Square bore carb / Spread bore intake question

[FLcustom10]

2 weeks ago I had never even heard the terms spread bore / square bore.
I picked up a used spread bore intake and a entry level Holley carb before I knew I had a mis-match. I have the adapter, but don't understand how to attach it. It's a small bolt pattern for the spread-bore gasket, and a large bolt pattern for the Holley Carb. Do I need a spread-bore gasket with a larger bolt pattern?

[GASoline71]

I wouldn't call that an "entry level" carb. It looks like an 1850 600 cfm Vac secondary. far from entry level.. I would call an Edelbrock carb "entry level"

The adapters are really just a vacuum leak waiting to happen. If it was me... I would try to sell the spead bore manifold and get a square bore manifold.

Gary

[FLcustom10]

That would probably be the best solution, but I really don't want to take this intake back off if I can make this work. What are my other options?

[turp mcspray]

Just use the correct gasket on each side. Bolt it on and don't worry about it, you'll be fine.

[NoNeck]

I haven't used the adapter you have, but it looks like it would work. I would bet there are more square bore carbs running on spread bore intakes out there than you could count.

You would start by installing the spread bore gasket (the one that matches your intake). Then, flip the adapter in the photo over to match that gasket. Now, place the square bore gasket (the one that matches your Holley) on the adapter. Install the carb and you should be good to go. As long as you have used new, quality gaskets you shouldn't have a vacuum leak. Just don't over-tighten the carb or you could warp or crack the base.

As another option, Edelbrock sells an adapter that I have used over the years and never had a problem. It only costs $5.95 at Summit, and is really simple to install. Here is a photo, part number and description:

Brand: Edelbrock
Manufacturer's Part Number: 2732
Part Type: Carburetor Adapters
Product Line: Edelbrock Carburetor Adapters
Summit Racing Part Number: EDL-2732
UPC: 085347027323

Adapter Style: Open center
Height (in): 0.093 in.
Hardware Included: No
Gaskets Included: Yes
Adapter Material: Steel
Adapter Finish: Natural
Quantity: Sold as a kit.

Notes: For use with Edelbrock spreadbore intake manifolds when installing a square bore carburetor.
Not required on EDL-2101 or EDL-3701 unless using a Holley square bore carburetor.

Good luck! NoNeck

[Lippyp]

Until recently my truck was running a Carter AFB sat on an adaptor similar to the one posted by the OP on the stock spread bore cast iron intake. It ran fine with no problems, its only changed as I've gone to a Performer EPS Intake.

[FLcustom10]

I hate to be dense, but my problem is that the Spread Bore gasket that seems to match the intake does not fit on the bolt pattern. The bolts are the outside pattern and the spread-bore gasket would fit an inside pattern. Do they make a Spread Bore Gasket that fits this bolt pattern or am I missing something else? This is the adapter kit that was recommended on the box for the carb. It almost looks like they want you to bolt the adapter to the intake with one set of screws on the inside, and then bolt the carb to the adapter with the outer set of screws, but that doesn't make sense to me. I would think you would just bolt everything on together. I know this is a rookie question, I'm just not getting it.

[Grimpala]

I used to run a square bore holley on a spread bore edlebrock manifold no problem. Just use the squarebore gasket and the corresponding bolt holes on the spreadbore manifold.

[geezer#99]

Put the square bore gasket you have (the one in your last pic) on the intake. Then post us a pic. It should cover the edges of the carb flange. Then bolt on the carb. Those studs are moveable to the other holes.
You don't need to use the adaptor.

[wildearp]

If it were me, I would use an adapter that kept the plenums separate. You can see some torque loss by separation. This would require a gasket that did the same.

[danleaman]

I would say the first thing you should do is make sure you have the correct gaskets. I'm not being a smart a** here, if the gaskets don't line up correctly it might just be a case of having the wrong one.

Dan

[turp mcspray]

You may have go buy another Quadrajet gasket.

[MARKDTN]

Originally Posted by geezer#99

Put the square bore gasket you have (the one in your last pic) on the intake. Then post us a pic. It should cover the edges of the carb flange. Then bolt on the carb. Those studs are moveable to the other holes.
You don't need to use the adaptor.

Me too. Get a squarebore gasket that is wide enough to cover the spreadbore hole and bolt it on without the spacer.

