Are u selling 4.9FD? Brand n price? Used or new? Well, since u mentioned bout 4.9FD .. here some info I read fr other forum and the thread wrote by the moderator _JT and I paste here just to share with all :
Choosing your final drive
Lately a lot of questions have been asked about swapping your final drive. It's an easy and cheap way of gaining virtual whp and wtq that transform into faster acceleration. Let's sum it up.
+ Gears shorter - much extra virtual whp/wtq = lots of gain in acceleration for the money
+ In the city you probably won't notice any increase in fuel consumption since lighter load of engine is needed for same acceleration
- Higher rpm on the motorway means more noise
- Higher rpm on the motorway means higher fuel consumption
- With a very short final drive your top speed is severly limited
There are different options. Honda B-series boxes contain 4.4 and 4.785 final drives. The latter one is found in the 98-01 spec ITR S80 boxes, the rest has 4.4 (correct me if I'm wrong). The two most common options are the OEM 4.875 and after market 4.928 final drive.
The 4.928
Most people agree that if you drive on motorways regularly the 4.928 is too short. Your engine will rotate at 3850rpm at 60mph. That's a lot. Also, if you drive on tracks where you easily run over 120mph, this will be too short as the gear limits your top speed at 140mph. You could overcome these problems by also installing a 5th gear that is a bit longer. The disadvantage of that is that the gap between 4th and 5th gear will be bigger, but you do get 4.928 acceleration in 1st-4th gear and stock fuel economy and noise on the motorway.
The 4.785
This is the best compromise. It will yield you almost 9% extra virtual torque/power in all gears over the whole range, but compared to the 4.928 your top speed is higher (4mph, which isn't that big but just a bit extra) and most important for driveability, rpm at 60mph is 400rpm lower. This is the best easy option if you drive a lot on the motorway.
98-01 S80 box
Another option would be to just get a 98-01 S80 box if you don't already have that. Given the same wheel/tire size, 4th and 5th gear is a small bit shorter but 1st, 2nd and 3rd gear are more noticable shorter. You don't have to open up your box, just change the box. This option has the disadvantage that the gap between 3rd and 4th gear will become bigger but you have noticably faster acceleration in 1st - 3rd gear while maintaining driveability in 4th and 5th gear.
In short:
Of course you can build your own box with custom gears etc but that is way more costly and if you already know how to do that and how to choose the parts that suit your needs, you won't be reading this topic
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