425 engine swap???

1)My father has just aquired a 65 dynamic 88 convertible and was thinking of an engine swap to improve mpg. Any one have any suggestions. he was thinking of a fairly modern motor.
2)If the 425 was kept he is thinking of a four speed on the floor,any recommedations here?

any recommedations would help thank you

[jdorour]

The 425 is a good design and will give you about 15 to 17 MPG on the highway (maybe a little more if it is driven with a light foot). I should return about 10 to 12 MPG around town.
A more modern engine may not return any better fuel consumption as these engines are generally small displacement and would need to work pretty hard to move around a big car like your 88. To get the best (if any) improvement you would need to pull the ECM and wire harness for the Fuel Injection if you use a late model engine. Fuel economy has a lot to do with the engine but it also has a lot to do with the rear axel ratio, transmission, weight, aerodynamics and driving style. It is also very dependent upon the quality of maintenance the car gets. I was around for the 1973 oil embargo and the 1978/1979 oil crunch. During that time many people would pull their big block engines out of their big heavy cars and put small blocks in place. They where always disappointed with the result. The fuel consumption was usually about the same. The smaller engine had to work just as hard to move the big car. It is simple physics. To accelerate 4000 pounds to a given speed in a given distance required X effort. If the energy content of a pound of gasoline is constant it will take the same amount of gasoline for a 5.0L engine to produce the same amount of work a 7.0L engine. Granted the efficiency of engines has improved but not by that much. A 5000 pound SUV still only gets 15 to 17 MPG on the highway. Most of the improvement has come in the form of reduced emissions and better drivability.

If you want to put a 4 speed in the car look for a wide ratio Muncie. Look for a Big Pontiac for the clutch and shifter parts. The Olds units are very rare (like I have only seen one Starfire with a 4 speed). The bell housing for Pontiac and Olds are the same. You will need to find a flywheel from a 65, 66 or 67 (later units had a different bolt pattern). You will need to have a driveshaft made. The Pontiac shaft will not fit (shorter wheel base). Another option is to put an overdrive automatic in the car. This will give the fuel consumption improvement he is looking for and is much simpler install. Look for a THM2004R from a 442 or Grand National (they also installed this trans in other Olds, Caddy and Buick engined cars) but the 442 and GN/GNX units are much stronger units. The trans will need to be overhauled and beefed up to work best behind the BB Olds but it will work. Another Trans to look for is the 4L80 from a Caddy limo or hearse (very rare). Last option for an Automatic Overdrive is a 700R4/4L60 from a Chevy or a 4L80 from a Chevy/GMC truck. Both of these transmissions will need an adapter plate (you can get them from a number of places).

[WEBBISH]

I HAVE A 66 DELTA88 WITH THE 425 2BBL AND I GET 20 AROUND TOWN AND 25 ON THE HIGHWAY JUST HAVE TO KEEP YOUR FOOT OUT OF IT, BUT IT WILL STILL SMOKE THE TIRES IF NEED BE.