OS Giken close ratio gears

[ScuttleRX]

Just seen these on Newera parts :

O.S. Giken Close Ratio Gear Set.  (new part)

Improve your RX-7\'s racetrack performance and shave seconds off your lap times at track days with this gear set! The following are standard ratios as fitted to RX-7\'s from 1st - 5th gear: 3.483 2.015 1.391 1.000 0.806 For making a close ratio box, the 1st 3 gears can be modified with an O.S. Giken kit to become: 2.714 1.742 1.267 This kit including layshaft and gear set is priced at: £1,090.00 The 4th and 5th gear ratios are not usually worth changing, as the difference is only marginal with the 5th ratio, whilst 4th stays the same: 2.578 1.772 1.289 1.000 0.821 If preferred, a 5 gear close ratio set is available at £1,695.00 Please note: For this item, lead time is approx 1-2 months from receipt of order, as these parts need to be made specially by OS Giken.


Now would this make the first 3 years taller....? How would that affect the drive (havent got GT4 handy at the mo!), guessing you\'ll be a bit slower off the line due to 1st gear being taller, but get a gain between say 40-100ish as the 1st 3 gears will be reaching greater speeds.

Is there a calc about that can work out what speeds would be at diff rpm with the new ratios?

[sdminus]

Yes andy i have a very complex calc for performance which takes into account aero drag and various factors..  If i get a chance i will put it in for you but cant see a great differance really.

Scott

[ScuttleRX]

Cheers fella, havent got the cash for it or anything just interested to see the effect it has

[John Yorke]

Are they syncro or dog?

[ScuttleRX]

http://www.neweraparts.com/Parts/pictures/1129187825620//pic1129187864983.jpg

Heres a pic, you tell me

Dog are straight cut arent they, so guessing these are syncrho, my knowledge of gearbox\'s is a little lacking...

[John Yorke]

  Yours and mine :wave

The \'other\' additional cost is the re-build. Sounds a good mod though, but wont make it any stronger, will have to look around and start saving and find some one who can re-con a gearbox and fit those parts at the same time, might be worth looking into buying a s/h one and start from there hmmmmm

[ScuttleRX]

lol, we better wait for an expert

[John Yorke]

Dont see much in the way of g/box experts............... anyone out ther?

[TonyBlair]

i have a very complex calc for performance which takes into account aero drag and various factors..  

I\'ve got GT3 if that\'s any help  :rollin

I\'ve tuned the Escudo to around 1800 bph, and tweaked to the gear ratios and spoilers to squeeze about 240mph out of it  

If only I could attach my Playstation to my Apexi Commander - I\'ve had it tuned in no time  

Cheers
Jon

[sdminus]

Andy i have dumped that info in for you and it shows the following

4658 RPM in 1st gear would see you at 30 MPH OS GIL
5973 RPM in 1st gear would see you at 30 MPH Stock box

4983 RPM in 2nd gear would see you at 50 mph OS GIL
5778 RPM in 2nd gear would see you at 50 mph stock box

5799 RPM in 3rd gear would see you at 80 MPH OS GIL
6362 RPM in 3rd gear would see you at 80 MPH stock

Basicaly it will give you about an extra 10 mph in each gear


Also it will drop the g force of a perfect launch from 1.33 G to 0.98 G. Figures based on a stock twin at about 300 wheel hp
I am no expert but how i have worked out the shift points will be no good for a high rpm engine or a twin turbo. More for the circuit racer i feel
Hope this helps

Scott :evillaugh

[ScuttleRX]

Cheers Scott, good info matey Reading the ad I think circuit racing is what its aimed for.

Rememeber seeing Pip\'s orange 2nd gen circuit racer go up the drag strip, 1st gear seemed to go on forever

[ScuttleRX]

If only I could attach my Playstation to my Apexi Commander - I\'ve had it tuned in no time

lol, like it

[TonyBlair]

Good info Scott   :cheers

Andy, did you find a somewhere local that has a 4-wheel laser alignment thingy?

Cheers,
Jon

[ScuttleRX]

No mate, but I havent really looked much to be honest...will start looking again soon.

Sorta lost interest a bit cos im not putting coilovers on for a little while

[kbareham]

Quote "More for the circuit racer i feel"

I think that Scott has it here.

I tend to evaluate gear sets by the difference in RPM when you change gear, rather than trying to make sense of speeds in gears. After all, since 4th gear locks the input and output shaft together, we aren\'t really going to make any big changes to top speed unless we make wild changes to 5th. I calculate the RPM drop figure - e.g. 0.75 would mean that the changing from one gear to the next would drop the engine revs to 75% of the previous value, 6000 to 4500 for example.

From the data above, we have the stock ratio\'s at 3.483/2.015/1.395/1/0.806

This gives changes of 0.58, 0.69 , 0.72 and 0.81

0.58 drop from 1st to 2nd is a big drop. Thats 6000RPM down to 3480.

The first option quoted gives 2.714/1.742/1.267/1/0.806 and results in changes of 0.64, 0.73, 0.79, 0.81

The second option quoted gives 2.578/1.772/1.289/1/0.82 and results in changes of 0.69, 0.73, 0.78, 0.82

Thats 6000 to 4140 RPM from 1st to 2nd.

Experience says that anything around 0.75 feels close to drive. I\'m not one for the 1/4 mile, so the longer 1st doesn\'t really matter to me. It then all comes down to how wide the engine\'s torque curve is and how much grip you have.
I have a very close ratio ZF gearbox in an old rally car. The car has a prehistoric engine (boinger) with sidedraught carbs and the torque curve is very narrow. The close ratio\'s allow me to change gear without dropping off the power, and even with the long first is still spins the wheels on launch, so having a shorter 1st wouldn\'t really help.
The FD has fairly wide ratio\'s, a wide torque curve and comparatively good grip as standard, so I\'m thinking that this gearset will only really make a difference if you have a big single turbo with a very narrow torque curve, and spend all your time on the track where standing starts don\'t matter.
Only my thoughts

Keith