rider384

iTrader: (3)

So I've been pondering about this for a while... All the calculators tell me the top speed for each gear in our Miatas, yadda yadda.

Mine are... Different. From both 4.10 and 4.30.

Top speed of mine (GPS confirmed) are:

1st: ~30
2nd: ~50
3rd: 80 (Almost exactly)
4th: 100 (Again, almost exactly)
5th: Dunno, haven't got it there yet.

Calculators and even stuff from m.net show the top speeds of each gear to be higher, and significantly higher when you get into 3rd and 4th.

Sorry if this is a retarded thread, if I'm missing something someone please tell me.

Any thoughts?

EDIT: I'm on stock tires (185-60-14). '96, so it should have a 4.10.

Joe Perez

iTrader: (8)

A 3.9 R&P was standard with all 6-speed equipped Miatas. Apart from 4.10 and 4.30, that's the only other ratio that was stock on a Miata in the US.

3.636 R&Ps were never standard on the Miata, but were found on all '79-'82 Mazda 626s, and are available from Mazdacomp. They are not particularly common, but some folks do retrofit them. (I've got a set sitting on the shelf.)

A more comprehensive listing: http://solomiata.com/RingandPinion.html

Which tires are you running, specifically?

rider384

iTrader: (3)

Would the 4.44 truck ratio fit in the Miata diff housing? 'Cause I put in all the numbers with that and everything is damn near exactly what I'm getting.

Tires are Altimax HP all-seasons in 185-60-14.

Joe Perez

iTrader: (8)

So, here's the bad news. When I run the numbers for your quoted top speeds and tire, I get an RPM spread of roughly 750 highest to lowest, assuming a 22.7" tire and a 4.10 R&P.

That's more than 10% measurement error.

If this is really killing you, jack up the rear end, mark the tires with chalk, put the transmission into 4th (which is 1:1), and spin the crank over 4.1 times by hand.

Or just have a drink and assume that some fool didn't decide to tear apart the diff in your car and install a rock-crawler gearset into it.

rider384

iTrader: (3)

Just Forza 3'd my car, once with a 4.10 and once with a 4.44. The 4.44 was DEAD ON what my car does. Exactly. 100%. And yes, I know that Forza is over 9,000% accurate.

So, ITT: ****.

NA6C-Guy

iTrader: (1)

Why a 4.44 and not a 4.3? I bet it's 4.3

18psi

iTrader: (76)

are you hitting the limiter in each gear?
could be your tacho is off and reading higher and you're short shifting?

mikeflys1

iTrader: (2)

this

rider384

iTrader: (3)

It's not a 4.3. 4.3 still reads too high in each gear. By a significant amount.

I could be short shifting. I'll take a log and see.

EDIT: Hmm, very possible it's a 4.3 I guess. I'll double check.

chriscar

iTrader: (24)

Take your readings at 3500 rpm for each gear and calculate from there. This way you don't need to bang the rev limiter, and your speedo error will be lower.

fooger03

iTrader: (2)

My '94 with 4.10 would hit the rev limiter at about 110mph in 4th gear way back when it was stock.

94blackmx5

http://cgi.ebay.com/ebaymotors/Honda...Q5fAccessories
i don't know if this has been tried yet. but i'm told the rear carrier in the s2000 is the same as he mazda speed miata and the mazda speed miata is interchangable. This one is made by mazda and does fit he s2000 so it might work. mazda designed that diff for the honda as well.

neogenesis2004

iTrader: (12)

Mazdacomp made a 4.8 also. I bought an open diff one time that came with one.

olderguy

iTrader: (19)

Speedometers are very inaccurate. Check against a GPS before using it to calculate ratios.

My 1991 with a 4:3 speedometer became extremely accurate when I put in a 4:1 torsen, but then my odometer is now off

Joe Perez

iTrader: (8)

Well, he says in the first post that he did use a GPS, though my experience mirror's Olderguy's- when I installed a 4.10 into my '92, without changing the speedo pickup gear, the speedometer went from being quite optimistic to being accurate to within about a needlewidth at 70 (again GPS-verified.)

And, as Chriscar suggests, so do I concur- with an addendum: the stock tachometer isn't exactly NIST-traceable either. You'll want to reference your logger to get an accurate RPM indication.


.....Or, just do what I said in the first place and measure it directly. In fact, you don't even need to muck about with the engine and tranny now that I'm thinking more clearly. Put it in neutral and just rotate the propshaft by hand while observing a reference mark on the diff input flange.

chpmnsws6

iTrader: (12)

x2 on that!

With a 7400-7600rpm limiter, my needle used to run WELL past 8k. Now with a 6400rpm limiter, it went to mid 7's before smacking the limiter

94blackmx5

from a bit more research i think this is actually the factory ring & pinion from the RX8

neogenesis2004

iTrader: (12)

Seeing as it was out WAY before the RX8 was even on the market, I'd say you're wrong.

NA6C-Guy

iTrader: (1)

Again I say, I bet $20 it's just a 4.3. No way a tack is accurate enough to tell a 4.3 from a 4.44, plus there is a very slim chance it is a 4.44 and not a 4.3, so I'm going with a logical assumption that it's a 4.3.

EDIT: I see you are saying these speeds are GPS confirmed? What is the history on the car. I just have a hard time believing the gears would have been changed to a less standard one than the 4.1 or 4.3, like a 4.44 or 4.8.

Your top speeds also look strange. What other Mazda 5 speeds fit the Miata, or what are the chances it's a modified trans using some other gears? Mostly 3rd gear looks too low to match the others.

94blackmx5

what does that have to do with my statment? How would you say i was wrong?

The 6spd rx8 comes with a 4.77 ring and pinion. i never said anything about who released what first.