Hi guys, need some help here. I'm looking at buying a 70 Cutlass that is believed to be a W31. The engine does not have the big balancer but does have the 7040255 carburetor. It does not have the original intake manifold. It is a factory 4sp car and has the 12bolt rear-end. Both the engine and the transmission are original to the car as they both have the partial matching vin. Was there any engine variations in the W31's such as the balancer?

 

No, the balancer is 1 of the man identifiers. The carburetor is also special. If you think the engine is original and if you can pull a sparkplug, look for flat top pistons. The distributor is the same as the 310 hp 350.

 

Every single A-body made by Oldsmobile in the 1970 model year came with a Type O rear axle that has a 12 bolt cover, but only ten bolts holding the 8.5" ring gear. This is NOT the Chevy "12 bolt" axle. Post a photo of the '255 carb number. It could be a restamp. Even if this car was a W31, the parts that make it so apparently are long gone. You would need to pull the heads to measure the valve sizes, and even then, it is easy to machine any SBO heads for the larger valves.

 

TLDR: Absent ironclad paperwork, there's really no way to authenticate a W-31, at least not with any certainty.

 

Be sure you do not over pay for it on the suspicion it is a W-31. For sure post a picture of the 0255 carburetor. There are lots of restamps out there. SOmeone may have just put a restamp on it.

 

Vin# 336870M2*****

 

Also the transmission is a M20. The internet research I've done says all W31's had 3.91 gears and a M21. Is this true?
VIN 336870m2*****

 

ai? 😂

 

1970 W31s did come with the Muncie M20 and 3.91 rear. The intake being changed to a Holley unit was common. For the missing balancer, well they had a high failure rate and therefore it was probably changed. However, to say it’s an actual W31; you will need a broadcast card or window sticker. If the car lacks paperwork, then, should be priced accordingly. Out of curiosity, what is code on the differential and date code.

 

Following. Return fuel line look original on a non AC car?

 

Special order color with a black bench seat...pics of the car?

 

The engine pic looks like it has #8 heads which are later year(s).

EDIT: I zoomed in closer and does appear as #6. Sorry to add any confusion.