difference between an S5 flywheel and an S4 flywheel?
 

something similar to the title....

I have an S4 block that I'm putting in a S5 chassis. Which fly should I use or does it matter?

Use the S5 flywheel with the S5 block.
They have different counterweights..

They're different diameter too -- don't ask me the dimensions though. :)

Hey by the way, what are the dimensions

225mm for the Non turbo (86 + ?)
dunno on anything else :)

If the S4 block has S4 rotors then you need to use the S4 flywheel and counter. I have S5 rotors between S4 irons and use the S5 flywheel and counter. The mazdatrix site shows the different flywheels but the S5 has a weighted edge that runs 3/4 the way around the flywheel. The S4 weighted edge goes around only partially.

All NA flywheels from 84-91 on 13b's are the same outside diameter/ringgear. They are all, however, weighted/balanced differently...

84-85 would say n304 and are for the 11lb rotors
86-88 would say n326 and are for the 10lb rotors
89-91 would say n350 and are for the 9lb rotors

Obviously, you wouldnt want to mismatch rotors to flywheel, or you'd have vibration and longevity problems.

By the same token, turbo flywheels from 87-91 are the same outside diameter/ringgear, but are balanced differently...

87-88 would say n318 and are for the 10lb rotors
89-91 would say n370 and are for the 9lb rotors

Note that the flywheel is it's own rear counterweight as well...automatic cars had a flexplate that was removable, and a half-moon shaped counterweight that bolted to the e-shaft just like the flywheel would. These counterweights are weighted just as described above, however have no markings on them to identify the year/model they were balanced for, so if you dont know what it came from, only a very accurate scale can tell you.

OF course, there is a front counterweight in every engine as well, and these are weighted specific to the rotors they're meant to accompany. There are, again, no markings on these, so you have to keep track of what they came from.

This is why you often see, on ebay for instance, "rotating assemblies" being sold...front counterweight, both rotors, and flywheel.

thnx...really helps :D