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Gentlemen, hello,
As I told you, I received my DOAE-9425-L intake manifold, with intake passage axle spacings which are identical to those of my future 4777-7, 4150, cfm650 HOLLEY carburetor. But my problem is that on my carburetor I have 4 diameters with a value of 42.5 mm, while on my manifiold intake I have 2 diameters at 42 mmm and the other 2 diameters at 38.5 mm , mensionned green circled !!!!!!! (see the dimensions of the carburetor in black color and the dimensions of the intake manifold in red color in the 2 attached photos).
Can be machined using a milling machine, should I enlarge these 2 diameters from 38.5 mm to 42 mm ????
On the other hand there is a groove that I circled in red on one of the 2 photos, what is its function? Will this match with my carburetor? If not what should you do?

Last question where can I find seals, the one between the carb. / intake and the one the intake / engine body?

Thanks for your help


Images (2)
  • modification machining  intake manifold
  • Modification machining intake manifold size
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1/2" spacer. It doesn't matter the size of the throttle openings with that manifold. It is not a maximum horsepower design. It was intended to balance thottle response with emissions satisfaction.

It is a bit restrictive if you want more then the 300hp it was intended to deliver  An open plenum design makes more power across the board, The four port is for better throttle response with something like an automatic transmission in a heavier car,

I suspect you have a 'spread-bore' intake manifold designed to work with an entirely different carb than a Holley. Most spread-bore manifolds are cast iron, made as part of 1970s emission controls. You would likely do better to find a more modern aluminum intake that fits your carb and is actually built for performance. Ford once sold such things for other models of 351-C than what they included on stock Panteras some 50 years ago

OkThank you but my goal is to modify my Intake so that it matches with my carburetor. SO how do we do it?


Take it to a machinest and ask them to bore it out to a regular Holley carb pattern if possible. It might not be.

Holley also made spread bore carbs for easy GM replacement applications. Of those that I knew who experimented with them, they were not well spoken of. I do not know why.

Dear, Why are there 2 different diameters on the intake manifold while on the carburetor the 4 are the same ???

That intake manifold uses a Ford carburetor, not a Holley carburetor. The Ford is what the "industry" describes as a "spread bore" which has small primaries and large secondaries.

Generally speaking, you can not mix the application. You match the carburetor to the intake manifold. You have the wrong carburetor.


I do not think you have a spread bore manifold, that would look like the photo posted.

Yours is a square bore manifold intended to accept a factory installed Autolite or Motorcraft carburetor on an Exhaust Gas Recirculation plate.

The groove you ask about has holes at each end that connect to the exhaust gas crossover passage in the bottom of the manifold.

The exhaust gas crossover passage does two things, first it allows hot exhaust gases to pass underneath the manifold intake ports to warm the manifold and help the fuel vaporize for easier driving when cold. The passage also lets exhaust gases into the groove and into the EGR plate. When the EGR plate valve opens, it lets a little exhaust gas into the intake side to lower tailpipe emissions. That feature is not required or desired for your application.

To use that manifold with your Holley I think you need to do two things:

1. you should have your machinist tap and plug the holes at each end of the groove. That will keep hot exhaust gases away from beneath your carburetor which will burn your carburetor gasket.

2. you will need a four hole carburetor spacer beneath your carburetor. This will cover the groove in the manifold and insulate the carburetor from heat from the crossover passage. I do not think a open spacer will work because it will not completely cover the groove in the manifold.

You should not have to increase the bores on your manifold to get your carburetor to work properly. You may, but it is not required.

Good luck.


Images (2)
  • spreadbore manifold
  • EGR plate -top
Last edited by larryw

Larry thank you, in fact I do not wish to keep the EGR anti pollution system, the fact to increase the 2 bores diameter 38.5 mm to 42 mm like the other 2 bores, on my DOAE-9425-L  intake manifold to get my carburetor, will perhaps bring a little extra HP breath to the engine ? Should I put a thermal insulating plate with a thickness of 5 mm between the carb. / intake ?

Your 4777-7 has throttle bores of 1.688" or 1-11/16" or 42.9mm.

Increasing the hole sizes in your manifold will not hurt, but I don't think you'll see any significant HP increase. The stock manifold is just not a high performance piece that would respond to such efforts. I really think you'll be happy with it as-is for now.

I would suggest a thermal spacer. I looked at Summit Racing and four hole Holley thermal (phenolic) spacers have 1.563" or 1-9/16" or 39.7mm bores.

So, if you ultimately decide to enlarge the manifold bores, you should bring the spacer to your machinist when he does the work so he can make the holes in the spacer 43mm too.

And make sure the machinist plugs the holes at the ends of the groove too.

Good luck

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