Gear Ratio difference NA6/NA8 / Import

[ZenArcher]

Been doing some reading and it appears that std NA6's sit on about 3340rpm in 5th at 100kph, while NA8's are meant to sit on around 3200rpm for the same speed.

After my 1.8 conversion I was expecting slightly less fuel economy due to the slightly higher revs. But on my round trip to Sydney and back to Canberra in a day I netted just over 40mpg and that was doing 110kph+. I filled the tank as I left Canberra and just so I could see the fuel coming up the neck of the tank and then the same again on the way home at the Shell servicestation on the highway. So I know I filled to roughly the same spot again. That is I didn't underfill my tank compared to my first fill-up.

I then took more notice of the revs my MX was doing and it was sitting at around 3150/3200 revs at 100kph.

Now my MX is a 92 model private import. Owner lived in Japan for several years and brought the car back home. Then took a job in England so sold the MX to me. Anyway, it has an LSD in it.

So wondering being that it is an import or maybe because of the LSD it is sitting at the revs that a NA8 is meant to be sitting on.

Or maybe the magazine writeups are wrong? or do Aussie MX5's have different gear ratios to the rest of the world?

Just wondering what rpm do other MX5's sit on at 100kph.

Not complaining about the fuel economy by any means, but just wonder if I have found another \"difference\" between the imports and the Aussie delivered MX's

[JBT]

Is that an actual 100km/hr or indicated? In 5th at 100km/hr true, our NA8 is doing 3330RPM and about 3200 RPM at an indicated 100 km/hr. It has a 4.1 LSD.

[Russellb]

considering that you are using the 1.6 computer and Airflow meter on a 1.8 engine Fuel consumpsion should be about the same toque and therefore Hp will be up but feul usage should be the same
As for Diff ratios the NA6 had a 4.3 diff ratio
and the NA 8 had a 4.1 diff ratio

[ZenArcher]

Indicated on the speedo.

I think my speedo is very accurate though as I have been through police speed traps that show your speed on a large digital readout and my speedo showed the same speed as the police digital readout.

[ZenArcher]

Thanks Russell,

I knew about the diff ratios, that is why I was wondering what rpm other MX5's were doing at 100kph in top gear. Just seems that mine is lower than expected. So I am wondering if the VLSD I have is a different diff ratio that what it is meant to be for a stf NA6 perhaps?

[Russellb]

come ove on arvo and we can take the GPS out in your car and then In my car and Compare RPM's

[ZenArcher]

OK sounds good. Need to get the sensor/switch replaced first (see other post - also PM) then get the intake installed and I will get right to go.

Still haven't worked out what that weird resonance sound is yet. Need to soon as it is driving me nuts.