Spread bore or Square bore

[dkterra]

In all this confusion I still haven't read anything that debated or referred to the difference between spread bore intake and square bore intake?
Both are 4 barrel, the only talk has been about 2 barrel or spread bore 4 barrel? For some reason FI was dragged into this as well?

The only reason I'm posting is because I'm curious myself on IH owners thoughts between spread and square bore performance. I realize it's all relative to what your after or certain applications.

I'm betting that square bore is the way to go if your choosing to buy an intake because adapting it for spread would make more since then the opposite way, but I feel this thread is dieing from the amount of confusion.

[Dennis Bernth]

I think the reason the talk is mainly about spread bore or two barrel is because those are what most people have. It's not hard to adapt the spread bore to take an Edelbrock carb, and as Jay said, if you have a spread bore with a properly set up Quadrajet, you'll get probably the best driveability and fuel mileage of any carburetor out there with the small primaries (Bill, notice I distinctly said CARBURETOR!). In my opinion, spread bore is the way to go for a four barrel intake, if you choose to go with a square bore carb you can adapt that a lot easier than you can adapt the square bore manifold to the spread bore carb. If you think you want to go FI, then stick with the two barrel. I've got a two barrel Motorcraft on my 79 Scout II 345 (engine is a 75, original engine was a 304) and although I've got a couple of spread bore intakes laying here, I doubt I'd gain enough to make it worth my while muscling those heavy suckers around to change them, so it's staying two barrel.

[Jeff Jamison]

I run 4 barrels on 4 IHs now,3 spreads and one square,I tow with 2 of them.I got about 1 mpg better when I went to the 4 barrel with a 392.The sguare seems to give me better power towing.Like said either can be adapted,and can be set up to run the same,its mostly a preference,I like holleys best,but run 2 edelbrocs as they where cheap and very easy to maintain
Jeff

[Jay Tabor]

i noticed that ,too, no talk of diff betwixt squares and spread bores.
but since the guy was gonna get a spreadbore . . we talked about spread bores.

the diff is spreadbores have smaller primary holes than square bores do,
and sooooooooooo they suck less gas while only using the tiny primary [thems the smaller holes drilled into the maneefold] holes.
a square bore is better if you stuff your foot into it all the time,
the primarys dump a little more fuel,
and so when the secondaries kick in theres not as dramatic a difference in necksnapping race winning acceleration, as one would feel with a spreadbore carb . .
thats because the primary bore grades are giving half the fuel and the secondarys are giving the other half,.
where-as a spread bore spread the fuel- 1 third primary and 2/3rds secondary..
and theres hundreds of variables with either or both types of maneefolds/carbohydrate combos . .
to cause one to make the engine produce more power than the other type at any given race track . . and place and time and air pressure gradient and humidity and temperature.
heck you may run the spreadbore on a cold moist high pressure day with 50% humdididty
and itll produce more power than the same engine and carb and maneefold and gas will on a dry day of 10% hummerdidity, with air pressure a whole 1 inch lower on the barometer and a ten degree dif of hotter temp . .
so then youll toss that 4bbl away thinking it aint no gooder thana 1 barrel 1904 hollywood carburator!
so youll need a dyno and a 1/4 mile race track to expaireement with your race scout,
to see what develops the most horsepower, tigerpaw traction and torque.
be that as it may, as Bill usn politely mentioned that 88 octane drinking fire breathing race machine will only turn 4500 rpms anyways- if youre lucky and did a good tuneup on it...
and any torque /pony or donkey power graph chart will show the lines crossing about the same place, anyhow . .
and all of that is moot when youve still got them 45 inch tall gambo monstah mudder meats on them 8 inch wide wheels running 3.07 gears . .!

[scoutboy74]

The most important consideration is to match the carb design with the manifold. Square to square...spread to spread. Adapter plates are a less than ideal means of crossbreeding. Besides, under hood clearance is very tight on a Scout. Scout II's with SV8 engines generally came with 2bbl carbs. The 304 engine was never offered with a 4bbl carb. Towards the later days of SII production, when a 4bbl carb could be found on a 345, it was a Carter Thermoquad, a spread bore carb on a spread bore intake. The mild increase in engine output was a byproduct, rather than a driving force behind the change.

