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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
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Originally Posted by 1QWIK7
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
Again, if you have a JDM tranny what are your RPM's in 5th gear at 80 MPH ? :-) neil |
Originally Posted by M104-AMG
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 |
Originally Posted by M104-AMG
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 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
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Originally Posted by dgeesaman
Keeping in mind that not all JDM trannys have the shorter 5th, you might not have gotten it.
Dave |
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 ? |
Originally Posted by M104-AMG
I'm seeing 3000 RPM @ 80 MPH in 5th gear.
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yeah... I think with my JDM tranny I'm more like 3500rpms at 80mph or so
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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 :(.
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Originally Posted by John Magnuson
yeah... I think with my JDM tranny I'm more like 3500rpms at 80mph or so
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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 |
1 Attachment(s)
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 |
Originally Posted by DaleClark
<SNIP> JDM 5th gear is .762. Using a gear calculator I googled (http://www.xse.com/leres/ss/calculator.html)
<SNIP> Dale Anyone have a definitive/reference source ? If so, I may have to update the chart. :-) neil |
bump for some answers.
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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 |
Originally Posted by aoc007
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 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 |
1 Attachment(s)
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 |
just so I don't have to search...yes, it's Friday I'm lazy and curious...when I take my JDM tranny apart, how many teeth = .806 and how many = .762.
:newbie: ?uestion of the day |
Just count the teeth on the gear and pinion and divide.
I'm going to guess: .762: 45/59 .806: 50/62 Dave |
where can I get the .806 5th gear? I know there was a chart I saw few years ago...
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Originally Posted by dgeesaman
Just count the teeth on the gear and pinion and divide.
I'm going to guess: .762: 45/59 .806: 50/62 Dave Dave |
okay...I have 27 and 53 for fifth gear, now I need to count input shaft and countershaft but what will the equation look like? Thanks.
also anyone know where I can get a new blocker ring for whatever 5th I have? |
The definitive answer:
55/25 = .719 (stock USDM) 54/26 = .762 53/27 = .806 |
thank you...do you know if the JDM 5ths had the same problem as USDM's?
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better question, does the updated 5th gear blocker ring have all the teeth? and does it fit the JDM tranny.
The one I picked up in the FS section doesn't fit but is very different looking than the one in the tranny. I did notice REVERSE has all the teeth and 5th did not. am I making sense? |
I can tell you that the 5th gear syncro from my JDM tranny fit the USDM 5th gear perfectly. I don't remember anything unusual about it--I think it had all of its teeth. Having held a US and JDM 5th gear side by side, I didn't see or measure anything that was different other than the ratio, i.e., the gear tooth counts (not the dog teeth--they are the same). I do not know for fact that my JDM syncro is the updated part; however, given that it much newer--post 96 for sure--I assume that it would be.
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Originally Posted by dubulup
better question, does the updated 5th gear blocker ring have all the teeth? and does it fit the JDM tranny.
The one I picked up in the FS section doesn't fit but is very different looking than the one in the tranny. I did notice REVERSE has all the teeth and 5th did not. am I making sense? I believe the old and new 5th synchro design have teeth going all the way around; the difference is the material. There is no correlation between the number of dog teeth which engage the synchro and the number of gear teeth. So there would be no reason for a different synchro for the JDM and USDM ratios. |
thanks for the help guys...I don't know the year or km's on the tranny, but everything looks good...5th synchro and 2nd synchro are the only things that looked like they should be replaced...to expect another 50k-75k miles (which would take another decade at this rate).
I ordered both synchro's, lock nuts, and seals from Ray...they will be here tomorrow, we'll see what the hell is going on here. |
If you have any stuff you don't end up using, PM me.
Dave |
Originally Posted by Speed of light
I think it had all of its teeth.
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bringing this bad boy back from the dead can anyone confirm
if i have a jdm post 99 model tranny at 3500 rpms 5th gear i am at 80mph -18"wheels any of you have the same |
Originally Posted by M104-AMG
(Post 6630062)
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 |
Originally Posted by Alex Rodriguez
(Post 11615404)
bringing this bad boy back from the dead can anyone confirm
if i have a jdm post 99 model tranny at 3500 rpms 5th gear i am at 80mph -18"wheels any of you have the same |
3500 sounds about right. my car doesnt run right now to check. i had to change the speedo sensor when i went to 4.30 rear end so mine might have 1mph difference too
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Originally Posted by GoodfellaFD3S
(Post 11615473)
Alex, we need to know your complete rear tire size to determine your overall diameter and match it against the OEM size.
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Originally Posted by dubulup
(Post 6845318)
thank you...do you know if the JDM 5ths had the same problem as USDM's?
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I have a JDM tranny. I am at 3500RPM in 5th doing 80 MPH. Rear tires are 265/35 18
It also grinds going into fifth unless I rev match perfectly. |
Originally Posted by Alex Rodriguez
(Post 11615404)
bringing this bad boy back from the dead can anyone confirm
if i have a jdm post 99 model tranny at 3500 rpms 5th gear i am at 80mph -18"wheels any of you have the same
Originally Posted by j9fd3s
(Post 11615610)
yep. small synchro needs to stop giant gear. the delicate 5th gear synchro is just an R box thing.
my sources -->https://www.rx7club.com/3rd-generati...os-you-984896/ this thread would of probably given you your answer LOL |
Jack the rear of the car off the ground, release the parking brake, pull a plug from each rotor, put the trans in 4th, hand crank the engine and measure rear wheel rotation for at lease 10 revs of the engine, do the same in 5th.
Thus you can calculate your diff gear ratio and 5th gear ratio. Put the car back on the ground and measure the rear wheel/tire radius. From all of this you can calculate theoretical rpms vs speed. Find a stretch of road with mile markers, use that at a set speed to verify real speed vs speedometer speed. Or use GPS to measure speed vs speedometer. It appears many are not good at math and problem solving. No wonder the forum and USA is falling apart. |
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