I'm running a T25 turbo on my 2002 Miata with a Megasquirt 3. Compression is bad in cylinder 3 so I'm swapping in a used 2000 engine. What changes, if any, will I need to make to the tune I have to get the new engine to run safely, other than turning off VVT control and changing the timing map? Perhaps it is better to just start with a raw base map even though every single part external to the new block and intake manifold is the same?

Thanks for any help,
Sean

 

Biggest difference should be that you're losing VVT and gaining VICS. So you need to control VICS (simple digital output, turn on above 5000rpm or so with a 200rpm hysteresis).
Other than that you need to re-tune fuel. Shouldn't really require a change in spark.

 

In to hear from experts. With lower CR, more advance could be possible, as well as possibly more boost, depending on where your limits are. Personally, I would start with the map you have, but re-tune from scratch starting with base timing, latency (different ignition), idle valve and idle control. Indeed, mod the MS to control the VICS.

 

put the 02 head on the 2000 motor, use the 2000 IM.

wire up VICS to work.

anything else and you fail.

 

This is my first time taking an engine out of a car, and at first I was nervous about taking the head off, but now I see that it's extremely easy considering all the other work I have to do to the new (used) engine anyway (like replacing the valve cover gasket and timing belt).

I guess I could take my 02 head to a shop and get it checked out. It's high mileage (180k). I already ordered a 2000 head gasket, but I'm also doing a coolant reroute so I assume this would work out perfectly anyway.

I'll have to look into wiring up VICS. I got the car second hand so I'm not extremely familiar with all the MS3 wiring and such. From what I've read I can simply leave the VICS unplugged for now and worry about it later, correct?

Thanks.

 

its worth the time to research now.

you dont want to lose vvt, and replacing VTCS with VICS is a bonus.

 

the answer is: everything. they use different timing curves and different fuel maps and then the whole vics vs vtcs and vvt stuff.
I would tell you to replace with another vvt engine then. The devil is in the details, and while it will be easy to physically swap, there will be lots of little things that will require modification. Not worth it to me, especially for a downgrade.