[haysonj]

Without seeing the other side of that adapter I would say you have the wrong adapter. That looks like it goes from square bore to spread bore. I had the spread bore to a square bore on mine before I went to FI and you do have to bolt the adapter to the manifold first then you need bolts of the right length to bolt the carb to the adapter.Or you can use short studs with nuts and washers.

[FLDBRED]

I had the same issue, just use Summit Part # SUM-G1420, it comes with a thin base plate and "TWO" gaskets. Place one gasket on each side of the plate and you are done. It works great!

[FLcustom10]

Thank you to all who responded. I think the correct answer for this adapter set is to use two sets of screws. I don’t know why I was struggling with that. I was just picturing it all fitting over the same studs.
About half of you said it would be fine to mount the square-bore carb directly to the Edelbrock Performer spread-bore intake manifold. You’re probably right, but I decided to go ahead and use the Holley adapter - at least in part so I don’t feel like I wasted $50.00. This is a learning experience and I can always adjust later. There was a bit of overlap on the gasket and I was concerned about it deteriorating and falling into the intake so I trimmed it a bit. Pictures show:
1 - Square-bore gasket directly on the spread-bore manifold (for show - not used there in final assembly)
2 - Spread-bore gasket on the spread-bore manifold.
3 – Trimmed gasket
4 – Adapter
5 - Carb installed

[wildearp]

Superb!

[Grimpala]

Those adapters rob a ton of power. FYI you can run the holley straight on the intake with a square bore gasket, no problems with leaks or anything.

It's your truck, run what you feel comfortable with, just putting it out there.

[prostreetC-10]

Originally Posted by Grimpala

I used to run a square bore holley on a spread bore edlebrock manifold no problem. Just use the squarebore gasket and the corresponding bolt holes on the spreadbore manifold.

RIGHT!!

Originally Posted by geezer#99

Put the square bore gasket you have (the one in your last pic) on the intake. Then post us a pic. It should cover the edges of the carb flange. Then bolt on the carb. Those studs are moveable to the other holes.
You don't need to use the adaptor.

RIGHT!!

Originally Posted by wildearp

If it were me, I would use an adapter that kept the plenums separate. You can see some torque loss by separation. This would require a gasket that did the same.

RIGHT!!

Originally Posted by MARKDTN

Me too. Get a squarebore gasket that is wide enough to cover the spreadbore hole and bolt it on without the spacer.

RIGHT!!

Originally Posted by Grimpala

Those adapters rob a ton of power. FYI you can run the holley straight on the intake with a square bore gasket, no problems with leaks or anything.

It's your truck, run what you feel comfortable with, just putting it out there.

RIGHT!!


Do you see a pattern here?? That adapter is not to bolt a square bore carb to a spread bore intake. It's to bolt a spread bore carb to a square bore intake. You need to take that spacer off. Not only because it is not needed but because you are killing the benefits and purpose of a dual plane plenum. You are weakening your signal to the primary boosters and creating turbulent air under the carb. This will really affect your throttle response. I have pics of one of my BBCs running the older Edelbrock 2.0 intakes. If you notice the back of the mounting area of the intake, it is formed to where it interferes with my vacuum port under my base plate and I can't get a seal. I use the little plate to make that seal. You would also need to use the plate if you run a 1" 4 HOLE spacer (which you should). Many of the spacers are not solid on the bottom and the plate ensures a good seal. Either way you need to lose that spacer and bolt the carb directly to the intake.

Justin
HP Carburetors

P.S. What you see is one of my famous "ghost carbs". It looks like it's just a base but the whole carb is there. Hard for the officials to spec it out!

[FLDBRED]

Google= sum-g1420 !

[FLcustom10]

Thanks guys! I do see the pattern and respect your experience. I'm sure I'll be making adjustments.

[prostreetC-10]

The cool thing is that it won't cost you a dime. You don't even need the G1420 in your case. You base plate will do the same thing.

I also can't stress enough to put a black 4 hole spacer on that like the one pictured. You don't need a fancy phelonic one. Plastic will work just fine. In this case you will need the G1420 because the bottom isn't solid. It will help to insulate the carb from heat and allow better atomization of the fuel. If you do a search on the forum for them, you will see many posts about their benefits. The one below is the Summit G1412. Quite simply the cheapest bolt on horsepower you can add and I run them on EVERYTHING I own. Really helps with low end torque and will not affect the upper RPMs in your case.