BB78, I honestly can't tell from the 3 pics you posted where it says anywhere what type of carb base it is. But from the 2nd pic, it appears to me that the base is square. That is, the four holes to mount the carb have a square pattern. The only "spreadbore" factory carb I'm aware of as Blade stated is the GM quadrajet.
Ok, well as far as not seeing what type it is, it's the Morotcraft 4350 4-bbl. This info is printed at the top of each one of the pages I posted and if you take a look at the first page it's printed up top just like the others, then move down an inch or so & it's printed in large boldfaced type. Under the large type it says "applies to 7.5L (460 CID) V-8 engines" and then if you scroll down to where the text actually begins the first sentence of the description is "The Motorcraft model 4350 4-V carburetor is used on 7.5L (460 CID) V-8 truck engines". As far as this entire issue being about the 4-hole mounting pattern that's used to physically mount the carb to the intake, I address that below in my comments to Blade.
As for being obscure & out of date, well I guess that's just a matter of opinion. 70's era 460 equiped F-trucks is not a collection of rigs I consider to be either obscure OR out-of-date but I can understand that some guys don't think much of the older stuff and that's a right everyone's entitled to. Without having a mid-80's manual to ck I honestly don't know if the spreadbore was continued on the carb'd 460's after the 1980 revision. I'll take your last statement that the majority of 78-87 Broncos have squarebores one step further and say that in all liklihood ALL of them did. Unless someone forgot to clue me in on some obscure options package that allowed someone to order a factory installed 460 in a Bronco then none of them did. It's a big-block carb used on 460's, the literature is quite clear on that point. I mentioned it because I've installed several 460's into several Bronco's and thought that it was perhaps something that I had some experience with. You clearly feel that isn't the case. My apologies for assuming that I had something to add to the thread.
As far as Blade's last comment goes, the mounting hole pattern ? Am I reading this correctly ? Are you suggesting that the term "spreadbore" in fact refers to the carb *mounting bolt pattern* ? Now I KNOW somebody's pulling my leg & funning with me. All I can say to that is "WOW", "wow" and then for a third time, WOW. The terms "spreadbore" & "squarebore" do *most certainly* refer to the venturi size. In a squarebore the primary and secondary venturi's are the same size, so as a result of that the butterfly's on the bottom of the carb are all the same size and line up into a nice *square* pattern, hence the name "squarebore". There are 4 venturis of equal size & they're arranged in a square pattern. Four bores arrainged in a square, Squarebore. In a spreadbore carb the secondaries are *larger* than the primaries and because of that they do NOT make a nice neat square, the rear of the carb spacer has to be wider than the front to accomodate the larger diameter venturis & butterfly's. They're larger, take up more room, and because of that they're more *spread* out. A spreadbore. Both a spreadbore and a squarebore will have a square, 4-hole mounting pattern that's used to attach the carb to the intake, that's pretty much universal in the carburetor world. The difference lies in the carb spacer, the spreadbores have the wider rear portion and therefore are *not* square. The attached photo shows the underside of the Quadrabog you mentioned alongside a 4350. Look closely and you'll see that they both use a square mounting pattern for the carb bolts. While you say you've never seen a spreadbore on a smallblock that's *exactly* why I said in my last post that it must be a difference between big-blocks & small-blocks. I agree that the one I posted wouldn't work on a smallblock ** for the same reason a quadrabog wouldn't work, it wasn't designed to. I don't ever remember suggesting that it *should* be used on an ** engine. All I ever said was that the info I'd looked up indicated that the 5.8HO's used a spreadbore, it was a very simply & basic statement.
In the interests of domestic tranquility I'm calling it a day. I spoke from the personal experience that *I* have and that's with late 70's bigblocks. Those are the only engines I've even spent the time or $$$ to build-up and the ones I've spent my time with. Anyone thinking I'm full of $hit is more than welcome to PM me and express that opinion. As far as this thread goes I'm willing to simply call it a disagreement and move on to other issues. Arguing with a *pair* of moderators is sorta like ******* on the steps of City Hall, regardless of where you stand you're not gonna win. It's sorta like trying to cross the Blue line, it just doesn't happen. I'm done with this one. As for answering the *original* question that initiated the thread, I guess the best & easiest answer is to simply pull the carb off and look. that will pretty much answer the question and I guess that's all I should have said in the first place.
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