Ever since I've had my swap the gearing has puzzled myself and a few others I've let drive my car.

My tranny out of a 98 spec JDM ITR (Along with motor).

Right now when I do 4000 rpm in 5th gear that's about cruising speed of 80 mph.

I have 16 wheels with 205/40/16's on them.

Using that info could one of you guru's estimate what my Final drive is??

It should be a 4.785 (Based on the year stamped on my old JDM ITR motor and the serial number matching up between the head/block/tranny) btu it seems geared long. Even longer then a regular ITR tranny (B18C5-EH drove my car and made that comment).

Ny help would be appreciated guys. Yes I've done a search but I can't seem to find exactly what I'm looking for. I tried that autocross calcualtor but it didn't work (Also wants FD number which is what I'm trying to determine also).

Thanks in advance guys.

 

Why didn't you crack the case open while the tranny was out of the car for so long? All you have to do is count the FD teeth and shaft teeth and divide for the ratio.

That's the only way to know for sure.

 

Even though the JDM tranny has the 4.7 it has a GSR 5th gear (0.787)

 

http://www.autocrossing.com/cgi-bin/gearcalc.cgi

http://www.a-t-s-usa.com/ats-product...mparison.shtml



[Modified by Black R, 1:32 PM 9/30/2002]

 

Because I wasn't eager to **** my own **** up.
Because I was scared to mess with it

Because I was DAMN LAZY lol.

I really wanted to but Rob didn't seem motivated to do it (With amount of other stuff he had) and our "Friend wanted to charge me 150 bux. I figured it wasn't that important that needed to shell out the money (Esp with me trying to buy parts and stuff).

 

This is all you need to do:
Get the gear info from this site:
http://www.ff-squad.com/Bgears.htm

then plug them into this site with the correct tire sizes.
http://www.autocrossing.com/cgi-bin/gearcalc.cgi - (this has some of the gear #'s already)
or
http://www.f-body.org/gears/
(which ever one is easier for you)

This should give you what you need.

-Nick

 

I cannot give you a precise answer because I don't have all the JDM gearing number but here it goes:

If we start with your input of 80mph = 4000 rpm in fifth then:

At 80 mph your tires (5.88 ft in circonference) will be rotating at 1197 rpm.
The total gear ratio should then be 4000 / 1197 = 3.342

If we suppose a FD of 4.785, this will give you a fifth gear ratio of
3.342/ 4.875=0.682

If we assume a FD of 4.4 (USDM) this will give you a fifth gear ratio of
3.342/4.4=0.759

If we assume a GSR fifth gear of 0.787, that will give you a FD of
3.342/0.787=4.426

Unfortunatly I cannot confirm if these gear s ratio are close to something existing.

The final assumption is a 4.785 FD with a GSR fifth of 0787

This will give you an engine RPM of 4592 at 80mph or a speed of 71 mph at 4000 rpm, which does not correspond with the initial fact.


[Modified by JPP, 1:47 PM 9/30/2002]


[Modified by JPP, 1:48 PM 9/30/2002]

 

Thanks for the attempt JPP. And Nick I was actually looking for that site but I couldn't find it (After searching on this one). Thanx guys. Anyone else's input?

 

How do you know you are going 80mph? If its by the speedo then all bets are off. The speedo "calculates" your speed based on the stock gear ratios, stock tire sizes. Change either and the speedo is worthless. Also Honda tachs and speedos are notoriously inaccurate. Usually optimistic by 1-5%

So my question to you is - why does this matter to you? Does the car behave the way you want? If so then be happy, don't worry. If not then change tire diameter til you are happy.

 

Actually that's only half true. The speedo gear is placed AFTER the final drive. I don't care what gears, final drive, etc you have, the axles will spin just as fast at 80mph as a car with stock gearing but same overall tire diameter. The tire size will make a difference in the tach (edit: tach? make that speedo) though.


[Modified by Dave-ROR, 3:13 PM 9/30/2002]

 

.....what Dave said.

Oh yeah, he wants to know so he can figure out what to upgrade - whether that's the LSD, final drive, or 1-5...

