STS Drivetrain question

I have seen reference to engines built to STS legal limit. The only thing I see in the rules is the .020 overbore rule. So, am I to assume that the aforementioned reference means all oem components with the allowed .020 overbore and no performance upgrades/changes? Those of you that have built engines specifically for STS, please tell me about them.

Also, my clutch is getting a little tired and really fast 1st to 2nd shifts are a little crunchy.(I have already replaced the master and slave cylinders) So, during the offseason I plan to replace the clutch. Since the rules don't mention anything about light weight flywheels, I assume this means we can't legally run them. What flywheel/clutch/pressure plates are you guys running?

When I started in STS I didn't worry about having the lightest car or making the most power. Instead I focused on getting the most practice and improving until I got to the point that I was within tenths of beating the fastest other STS guys at big events. That would be my advice to you if you want to improve.

To answer your specific question you are allowed to overbore the piston sleeves to the first limit listed in the Mazda service manual (most likely .010"). Additionally you can resurface the head a tiny amount. The combination of these changes raises the compression ratio about .1 point and together are likely only worth 2-3hp. You aren't allowed to make any other changes.

If you are getting transmission grinds that would be a transmission problem not a clutch problem.

I get what you are saying about learning to drive and then worry about performance mods...and I agree. I am making as many events as I can to get as much seat time as possible.

However, I enjoy tinkering with the car too. In fact, I have always felt that gearing up is half the fun of any hobby. So, while I realize I can't buy better times, I don't feel like I can be hurt by having the best prepared car that is possible within reason.

I guess I will start looking for a low mileage transmission as well. But the clutch questions is still valid, since it will get changed if I pull that transmission. The car has around 120,000 on the clock, and since I don't know if the clutch has ever been changed, I have to assume it hasn't.

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Originally Posted by riverman1

\Also, my clutch is getting a little tired and really fast 1st to 2nd shifts are a little crunchy.(I have already replaced the master and slave cylinders)

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Good stuff here on GL4 Gear oil - http://www.dfwmiata.com/threads/1933...e-me!-Gear-Oil

Thanks POS Racing. I have the Motorcraft Unicorn Blood in there. I may try one of the others to see if my transmission reacts better to it.

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Originally Posted by Davidss

I focused on getting the most practice and improving until I got to the point that I was within tenths of beating the fastest other STS guys at big events. That would be my advice to you if you want to improve.

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Exactly +1

- clutch and flywheel have to be stock style. Mazdaspeed membership is very helpful at times

Flywheel can be resurfaced to the fsm spec. If this is a 1.6 there are 2 oem clutch part numbers. One is a pound or so lighter. I believe it is listed in the GRM sts build article. If you have a trans issue spend a few extra dollars and have a repitable Spec Miata shop rebuild it. Quite a few of the 1.6 bits were superceded by later model parts and you get a really nice box. Things like dual cone synchros...