JDM tranny owners, RPMs at 80 MPH in 5th
 

I finally got my JDM tranny installed, and was wondering what RPM are JDM tranny owners seeing at 80 MPH in 5th?

I'm seeing 3000 RPM @ 80 MPH in 5th gear.

Thanks,
:-) neil

Stupid question but if you have your JDM tranny at 3000rpm in 5th, im sure everyone else with a JDM tranny will be at 3000rpm in 5th too right? :D

To clarify, I want to make sure I got a JDM tranny with the lower fifth gear.

Again, if you have a JDM tranny what are your RPM's in 5th gear at 80 MPH ?

:-) neil

ahh, now it makes sense...

Well you shoulda said that in the original post ;)

Stock 4.1 diff ratio, stock tire size, with a USDM 5th ratio of .719, 3000rpm will produce 75mph.

With a 3.9 diff ratio, stock tire size, USDM 5th, 3000rpm => 79mph.

What diff and wheel/tire size are you running?

Keeping in mind that not all JDM trannys have the shorter 5th, you might not have gotten it.

Dave

I See 70 At 3k

That I didn't know. Is it model specific or year specific?

I also see roughly 3000rpm@80, but my speedo is fast according to my GPS, even with stock wheels/tires. Standard USDM ratios here.

It doesn't sound like you have the lower 5th ratio.

Did a little digging for you, Neil. US 5th gear is .719, and JDM 5th gear is .762. Using a gear calculator I googled (http://www.xse.com/leres/ss/calculator.html) and putting in the 4.10 rear end and 25" tire diamter (close enough, just took the default) I got 75.5 MPH at 3000 RPM in 5th with the US 5th gear, and 71.4 MPH with the JDM 5th.

Dale

Sorry, I just did a search to check and it looks like I'm mistaken. So far, what I've read all says the JDMs have the shorter 5th across the board. The JDMs had varying final ratios.

https://www.rx7club.com/showthread.p...hlight=jdm+5th



Dave

I have the stock wheels and tires (25" diameter) and the stock diff (4.1).

I'll take a look at the RPMS @ 70MPH and post them.

I sure hope I have the lower 5th . . .

:-( neil

BTW: are there any markings on the diff to know you have a 4.1 instead of the automatics ?

Based on this^^, it seems like you have the 'standard' FD tranny internals. 3k rpm in 5th at 80ish mph is stock.

yeah... I think with my JDM tranny I'm more like 3500rpms at 80mph or so

Correct me if I'm wrong, but didnt the JDM rx's like from 99 and up came with the lower 5th gear? And those that came with it had came with 4:30 rearend. So your combination didnt come from factory from japan. But I could be wrong. My car has the shorter gear with the 4:30 but where I live, you have to brake before you reach 50mph :(.

according to some calculations (JDM should be .806, no??) this seems correct.

Using the calculator posted, I think I might have a 3.9 rear-end !

Time to get the GPS out, hopefully I can at least trust the tachometer . . .

:-( neil

Using the calculator posted, I compared all the different diffs and 5th gear ratio combos that I know of, including the higher Pettit Racing 5th gear combined with the 4.3 diff.

In order to make the comparison easier, 5th gear is the JDM tranny ratio, and 6th gear is the USA tranny ratio. Reverse is probably wrong, and the calculator rounds up to two decimal places.

Note, that the 3.9/automatic diff, with the stock USA tranny ratios, yields the closest to my observed 80MPH @ 3000 RPM, hence my belief (and dgeesaman's) that I have an automatic diff.

:-) neil

PS: anyone have a 4.1 or 4.3 diff for sale . . .

https://www.rx7club.com/attachment.p...hmentid=221700

Seems to be a discrepency on the JDM 5th gear of 0.762 or 0.806 ?

Anyone have a definitive/reference source ? If so, I may have to update the chart.

:-) neil

bump for some answers.

My car has manual rear end 4.10, 17x9s wrapped in 255/40s, stock 5th and I get 3000rpm at 80mph, could this be attributed to a speedo thats off or the non-stock (but very close) tire/wheel size?

-Andy

A 255/40R17 supposedly has a diameter of 24.8-inches.

With the referenced calculator your RPM @ 80MPH should be 3,201.

BTW: I measured the diameter of my tires, and they are 25.3-inches.

I also marked the driveshaft, and have verified I have a 4.1 diff.

In short, I don't have the taller 5th gear. . . yet!

My last question still remains:

Seems to be a discrepency on the JDM 5th gear of 0.762 or 0.806 ?

Anyone have a definitive/reference source ? If so, I may have to update the chart.

:-) neil

Why can't people do simple math anymore?

The TSM has the gear ratios for stock and it only takes simple math to calculate the differences.

cewrx7r1: I looked at your attached doc. Do you know what the JDM 5th gear was for 1992-1994 (your JDM starts at 1995 and goes thru 2000).

TIA,
:-) neil

(digs out JDM dealer brochures)

OK, first dealer brochure from '92-95 model years show .806 5th gear. I have one that says "95 model year" and it shows BOTH .762 and .806 5th gear ratios - the Type RZ having the .762, and the Type R-S having .806.

Spirit-R brochure shows the Spirit-R itself having the .762, and the Type R Bathurst having the .806.

Another one I have (it's a '96-98 brochure) shows type Type RZ with the .762, and all others with the .806.

So, in a nutshell, there are TWO JDM 5th gears. The US 5th is .719, for those of you just joining us :). So, there's quite a selection :).

Dale