392 vs. 345

[Teoeleven]

Hey folks, Im new here but this looks like an incredible resource for anything that has to do with a scout. I have a 72' with a 392 in it but its a little tired and was wondering what the general consensus was on those engines? Is it worth rebuilding or should I just go with a rebuilt 345 and get rid of the 392? Thanks for any help..

[John Donnelly]

Moved to General Tech from the Vendor forum.

"There is no substitute for cubic inches".

That is a motto many of us know, and if you have a 392 I *personally* would overhaul it before I went on the hunt for a 345.

I am sure there are going to be differing opinions on this subject, mostly centering around economy, but in my experience the 392 isn't any worse in that regard than a 345.



-John

[Tom Mandera]

I have a pile of SV (266,304,345,392) engine cores here.

I am scrapping the 304s. I just don't have room for them. The 345s are going next.

I have enough 392s to outfit all of my IHs (that don't currently have a 392), and since the cost is about the same (used to be, at least, the 392 slugs seem to cost 2x what the 304/345 pistons do now) and the fuel economy is the same, why would I build anything BUT a 392?

I would trade a tired 392 for a good 345. I probably wouldn't pull a good 345 to put in a good 392, and I definitely would pull a good 392 to put in a good 345.

I did pull a good 392 to put in a GREAT 392, though.

I would consider a 304 if I wanted high RPM (and I do), or just "that much" more engine bay room (like the blown-304 for Robert's 34 pickup)

-Tom

[Brett Whitaker]

In my opinion the 392 is the way to go. I was amazed at the difference when I went from the 345 to 392.

Brett

[Doc Stewart]

All depends on projected use.
My 65 Scout 80 has the original 152 four banger and goes up and over all the trails my 78 Scout II with 392 did. It won't pull others out of deep ravines without several snatch blocks and lots of cable however.
My 67 Travelall had a 304 and went well enough and towed well enough but rolled over the Sierras and towed the same roads much better when the 392 replaced the 304.

A Scout 800 or Scout II for trail work will do with a 266 or the AMC 6 banger. Hauling loads of firewood up hills with a trailer - the 392 is a decided advantage.

[redhead_823]

I don't have much experience with "good" IH engines, but I know that increasing stroke does not increase hp (only changes torque), while increasing bore does.

[Will Marsh]

I agree with Tom here.

Any "good running" SV is better than a bad SV.

I probably won't pull a "good running" SV to replace with any other "good running" SV regardless of the different displacement of the engines. They are all adequate to do the job in the trucks they're installed in from the factory for 95% of the general uses you might want them to do. The differences between them are really only noticeable at the extremes.

I might pull a "good running" SV to replace it with a "GREAT RUNNING" SV depending on the specific truck and it's intended uses. In that case the "GREAT RUNNING" SV would be built to meet the intended use of the specific truck it's going in, and the "good running" SV would find it's way into a different truck with a bad one. Two good examples of this are Tom's "Race 304 " and his "Stroker 392". They were both purpose built for the trucks they're in.

HTH,

Will Marsh

[Will Marsh]

Originally Posted by redhead_823

I don't have much experience with "good" IH engines, but I know that increasing stroke does not increase hp (only changes torque), while increasing bore does.

This is Hot Rod 101, and you need to go back to school.

Any increase in displacement will increase both torque and horsepower since HP is derived from torque x rpm. It may not increase MAXIMUM TORQUE depending on where that torque occurs in the rpm range.

Since all modern V-8 engines are oversquare (bore size is greater than stroke length) in general going more oversquare results in more hp at high rpm and less torque at low rpm, while going closer to square results in more torque at low rpm but limits hp at high rpm.

A 302 SBC (way oversquare) pushes a corvette or camaro just fine, but won't move a loaded pickup worth a dang. A 305 or 307 was the preferred engine in the pickups for a reason, they produced more usable power in that application.

Do you want to move a light object fast or a heavy object at all? Use the right engine for the job.

Will Marsh

[redhead_823]

Originally Posted by Will Marsh

This is Hot Rod 101, and you need to go back to school.

Any increase in displacement will increase both torque and horsepower since HP is derived from torque x rpm. It may not increase MAXIMUM TORQUE depending on where that torque occurs in the rpm range.

Will Marsh

Sorry, but I was just trying to explain what you gain between 304-345 and 345-392. And it's going to be kind of hard to go back to school when I'm currently in school. I'm trying to learn.

This is straight out of GM's base engine design class: A change in stroke will not greatly affect horsepower, only change peak torque and where it comes. A change in bore will directly affect horsepower.

This is why you don't gain hp when going from 304 to 345, but you gain torque.

[ihairman]

the stroke is the same in the 345 and 392 the only difference is the bore size the 304 and 345 shar bore size but different strokes Ed