Open carb spacer - wow, what a difference!

[66 Sat]

About 4 months ago I spent many hours porting the intake manifold on my poly engine and opening up the 4 hole plenum into one open space with a cut down divider Porting a Factory 4 Barrel Poly Intake Manifold
The poly intake requires a carb adapter to take the standard Holley or Edelbrock spacing and I had a 1/2" alloy spacer, also with 4 holes. I cut that out to make a twin opening and have been running it like that since June. To be honest all that porting seemed a bit of waste, the car felt pretty much the same and was only 1mph faster in the quarter.
I watched an Engine Masters episode and they reckoned a 1" open spacer was the go for a dual plane manifold so I started searching. In the end I could only find a 3/4" adapter spacer, reversible for square and spread bore from Mr Gasket, so I bought that.
Well fitting it was a ball-ache as the side I needed to use didn't have the right configuration of bolt head for carb, Allen key stud for manifold. I ended up having to drill it out and epoxy the bolts in but it worked.
I just went for a drive and just that minor change, from 1/2" divided spacer to 3/4" open spacer has made an incredible difference. The throttle response is razor sharp now and the car just wants to run. Interesting how these small changes can have a big impact.

 

[1967coronet]

I know what you mean . I had my wow moment with a distributor plate,and spring kit

 

[AR67GTX]

Interesting. I would read your plugs and manifold temps sometime as that hogged out plenum may upset your stock jetting to some degree. But what ever works is always good.

 

[moparedtn]

Is there any particular reason you want to run a spread bore carb?
Not intimately familiar with the stock poly intake - is it not a standard square bore dxesign?

 

[furious70]

30 years ago I was messing around with a mild 383 in my Coronet. .454 cam, torker intake, 750 Holley, 906 heads, headers, 3.91 gears. I kept adding spacers on top and with 2" of spacer on top of the torker it 60' and mph the best. We were really surprised a mild engine would like that best.

 

[toolmanmike]

About 4 months ago I spent many hours porting the intake manifold on my poly engine and opening up the 4 hole plenum into one open space with a cut down divider Porting a Factory 4 Barrel Poly Intake Manifold
The poly intake requires a carb adapter to take the standard Holley or Edelbrock spacing and I had a 1/2" alloy spacer, also with 4 holes. I cut that out to make a twin opening and have been running it like that since June. To be honest all that porting seemed a bit of waste, the car felt pretty much the same and was only 1mph faster in the quarter.
I watched an Engine Masters episode and they reckoned a 1" open spacer was the go for a dual plane manifold so I started searching. In the end I could only find a 3/4" adapter spacer, reversible for square and spread bore from Mr Gasket, so I bought that.
Well fitting it was a ball-ache as the side I needed to use didn't have the right configuration of bolt head for carb, Allen key stud for manifold. I ended up having to drill it out and epoxy the bolts in but it worked.
I just went for a drive and just that minor change, from 1/2" divided spacer to 3/4" open spacer has made an incredible difference. The throttle response is razor sharp now and the car just wants to run. Interesting how these small changes can have a big impact.
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It looks like you have something going on with that Poly. I have heard people complain about how doggy a Weiand intake is on a stock engine because it's an open plenum intake. It seems, adding a 4 barrel would be best with a hard to find stock 4 barrel intake or an adapter from 2-4 on a stock 2 barrel intake. (that would work but not the best option) What's your Poly build?

 

[threewood]

Nice work on the intake. How long did it take you to do and did you do any work on the runners?

 

[66 Sat]

Interesting. I would read your plugs and manifold temps sometime as that hogged out plenum may upset your stock jetting to some degree. But what ever works is always good.

I did re-tune it after the original plenum work and I'll check it again with this new spacer. The open plenum wasn't my idea, it came from Poly guru Gary Pavlovich.

 

[66 Sat]

Is there any particular reason you want to run a spread bore carb?
Not intimately familiar with the stock poly intake - is it not a standard square bore dxesign?

It's a square bore carb - 650 Double Pumper. The spacer was meant to be on the other way - upside down. But when I went to put it on there was a 1/4" gap into thin air where the spreadbore "scallops" were. So I had to turn it over and put the square side down. It's probably unacceptable for a F1 car, but it seems to work just fine for an old poly.

The poly manifold will accept any standard square bore carb but the bolt holes are outside of the manifold carb pad i.e. there's nothing to bolt it onto. Hence the need for the adapter spacer.

 

[66 Sat]

Nice work on the intake. How long did it take you to do and did you do any work on the runners?

Thank you. It took 3 weekends...including removal, re-installation and usual family/house commitments. Opening up the plenum was the slowest part. All the runners were opened up to match the gaskets/heads. It was slow work because I'd never done this before and was being careful, and it was hard as nails cast iron. I reckon I spent 3 hours cleaning it at the end, power wash, hot soapy water, powerwash, soap, compressed air, powerwash and so on. I was paranoid about leaving any debris in there and it going through the engine.

 

[66 Sat]

It looks like you have something going on with that Poly. I have heard people complain about how doggy a Weiand intake is on a stock engine because it's an open plenum intake. It seems, adding a 4 barrel would be best with a hard to find stock 4 barrel intake or an adapter from 2-4 on a stock 2 barrel intake. (that would work but not the best option) What's your Poly build?

The Weiand 7503 is a weird cross between a single plane and a dual plane manifold. I had one on the car when I bought it and after the first re-build. Very poor below 3,500 rpm, but it takes off after that. It was exciting in some ways but completely painful on the street and wouldn't even take full throttle until you were up and running. Not ideal for the street or if your engine tops out at 5,000rpm. Gary Pavlovich reckons a 500 Holley 2 barrel on the stock 2 barrel intake will outperform it on stock or even mildly built engines.

It's a 318 poly that's now a 354 with a 3.58" forged crank, forged rods, Ross pistons, 1.94"/1.60" valves, mild-ish 264 solid lifter cam (Schneider Racing Cams), factory 4 barrel intake and custom stepped headers (1 5/8" to 1 3/4").
It's a nice torquey engine, will run with stock big blocks. It made 341hp at the wheels on the chassis dyno at the height of summer - as a comparison a stock Shelby Mustang with a 428 cobra jet made 290hp that same day. This was before the intake porting though, maybe it will make 342hp now...
I've got a bigger cam in my office waiting to go in (274 solid lifter cam) - a job for the future.

 

[furious70]

Can you not get these non spreadbore adaptor style ones down there?

JEGS Carburetor Spacer - 1 in. Holley Carburetor Spacer Online - JEGS https://share.google/tBjqLBYB0Fir6lgfe

 

[66 Sat]

Yes I could...but I was looking for the type where the carb hold down bolt is captured flush underneath the spacer i.e the spacer is countersunk and machined to hold the bolt head. The reason being the poly manifold outside "ears" of the carb pad will encroach on the stud/nut needed to hold the carb down. I ended up having to countersink and epoxy the bolts in anyway so yes using that method the spacer you linked would work.

I could possibly have machined that area down on the intake when I was porting it, maybe I will next time I remove it, but there's not much meat there. It's the blue highlighted area, there's no space for a nut underneath.