the net calculator above has both metric and imperial options. According to net conversions 100kph is actually 62.1371 mph not 60 mph as many think.

http://www.goconvert.com/cgi-bin/speed.asp

RPM = GR x MPH x 168 divided by LWR

Ok, you want to know the rpm's at 100kph in overdrive and you have a R150, 4.56 diff and exactly 16" LWR tyres.

The R150 overdrive rounded is 17% so 4.56 x 0.83 = 3.7848 which becomes the overall gear ratio (GR). You can use any gear ratio multiplied by your diff ratio to get the overall ratio, ie 2nd is 2.06 x 4.56 = 9.39 (GR).

So 3.7848 x 62.1371 = 235.176... x 168 = 39509.65 divided by 16 = 2469 rpms at 100kph.

This will immediately show that despite what many think going up exactly 1" to a 33" LWD does not gain a meaningful drop in rpm's, Very Happy

39509.65 divided by 16.5 = 2395 rpm's, a difference of only 74 rpm, which shows its not worth doing if you were actually chasing an rpm drop!!!!!!.

Going up 2" to a 34" LWD is 39509.65 divided by 17 = 2324 rpm again only a 145 rpm drop.

If I did a diff ratio change to 4.3 it becomes.

4.3 x 0.83 = 3.569 x 62.1371 = 221.767 x 168 = 37256.85 divided by 16 = 2329 rpm, again not as great drop BUT note its virtually the same as a 2" tyre increase.

But if you were only chasing an rpm drop of around 150 then this information now gives you two options to consider, ie a 2” tyre increase or a 4.3 diff change. The tyre increase probably means a body lift and the cost of new tyres and maybe rims etc versus cost of two diffs from wreckers.

If we go to 4.1 it becomes 4.1 x 0.83 = 3.403 x 62.1371 = 211.452 x 168 = 35523.937 divided by 16 = 2220 rpm a difference of 245 rpm which is more meaningful.

Using this information you can do comparisons using various diff ratios and also include different tyre diameters etc etc. I do spread sheets for all my possible combinations when making choices along these lines.

But it is also wise before making a decision to consider the other equation, ie what will my other gears be like if I did a diff ratio change etc and more so first gear.

The R150 has a 3.83 1st so 3.83 x 4.56 = an overall ratio of 17.46 versus 3.83 x 4.1 = 15.70. Which overall 1st gear ratio would be best suit your purposes or driving style.

I do all these calculation for all gear ratios and compare to what I currently have as it can make a huge difference in how your vehicle will behave if you go the wrong way.

To add to the list the following formulas can provide a quick guide and add to the information needed to make a selection.

To ascertain speed (mph) at a set rpm and ratio

RPM x LWR
---------------- = MPH
GR x 168

To ascertain what ratio is required to obtain a set speed at a certain rpm.

RPM x LWR
----------------- = Gear Ratio
MPH x 168

To ascertain what diameter tyre is required for a set speed, rpm and ratio, remembering the answer means you would have to find a tyre that will give a LWD of the same amount, not what the manufacture plaque says etc.

MPH x GR x 168
--------------------- = Tyre Diameter
RPM


By making up charts with all this information for comparison you can make smart decisions, Very Happy

JD

================
Copied from toyotasurf website...

[sudso]

and the axles and diffs are the wrong ratio and too weak for big power - so if you do go down the 350 path,

It's only a carbed stocker with a few miles on it. Prolly only makes 250ft.lb's. that's prolly twice the 22r though

[sudso]

I have been using the loaded wheel radius for many years, ie from the ground to the centre of your wheel as your vehicle currently sits. This is the true height that will determine your vehicle speeds/rpm etc and not the overall measured static height.

Yes that would be more accurate.
But doesn't the LWR increase the faster you go, as the wheel spins faster the centrifigal force increases the static diameter of the tyre?
Not that there'd be much in it though.