Hey guys! I picked up my first rx7 not too long ago with blown coolant seals. After I rebuilt the motor I noticed a pretty drastic change in cruising AFRs, I was wondering if that's normal or maybe I missed something.

I did a mid-range Pineapple street-port while I had it apart. It went from cruising highway speeds around a 14 AFR, to cruising around a 12 AFR. Boost is pretty similar, although turned way down.
I would have imagined the ECU would compensate for the increased airflow and run about the same, but if anything, the increased airflow would lean it out a little, not richen it up?

Could a missed vacuum leak cause it to richen up that much, or do vacuum leaks even change it much since it's MAP based?
Any other thoughts on what could cause the change?

I will be getting a new dyno tune hopefully within the next couple of weeks, but if there is a problem causing the change, I would like to address it first.

Thanks guys!

 

What ECU are you running? And yes, porting would change airflow enough to require a retune.

 

It’s a speed density system. More than likely the ecu is just sending whatever fuel is called for based on the parameters it’s operating at now with those changes. A porting change will obviously impact volumetric efficiency among other things.
.

 

I've got an apexi power fc. Yes I certainly plan on getting a retune shortly

 

Ok yeah that's kinda what I was hoping the reason would be. I know the VE would be changed up a decent bit, just surprised it made such a big impact while cruising and idling.

 

it's like putting a cam on an old school piston engine without variable valve timing. You have more overlap and different timing of the intake and exhaust events, which then changes how much internal exhaust gas recirculation you get and overall combustion efficiency.

 

^^sums it up well

 

AFR, changing any of the two will require a retune (air/fuel)