I ran into a guy recently that was towing a 35ft. 5th wheel trailer weighing 14k lbs. with a 98 F250. I didn't see the truck, we were just talking about it. We were talking and I assumed it had the turbo diesel in it, and was fairly impressed when he corrected me by telling me it was a gas burner. That is a lot of weight for a gas burner, so I asked him what size motor it had in it. He told me 351 at that point. We were discussing it further, and he told me it was a big block 351. He said it was more powerful than a small block 351.

I don't know much about motors, but I didn't know you could buy a 351 in a small block and big block option. If this is true, how much of a difference in power would there be between the two??

 

The 351 is a small block.

Maybe he's a Chebby guy and thinks that, because of the spacing of the center exhaust ports!

Edit: The '98 was only availible, with the mod motors. Most likely a 5.4.

 

No such thing as a 1998 F250 (unless its an LD, and that would have a mod motor). No such thing as a big block 351 these trucks. The 351 after 1980 is a Windsor block (as in 260/289/302 based). Before that they had the Cleveland block 351 (went in cars only after 1975) and the Modified block 351 (same architecture as the 400) which is the only semi big block 351, but you can only get one in a pre-1980 truck. Actually the labels "big-block" and "small-block" dont even really apply. Ford never used the designations "big-block" and "small-block", GM did that. Just like people that call all Limited Slip Differentials "Positractions," another GM term, the appropriate Ford term is "Traction-Loc". So really if the guy has a 351 its a 1997 or earlier truck, if its a "big-block" he must have put a pre-1980 351M block in there. As far as power difference the main thing is with modifications. With a Windsor 351 you can build a 408 stroker. With a 351M you can turn it into a 400 (which Ford actually made, it was an option in trucks until 1982 with the first Gen7 facelift) and stroke it from there. 400s are great Torque motors, and the Windsors are good for big horsepower. And the Cleveland blocks are just obsolete.

 

Um, yes there is.

http://dealerrevs.com/gallery/12078433.html

 

thats why he said LD, light duty

 

So, educate me. What makes it light duty, if it has the heavier springs and axles?

Trying to learn something here, I guess!

 

the LD looks like an F150 w/ heavier axles/springs/wheels etc. the HD looks like the older mid-90s body style

 

Basically I answered every aspect of the OPs post in excruciating detail, haha.