1993 940 non turbo with 290K miles, with pulse-air system. I replaced the original head with a rebuilt head because the original head had a cracked exhaust port. The replacement head did not have pulse-air ports so I did not reinstall the pulse-air manifold, and I plugged the pulse-air vacuum control line from the controller. The car runs and drives well and idles smoothly. I'm pleased with how it performs, except that it's dropped 2-3 miles per gallon. I'm getting about 19-20 miles per gallon now whereas before I was getting about 22-23. There are no fault codes in the ECU.

From what I've read about the pulse-air system it's mainly to reduce emissions. I've not read anything about it improving fuel economy, so I'm assuming my loss in fuel economy is due to something different about the replacement head other than the fact that it's not equipped for pulse-air. If I've lost the fuel economy for good, that's okay because the car is performing well otherwise. However, if I could recover the 2-3 miles per gallon by retrofitting my replacement head with my original pulse air manifold I would consider doing that. I no longer have the original head as I scrapped it. I've driven the car 3K-5K miles since replacing the head.

In replacing a pulse air head with a non Pulse air, you now have a head from a different sales market, different year, or both. Could it be you now have a different compression ratio, thicker/thinner gasket, different shaped combustion chamber, larger/smaller valves, different cam?, different shaped intake/exhaust ports.... who know what else?

Maybe a heavier foot because you like the way it runs now 😊?

93 940 base,,no pulse air tho,,I fixed air leak at the header to cat connection & my mpg went up to 24 from 17 for two tankfuls,,then it went back down,,then I checked the slides on the front brakes &they were frozen in place,,maybe the syn lube doesnt last that long,,,Ive tried to nail down every possible vacuum air leak,,& maybe next Ill find another set of injector to clean & reinstall?

I would regard that as normal variations, even if no change to the engine was made. Depending on driving style and conditions, I'd say a 5 mpg variation isn't extraordinary.

However, I too had a head replaced on my 245 because the waterways were corroded and leaking past the head gasket into a cylinder. I got a similar change in mpg, however it was an improvement in my case.

so you have a B230 engine--Vintage 1993
with a replaced Head----specs Not specified

The last thing I would do is to ReFit some Emissions Control System circa 1993 to solve your more costly (cnts/Gal Gas) aka MPH, Problem.

Let me count the ways the MPG could rise(plz U GOOGLE that)with a "new" head.

Just enjoy the fact that, as you Wrote: """""" The car runs and drives well and idles smoothly. I'm pleased with how it performs""""