OT: Loaned out a '97 NA today....

Cool! I wish I was neighbors with ya!

Oh yeah, they are both nice ones. Gotta talk good about that NA too. ;-)

Pat

This is not OT! That's for sure ;-)

Chris

99BBB

That's cool. I had a similar experience recently when I let one of my co-workers drive my MSM. Now, I get my share of good-natured ribbing about driving a chick car and all the rest of it. I'm sure you've all heard it. But he came back with a big smile on his face and I believe he uttered the word "awesome" about a hundred times. That was about my reaction the first time I drove it as well.

I've never driven in any Miata besides my MSM. I'd be very curious to try an NA for comparison.

I will say this...they are two entirely different beasts. The 1997 NA that I have is a fine, fine driving machine. Honestly, it seems like it is a bit more responsive throttle-wise than the MSM. I find it easier to get a good launch out of the NA than the MSM. It could be in my head, but when I drive the MSM I find myself waiting for the turbo to spool up and the ECM to make up its mind about "Boost, or not boost? That is the question". In first and second gear, the ride is over before it starts. You have to shift again...and again...and again.

The NA....push the gas, it's there. All 120 horses. First gear goes a long way. And as far as the 6 speed versus 5 speed goes, don't get me wrong, having six gears is pretty damn sweet, but with the short ratios in the MSM gearbox I could almost shift twice getting out of my driveway. And to hit 60mph in the MSM, you have to go into 3rd gear unless you have a modded ECM that lets you go past the strangely-low

6500 RPM fuel cut. I haven't figured that one out...1997 cuts at 7,300 RPM, 2004 MSM cuts at 6,500. It's the same engine AFAIK...so why is it like that? You can hit 60mph in 2nd on an NA.

Anyway.....if you wanna borrow an NA the place 2 houses down from me is for sale..... :-)

Chris

To add to the weirdness, the Japanese market normally aspirated early NB

1.8 with BP5A (similar to BP4W) motor has the same intake cam as the MSM (higher lift and longer duration than the BP4W), yet fuel cutout / engine red-line is 7500 rpm.

I have driven and/or ridden somewhere in the neighborhood of 40 NA's, but I have never been at the wheel of a MSM.

In fact, I have only driven 2 NB's, and also 2 NC's, so far.

All of the 1999+ Miatas I have driven were naturally aspirated, and the only "charged" NA that I have driven is my current 1991 turbo Miata.

Pat

Montego Blue, no doubt, like my '96.

An indicated 60, perhaps, but I don't think it'll quite reach an actual

60 without oversized tires. Doesn't matter, of course--it's just an arbitrary speed.

I dunno, I could be wrong but my 97 NA is wearing 185/65 R14's I think....whatever the alloy rims from the factory came with,and I was able to go past 60 in 2nd gear...but I was past 7,000RPM when I did it. The MSM just starts bouncing off the revlimiter at 6500....can't get there in 2nd.

Does anyone know what the ratios are for the 5spd and 6spd gearbox? I managed to snag a copy of the FSM for the 6 speed that I have the '04 MSM, but I didn't see mention of the ratios..just how to take the thing apart and put it back together.

Chris

My point was, how do you know? The Miata speedometer is typically 3-5 mph optimistic at highway speeds, and although it may have read 60 you were probably doing no more than 57 or 58 at the rev limiter.

Scroll down this page for a table:

'Tis a good point. The only way to know for sure would be to do the math and see, based on the tire diameter, what the theoretical maximum speed would be at 7,300RPM.

So...I have a problem. I don't know what differential is in my '97, and apparently two were available. If it has the 4.10, then I would be going 63.5MPH in 2nd gear at 7300 RPM. That would seem to match what I saw on the speedo, being a bit past 60 before I hit fuel-cut. If it has the 4.30 unit, then that speed drops to 60.6 MPH

Check this out,I found a cool calculator and if you use this link it has the miata 5 speed box ratios already plugged in for you:

5&Num2e&Num3&AxleRatio=4.30&Ratio1=3.136&Ratio2=1.888&Ratio3=1.330+&Ratio4=1.00&Ratio5=.814&Ratio6=&Ratio7=&Redlines00&IncrementP0&B1=Recalculate

Thanks for the link, that page has a lot of good info on it. As I suspected, the 6 speed has a -much- shorter first gear, and the ratios are very close compared to the 5 speed unit. I re-did the link above for the 6-speed box just to see what the max speeds would be on an unmodified car that cuts at 6,500 RPM. With a 3.909 rear end(which I think the mazdaspeed probably came with in '04 and '05) you're only going to get about 50mph out of 2nd gear.

Check this one out(99+ 6 speed box):

5&Num2e&Num3&AxleRatio=3.909&Ratio1=3.76+&Ratio2=2.269+&Ratio3=1.645&Ratio4=1.257&Ratio5=1.00&Ratio6=.843&Ratio7=&Redlinee00&IncrementP0&B1=Recalculate Thanks,

Chris

Chris, are you an engineer? :)

Actually, you won't know the speedometer error for sure unless you time the car between mile markers, or use police radar. GPS may be close enough, I dunno.

Math is fun, but it's no substitute for empirical measurement. Tire dimensions will vary from one tire brand/model to another, even when they're all nominally the same size. And there's treadwear, inflation pressure, load, centrifugal growth at speed, yadda yadda.

FYI, your stock tire size was 185/60-14. With a manual transmission, you have 4.10 differential gears. The rev limiter isn't necessarily at 7300 rpm; it might be 7200, or even 7000, according to reports from miataforum members. Don't trust the tachometer any more than the speedometer.

I recall that motorcycle tire manufacturers used to provide actual dimensions on their websites, don't know if car tire manufacturers do that or not?

Some do, some don't. The most valuable number, if available, is revolutions per mile.