The square bore 4bbl intakes and matching Holley carbs could be found on 345 and 392 engines in light to medium duty trucks. Constant power output trumped fuel economy in these applications.

As far as which style is better than the other, good luck finding credible data anywhere that will allow you to objectively compare and contrast, especially with regards to an International Harvester application. I seriously doubt that kind of data exists even with much more common ChryFordrolet offerings. Too many variables, but the difference, especially in a Scout certainly won't be night and day. More like mid-afternoon versus early evening.

[lightningflash]

Originally Posted by Bill usn-1

If it runs and drives fine and does what you want it to do then there is no need to change.

What are your reasons for wanting a 4 barrel?
What do you want to do with your IH that it is not doing now?

If you google "CFM calculator" and input your engine, it will give you an idea of how big of a carb the engine needs. Keep in mind that stock the engine normally doesn't exceed about 4000-4500 rpm.

I'd just like a little more power when needed. We have some sand dunes 45 minutes away and I'd like to get the most out of my motor that I can to climb hills.

[Thomas]

Originally Posted by dkterra

In all this confusion I still haven't read anything that debated or referred to the difference between spread bore intake and square bore intake?

---I type too much as it is so since I didn't see any inclination that he was considering purchasing a squarebore, I just stuck with commenting on the intake he has now, and the one he was considering purchasing.

---If he wanted to know if he should save the $150 for a squarebore, I didn't see any hint of that, so I tried to Keep It Simple _. I stated and stand firm to my feelings that the 2v does all it needs to do on the 266-345... and FWIW, can even be built to work well on a 392 since they can be had/altered: cfm of 650+ (overkill for our engines) for circle track and CART. Remember, I was the misunderstood one who would have liked to see an "adapter plate recess" idea built into the wonderful aluminum intakes.

---Ahhh yes, Michigan (sugar) sand dunes! More chance of vehicles running on those than the protected Mt Baldy, West Beach, etc. in Indiana. Do you have a M/T or A/T?

---Understand these aren't wrappers like a Toyota or a AMC/Jeep. They get through mud, sand, snow and such without having to put your foot in the engine bay. Just like I have respectfully feathered the pedal to get through thick stuff, many a Farmall has pulled multiple Deer Johns out of muddy fields with throttle near idle. Knowing when to apply (before the grade), hold (when momentum is gained) and let off or feather the gas (to each his/her own) is oftentimes better than stomping on the floor for the rubbernecks and snapping an accelerator cable or return spring, looking like a fool. I've played in ARM which to this day was the most haunting of all terrain and gotten through nearly everything that was pointed at (though sometimes in as many as three attempts)... but I've never played in MO which I hear also has unforgiving mud/clay/sand mix.

---If you want to throw rooster tails to be cool, your engine will quickly disown you. If traction in sand is desired, I'd use tires with little tread and air them down... then an early grave for each tire won't be dug.

[Davedog]

I understand that the Scouts have low rpm engines, and build their power at low speeds. I still think all 50's, 60's and 70's V-8's should have four barrel carbs on them. The spread bore intake manifolds are great for the 345, because they should still be snappy at half throttle, and then give you the power you need when you floor it. I bought the aluminum 4 barrel spread bore intake manifold for my scout when they were still available.

[Albuq. Henry]

Since this topic is up, I was talking with a local IH guy and he had said to get the most out of the 4 bbl, it should be on 4bbl heads. He was saying the ports on the heads are larger or smaller. I see no mention of that here. anyone know what he is talking about?

[sdowney717]

what is so good about quadrajets is the air valve in the secondaries.
a carb with an air operated valve will only flow as much as the engine can take.
Sure the lower plates open, but the upper air valve only opens as the air flows past the plates. Engines which cant flow 850 cfm, the quad will still work as the degree of airvalve opening adjusts to the air flow.
Some engines will only open that air valve half way. A spring adjusts the tension on the plate, too little tension and it will bog and too small engine with too little tension and that wont work at all.

The small primaries with triple venturi means quick throttle response at low engine speeds and more efficient running.
The single small fuel chamber means less gas to go bad and heat soak the motor when it sits. Ideally tiny float chamber is better but not for racing. I mean just normal driving. As long as the fuel pump can keep up, then smaller amount of gas exposed to air the better.
The older 4GC carb had separate chamber for secondaries, the fuel volumes were huge in the carb.