Hey everyone, this is my first post on this forum. I am actually a vendor on many other car forums and know the scene very well. I wanted to make that known before I get flamed for wanting to put a smaller motor in my car! I realy do not need any comments trying to convince me to not do this.

Here is some background info. My younger brother just turned 17 and wanted a mazda 3, unfortunatly the car was out of the price range my parents wanted to spend for a first car so I kept my eye out for a good deal. I just picked up a 2005 mazda 3 four door with the 2.3l motor. The car is fully loaded but does have a reconstructed title. This does not scare me and after checking out the body on a rack, everything is straight and all repairs were done within specs. unfortuantly the motor had some issues and the previous owner threw a rod, and the car has been parked ever since.

I ended up purchasing a used 2.0l motor with 30k miles on it, without doing much research, because I got the motor for next to nothing and I had to make a decision shortly after I found it. After picking the car up I relized the car is the S model with the larger 2.3l engine. My brother will not care if the car has the 2.0l or 2.3l in it, and my parents would actually prefer a less powerful car for him. I do not care about resale value on this car as he will drive this car until it dies.

Since the old block is not salvageable at all (piston knocked a hole in it) I wanted to see if putting the 2.0l in would be a direct swap? The only issues I thought I might run into is possibly the 2.3l transmission (Am not sure if they are different at all) and the possibility of needing a 2.0l ECU to make everything run correctly.

Can someone let me know what problems I might run in to? If the only issues in the ECU I am not worried in the least, if the transmission is completly different (I doubt it) then that might throw a wrench in the procedure.

I also assume that the 2.0l and 2.3l use the same block, and the larger motor is just bored and stroked to achieve the larger displacement? If this is the case then will all of the motor mounts match up to both engines?

Thank you everyone for taking the time to help me out, I greatly appreciate it.

Steve

 

I'll take some shots int he dark here, but I'm not an expert.

Electrically you should not have too much trouble as long as you keep the ECU and engine harness intact back to the C1 connector on the fusebox.

All the pins in are fairly standard between the 2.0 and the 2.3 (some minor differences on the MazdaSpeed at least in 2008, which is the year I've been dealing with). The ECU is part of the engine harness. Hope you have a 2.0 one.

The antitheft system will have to be reprogrammed if you don't have the dash from the donor.

Mechanically I don't know the differences.

 

I will need a 2.0l engine harness? why will the 2.3 engine harness not work and just use the 2.0 ecu?

 

The motors are nearly identical in every way except for the longer crank used in the 2.3l. The transmissions are the same. (more information is needed but even if the transmissions are different they can still interchange) The harness will match up if the cars were equiped the same.