I was gathering information on the engine specs from Mazda, as I am going to turbocharge it.

Mazda mechanics told me the compression ration on the MP3 engine is 10.3 and not as low as the P5 engines or the sedans.

I was also told they were the ones who put the premium fuel sticker on the car. They told me, its a must that I use 93 octane.

Basically the P5 engine and sedans are better for turbo applications, being they are almost one full point lower compression ration.

I was a bit confused, so I called up Calloway and asked questions about the boost pressure and was the engine any different than a standard production unit used on P5, etc. They said yes, it has different bore and stroke! I was totally ******* amazed. The bore is smaller and the stroke is longer. The new numbers were 3.36 + 3.96 compared to 3.69 + 3.70.

The also said they didn't not change any internals.

 

Never seen one with the head off. Why?

As far as those bore and stroke numbers, they may be off slighty, as I am going from memory, not writen down data, sorry about that. But they said the bore had to do with the compression being higher.

They told me nothing was done to the ECU, and Racing Beat said the same thing.

 

how do you change the bore and stroke without "changing any internals"? pistons and the crank are main components of the "internals"
i don't know how you make a block have a smaller bore, unless they sleeve it?
with custom pistons you could have a longer stroke with the clearance between the piston and head.

also just for future reference it is compression "ratio" not compression "ration"

 

Yeah. I was pretty sure that the MP3 had some ECU changes. But they did something pretty serious to the internals if they changed the bore and stroke of the engine. Doing internal changes should have yielded a lot more than just 10hp.

 

I read his post as saying, Callaway did not change any internals when going turbo. P5 and MP3 internals would be different if bore and stroke are different.

 

I was told by Calloway, that the MP3 engines are different, but use all factory parts, and are built like this from the factory