Home Porting the Holley Carb!?....

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Cudafever

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I have never ported any carb in my life but that's about to change!

OK this is why i'm going down this road. As most of you know my 340 has gone to rest and replace with a 408. My original carb being to small (600 Vac sec) had to go. had a 750 carb that i have been setting on for years. rebuild it and put it on. Works Good!

Then one day, on some ones other thread, there is a Holley carb sheet posted up with all the jets, PVs, squirters, cfm exc.
What i learn, real fast was that my 750 DP (Double Pumper) was in fact a 600 DP.

We all know that 600 cfm leave a lot on the table for a 408. even a some what mild cam.

already had to drill small holes in the primary side butterfly to get the idle mixture to come around.
I have the 600 DP Carb or a 850 Demon DP that has already had all 4 butterfly drill out for a 500+cube bottle motor.
So my choice becomes a rebuild kit, hand full of jet, two new 30 cc squirter kits and welding up the holes in the throttle plates........or try my hand at porting a carb.

I have had a book on this and have wanted to try this for years. I have all the burs, sand paper roles, flapper wheels, exc so it wont cost me any money to try!

SO HERE IS WERE YOU ALL COME INTO PLAY!

How many have done this, and what are the pit falls or problems to look out for?

Thanks in advance,
OH and the carb is a Holley 4776
 
I cut the choke tower off and radius the top a little. I like to leave the air cleaner stud boss intact. I also put in the small butterfly screws. I use red Locktite on those. I don't know how much benefit I receive from this but I like doing it.
 

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Thanks for the pics! That's basically What i'm going to do. Cleaning the inside and out side of boosters. Which will be difficult, as they are so small.

They claim that you can get 100 more CFM by doing the mods in the book......we will see.
 
I think you are going to go to a lot of trouble for basically nothing when you could simply get a bigger carburetor.
 
RustyRatRod said:
I think you are going to go to a lot of trouble for basically nothing when you could simply get a bigger carburetor.
Click to expand...

Thanks Rusty! and your right! but i have always wanted to try this. and i'm not out a lot if i don't work.
 
Do yourself a favor and don't bother, you're gonna ruin your carb for not much gain. Just get a Profrom main body and be done with it. It's got all the work done for you already. $125 is money well spent.

Click here dude.
 
In order to change a 600 cfm into a 750 cfm you'll need a whole new body (because the venturi sizes are different) and a new throttle plate (because the butterfly sizes are different). In other words, most of a whole new carb.
 
Pro form also makes base plate, that and new Pro form center still cheaper than a new carb.
 
Cudafever said:
Cutting off the choke horn will kill CFM!
Really? why is that?

Because the thing was engineered to move air thru at the designed height. Changing that height will undoubtedly upset the velocities of all the metering BUT, I'm sure it can all be retuned, if a person has enough time and patience.

GOOD LUCK!!
Keep us up to speed, on how it works out, please?
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This week is hell, won't be able to do any thing until next week.
But i will keep you posted!:D
 
forphorty said:
If you have to run a short air filter element, removing the choke horn may benefit you some. I like grinding and shaping things. Takes me about an hour to cut off the horn and blend it in. Here's a link I found that you might find interesting. http://www.ryanbrownracing.com/Bill_Jones_Page_4.html
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Vary interesting how he epoxy, and didn't cut the dividing wall between the primary and secondary side. Hmmmm
 
4 corner Idle? Cool.

Nice work....I've done it before....but learned.

I daily drive a Proform main body 4777-2 650 DP....It runs flawlessly here in Oregon...3300ft.

The OE oldschool Holley DP's have pressed in downleg boosters and pressed in, non changeable Air Bleeds.

Its almost not worth messing with a Holley Double Pumper Main body and just leave the choke tower alone.

If you want more "potential" FLOW, and some more tuneablility,... scrap the main body and get a Proform.

http://www.jegs.com/i/Proform/778/67100C/10002/-1
 
sst3193 said:
Cutting off the choke horn will kill CFM!
Click to expand...

Uh... NO!

