Different FDR - Final Drive Ratio

[Taffyteg]

Been thinking and looking at ways of potentially making the FD2 a little more user friendly, one being making it potentially better fuel economy as well as possibly 0-60mph time. You can do this by potentially altering the final drive ratio, for those of you who do not know what this, this is the output ratio of your transmission and affects all gears.
The table below shows the gear spread for the standard FDR of 5.06. As you can see the axis are vehicle speed in Y and engine speed in X, basically if your travelling at 80mph in 6th gear you are running at 4000rpm by going from the graph.

The graph below is derived from using a FDR of 4.7 (basically the lower the number the taller the ratio spread, i.e. you go faster) and it shows that in 6th gear at 4000rpm your vehicle speed is now 86mph

The graph below is derived from using a FDR of 4.4 and it shows that in 6th gear at 4000rpm your vehicle speed is now 92mph. The other thing to note on this graph is that you can 60mph in second gear now meaning only 1 gear change.

J's racing do these 2 FDR, there expensive and it's a major hastle fitting them, gear box out, strip it down and you may have to recalibrate your speedo.

Anyone else looked at this at all, and apologies for the mistakes I've done this on the iPhone.

 

[Allen]

Thanks for the post. Found that interesting, I knew doing it helped with acceleration but never knew how/what it done.
But your right... Sounds expensive

 

[Lunar Tick]

That's really interesting. I recently read an article on Motor Prime here:
http://motor-prime.com/content/fd2r-gear-ratio-swap

Basically, they just swapped the 6th gear cog for that out of a '06-'07 US Honda Civic coupe /Acura TSX into an FD2, which dropped revs at 100kmh from 3110 to 2777. Obviously, all the other gears 1-5 are unaffected - so a bigger leap from 5th to 6th but much better for cruising. Be good to know what if any UK Hondas have a 6th gear of about the same (0.659) size as it could be a fairly economical solution.

 

[Taffyteg]

That's really interesting. I recently read an article on Motor Prime here:
http://motor-prime.com/content/fd2r-gear-ratio-swap

Basically, they just swapped the 6th gear cog for that out of a '06-'07 US Honda Civic coupe /Acura TSX into an FD2, which dropped revs at 100kmh from 3110 to 2777. Obviously, all the other gears 1-5 are unaffected - so a bigger leap from 5th to 6th but much better for cruising. Be good to know what if any UK Hondas have a 6th gear of about the same (0.659) size as it could be a fairly economical solution.

That's a good idea and would work well - if it is possible :think:

Ive been on the motor prime site a few times but never read that, went on there to check out the rear shocks.

 

[uknowiama]

I was thinking of if possible to change the 6th gear to make it better for cruising. I don't think I would change the other 5 gears though.

 

[simon82]

I see what your saying with regards to economy but as for making it accelerate quicker i'm not so sure. By changing the final drive you are essentially making the gearing longer which would not equate to quicker acceleration as far as i'm aware. :???:

 

[Rtb]

I see what your saying with regards to economy but as for making it accelerate quicker i'm not so sure. By changing the final drive you are essentially making the gearing longer which would not equate to quicker acceleration as far as i'm aware. :???:

Defo won't help acceleration.....the car will be faster at top end but slower to get their.

 

[jonster]

Put smaller or bigger wheels on depending on what you want

 

[Taffyteg]

I see what your saying with regards to economy but as for making it accelerate quicker i'm not so sure. By changing the final drive you are essentially making the gearing longer which would not equate to quicker acceleration as far as i'm aware. :???:

The in gear acceleration will be slightly affected by making the FDR taller, however you will only need to change gear once and I believe this will make it quicker 0-60 than standard where you have to change twice.

We are talking small numbers here with regards to time by the way.

I had a quick look for the 6th gear part numbers listed on Motor Prime and they are available in the US.

 

[murrayl]

It may be something to look into... hmmm maybe another mod while the car is being stripped down

 

[simon82]

I see what your saying with regards to economy but as for making it accelerate quicker i'm not so sure. By changing the final drive you are essentially making the gearing longer which would not equate to quicker acceleration as far as i'm aware. :???:

The in gear acceleration will be slightly affected by making the FDR taller, however you will only need to change gear once and I believe this will make it quicker 0-60 than standard where you have to change twice.

