Making 1.6 into 1.8 for ITA?

[gpeluso]

I see different things used on 2nd Gen RX7's from different years that were not options each year(EX. Something from the 1989 engine and body wing). I also see BMW built from 1992 Chasis, but ad Vanos motor even though it was not available. Why can you not make a 1990 miata into a 1.8 1994 miata. The body is the same. I understand the brakes are different too. Just confused due to the BMW and RX7 combo's out there.

Greg

[zracre]

I believe all those cars are on the same spec line...the 1.6 and 1.8 are separate...

[Andy Bettencourt]

Evan is right on the money. Those cars are utilizing the update/backdate allowance for cars on the same spec line. The 1.6 and 1.8 Miata's are on different lines so no swapping is permitted.

[HOOSER 99]

Just curious...

Is there a external size difference between a 1.6 and a 1.8 or are they based on the same block?

jerry

[tnord]

i think they're the same as i think the 1.8 will sit in the 1.6 subframe, the transmissions are the same, and they all mount up the same way.

keep an eye out for the VIN rule to get changed which i think would allow us to do just what you're asking.

[leawil]

There are several other factors that would argue against upgrading a 1990 Miata to a 1.8, to wit:

1.6L diff is a well known weak point - ring and pinion notorious for shredding, so you'd have to swap the diff for a 1.8 diff to handle the extra HP and torque, and

rear subframe braces are on the 1.8's, not on 1.6's - you'd want to add those, if that would be legal, which requires removing rear subframe and welding mounting points, plus

1.8 has larger diameter brake rotors, much more effective brakes - you'd probably want to upgrade to the larger brakes, because...

if you went to a 1.8L engine, you'd have to meet the 1.8L minimum weight.

All in all, sounds like you'd be better off looking for a good 1.8L donor car, since that's what you'd have once you got done with all the upgrades you'd be making.

[lateapex911]

Why can you not make a 1990 miata into a 1.8 1994 miata. The body is the same. I understand the brakes are different too. Just confused due to the BMW and RX7 combo's out there.

Greg [/b]

This is an example of a percetion that could become trouble. My unsderstanding is that the 1990 body is NOT the same, and that making a 1990 1.8 would result in the lightest best handling Miata out there, with the bigger motor. This would clearly be an issue, and they are on seperate spec lines for a reason. This is one of the "unintended consequences" that could result in the VIN rule change.........

Now, of course, there have to be some physical charactersitics that are identifiable, so it SHOULD be possible to protest such a combination, but, as you can see, that knowledge is not common.

[tnord]

i thought the bodies were the same, and that the brakes, motor, axles, wiring harness, ECU, driveshaft, and diff would be the only differences between the two in race trim.

the brakes and diff weigh more than the 1.6 pieces, so that may be what you're thinking of.

1.6's have the same subframe braces available from mazdaspeed and are on many SM cars. this should not require a removal of the subframe, and it's debateable whether they actually do anything.

i would be more than slightly interested in changing my 1.6 car to a 1.8 without getting a new tub. i've got the suspension, brakes, radiator, car gutted, caged, wired, etc etc. 1.8 donor motors are all over the place for cheap, transmissions are the same, and 1.8 diff swaps aren't hard either. if you ask me, this route is WAY easier and cheaper than building a whole new car.

[Andy Bettencourt]

The bodies are the 'same' but just like many iterations of cars, older ones tend to be lighter. If you bent your 1994 1.8 and had a 1.6 laying around, it wouldn't be hard to do a part for part swap and end up with a very light 1.8. Possible? Yes. Legal? No.