Holley Metering Block Mod

[Ernest]

Since im still on carburetor duty, i came across a used 600 metering block for cheap and decided to modify both upper and lower IFR and the PVCR channels for practice.

Knowing full well theres aftermarket billet metering blocks available that feature the same, affordable enough, it doesnt hurt to learn and do things yourself, figure i'll use it one day and see how it goes.

The metering block came without the holley inserted lower brass IFR, so there was a .090 hole in its place that it gets pressed into, the PVCR was .046, emulsion at .028 and the antisyphoning(kill bleed) is .027, typical for 600cfm vacsec.

I started off with a 1/16(.060) drill bit to open the PVCR and gradually worked my way up to the 7/64(.106) drill bit using a hand held pin vise for more control and accuracy, using a dremel tool would be faster yes, but unless you have the hands of a surgeon, chances are you just might screw up the hole up or worse.

I then used a 6-32 plug tap(NC) to make the threads, better with bottom tap for almost instant tapping for better dept control for the 6-32 x 3/16 set screws, but its all i had on hand, i did get a pich into the PV top thread only, it happens, but i carefully lined up the PV to rethread it so it installs and removed without issue.

Next up was the lower IFR holes, since they were already .090(3/32 bit), next in line was the 7/64(.106) drill bit, opened it up slowly to go all the way through, but not with the tap, so when i get the set screws, i will set them to sit flush and tight just like the original pressed in ones do. I also threaded the upper IFR as well to experiment with, since aftermarket billet metering blocks have them set up on top, the hole there was already the correct size as the 7/64 drill bit, so all i had to do was just use the 6-32 tap to make the threads.

I currently dont have any set screws to put in, i'll have to get a few here soon, the brass ones are prefered to easier drill through to make the hole sizes needed, so after insertion, i'll post an updated picture then.

Enjoy

 

[69hurstolds]

No fear. I like that. It's how I learn best. Breaking stuff. Not like you're working on unobtainium.

I have no real love for Holleys, although I don't dismiss them like I would an Edelbrock AVS. Even as I haven't touched a Holley in years, I'm in the "move the IFR to the bottom" camp. It stays submerged in the fuel and usually nets better transitioning/throttle response with bigger overlap cams. There are those in the Holley world that would disagree with that, though. It's like arguing which oil is better. I thought they did the upper IFR for emission considerations, but I'm no Holley expert. Well, I'm not an expert on anything, really.

 

[Ernest]

Finally got the 6-32 x 3/16 brass set screws in hand and test fitted.

What i've learned... after slowly and carefully drilling through the holes with the proper size drill bit using a pin vise, or a dremel if you're feeling bold enough and impatient, dont go too far in or you will drill into the backside heavily of the main well potentially ruining the entire metering block, start cutting threads with the tap 1/4 turn at a time, remove, blow out the threads, then test and retest with set screw till it gets snugg enough at flush depth, then tighen lightly to finally secure it. If you go to far, the set screw will fit just a pinch loosely and will probably have to use blue loctite to secure it, not even sure if it will work in a gasoline environment.

By accident, i went just a tip too far into the right side PVCR hole so it sits just a tad below flush, but all the others i got spot on, and from what i've seen around the web, 8-32 x 3/16 is primarily used for the PVCR because of the hole you might have to drill out at .060+ , the 6-32 x 3/16 im using looks to only accept up to .060 which is perfect for the IFR because its way less than that, but judging by the looks of the 8-32 size, it could very well start biting into the PV threads in the block.

Since all i could find locally was a 6-32 and 8-32 plug tap, which works perfectly fine if you're carefull enough because of the cone like exetended tip, i'll be using the bottom tap next time on future endevours so it cuts the threads almost imediately and finding a proper drill set for the brass set screws.

 

[565bbchevy]

Billet aluminum (no porosity issues) like those old style cast metering blocks plus they are the redesigned style that comes in all the newer carbs. Ready to install with full adjustability.

Billet Aluminum 4 Barrel Carburetor 2-Circuit Metering Block | eBay

Retains vacuum passage for distributor vacuum advance.

www.ebay.com

 

[Ernest]

Thanks.

Im well aware of the aftermarket tuneable billet metering blocks, perhaps i'll try one someday, but for now, i like experimenting, i find it fascinating and its something i would never have thought of when i got into hotrodding back in the mid 90s... so in closing, after all and said and done, going EFI(Edelbrock Pro-Flo 4) will be my next and final destination.

 

[565bbchevy]

Have you considered doing this procedure to the main body of your carb to make all of your air bleeds adjustable to give you more accessible tuning capabilities

 

[Ernest]

Not really.... original holley carburetors typically have very little material left after drilling out the pressed in bleeds and tap for 10-32 threads, and besides with the choke horn in the way, it lQQks to be a pain in the rear to do so.

So i picked up a Proform 67101C mainbody(vacsec) that has adjustable air bleeds instead, no choke horn present, so i will not have auto or manual one to use, which is fine, then i'll need to swap the original unmoded(yet) front and rear metering blocks, base plate and adjustable vacsec pod, along with the fuel bowls from my 770SA carburetor and i should be good to go.

From what i can tell, it looks like it was an originaly produced as DP main body, but it sports a plug on the secondary squirter hole, it does have the full length squirter hole from the metering block side as well, same as the front, i could probably convert back to a DP. Its appears to be 4corner idle mixture capable, it has holes drilled into the main body from the metering block surface as well as the bottom side, the included primary only squiter is #31, the primary side idle bleeds are #75 and the high speed(main) bleeds are #36, the secondary side idle bleeds are #45 and the high speed bleeds are #36, and it doesnt have the provision for timed spark port, i could probably do that mod myself by taking accurate measurements from my 770SA mainbody that has it.

Picked up the brand new mainbody off ebay for the same price as the retail peice, but it came with a host of extras, secondary metering block with absent IFR, probably drill and tap a set in later, extra pair #72(loose) and #76(attached to metering block) jets, metering plate seperator plate and asociated gaskets, four full length fuel bowl screws and nylon orings, baseplate gasket, fuel bowl and metering block gaskets.

Who knows when i'll put this frankencarb together, but im lQQking forward to it, again, i just need to get my AEM wideband 02 system installed first, been stupid lazy doing it now for over a year, still sitting brand new in the box.

 

[Ernest]

Just picked up the PROFORM 67166C billet metering block.

Nice piece, i just need to remove the upper IFR jets and modify the lower IFR location and use 6-32 x 1/8" brass set srews.

This block just happens to have four per side emulsion holes, instead of the three per side so i could just block off the middle ones... would anyone happen to know which two holes to block off that closely resembles the holley setup?