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392 4 barrel intake on a 345...?

jayman2003

Member
I was hunting down a new master cylinder seal/bladder for my 1977 Scout II when a local parts guy who couldn't find it in his system said "hey go check this old place downtown called the u joint, they used to be an International dealer..." I knew they were most likely dealing in big rigs and the like but thought what the heck I'll give it a try. Went on down and they didn't have what I was lookin for either but...were able to give me a part number at least. Well after not finding the part I started talkin to the gentleman behind the counter and found out he used to work in one of the factories that produced IH vehicles. He started talking about a modification that was performed on a rush to get a vehicle out of their shop one night where you would take the intake manifold off of a IH 392 and put that onto a 345 using the stock 4 barrel carb that came on the 392. I guess after this mod was done they were flooded with more internationals "needing" work of the same nature. The gentleman said doing this you would see improved mpg, as well as performance...the phrase "would pull anything up a mountain" was used. Now I know my 345 has some good tq but this still got my brain turnin. Just wondering if anyone has heard of this modification, or used it on their Scout. Thanks for your time :cornut:
 

Michael Mayben

IHPA Tech Moderator - Retired & No Longer Online
The 345 engine in a Scout II application was only offered with a 4v carb in a few years and a few emissions configurations. And the manifold/carb combination was a "spreadbore " design using only a carter thermoquad carburetor. All of this kind of stuff was predicated because of emissions regulations /requirements that ihc chose based upon making the emissions numbers and holding cost down, had nothing to do with "improved" overall engine performance.

A light line dealership service department outside of the state of kalifornikate back in the day May never have seen a "kalifornia only" 4v 345 in a Scout II thus they aren't even aware those were ever available.

Likewise, the Scout II platform was never offered with a 392 engine option, though no doubt a few were done for special projects and many dealers routinely swapped motors at the point of sale, though that in itself was dicey proposition due to federal and state emissions regs.

The intake manifold configuration used on the 345 in a Scout II app is identical to the 392 intake manifold used in fullsize "light line" vehicles during the same era. The manifolds are completely interchangeable on the engine, though the peripheral components used May vary considerably based on the donor vehicle/emissions/production date configuration.

The 392 engine in a "light line" application likewise was never offered with a 2v carburetor, but there were many 2v 392 motors used in medium duty trucks and school bus chassis, both non-governed and governed.

While many components of the complete "light line" product offering (Scout II, pickup, Travelall) are shared, the majority of individual parts are not common to all. We treat pickups and travelalls around here as their own platform, same for Scout II, same for Scout 80 and Scout 800.

And to take this a step further, there are many varying configurations of both 2v and 4v intake manifolds used on the various incarnations of the sv engine, don't fall into the trap of..."they are all the same"!
 

jayman2003

Member
Well thank you for the informative response, I don't think this is something I will be doing anytime soon but none the less I wanted to know if anyone had tried it out.
 

Scoutboy74

Moderator
When I got my '74 Scout 9 years ago it had a 345 engine it. I have no idea how many times this rig has changed hands before me. Someone prior to me had adapted a GM rochester quadrajet carb onto what I later discovered was a squarebore 4bbl intake manifold, quite possibly sourced from a 392 engine. That particular carburetor was never original equipment on any International vehicle, but it is a common swap modification. Even so, a spreadbore carb on a squarebore intake isn't a great match. As Mike alluded to, the engines installed in scouts did not start showing up with 4bbls - the carter thermoquad - until (correct me if I'm wrong mayben) 1978. The correct carb for my '74 would have been a Holley 2210 2bbl with matching 2bbl intake. One of the other oddities of my Scout engine was a delco distributor. I eventually learned those distributors were common on IH engines produced prior to 1970, but were phased out shortly thereafter. The correct distributor for my '74 Scout would have been a Holley points model. So at the very least, some parts had been swapped onto the original engine. It's also possible that the entire engine was a transplant from something else. I'll never know for sure. Now it has a 392 with an identical squarebore intake and a Holley 4150 carb, but at least I'm more familiar with the history of this engine. These are the kinds of "learning opportunities" new owners often encounter when dealing with old rigs that have changed hands numerous times. That's why some of us tend to make a big deal out of stumbling on an unmolested virgin.
 

int77345

Member
I swapped a 4 bbl 392 square bore manifold on to my 345 that had a 2 bbl manifold . I didn’t really see much of a performance gain, or mpg gain, I just wanted to run 4bbl carbs, is the main reason I did this. I was just trying something different for me, if I had to do it over again, id probably leave the 2bbl on. I got my 4bbl manifold off a 392 that was in an International dump truck.
 

paul hoffman

New member
i just got a holly truck avenger 470 sq bore carb for my 4 bbl 392 intake that i plan on putting on my 345 what are the 5 ports on the underside of the manifold am i going to need some sort of seals for them i havent pulled the 2bbl intake off yet so im not sure whats there i would like to replace the seals or o rings with 5 new ones its the start of my 74 200 1 ton restoration get it running
 

Scoutboy74

Moderator
I think you're talking about welch plug ports, smaller versions of the freeze/expansion plugs found on the engine block. There'll be coolant sitting inside that manifold that could expand during a really severe freeze.
 

int77345

Member
let me know how that truck avenger works out. i tried for a few months on mine never could get it right.

if you want/need jets or accel cams let me know i will send ya all of mine
 

FDChappie

Active member
Running a 390cfm Holley on a mildly warmed over 345 with great results. From my discussion w/Holley that carb is setup for off road racing and won't meter right without a lot of work. There is a thread here on how that was setup.
 
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