Ratios; searched but can't find them

[81xsproject]

In order to use MegaLogViewer (program I use to analyze my data logs and tune my FI) to compute HP and TQ, I need a weight (which I got at the dump on Saturday), a transmission ratio (which Clymers says is 1.285 for 3rd), a final drive ratio, and a wheel diameter. I searched and searched for the answers with no luck even though I KNOW it is all there.

So, my first and stupidest question is, when a ratio is shown as one number, as "1.285" is shown above for third, is it 1:"1.285" OR "1.285":1? My guess is the latter.

Is the middle drive 1:1? If not, what is it.

What is the STOCK final drive ratio?

If the middle drive isn't 1:1, I will have to factor it into one of the other 2 ratios that it asks for. If someone is really good at these ratios and can lend some numbers, I would greatly appreciate having something to check my calcs against.

thanXS in advance

[crazy steve]

>So, my first and stupidest question is, when a ratio is shown as one number, as "1.285" is shown above for third, is it 1:"1.285" OR "1.285":1? My guess is the latter.

The latter; the input turns that much for one turn of the output.

>Is the middle drive 1:1? If not, what is it.

Nope; it's 1.056:1. But don't forget, there's also a 'secondary drive' between between the trans and the middle drive and it's ratio is .936:1. And there's yet another 'gear ratio' between the crankshaft and the transmission, and that ratio is 1.657:1

>What is the STOCK final drive ratio?

3.3:1.

So if you 'stack' all the ratios, you get: 1.657 x 1.285 x .936 x 1.056 x 3.3 = 6.95:1. So the crankshaft turns 6.95 times per each turn of the rear wheel in third gear.

And wheel/tire diameter if you're running the 'typical' 130/16 tire is 25.3", give or take. These can be as small as 24.7" or as large as 25.7", depending on brand/model. If you're running a 17" tire, these run right around 26.1".

'78E original owner

[81xsproject]

So, given the available input fields in the program I think I will attempt to lump all the extra ratios into the final drive.

Transmission 3rd gear
1.285

Final drive (combination of all other ratios)
5.405

Sound correct...?

[fredintoon]

- - - wheel/tire diameter if you're running the 'typical' 130/16 tire is 25.3", give or take. These can be as small as 24.7" or as large as 25.7", depending on brand/model. If you're running a 17" tire, these run right around 26.1". - - -

Hi Steve,
another thing to consider in actual tire diameters is the wear factor. If you reckon on there being 1/4" of tread thickness between new and unsafe there's a 1/2" difference on the same tire.

[crazy steve]

So, given the available input fields in the program I think I will attempt to lump all the extra ratios into the final drive.

Transmission 3rd gear
1.285

Final drive (combination of all other ratios)
5.405

Sound correct...?

Yep, that'll work. Plus if you decide to use another trans gear, you only have to change that input. That 5.40 number is fixed, so the only variables are the trans gear and tire.

And Fred's right about tire wear. If you want your tire diameter number to be dead-nuts on, the best way to determine that would be to measure circumference with a cloth tape measure (which will be somewhere between about 79" and 84") and calculate it via circumference/pi = diameter. Do you need to be that close? Probably not; under full-power runs, there will likely be some tire 'slippage' and 'tire growth' from centrifigal force.

'78E original owner