gear ratio's not making sense.

[SVOeric]

I've been looking at several websites with gear ratio calcs...

created a lil java (borrowed a bit too )

and came up with this
www.svoca.com/gears

problem is, I don't think it's right...

We all know stock, 85/86 SVO's run right at 70 mph at 3000 rpm in 5th, but it don't calculate out that way!!

Here is the formula I'm using
mph = ((rpm * tire_diam) / (gear_ratio * axle_ratio * 336.1352398))

I'll add a default selection for 84 SVO's too shortly, and several other common T5's.
I need to look up the ratio's for them.

** If you don't hit the clear right button, and you run a second set of calcs, the calcs will be below the first set you already see **

[BrianO]

your figures match up exactly to the spreadsheet I've used for a long time, only your numbers round up to the next digit.. no biggie.

I think the driven gear is going to compensate for that 5mph since it won't be dead on so the closest one puts it a bit under showing 3k@70mph.. that is my experience anyways.

[SVOeric]

there's no reason for it to be off any more than .5 mph. (for rounding to the nearest mph) tho... everthing is taken into account there, unless the speed-o's are all wrong, but I'd think I'd have gotten a ticket for that much, considering I tend to push the limits

[tateg]

It works out for me, but I'm running the 3.73 rear with the '84 trans. I'm running 70 at about 3000rpms and that's what it shows.

[GAboySVO]

If you put 0.83 in for 5th gear, you will closer to what you are expecting. The speedo uses spring tension to determine what the guage reads. It could be off just a smidge and the needle will jump 5 MPH.

Maybe double check with Hanlon on the 5th gear ratio for our tranny.

[BrianO]

It works out for me, but I'm running the 3.73 rear with the '84 trans. I'm running 70 at about 3000rpms and that's what it shows.

that is exactly what I had with the NWC and 3.73's as well.. once swapping back to 3.45's is when I had to find the right driven gear.

I've tried like 6 different driven gears trying to find the right one and end up pretty close, but never dead on.

[SVOeric]

so all of us that show 70 @ 3000 on stock geared 85-86 SVO's have speedo's that are off 4mph ?

It wouldn't supprise me, I'm just trying to figure the math, cause I've heard lots of people say 3K = 70mph.

[Pat_in_L.A.]

I think that you may be noticing the difference between a "gauge" versus an "instrument". An accurate digital tach (like on a high end timing light) and a GPS would tell you for sure. I should think that any production speedometer would tend to read on the high side slightly, for liability reasons. Tire wear changes things as well.

[SVOeric]

very good point pat, the tac could be off as much as the speedo...

[Pat_in_L.A.]

I can bring my radar speed gun to the reunion and we can test some cars. Again.

You could also use an EEC Tuner to reset the redline in the EEC to 3000 RPM. Volunteers? Don't everybody speak up all at once!

Actually, isn't there already data logged from Dyno Day at previous Reunions? Didn't they have speed readings on some of those charts?

[SVOeric]

no, I have my eec tuner...

[85ttops]

3000 = 73.5/74 mph in my black car . running 87tc 8.8 and 91wc t5 tranny with the pink tranny gear

[GAboySVO]

Eric, i double checked the '86 Norcal car on the way to work today and 70 MPH =~2900 RPM where as 3,000 RPM = ~73 MPH.

[SVOJames]

On my stock geared & tired 86, my GPS would show 72-74 mph (weighted to the 74 side) at an indicated 3K on the electronic tach.

[Keasbey]

for the ratios in the 2.3L tranny (These #s are from All-data)

1st= 4.03:1 2nd=2.37:1 3rd=1.49:1 4th= 1:1 5th=0.86:1

don't know if it could help.. but "all-data" gave me those numbers for either 2.3n/a & 2.3T mustangs.. sooo I can't tell if its right.