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The parts truck I recently bought came with a set of heads and a Spread bore manifold.
I would like to use this spread bore manifold on my 69 rather than the two barrel.

I plan to restore my Truck soon its a 4x4 short box manual trans to use as a Tow rig for my other toys.
I like my Two barrel manifold and I know its original to the truck but I think the 4 barrel spread bore would be a good upgrade for more power.
I have already rebuilt the original 318 with a factory steel crank with forged pistons and a double roller timing chain and hi volume oil pump with a nice RV cam.

What spread bore carburetor would be a good choice ? any ideas or opinions? looking for date range originality correct type equipment NOT new junk.
I have not gotten any dates off the manifold or the heads yet so not even sure what year they are.

I am suspecting the manifold is off of a 340 or 360 if it is indeed a 71 manifold it would indeed be a rare part at this point.

Doright wrote: ↑

Mon Nov 06, 2023 8:43 am

The parts truck I recently bought came with a set of heads and a Spread bore manifold.

Lucky you! I'm a big Holley fan, but that's because I like to tinker. I don't know the model numbers these days. I like center-hung float bowls, vacuum secondaries, dual metering blocks, and dual stage power valves. Even back in the early 80s, I had to make one by modifying a double pumper to take the second metering block and add the port for the vacuum secondaries. Fortunately, the drilling site was in the casting. All it took was a very long drill bit.

The cool thing about a spreadbore is that the primaries are small, making better efficiency at lower RPMs due to higher port velocity. Don't go over 600CFM.

There are those who swear that switching to a 4 barrel on a 318 (without other engine mods) turns it into a dog. I can't say.

I do think the spread bore manifold would likely be 1971 or newer. Carter Thermoquad would be the most period correct carb to use. Not saying its the best, just what Mopar generally used during the 70s.

Bucky

i was thinking a carter afb ...edobrock must have bought the plans cause they selling them new
easy carb to tune
i like the themo quads but thought they where emissions carbs ,fixed many of them back in the days
they would rot out the seals under the float bowls where they mount to the throttle plate
and yes 600cfm would be plenty don't over carb it

712edf wrote: ↑

Mon Nov 06, 2023 5:11 pm

There are those who swear that switching to a 4 barrel on a 318 (without other engine mods) turns it into a dog. I can't say.

I can. I had a 4bbl 318 back in the 80s with an A833/Hurst, racing clutch, and 8-3/4 Dana dropout axle that was an absolute Porsche killer (Turbo Carerra being the only exception). If one blops an 850CFM double pumper on a 318, absolutely it would be a dog. Vacuum secondaries at 600CFM prevent manifold vacuum falling on its face and maintain mixture velocity (had a vacuum gauge on an oak dash). One does have to wait for the RPMs to come up for them to actuate, but when they do...

I have a thermoquad on my 383. Not a big fan of orifice pins for adjusting jets in a machine that vibrates. But then I absolutely hate that transfer tube on so many Holleys, which is another reason for the center-hung float bowls.

I know it’s not period correct but I would run a quadrajet.
Yes. They put millions of them on GM vehicles but they also were used on mopars in the 80s. There are a ton of options.
I bought the book from cliff ruggles and learned how to properly rebuild them. I have done two so far. Both run quite well.
Just my two cents.

Isn't the Carter AFB a square bore?

1985 was when the Q-jet appeared on 360's in D/W350 & possibly others. I can't say if they appeared earlier on cars.

Yes anything after 1970-72 is emissions/smog stuff.

Those who claim the switch to 4v making the 318 a dog base this on the manifold ports not matching the heads properly.

I have never owned a 4v 318 nor really modified any LA engine.

Bucky

oh maybe the afb is a square bore
quadrabogs are good carbs too done my share of tuning them and as long as you don't go too big or let them open too quickly they can work great

don't remember ever seeing a quadrajet on any car ,only themoquads ,around 84 they added lean burn
didn't think they ever made a 4bbl 318. small block
but i'm sure you could find a 273 camando intake / or 340/360 if you wanted oe

nutz wrote: ↑

Wed Nov 08, 2023 10:07 pm

didn't think they ever made a 4bbl 318. small block
but i'm sure you could find a 273 camando intake

That may have been what I had, as the car was originally a 273 that eventually threw a rod. I probably kept the manifold. The late 70s were a great time to go to the wrecking yard though. They had lines of them on certain roads in this area in Hayward and Martinez, CA. Now all long gone.

As to the 340/360 intake on a 318, the ports are bigger and that would make significant turbulence right at the intake valve. Not sure how well that would work.

yea back in the day
was a great time going out to the yards hunting down that elusive part
now its a few clicks away ...not the same