I did this to a few carbs back in the day and it did improve performance. The increased airflow will require a little jet adjustment. The main thing is to make sure your main body surfaces are flat. That has been the biggest issue with Holley carbs for me. I have had to file almost every one to get rid of the low spots around the power valve cave. A body file is perfect for truing up a Holley. The same type file may also be found in a feed store as they are used on horses hoofs.
20520.jpg
 
People quote big numbers but I'd like sure like to see 100 cfm on a flow bench. If the air horn is cut off properly and then the edges carefully contoured and you use a K&N stub stack and you smooth the boosters and venturi you may gain 40-50 cfm max. You have to be extremely careful when smoothing the boosters too because if you take off much meat from the o.d. you'll cut down on the amount of air passing through the booster reducing it's efficiency ruining any cfm gain you might achieve.. I have done several Holley's over the yrs. and the gain really isn't nearly as much as you might think. IMO it's not worth the time cause that carb is too small for any serious stroker. I have a very mild 408 and am running a 750 HP and it's really not big enough to make max power
 
Prine said:
4 corner Idle? Cool.

Nice work....I've done it before....but learned.

I daily drive a Proform main body 4777-2 650 DP....It runs flawlessly here in Oregon...3300ft.

The OE oldschool Holley DP's have pressed in downleg boosters and pressed in, non changeable Air Bleeds.

Its almost not worth messing with a Holley Double Pumper Main body and just leave the choke tower alone.

If you want more "potential" FLOW, and some more tuneablility,... scrap the main body and get a Proform.

http://www.jegs.com/i/Proform/778/67100C/10002/-1
Click to expand...

Hay Prine Thanks for posting up!

I looked at that one but its for a 650 and up. mine is a 600 (4776-2)

No only two corner idle.
 
Thanks every one for your opinions, yes it may have been a waste of time but i did it!

The only thing that i didn't do was the inside of the boosters, as i would have had to use a dreml(sp) tool to get in there. it's not the "open" design, half tube thru the middle of it.

It sounded like it had a bit more throttle response......Maybe wishful thinking. have no head lights and dark. Will have to sneak out for a quick stomp tomorrow. but will have to wait for the track to put a period on this.

The good thing is, that i don't think, i broke it!:D

fishy68, you say that you could us a bigger carb then a 750?
Remind me what cam shaft and compression you have.
 
Cudafever said:
fishy68, you say that you could us a bigger carb then a 750?
Remind me what cam shaft and compression you have.
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10.06 to 1 comp... Solid flat tappet, 238 at .050 and .500 lift on a 108 lca. I ran a 830 annular on it that had the air horn milled, contoured and a K&N stub stack for a while and it was a little faster than my 750HP but it was terrible on fuel even when I cruised like an old lady (10 mpg vs. 15 mpg with the 750) so I sacrificed a little performance for a bunch of fuel mileage since I drive it a lot. Honestly the tricked 830 was a little too much. I think a stock 830 or 850 would have produced as much power but done it more efficiently but I got a super deal on it so I gave it a shot
 
Even in spite of my opinion that it was a waste of time because it's too little for the application I didn't take into consideration your wanting to learn and that's worth the time and effort spent. If you want to learn something about Holley's David Vizard put a book out about a year ago that covers them pretty well and does it in layman's terms. You can find it on Amazon for about $20
 
fishy68 said:
People quote big numbers but I'd like sure like to see 100 cfm on a flow bench. If the air horn is cut off properly and then the edges carefully contoured and you use a K&N stub stack and you smooth the boosters and venturi you may gain 40-50 cfm max. You have to be extremely careful when smoothing the boosters too because if you take off much meat from the o.d. you'll cut down on the amount of air passing through the booster reducing it's efficiency ruining any cfm gain you might achieve.. I have done several Holley's over the yrs. and the gain really isn't nearly as much as you might think. IMO it's not worth the time cause that carb is too small for any serious stroker. I have a very mild 408 and am running a 750 HP and it's really not big enough to make max power
Click to expand...

This,is dead on... Tracy knows his stuff. I am surprised, no one thought to match the air cleaner base. Take a look at a Mopar Six Pack, or a L88 'Vette (single four Holley), those really work. The Stub stack helps clean it up,big time.
 
Just when and look at them stub stacks. Not bad, only $30

But will have to wait to see what performance, my afternoon porting session did.
 
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