Good idea needed for RWD 4cyl engine swap
 

I have a 66 Volvo 122 (Amazon) estate (wagon) its got a B20 Volvo engine that has promise. I know someone who gets 38 mpg with his.
My thought are what engine would be powerful enough to run an atm. and still get decent MPG 40 would be awesome but I could live with 30-35.
Swapping engines does not scare me. But spending more than needed does.
No dream builds, needs to be reasonable. And since its RWD platform no expensive adaptors unless its worth it in the long run.
The current set up according to the original owner got 25 MPG. No O/D.
This car has 4.56 gears factory to help the low torque B18 it originally had.

Ideas/thoughts welcome!

Miata drivetrain...1.6 or 1.8, 110-125ish hp. You could drop some gearing then I bet.

An EFI B20 bolts right in. Same with the later OHC B230 with 10:1 CR and LH3.1 EFI. You could even convert your existing engine to EFI.
http://www.volvoadventures.com/1800FrankDerks9.jpg

Good food for thought. Ideas on what MPG those might get?
I want a Quad 4 Oldsmobile but fear the costs involved.(I've done some checking)
Not 100% sold on a 4 cyl. I've heard good things about 2.8 V6 GM engines.
Had a friend with a late 80's Firebird that got high 30's. He loved that engine.

Or keep it simple and drop in a Volvo transmission with overdrive. That in itself should get you about 4 MPG. The B18 and B20 will mate up to the same transmission. The Volvo 4 speed from those days was available with an overdrive. I think it was a simple boltin swap that needed only a switch for the overdrive solenoid and a shortened drive shaft.

If you do that, BEWARE. The spec for the overdrive transmission is (I think) 10W40 engine oil, while the spec for the 4 speed without overdrive is 80W90. If you put 80W90 in the overdrive transmission you will shear off a key inside the overdrive.

I actually have a 4speed and O/D set up (driveshaft too) but the trans needs
work and momma wants an ATM. I figure if I'm swapping trans might be a good idea to get a more modern engine with a bit more torque.
the factory atm in these old dogs did not have O/D. adaptors to put an O/D atm are around $900. I'd swap the whole mess 1st.

B230 EFI motor with the matching AW70L 4 speed auto with lockup. Dirt cheap, plenty of torque and it bolts right in. 93-95 NA 940 drivetrain is the ticket.

With the accumulator mod... :p

Curious? Whats the accumulator mod.

Google:
AW71 free accumulator mod - Turbobricks Forums

Reduces shifting time to save your transmission. Bonus: It's a Volvo forum too.