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All right guys, I need your help in this one. Some years ago I had this MX-3 V6 1.8 that has no RPM Limit, at that time I didn't know much about mazda tuning and swapping, etc... and I have been asking since then about ECU tunnings or if that ECU had something special. Not too long aago someone told me that the ECU was from a ford and those not have RPM limit. Is that true? I am planning on Making my MX3 with a 2.5 V6 from a Millenia and Transmission from MX-6 and the Ford ECU if that is true. What do you guys think??

They do have a rev limiter, unless chipped. Probe ECU = MX6/626 ECU, given the same engine.

You want a rev limit, and the factory one isn't bad... It could go a little higher safely(usually), but it is far from limiting, without supporting mods to assist in reliable operation.

Speed limitor/Governor maybe, but I've never heard of one with no RPM limit.

MrMazda92, well said.

You need a limiter to save your engine. Some decent valvetrain work will let you push it up a bit, but your power will drop off before redline, so there's no advantage of going even higher. The KLZE valvetrain is more fragile than a KLDE's and can handle daily abuse if you don't push it above 7000.

In the end, you're jumping way ahead of yourself:
1) You need to upgrade your valvetrain do it can regularly handle higher revs regularly
2) You need to upgrade the cams to actually make power above the OEM redline, along with supporting mods (intake, exhaust)
3) With the upgraded performance mods, you'll have to move away from the OEM ECU (Megasqurt and the like) anyway to be actually able to benefit from them, and when you do that, you set the RPM limiter as you wish.

Ok so it was chipped after all, so in other words it is useless if i go beyond 7000 rpm without modding it. Its was soo good when i shift 2nd to 3rd and it goes li praaaarararararraarrrraaar (shifting at 8500 rpm) boooom, praaaaaa (lol). Ok so another thing, Is the combination I want to make good or can I do a better one? What I plan to do is buy the Millenia, take out the engine and refresh it.

In stock form, depending on cams, you will not make power above 7,200 RPMs.

As for shifting at 8,500, I would NEVER do this unless you have upgraded both the valvetrain AND the oiling system. You MAY drop valves at high RPMs, but you WILL spin bearings. It's not a question of if, but when.

I would set the limit at no higher than 8,000. For my own purposes, mine is set at 7,800 when I have the choice.

There is not really any "best" setup for these cars, or any other... Set yourself some speed/handling goals, and build the car to suit the intended purpose.