We are talking small numbers here with regards to time by the way.

I had a quick look for the 6th gear part numbers listed on Motor Prime and they are available in the US.

I know what your saying and why you would think that but in reality it wouldnt work like that. It would decrease acceleration. Think about how our engines work and where all the power is- right up the top of the rev range. If you essentially extend the gearing then your going to make the car feel very lazy and slower in my opinion. Hondas have always had shorter gearing to give good acceleration by allowing you to access the power further up the rev range quicker. Also it may have a theoretical top speed increase but the power increase you would need to reach it would be considerable.

 

[Lunar Tick]

Good point Simon. That's why just swapping out just the 6th gear cog might be a better idea; all the acceleration up to 5th (which is probably as high as you need on 90% of tracks) but a relaxed and quieter cruising in 6th :-D

 

[murrayl]

Good point Simon. That's why just swapping out just the 6th gear cog might be a better idea; all the acceleration up to 5th (which is probably as high as you need on 90% of tracks) but a relaxed and quieter cruising in 6th :-D

This does sound like the best idea.

 

[Taffyteg]

I see what your saying with regards to economy but as for making it accelerate quicker i'm not so sure. By changing the final drive you are essentially making the gearing longer which would not equate to quicker acceleration as far as i'm aware. :???:

The in gear acceleration will be slightly affected by making the FDR taller, however you will only need to change gear once and I believe this will make it quicker 0-60 than standard where you have to change twice.

We are talking small numbers here with regards to time by the way.

I had a quick look for the 6th gear part numbers listed on Motor Prime and they are available in the US.

I know what your saying and why you would think that but in reality it wouldnt work like that. It would decrease acceleration. Think about how our engines work and where all the power is- right up the top of the rev range. If you essentially extend the gearing then your going to make the car feel very lazy and slower in my opinion. Hondas have always had shorter gearing to give good acceleration by allowing you to access the power further up the rev range quicker. Also it may have a theoretical top speed increase but the power increase you would need to reach it would be considerable.

Its not power that gives you acceleration its torque!!!!!! Torque should occur low down in the rev range and the K20 is pretty good at low down grunt.

 

[simon82]

Its not power that gives you acceleration its torque!!!!!! Torque should occur low down in the rev range and the K20 is pretty good at low down grunt.

Are we talking about the same engines here? K20's have crap torque figures although admitedly the K20z that we have has better torque range than the K20a's but its still rubbish. Peak torque is developed just after the vtec change over which in the standard car is a 5800rpm, hardly down the lower end of the rev range.
It depends what you want from the car, if you are looking for lower revs at motorway speeds a a fractional increase in fuel economy then by all means fit one. To say it will improve acceleration is inaccurate.

 

[jonster]

I wasn't really joking when mentioning changing wheel+tyre diameter to affect your final drive. This is exactly what I do for trackdays by running 17s. Apart from the weight saving advantages offered the smaller diameter also aids better acceleration. Going the other way to make the gearing longer is a bit more difficult to achieve by needing a bigger diameter. I guess a taller tyre wall tyre on 18s would do it to some extent. 19s more so but I wouldn't like the ride that would give.

A taller 6th gear may be an idea but a large gap between 5th and 6th off-cam might be undesirable (ie a bit sluggish).

Personally I think Honda really thought about how they matched the engine characteristics to the gear box on our cars. Much more than the DC5 which felt mis-matched.

 

[Taffyteg]

Its not power that gives you acceleration its torque!!!!!! Torque should occur low down in the rev range and the K20 is pretty good at low down grunt.

Are we talking about the same engines here? K20's have crap torque figures although admitedly the K20z that we have has better torque range than the K20a's but its still rubbish. Peak torque is developed just after the vtec change over which in the standard car is a 5800rpm, hardly down the lower end of the rev range.
It depends what you want from the car, if you are looking for lower revs at motorway speeds a a fractional increase in fuel economy then by all means fit one. To say it will improve acceleration is inaccurate.

I disagree

 

[Rob84]

Thread revival.

Does anybody know where to buy aftermarket final drives from? Are they exactly the same as EP3/DC5 fitment or slightly different? Also, which ones are available and how much?

(i would be looking for shorter gearing, not longer, so i'd prefer something between 5.45-5.85 )