Poly 318 duel four setup

Canadian 66 Fury

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Hello everyone
I am looking for some input into the duel four intake for a poly 318. I’ve read some much about what carbs is correct for this setup but I am wondering if anyone has done it with current carbs that are available. I’ve looked at doing the Holley 390 cfm carbs and upgrading the ignition. Open to hearing what others have done or attempted before I go deep into this. Also my motor is .30 over and has a decent cam, I can’t remember off the top of my head.
 

MONC440

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I've done it with two holley 450's. The carbs have to be tuned for duel quads. Out of the box the jets and springs for the secondary's are off. I also ran it with both carbs working at the same time and progressive linkage. After I got everything dialed in I liked it better with both carbs working at the same time vs progressive. Progressive was easier to tune.

I tried with two stock AFB's and I could never get it to run correctly at higher RPM. The drawback with the edelbrock's/AVB's is you are limited on secondary tuning, or maybe it was just me.

rebuilding%20carbs.jpg
 

Canadian 66 Fury

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I've done it with two holley 450's. The carbs have to be tuned for duel quads. Out of the box the jets and springs for the secondary's are off. I also ran it with both carbs working at the same time and progressive linkage. After I got everything dialed in I liked it better with both carbs working at the same time vs progressive. Progressive was easier to tune.

I tried with two stock AFB's and I could never get it to run correctly at higher RPM. The drawback with the edelbrock's/AVB's is you are limited on secondary tuning, or maybe it was just me.

View attachment 536443
I was worried that going with two 450 carbs it would be to much for the engine but you found it fine.
 

MONC440

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I was worried that going with two 450 carbs it would be to much for the engine but you found it fine.
It worked but you need to define "fine". Did it work as well as a correct size single 4. Probably not. It was very streetable and looked cool.

I worked for hours getting it dialed in to work at idle, mid-range and wide open. Changing jets, pump shot, secondary springs. I wish I would have written down the final specs.

Do you have much experience tuning Holley carbs?
 

Canadian 66 Fury

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It worked but you need to define "fine". Did it work as well as a correct size single 4. Probably not. It was very streetable and looked cool.

I worked for hours getting it dialed in to work at idle, mid-range and wide open. Changing jets, pump shot, secondary springs. I wish I would have written down the final specs.

Do you have much experience tuning Holley carbs?
Yes I have experience tuning holley carbs, I typically speaking tune all my carbs with a vacuum gauge in the car so I can see what the car is doing even while driving. I just want it to be streetable so I can enjoy it and show it off when I open the hood. I have a second hood for the car with a scoop on it that I was going to use with the setup to force more air into the engine to help.
 

MONC440

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Yes I have experience tuning holley carbs, I typically speaking tune all my carbs with a vacuum gauge in the car so I can see what the car is doing even while driving. I just want it to be streetable so I can enjoy it and show it off when I open the hood. I have a second hood for the car with a scoop on it that I was going to use with the setup to force more air into the engine to help.
A vacuum gauge is good but will not help you dial in the jets you need to be able to read your plugs or have a O2 sensor that you can put in the tail pipe to make sure you are not running lean or rich.

If you are mainly looking for the look my dad ran a poly with 2 4's and only ran off the rear carb and the front one was blocked off. it tuned easy and ran like that for years.
 

twostick

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This Uncle Tony video should help get those 4150 Holley carbs in the ballpark for you. Idle circuits are calibrated different for dual 4's compared to single 4. He goes into some detail on what's required.



Kevin
 

Snotty

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It's nit-picking but, you're looking for dual. It you put duels on they would fight each other.
 

57fury440

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I had the poly 318 with the factory dual 4 barrels back in the mid sixties. If I remember correctly, they were CFBs. At that time there were speed parts available for that motor. Mine was .060 over with I think they were Jahns pistons. It had an Isky cam and kit, Mallory dual point and Hedman headers. I took the carbs to Jack Merkel and he sent me to a guy that did some work on them. I thought they worked pretty good after that. That being said, If I had that motor today I would try running the small Holley carbs.
 

CBODY67

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WCFB = Will Carter Four Barrel, preceded the AFB and later the AVS.
 

MONC440

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It's nit-picking but, you're looking for dual. It you put duels on they would fight each other.
It's nit-picking but I think you meant to say If. LOL

When they are out of tune you can refer to them as duel carbs. :lol:
 

Canadian 66 Fury

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I had the poly 318 with the factory dual 4 barrels back in the mid sixties. If I remember correctly, they were CFBs. At that time there were speed parts available for that motor. Mine was .060 over with I think they were Jahns pistons. It had an Isky cam and kit, Mallory dual point and Hedman headers. I took the carbs to Jack Merkel and he sent me to a guy that did some work on them. I thought they worked pretty good after that. That being said, If I had that motor today I would try running the small Holley carbs.
Yeah I still have stock exhaust manifolds on it and I am concerned that it will restrict to much but I have 2 1/4” duel exhaust. If it is a problem I may build my own headers as the TTI ones are super expensive and the exchange rate to Canada is brutal.
 

Canadian 66 Fury

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WCFB = Will Carter Four Barrel, preceded the AFB and later the AVS.
I may try and do the Holley 390 cfm with progressive linkage as that is the smallest I can find. I think that would be the best combo for low end and still have plenty of top end fuel supply.
 

twostick

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You're overthinking it. That engine was at one time available with factory 2x4s and it had similar exhaust manifolds to what you have now. Would headers be an improvement? Probably but your butt dyno will still tell you that the 2 fours are hauling a lot more mail than the 2 barrel ever did, even with stock manifolds. Put a good 2.5" dual exhaust system on it and go. You can always add headers later but the biggest bottleneck currently to really big gains as in ones that headers would be serious advantage is the cylinder heads themselves. Ports are a lot less than ideal in stock form.

Carburetors: If you have a set of 390 Holleys, good but I wouldn't go out of my way time or money wise to find a set if I had a pair of 4150 600s or a pair of 1401 Edelbrock 500s for cheap. Properly tuned per the Uncle Tony video, they would run like nails.

Contrary to popular belief, carburetors don't force fuel into your engine. Within reason ie not putting a pair of 1150 Dominators on it, it's hard to over carburate an engine. It will only inhale what physics dictates it can inhale and that's it. The only downside to a really big carburetor on a smallish engine is response. The Dominators could likely be tuned to idle decently and run WFO but part throttle stuff would just suck.

Kevin
 

Snotty

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It's nit-picking but I think you meant to say If. LOL

When they are out of tune you can refer to them as duel carbs. :lol:
You are so right!!! That's why I hesitate to point out grammatical errors; my typing is so bad I often do what you caught me doing!
 

CBODY67

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I would suspect that the OEM 4bbls would not flow much more than 400cfm, back then. 400cfm each.
 
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