351 or 460?
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351 or 460?
My daughter gave me an 1981 2WD F250 Custom long box for Christmas. It has a 3 speed auto tranny. She got it from the executor of a neighbor's estate.
According to the VIN, the engine is a 351. According to the executor it's a 460. I checked all the usual places where there should be a tag on the engine, but can't find any.
Can anyone suggest how to tell which engine this is?
Thanks in advance for any assistance offered.
According to the VIN, the engine is a 351. According to the executor it's a 460. I checked all the usual places where there should be a tag on the engine, but can't find any.
Can anyone suggest how to tell which engine this is?
Thanks in advance for any assistance offered.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
As an '81 F250 the engine should actually be a 400, not a 351M. However, you really can't tell the difference between the two from the outside as only the pistons and crank are different. There should be a label on the radiator filler and/or valve cover telling which engine family it is. And if you post the Certification label from the door jam we can decode it.
Bubba's site has lots of info on the 335 Series, which includes the M and the 400. the 351M/400 has 8 valve cover bolts and the 460 has 7, IIRC. And the M/400's thermostat housing bolts to the block while the 460's bolts to the intake.
Bubba's site has lots of info on the 335 Series, which includes the M and the 400. the 351M/400 has 8 valve cover bolts and the 460 has 7, IIRC. And the M/400's thermostat housing bolts to the block while the 460's bolts to the intake.
Senior User
Joined: Dec 2010
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From: Lajord, Sk,Can.
My 1981 F250,4X4,Super Cab, Long box, has the 351M. When I bought it, I was told it had a 400. The label by the radiator, reads, Engine family 6.6/5.8 Engine displacement 5.8. When I had the motor rebuilt, it was confirmed to be a 351 M. I have an R V cam in it and the original 2 bbl. carburetor, wow did that wake this motor up.( Rebuilt in 2001. still runs very strong)
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Interesting. There goes another of my beliefs. (Soon I won't know what to believe.)
Yes, a cam swap, and a good timing set, can really make the diff on an M. Rusty is similar although his M has a Eddy manifold and 4bbl, and he gets the job done. I recently pulled a car-hauler trailer quite a ways, and light I got 10.5 MPG, which is better than Dad's truck did with a stock M and no trailer. And, during the return with a 50 Chevy pickup on the trailer the right rear spun as I pulled out from a stop with lots of throttle. No sand, no bumps, just torque.
Yes, a cam swap, and a good timing set, can really make the diff on an M. Rusty is similar although his M has a Eddy manifold and 4bbl, and he gets the job done. I recently pulled a car-hauler trailer quite a ways, and light I got 10.5 MPG, which is better than Dad's truck did with a stock M and no trailer. And, during the return with a 50 Chevy pickup on the trailer the right rear spun as I pulled out from a stop with lots of throttle. No sand, no bumps, just torque.
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
No 460's in that year.
They came back in '83.
You can tell a 351 M from a W by the fuel pump.
Or whether it has a timing case (W), or just a funky 'shelf' (M) at the front of the block.
They came back in '83.
You can tell a 351 M from a W by the fuel pump.
Or whether it has a timing case (W), or just a funky 'shelf' (M) at the front of the block.
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