 

Well, if this were all on an ITR, the speedo would be reading 4.2% too fast. (because of the difference in revs per mi between 195/55-15 and 205/40-16) So, at a speedo-listed 80mph, you would actually be going 80 x .958 = 76.64mph.

Since I'm not sure what the stock tire/wheel setup is on your car, I can't tell you what the adjustment would be on your car. Sounds like you have a 4.785 FD with a gsr 5th, and the rest of the confusion may be explained by the change in wheel/tire circumference. My understanding is that the speedo is measured after the FD, but is based on the stock circumference of the wheel/tire.

 

Since it is a JDM tranny I think it is an R 5th. JDM R and USDM GSR have the same 5th gear. (0.787)

 

Well, at least I wasn't entirely wrong. So, USDM R has a different 5th?

That said, you're speed is very incorrect.

 

I care because I'd liek to know. I'm happy wit hthe car but I was thinking about upgrading my FD. I don't want to buy a JDM FD and realize I already have it. Conversly i don't neccesarily want to by a ATS FD if I have a 4.40 (I would only want to go to 4.785 then).

I'm running 16 Gram Lights 205-40-16 series Toyo's.

I'm reading the speed off my Apex'i Rev Speed Meter. I had a friend with a GSR ride along side me and he cruises @ 80 mph @ 4000 rpm as well. I can still accelerate faster then him but I figured that was due to the weight diff, engine, flywheel (Mine is lighter then his).

Looks like this has sparked more ?'s then answers. Serves me right for not gettign the gumption to crack the tranny case open when I had the chance.

 

USDM R 5th is 0.848

 

Man, if you can afford it just get the ATS! IF it is a JDM R tranny your 5th gear will cruise better than a USDM R with an ATS anyway and it is definitely worth it.

 

Thanks Trey. I guess this is like the annoying math problem in school that you just can't seem to figure out. It drives you nuts and even though its not important, you still want to know the answer before moving on.

 

Hurell, if you can tell me what speed you hit the rev limiter at in 1-4 I can figure it out for you...

 

ATS is def worth it.

I figure 77mph at 4000 RPM with the JDM transmission and your tire size. Which seems about right considering the speedo difference, etc.

 

Dave you are saying that it does indeed seemed to be the 98 JDM ITR gearing (W/the 4.785 FD). The reason I'm also asking is because I'm @ a cross roadds right now. I need to figure out which way I'm taking my snatchback (N/A or F/I). Cost is a determining factor (I can afford either way I'm figuring dollar to performance to headache to driveability ratio). I've already been N/A once (Toda Spec B's) but I could have went further.

 

I just reran the numbers and realized I was using a 4.400 FD sorry man. 71mph is a JDM ITR tranny.. however one thing to keep in mind is the speed sensor and how the speedo will interpret it's signal. In the "old" days it was easy to figure out since it was printed on the gauge (since it was gear driven and the calibrated revs/mph was listed).... did your car remain at the same speed as your friends GS-R when both indicated 80mph? If so, I'd think you had a 4.400.

You sure it's a 98 swap?

 

Yeah, with 96 spec internals.....

I say do an ATS final drive... If you go turbo, it'll be great in vacuum and around town. Rev to 10k just for the hell of it and you'll have quite a beast.

 

Positive. The 3 circles were on the head of the original motor (The circles that give info about the head casting ie: Year made). Mine said 98. I matched the Tranny and block up with the head serial number wise so I know the entire motor (Tranny included) comes out of a 98 spec ITR.

This has lead me to believe that a) Previous owner for whatever reason took the tranny apart and rebuilt it with a 4.40 (This makes no sense, the 4.785 would be more desireable with the mileage on the motor and cost of doing something like that, to me seems highly unlikely). Or b) Some 98 Spec ITR's did infact coem with 96-97 ITR gearing (Which is like the USDM ITR motor).

Its too late know but one of the reasons I went for this swap is because I wanted the 4.785 in there already. The guy/company I bought it from assured me that it was out of a 98 ITR and it did have the 4.785 FD in it. Small thing (And really moot since I blew the motor anyway) but it would still kinda irk me.
I'm running a new motor and I haven't quite broke it in yet Ken, no redline shifting yet.....but very soon.