Poly 318 4bbl conversion goes splat

[66 Sat]

I ran a 650 Holley with mechanical secondary on a tired 318 poly. It took awhile to get the carb dialed in. I changed power valves, jets, accelerator pump cams, etc. Youi may need to make some adjustments. I'm now running at 349 cu in, with 9:1 compression, ported heads and long tube headers. Best timing for me is 12 base and 32 total with all in around 2400 rpm. it is a daily driver that goes drag racin' on the weekends.

Sorry to hijack the thread, but how fast are you running the quarter with this set-up? I'm currently having my poly stroked with the 3.58" crank to about the same cubes and was wondering what to expect. I'm having the heads done too, with 1.94" intake and 1.60" exhaust valves.

 

[Dave145]

Really odd that the AFB doesn't line up. The intake came off a 61 Dodge?
AFBs came out in 1957.

I'm not sure when exactly it came out. I was told it came off a '61 but I'm not positive.

 

[Dave145]

Yes my thought from the get-go. Get rid of the vacuum secondary carb and ditch the Holly. Not sure why it was felt the exhaust need to be larger. Bigger does nothing but kill bottom end if the added size isn't needed.

I cant/won't get rid of the carb, because I can't afford to fling more parts at this car. I have to work with what I have. The exhaust was enlarged, again, because that's what "everyone else does/recommends".

 

[Dave145]

I’m on board with re-installing the original 2bbl intake/carb, and re-establishing the performance and mpg baselines to make sure there isn’t something else going on.

This is likely what I will do. I just want the car to run well until I can afford an engine swap in the future. Not a fan of this poly boat anchor at all.

 

[POMONAMISSEL]

here this will get you more cfm , you can double your cfm with this intake .

 

[Demonic]

There's nothing wrong with a Poly motor. I would start from scratch in the verification:

Piston stop tool and check the mark on the balancer is correct.

Compression test, you can read the plugs at the same time.

Then a leakdown test, also easy and cheap.

Check the cam lift maybe. It's likely a mini poodle dookie cam.

 

[mopar 3 B]

All this check this and check that. No one has asked the obvious what the heck is the engine vacuum question?

 

[Geoff 2]

I mentioned earlier in this thread that I believe the carb mounting on that intake suits AFB [ narrow pattern ]. In post #45 you can clearly see both bolt patterns drilled on that AFB. Every AFB I have seen as the wide foot, but both sets of holes might not be drilled.

 

[mopar 3 B]

Should be the same pattern as the early BB

 

[440 4 speed]

It's quite possible. The Poly Engines were slightly different between Dodge, Desoto and Chrysler Plymouth.I think Canada's version was a 303.
Not sure as I don't know allot about the Poly's. The manifold could be from the late 50's.The early AFB's were very small.

1961 Canadian Dodges had 313 polys. A friends dad had a 313 4 barrel and it would move very well. I think they were rated at 260hp. 361 2 barrels were rated at 265hp. My older brother tried to get Dad to order a 61 383 auto, best he could do was get Dad to get a 313 3 on the tree. Better than a 6. It would roll the speedometer all the way across. They had poor clutches, and a choppy shift pattern. Mom would bring it up to about 200 rpm and slowly ease of the clutch . Went through 4 clutches in 10 years. Some was caused by spirited driving.
I wouldn’t give up on that intake, but I would look up the old stats and find a carter carb close to those specs.

 

[Dave145]

It looks like at this time the stock setup is what's best. I don't have the spare cash to shot gun another carb at it for grins, when my existing carb is tuned and jetted correctly for my car. Plugs look good, vacuum is good...nothing wrong with that carb. An engine doesn't know what carb is what, all it cares about is that it gets air and fuel.

I'll put my 4bbl setup on the shelf for now and just get the car running again until I can swap the Poly for something else.

 

[66 Sat]

I don't understand how you can't afford to fix your current engine but can afford to swap a whole new engine in?
What are you wanting the car for? Your first post described it as a nice cool cruiser.
The poly is a great engine for this. My stock stroke 318 poly with a 4 barrel factory intake, 600 Holley, factory exhaust manifolds, 3.23 rear and about 3,800 lbs with driver, ran 15.3 @ 93 mph so it's fast enough for cruising around.
I'm stroking it just for fun, but honestly it ran like a watch.
Good solid reliable engines.

 

[mopar 3 B]

At least shell out for a 2-barrel adaptor till you find the right 4.

 

[Dave145]

I don't understand how you can't afford to fix your current engine but can afford to swap a whole new engine in?
What are you wanting the car for? Your first post described it as a nice cool cruiser.
The poly is a great engine for this. My stock stroke 318 poly with a 4 barrel factory intake, 600 Holley, factory exhaust manifolds, 3.23 rear and about 3,800 lbs with driver, ran 15.3 @ 93 mph so it's fast enough for cruising around.
I'm stroking it just for fun, but honestly it ran like a watch.
Good solid reliable engines.
View attachment 1310310

The engine swap is a long way down the road. Hence why I just want the damn thing to run and drive until then. I don't have money at this time to throw at shotgunning another carb at this car, nor do I have it at this Second for a motor swap either.

To me, the Poly blows chunks. Eventually it'll get either a magnum or an LA just for serviceability, aftermarket parts support, and the ability to make horsepower on a budget.

 

[mopar 3 B]

You bring the poly we can do a swap teen for teen. Will not guarantee it to run any better but you can go home with an LA.

 

[Belle66]

Sorry to hijack the thread, but how fast are you running the quarter with this set-up? I'm currently having my poly stroked with the 3.58" crank to about the same cubes and was wondering what to expect. I'm having the heads done too, with 1.94" intake and 1.60" exhaust valves.

I run 14.50's, 2400 stall, launch at 1600 rpm, shifting at 6200 rpm, 3.32 sure grip, MT ET Streets P255 r60/15.

 

[Ron H]

Dave,
Great to see the Poly. The most underrated engine to come out of Detroit...
- these were low compression engines, 9:1.
- adding an intake that has larger runner CSA will kill off the low end. I suspect this could be some of the problem.
- if the carb spacer you added is an open one, that will also kill off the low end. A spacer for this combo needs to be fully divided.
- the best place for Holleys [ & clones ] is to leave them in the box they come in.
- use a carb that has small primaries such as an Edel 500; you could also use the 800 TQ. They were used here on Ford 302s.

Interesting about the divided spacer; never gave it a thought as I'm disappointed with my low end performance after a heady rebuild. Have a '62 stock 4bbl manifold on it with spacer (throttle plate clearance) ed 650...open spacer..

 

[Diodedog]

That is a 61-62 mani and it's meant for the small AFB and bolt pattern, 62-66. The origanal carb is the same as the 361-305 but with a different part number and slightly different jetting and they flow about 500 cfm and about 520 with a good base plate on my flow bench, the 383/426SW carb is about 580 abd 600 with base. Those carbs 318-426 street wedge can be had very reasonable on ebay or any swap meet. That adapter you're using is all wrong for that mani. the cam lift difference between the 2 and 4 barrel is very minor and not an issue. send me a pm if you like and I'll give you my phone no., I can answer a lot of questions.

 

[fratzog lover]

Dont give up on the Poly. It is not a dog.

 

[Geoff 2]

What he ^ said.