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Engine power

116 bhp = 1.6 Mk1 before the 1.8 came out

Early 1.6 (up to mid '91) cars had weak front crank pulley/crank the first year, less than 500 of those were shipped to the UK. Strengthened crankshaft was fitted to cars with UK chassis numbers from 00110630 (final digits). If your Miata is a 1990 or 1991 with VIN 209446 or less, you have a crankshaft with a smaller diameter nose. VIN numbers not 100% accurate If you'd like, verify the stronger/later crankshaft and larger bolt are fitted by measuring the bolt shoulder diameter to be 1.455 inches. The old/weaker pulley bolt shoulder diameter is 1.128 inches. There is an intermediate fix in the form of a longer nosed crankshaft with the same small diameter supplied by Mazda. This fault can and does still turn up on all the engines. Other odd one is con rods breaking – this seems more prone on post ’99 cars. Both failures are rare in the main.


90 bhp = 1.6 Mk1 after '94

http://www.fortunecity.com/marina/po.../igncurve.html to show it is nearer 105hp

130 bhp = 1.8 Mk1

110 bhp = 1.6 Mk2

140 bhp = 1.8 Mk2

90 v 116 bhp 1.6; has a different ECU, different cams, and lower compression. Runs pretty well (better than the old 1.6 (115hp) in the very low range) up to about 5.5 k RPM, than the difference becomes obvious. A tach redline at 6500 and rev limit at 6750. Some indicate >7000 but so far they all show 6750 upon datalogging. No need for a higher rev limit because the power drops bec. the cams are milder (same as US 1.6 auto tranny cams) and peak at 4000. The injector pulses narrow after 6500 with a matching drop in torque. This is probably so the driver will feel the drop and shift up instead of banging into the limiter all the time. http://www.fortunecity.com/marina/po...ta/bobhall.txt has Bob Hall’s take on this

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