2+2 diffs....

[qunvat]

Am I mad or do I remember reading in the Haynes book of shite that 2+2's had 3:7:1 diffs as standard as oppose to 2 seaters which had 3:5:1 's ??? The previous previous owner had it reconned (£350+ !) and I'm sure he told me it was the 1:3:5 gubbings..........

It may explain why it struggles to hit 30 in first and 50 in second AND with a 2.8 engine .....ummmmmmm wa you think?

Si

 

[Mr.F]

In theory, all UK 260Zs should have a 3.7:1 R200 installed according to the parts book. However, 3.364:1 and 3.545:1 ratios were offered in other markets for automatic cars. Also automatics from 08/76 on reverted to a 3.345:1 R180 diff.
It is possible that a few of these 3.5 diffs have found their way into UK manual cars....always worth a check.

 

[Black Bug]

Any idea which gearbox you've got fitted as the combination of ratios of that and the diff will be significant. Also what tyre size are you playing with this week?

What sort of revs are you struggling to get up to? If you've got a 3.54:1 diff and a late 280ZX box with a 3.062 1st, 1.858 2nd then at 5000rpm you should reach ~33mph in 1st and ~55mph in second.

Cheers,
Rob

 

[qunvat]

Very intersting guys....Rob, answers in caps:

Any idea which gearbox you've got fitted as the combination of ratios of that and the diff will be significant. YES A280ZX GEAR BOX MATE...Also what tyre size are you playing with this week? 225 / 60 /14's REAR and 215 /60 /14 FRONT HANDLES WELL....

What sort of revs are you struggling to get up to? NOT RECORDED THE HIGHEST (WOT WOULD / SHOULD THAT BE??) ...FEW MORE NOW I'VE MOVED THE JUBILEE CLIP SOMEONE PUT ON THE CLUTCH MASTER CYLINDER THAT WAS STOPPING FULL PEDAL MOVEMENT!!..If you've got a 3.54:1 diff and a late 280ZX box with a 3.062 1st, 1.858 2nd then at 5000rpm you should reach ~33mph in 1st and ~55mph in second...THAT SOUNDS ABOUT RIGHT!!.....SO WHAT WOULD A 3 : 7 : 1 DIFF DO FOR ME MATE??...IT MAY BE THE ANSWER I'M LOOKING FOR...SI

Cheers,
Rob

 

[Black Bug]

OK, correcting the previous values to take in to account the 225/60R14 tyres you get this:

3.54:1 Diff, speeds at 5000rpm
1st = 34mph
2nd = 56mph
3rd = 80mph
4th = 104mph
5th = 140mph (unlikely )

3.7:1 diff, speeds at 5000rpm
1st = 32mph
2nd = 53mph
3rd = 76mph
4th = 99mph
5th = 133mph

So the 3.7 actually takes the top speed in the opposite direction to where you want (assuming you do have a 3.54:1 diff, as let's face it the speeds are pretty similar anyway) The advantage of a 3.7 over 3.54 is that it gets more torque to the wheels so in theory you accellerate a bit quicker, at the expense of top speed. If you have got a 3.54 diff then you probably won't notice much difference going to a 3.7. You might notice a slight difference going from a 3.54 to say a 3.9 but it would be hassle for the amount achieved I'd say.

You'd be better off IMHO looking at the engine end of things, trying to improve carb breathing (you've got 2" SUs right? They should be more than adequate) Maybe a swap to a slightly friskier cam to get more top end. What sort of exhaust manifold do you have, standard or some fancy bit of piping to help free up the engine?

Might also be worth letting other people (who know 2+2s of course!) take it for a drive and see if they think it's behaving as it should if you're worried it's not running right.

Sorry, I dunno what the engines should rev to as my SUs are crap and struggle to get over 4k anyway, probably around 6-6.5k rpm would be about max I'd say for a stock engine setup.

Cheers,
Rob

 

[qunvat]

Thanks Rob...I got a standard exhaust manifold with a Scorpion exhaust....will look at revs in a min mate.....yeah I'd much prefer more gumph in 1st and 2nd to be honest...

Si

 

[zedhead260]

How do you know if it's a late 280ZX box ???

If it aint a late one, then all that math gives a far worse result.

 

[qunvat]

How do you know if it's a late 280ZX box ??? If it aint a late one, then all that math gives a far worse result.

...so IF its an early one...would that explain why i get 30 at a push in first and 50 at a push in 2nd?

Si

 

[zedhead260]

Stick your head underneath the car and check out the shape of the rear casing. If it is smooth you have a crappy early one, if it has finning on it then it's the good late one.

 

[SeanDezart]

"my SUs are crap and struggle to get over 4k anyway, probably around 6-6.5k rpm would be about max I'd say for a stock engine setup" all that and a square front spoiler ?
Rob, your car should rev to 6500 no problem although for most 'road' engines there's no point in going over 6200 max !

 

[qunvat]

ANSWERS IN CAPS!!

(you've got 2" SUs right? ....1 3/4" BUT WAS TOLD 2" WEN I BOUGHT IT!...NEW K UN N'S TOO..... They should be more than adequate) Maybe a swap to a slightly friskier cam to get more top end.... ITS MORE ACCELERATION IN 1ST AND 2ND I'M AFTER (CALL ME STUPID....IS THAT 'TOP END' ?!....sorry) What sort of exhaust manifold do you have, standard or some fancy bit of piping to help free up the engine? Might also be worth letting other people (who know 2+2s of course!) take it for a drive and see if they think it's behaving as it should if you're worried it's not running right.

Sorry, I dunno what the engines should rev to as my SUs are crap and struggle to get over 4k anyway, probably around 6-6.5k rpm would be about max I'd say for a stock engine setup....WILL TEST REVS TOM. THE ENGINE IS A 2.8 ALSO...



Cheers,.....CHEERS, SI



Rob

 

[Black Bug]

"my SUs are crap and struggle to get over 4k anyway, probably around 6-6.5k rpm would be about max I'd say for a stock engine setup" all that and a square front spoiler ?
Rob, your car should rev to 6500 no problem although for most 'road' engines there's no point in going over 6200 max !

Yeah my carbs are screwed up, idles around 1.5k, runs out of breath around 4.5k, needs a major tune up, or hitting with nearest large hammer Granted I haven't run the engine in far too many months either, probably isn't helping!

Si, bummer about the 2" carbs. Top end just means the high end of the rev range, if you have a hotter cam it will help the engine work higher up in the rev range, at the possible expense of some low end power. Mr. F. should be able to advise you on the whole cam front. I remember you had AdrainF check out your car, did he do anything with the carbs? Just plonking 240 carbs on a 2.8 won't give the best results as they need to be adjusted for the extra engine size, might need different needs and all that tricky gubbins.

Back on the gearing front, if you've got an early 280ZX box with a 3.321 1st gear, that will give you better accelleration compared to a late 280ZX box, at slight expense of top speed, 1st should see around 30-31mph @ 5k, 2nd around 51-52mph @ 5k. I've no idea how to visually tell the difference between an early and late 280ZX box without pulling to bits (which I'm good at, it's going the other way that I have problems with ). Same with sussing the diff ratio, best way is to pull the cover and check the markings on the crown, just raising the rear, turning the prop and counting how many times the wheel turns never seems to work too well for me.

Cheers,
Rob