Diff ratio for R200

[Mr.G]

Having spent a whole evening searching the archives and using the Transmission calculator (http://www.geocities.com/z_design_studio/transmission.html), I am still not sure as to what Diff ratio i should try and locate.

I have a 240Z with a 5 Speed box, tyres for now are 195/70/14, redline at 7K.

I have always thought that an R200 3.9 would be best.. however it looks as if a 3.54 would be better.

Results:

3.54 DIFF
1st 49mph
2nd 78mph
3rd 111mph
4th 146mph
5th 171mph



3.7 DIFF
1st 47mph
2nd 75mph
3rd 106mph
4th 139mph
5th 162mph

3.9 DIFF

1st 45mph
2nd 71mph
3rd 101mph
4th 132mph
5th 155mph


Am i right, or do all these figures mean nothing in the real world is one ration more likely to lose traction the with another?

Appreciate any help and advice.


What years of 280ZX were these diffs offered.

 

[Zed2k]

I was running a 3:9 diff and am now using a 3:7 which should allow me to top 160mph but whether I would ever see this is another thing. I am personally looking for a 3:9 or 4:11 which will be better for short straight track layouts and Drag strip use.
They all are ok but I would go for at least a 3:7 IMHO.

Nick..

 

[SKiddell]

Hi MrG240Z

Using the transmission calculator I dont get the same figures as you have posted, what gearbox are you using?

 

[SKiddell]

Or with another 5 speed

 

[Mr.G]

Thanks for the input guyZ.

Steve I am assuming my Z has the original 240Z 5 speed box, even though I bought the car with an L28 installed I do not know if the box would have been changed to a 280ZX one? (Any way of knowing which box I have for sure?)

As the program is US based and their box ratios differ from UK ones I manually inputed the gear ratios of a UK 240Z 5 Speed box (the FS5C71A box to be precise):

1st 2.957
2nd 1.857
3rd 1.311
4th 1.00
5th 0.852

From my understanding then a 4.11 will give you the best 0-60 times but you will lose top end mph, and with the lower ratios you wont be as quick but you will have more power in top gear.

 

[SKiddell]

The 5 speed box I originally had was an early 280ZX and had an abysmal 2nd to 3rd "hole" (which is born out on the 2nd diagram) this created big problems at the drag challenge as when you change up into 3rd you drop into a huge torque hole which seems to be a regular characture of tuned L6's (whether the owner knows it or not is a differant matter) this hole can be exacerbated by combinations of poor exhaust and collector design-- you most certainly want to avoid that, early this year I managed to "aquired" a late 280ZX box (cheers Pete) and just to check the ratios we measured it at

3.00
1.85
1.3
1
0.75

This closely matched the one on the transmission calculator
I am unsure what the original 240Z 5 speed ratios were .

But it leads me to believe that later boxes from UK 280ZX's were of similar gearing to the states (possibly flawed assumption)

I would guess that at some time most cars have had their transmissions swapped in order to cure one of the interesting faults that Z box's develop over time.

A big factor when choosing diff or gearbox ratios is to match it against the power and torque curve of your car and the type of driving you are targeting the car at.

Interestingly could you check the stamped number on your bellhousing top (can just be seen from inside engine bay)

Scratch that, some boxes have a number on the top flange (mine has) so it may not be visible

 

[zedhead260]

I am unsure what the original 240Z 5 speed ratios were .

240Z box for 3.9:1 diff –

1st 2.957
2nd 1.857
3rd 1.311
4th 1.000
5th 0.852
Rev 2.922

 

[johnymd]

I can't decide whether to use the 3.9 I have or get a 3.7. I have a new quaffe to go in it so I don't want to pick the wrong one and have to rebuild it into another. After speaking to lots of people about it I have come to the conclusion that it depends on how much power you are making as well as what you are using the car for. As a guide: if you are only making 150 – 200HP then go for a 3.9 to get you off the line quicker, but if your making say 250 – 300HP then using a 3.7 or 3.5 you will reduce your wheel spin and help you get the power down.

I do know of a 240z that has run a 12.6ish with a 3.54 (don’t know what that means but I thought I’d mention it) but he was getting good power from an L series.

 

[Mr.G]

Thanks for that Jonny, an interesting bit of info.

What Zs and years was the 3.7 Diff available in and how about the 3.5?

 

[SKiddell]

but if your making say 250 – 300HP then using a 3.7 or 3.5 you will reduce your wheel spin

I'd rather run decent tyres first then swap diffs

 

[johnymd]

Steve
What you using?

 

[SKiddell]

Tyres or diff

Diff = R200 3.9 plate LSD (creates a little too much understeer in normal driving)
Tyres = Kumho Ecsta MX, Poor in wet/cold (spins up in all the gears )but excellent when warm.

The Kumho Ecsta MX is a high performance road tyre designed for occasional use on the track and has a blocky high contact tread pattern.

Once both sets that I have are trashed we will try some more "interesting" tyres ---- 888

 

[johnymd]

Is the plate LSD aftermarket?

 

[SKiddell]

Is the plate LSD aftermarket?

Very much so, I fitted it early last March, just before I got the injection project finished -- kinda thought I would need a strong LSD.

Changes the handling of the car in that under moderate driving there is slightly more understeer than before but when you push on into fast tight corners it really is noticable and holds the power evenly allowing a degree of streering on the throttle.

 

[johnymd]

Any reason why you didn't go for a quaffe?

Have you done a CV axle conversion or do you not feel this is neaded?

One last thing......Hows the carbon fever?...............or is the whole car carbon fiber now?

 

[SKiddell]

I didnt go for a quaife as I was offered the R200 and plate LSD as a unit ready set up from a very reliable and reputable source so it kinda suited the circumstances.

I have all of the componants for the CV swap out which I am very keen to do as I have got through 2 sets of UJ's in under 18 months

I now use a modified prop with cosworth ends as well just in case.

Carbon fever is still underway with a cold air box coming soon hopefuly followed by other choice bits (door cards and bonnet cowlings)

 

[HOUSEQUAKE]

Tyres = Kumho Ecsta MX, Poor in wet/cold

You take her out in the wet?

 

[Mr.G]

Jonny I was thinking about what you said regarding the 3.7, 3.5 being better then the 3.9 for high power (+250bhp) applications as you wont so easily spin the wheels on launching.

Well since we are both turbod I was thinking of using a 3.9 but with a dual stage boost controller, standard boost can be specified at 7psi (or whatever) at launch and then on the fly flick the switch and a solenoid opens the wastegate even futher (to whatever setting you set it at). Could be a way of getting round the wheel spin that may occur with a 3.9 diff? (Just my mad thoughts here never put it into practice)

The one I would probably go for is the Turbo XS Dual boost controller - mainly as I think it will be safer to only unleash the cars performance potential at certain times, and in that way acts as a little safety feature.

 

[johnymd]

Steve
Have you found someone to do the output flange adaptors in the UK?
Does your source do carbon fiber bumpers?

George
Sounds like the best of both worlds(on the strip).

solenoid opens the wastegate even futher

you mean: puts greater pressure on the wastegate to stop it opening untill a higher boost PSI. (I think)

 

[Mr.G]

yes that's what i meant!

Here is one on ebay, http://cgi.ebay.com/ebaymotors/TurboXS-Dual-Stage-Boost-Controller-NEW-Turbo-XS-DSBC_W0QQcmdZViewItemQQcategoryZ33742QQitemZ8020784523QQrdZ1QQsspagenameZWDVW