I have a '98 spec jdm ITR trans that I am considering installing a LS 5th gear into. My first questions is rpm @ 80mph. Second question is will the 4th to 5th gear change like a overdrive? Keep in mind this trans has the factory GSR 4th & 5th.

I've had a B17 gear stack with a LS 5th (3800rpm @80mph). The jump from 4th to 5th seemed huge. Just like a overdrive.

 

I've found my text book answers I think from Mfactory gear chart. Any real world input would be appreciated.

 

Well I can only guess about what it would be from my experience with both transmissions. My b17(4.4 final drive) with an ls 5th is at about 3400 rpms at 70mph. A friend of mine with a jdm itr 98+ tranny's(4.7 final drive) rpms are at 3800 at 70 mph. So obviously the rpms are going to be a little higher with a 4.7 final drive vs the 4.4 so I would guess around 3500-3600 rpms at 70 mph.

Now I don't know what his rpms are at 80. I can only go off of mine. Im at 4000 rpms at 80 mph so I would guess around the 4300 range with an ls 5th and 4.7 final drive.


It also depends which ls 5th we are talking about. Im using a cable tranny ls 5th. I believe the ls hydro trans has a slightly longer 5th than the cables.

 

I just recently installed a 4.7fd in my trans and also utilize a LS 5th. 4k rpms @ 80mph. This is the same as a stock gsr trans in 5th. I compared to my friends stock gsr.

 

Dude thank you I was looking for this answer forever. If I'm gonna build my tranny that's the exact setup I'd go. 98up jdm itr 4.7 fb with ls 5th. Perfect for DD and 1/4mile race.....

 

I use B16 2nd and 3rd, GSR 4th, and LS 5th with the 4.7fd. No drastic rpm drop offs going from any gear to gear.