Definitely enlarge the carb holes in the intake so they at least match the bore size of the carburetor and/or the carb spacer.  The step created by using a large hole spacer on an unmodified smaller hole intake is a detriment to performance.  I'd not be overly concerned about the hole in the intake being larger than the carb bore size if it comes down to that but as an alternative, tapered sleeves can be used in the carb spacer to transition from one hole size to another.

Lorena, Texas (South of Waco)

Like Steve I have considered some form of tapered spacer but think I will go with enlarging the manifold inlet to match. The 1" phenolic spacer matches the carb. Placing the spacer on the manifold there is approx. a 3/32" lip to be removed.

cheers  Pete  

Pete, one of the Aussie mob. Beechworth, Victoria60 F100 Panel Van, Y-block. 65 Galaxie Country Sedan 390

Steve,

           I can't imagine anyone anal enough to actually measure the bores, but then....

      You guys who are changing carbs might want to take a look at the little Demon 575 street carbs. I run an 850 on my pro street 408" Windsor. I'll never go back to Holleys after using  it. It just flat works, doesn't leak, doesn't have any flat spots. Have reset the idle once after 4 years, runs 11.90's @ 116mph and will get about 15mpg on the road. 

Frank/Rebop

Bristol, In ( by Elkhart) 

I put a Holley 4160 (600 cfm) carb on my "9425-B" manifold and used a thin (1/2") phenolic spacer made by Moroso to get a thermal break. It was the right size for the bores in the manifold (probably OK for a 390 cfm carb) - but it didn't fit the throttle blades of the bigger carb worth squat. Opening everything up wide open and looking down through there with an inspection light showed that there was a serious "step" at the exit of the carb bore and a little bit of an interference with rotation of the blades. This can't be anything but bad for performance......

I put some masking tape on the top of the spacer and transferred the throttle bore diameters concentric to the existing holes in the spacer. And then (is that laughter I hear?) - I methodically filed and sanded a venturi shape down into the spacer to get a smooth transition to the manifold bore. It looks like there is enough "meat" to bore out the manifold to the right size - but I figured an "unmodified" manifold might be worth having some day. Dunno.

I can't be the only person to have this problem - but I'll bet there are some adapted carbs around with some ugly steps under them.    

 
 Steve Metzger       Tucson, Arizona

Pete,

              Wouldn't hurt a thing, might actually help by disturbing any reversion tendancies

Frank/Rebop

Bristol, In ( by Elkhart) 

The next concern is if I take the rear inlets on the ECZ manifold out to the same size as the Carter secondarys will it mean that is the only carb I can use on this manifold? Would a smaller bore carb just be falling into a "hole" or would it not make any difference? 

cheers Peter 

Pete, one of the Aussie mob. Beechworth, Victoria60 F100 Panel Van, Y-block. 65 Galaxie Country Sedan 390

Hi Pete,  Your carb sounds like the same as mine except for the manual choke.  Your 1" spacer should work well, just make sure the rear butterflies will clear it when they open.  I would like to try a 500 CFM Carter if one turns up that I can afford to buy, just for comparison.  But my 625 Carter has good driveability, I can floor it in high gear at 1500 rpm and it will accelerate all the way up very smoothly.  If you want, you can buy an electric choke conversion kit.  Sorry but I can't crack the Carter manufacturing date codes.  The cam you have sounds good, especially the dual pattern, maybe a little short on lift.  But Ted and Hoosier and the others know lots more about cams than I do, perhaps they will jump in.  My Schneider is 274 degree/230 @ .050", 110 lobe separation and .320 lift.  Be sure to get some headers if possible and don't run the stock small tailpipes, let that exhaust get out of there.   

Good luck, Nick

Yes Nick have several friends running Holleys that say the same thing, good power at the expence of economy.  The numbers on my AFB are  4H4 9635S  it has a manual choke. is there a manufactured date in these numbers? The cam I'am going to use is a Crow Cams [Aust] dual pattern    228/234 @50", 109 deg. seperation,  280/286 lift,  440". Engine is due back from the machine shop in the next day or two, aimed for a compression ratio in the low to mid 9s.

cheers Peter

Pete, one of the Aussie mob. Beechworth, Victoria60 F100 Panel Van, Y-block. 65 Galaxie Country Sedan 390

Hi Pete,  Personally I'm running a 625 CFM Carter AFB on my 312 and I like it a lot.  If you go to the old forums, you can find a lot of info that Ted wrote about the advantages of the Carters & edelbrocks vs. the Holley 4150/4160 carbs.  I've used a couple of Holleys and they ran OK but I didn't like the cold start characteristics and the fuel mileage.  I would say that I'm getting about 1.5 more MPG than I did with either a 600 or a 465 Holley replacement carb.  My Carter is their #9635 which is supposed to be for GM applications, they also made a 9636 (Chrysler) and 9637 (Ford) which are very similar except for the linkage hookup.  With a little trimming I was able to use the stock '57 T-Bird air cleaner, but I had to get an edelbrock #8089 banjo fitting for the fuel inlet to clear the air cleaner.  I'll try to enclose a photo.  There was a hesitation at first when coming off of idle, but I leaned out the accelerator pump plunger and the driveability now is excellent.  I'm running a Schneider cam (230 degrees at .050") and the max vacuum at idle is about 15 at 800-900 rpm.  Since the rear barrels are bigger than the front, I couldn't use the stock T-Bird carb spacer.  I got an edelbrock #8725 which is a wooden two-hole affair.  I'm using the electric choke with a 3 amp fuse in line.  Hope this is helpful, let me know if you have more questions. Nick Brann

I ran both the 625 and 525 Carters on my 272 and the 525 was more throttle responsive at the lower rpms.  I was just borrowing the 625 at the time so I didn't have the opportunity to tweak on it as I felt it needed more accelerator pump shot to get rid of the slight hesitation or stumble it had on take off.  Once the 625 was moving, it was fine otherwise and did get decent fuel mileage.

Lorena, Texas (South of Waco)