Poly 318 4bbl conversion goes splat

[Geoff 2]

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.

 

[Dave145]

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.

The carb spacer I'm running is an open one, but I'm only using it because the carb flange on the manifold is TINY. Even the 600cfm edelbrock I ran on it for a bit was too big to bolt on to the flange and the butterflies were spaced too far apart. I'll grab a picture or two when I get home to show my spacer/carb setup.

 

[Darter6]

- the best place for Holleys [ & clones ] is to leave them in the box they come in.

My kinda guy.

The carb spacer

This may be the cause of all your trouble.

 

[Ron H]

I have not done any currently. I just have the intake off to address an oil leak at the front seal. I can check it hopefully sometime next week. We only honed the cylinders and replaced the rings, so honestly I don't expect there to be much improvement.

That should have provided better compression - if you're getting the #'s you posted this is going to be a performance problem.

 

[Challenger340]

The 2 BBL Cam doesn't have sufficient Lift nor Duration to take advantage of the added Airflow the 4 BBL Intake provides.... forget it !
Placing a 4 BBL Intake on a 2BBL Cammed Engine was/is and will always be a waste of time, except for 'appearances' which is all anyone ever gets.

All you did gain a shittier A/F mixture by reducing velocity across the larger 4 BBL venturi's.... to the even lower than what there before for remix/turbulence punched up by the Piston in the chamber under a now thicker Head Gasket(95-110 psi)

Dis-assemble
Change Camshaft, and this time degree it....
or
get one custom ground up mid 215's @ 050 Intake and low 220's Exhaust on ~113/114* lsa
Mill the Heads to get a bit of compression back in there with the thicker Head Gaskets(min 9:1)
and while you are in there....
re-do the V/seat contacts out closer to the edge of the valves, apply a 30* back-cut and 75* throat

My apologies
But if what you are hearing is to rebuild it properly this time ? then you heard right..... sometimes the truth hurts and best policy is to be honest because all you are gonna do at this point is chase your tail trying band-aides that won't work

 

[Dave145]

The 2 BBL Cam doesn't have sufficient Lift nor Duration to take advantage of the added Airflow the 4 BBL Intake provides.... forget it !
Placing a 4 BBL Intake on a 2BBL Cammed Engine was/is and will always be a waste of time, except for 'appearances' which is all anyone ever gets.

All you did gain a shittier A/F mixture by reducing velocity across the larger 4 BBL venturi's.... to the even lower than what there before for remix/turbulence punched up by the Piston in the chamber under a now thicker Head Gasket(95-110 psi)

Dis-assemble
Change Camshaft, and this time degree it....
or
get one custom ground up mid 215's @ 050 Intake and low 220's Exhaust on ~113/114* lsa
Mill the Heads to get a bit of compression back in there with the thicker Head Gaskets(min 9:1)
and while you are in there....
re-do the V/seat contacts out closer to the edge of the valves, apply a 30* back-cut and 75* throat

My apologies
But if what you are hearing is to rebuild it properly this time ? then you heard right..... sometimes the truth hurts and best policy is to be honest because all you are gonna do at this point is chase your tail trying band-aides that won't work

I more or less went off of the reading I had done that said the swap would work on a stock engine. Hell my old 72 318 woke up nicely with just an intake and carb swap so I kinda figured the same would apply here. Guess not.

I don't have the funds to tear down the motor and buy a custom cam. If the best verdict is to put the 2bbl back on for the time being, so be it.

 

[Dave145]

My kinda guy.

This may be the cause of all your trouble.

The holley has to stay at least for now. I'm not an edelbrock fan at all, nor do I have money to buy another carb right now. Never had any luck with them for anything other than a door stop.

The carb spacer is probably hurting things more than helping them. The intake's carb flange looks to be much much smaller than a traditional 4bbl pattern, so I'm beginning to wonder if it's meant to fit a WCFB carb instead of an AFB.

 

[Darter6]

wonder if it's meant to fit a WCFB carb instead of an AFB.

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.

 

[Demonic]

The intake's carb flange looks to be much much smaller than a traditional 4bbl pattern, so I'm beginning to wonder if it's meant to fit a WCFB carb instead of an AFB.

Usually, yes, they used a WCFB.

 

[Dave145]

So here are some pictures of my setup. It's far from ideal but it's all I could come up with at the time. Pretty willing to bet my flow is severely impeded!

 

[Geoff 2]

[1] Carb pad is for an AFB, narrow bolt pattern. AFB mounting feet are wide; some AFBs came drilled with the narrow pattern; some were drilled with the wide pattern. Either way, the mounting feet can be drilled to accommodate either/both. Same for AVS & Edel carbs. I would get rid of the POS Holley. You know the boat anchor you need.....
[2] That spacer is killing the performance. What you need is a 4 hole spacer. You might be able to find a Holley spacer that has the dual mounting pattern mounting pads [ the outer mount holes on AFBs are the same bolt pattern as the 4150 Holley ], so outer holes would be drilled but enough room inboard to drill the narrow pattern. Or you might be able to find an AFB spacer, narrow pattern. Offenhauser used to make a huge range of spacers, not sure what is available.
[3] The smartest thing you could do would be to get the Edel 500 AFB or AVS. You can drill the mounting feet & it will bolt on, no spacer reqd. Get the credit card out!

 

[Dave145]

[1] Carb pad is for an AFB, narrow bolt pattern. AFB mounting feet are wide; some AFBs came drilled with the narrow pattern; some were drilled with the wide pattern. Either way, the mounting feet can be drilled to accommodate either/both. Same for AVS & Edel carbs. I would get rid of the POS Holley. You know the boat anchor you need.....
[2] That spacer is killing the performance. What you need is a 4 hole spacer. You might be able to find a Holley spacer that has the dual mounting pattern mounting pads [ the outer mount holes on AFBs are the same bolt pattern as the 4150 Holley ], so outer holes would be drilled but enough room inboard to drill the narrow pattern. Or you might be able to find an AFB spacer, narrow pattern. Offenhauser used to make a huge range of spacers, not sure what is available.
[3] The smartest thing you could do would be to get the Edel 500 AFB or AVS. You can drill the mounting feet & it will bolt on, no spacer reqd. Get the credit card out!

I already had an edelbrock carb on this exact engine in the beginning right when I put the manifold on, and it didn't line up with anything. The bolt holes lined up, but the butterflies did not. It was a square bore carb and neither the primary nor secondary butterflies were able to open. It was weird. That's why I thought maybe this intake was meant to fit a different type of carb.

 

[PRHeads]

I think I’d be looking for something like:

Holley/Edelbrock to Carter WCFB 4-Barrel Carburetor Adapter Plate

I’m not sure that’s exactly what you need, but something along those lines is what I’d be looking for.

 

[Dave145]

From the pictures it kinda looks like that might be the ticket to at least getting the carb on to the manifold correctly. Whether it would fix any of the issues would be the real question.

 

[PRHeads]

I don’t know if it would cure all the ills, but I doubt that adapter situation you have going on now is doing you any good.

 

[Dave145]

I don’t know if it would cure all the ills, but I doubt that adapter situation you have going on now is doing you any good.

Agreed. If I do put the 4bbl setup back on, I will order up that spacer or something like it.

 

[PRHeads]

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.

 

[Belle66]

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.

 

[mopar 3 B]

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.

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.

 

[Geoff 2]

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