Carb porting

Just about.
A silver dollar is pretty wide. I doubt the other carb was that big.

The 6425 doesn't have boosters. If the carb he was talking about did, there ain't no way a silver dollar is going through.

If you start messing with the airflow of a Holley and don't have the flowbench, dyno, or track times to tune the new fuel curve in, you will ruin a perfectly good Holley. Don't allow yourself to be so naive to think that you will be able to tune it by ear.

The best thing to do is to buy the right carb. They are cheap on Ebay.

Another good thing to mention is that when you bore out a venturi it will end up flowing less than it did before. The venturi shape speeds up airflow.

Silver dollar trick was without boosters installed.

I took out to much metal and had to build some back up with epoxy to get some kind of venturi effect. This carb runs like crap below 4000. It doesn't have proper booster signal below that. The engine is 2 barral 388 GMsb2.2 block with Dart 18' heads ported by Hendricks engines, and a 4/7 swap cam. The engine turns 8500 in corner entry and never falls below 6000 through the middle. The track is oval rather than any kind of paper clipped so throttle response isn't a huge concern. The driver never lift's anyway. Plugs on the left side look a little lean and 6 and 8 look a little fat. Earlier this year I was working on Individual Cylinder Timing to help with damage from going lean on the left side. 1,7, were decreased from 37 to 35 with the center cylinders remaining at 36 while 5 was adjusted to 34 and 6 increased to 39. 3,2,4 were matched to 36. The engine responded a little better but when the ambient temps got to low(58 degrees) we couldn't get fuel mixtures right with the higher mass density. I'm working on a offset carb spacer to get the right and left side clocked better in line. I'll see if I have pic somewhere. All in all I wouldn't do a carb to this extreme again. While the car is faster a new chassis set up was needed to compensate for throttle response. We had to calm the car down on entry so it would come up on the bars better for forward bite without blowing off the tires. I don't think the time is worth the results. But the topic of discuusion is was can it be done?. I don't really see this carb making any better throttle response in a circle track car which is usaully paramount, I have my theories to a drag car though. I haven't yet been able to dyno the motor.

You should not port a carb for the simple purpose of flowing more air.It will not work out that way.The difference in the sizes between the throttle bore at the bottom of the bore and the narrow part of the bore that the booster sits in determines how much pressure drop will occur between the top and the bottom of the bore as air flows throug it.The designers of the carb build this taper{called a venturi} into the carb and base the sizes on creating how much pressure drop they want at a particular amount of airflow.They then use fuel circuit metering to create a carb that will flow the desired amount of fuel to match the airflow they anticipate.They use jets to limit how much fuel flow will be available overall,and use air bleeds drilled into the path that the fuel flows through to control how much strength the pressure drop in the carb has on drawing fuel up thru the jets and into the boosters.If you change the shape of this venturi,you will have to change all the calibrations in the carb,and if you make the difference too slight between the smallest and largest parts of the bore,you may have a carb that will have no fuel "curve",and might want to only move fuel at a very narrow range of airflow amounts.Dont hog out the carb unless you are after that effect.Some race engine builders may desire that effect for a particular application,but I can tell you,if you were that far into it,you wouldnt be here asking us about doing it.Good luck either way.

so, I guess the same would hold true for throttle plate swaps? You would have to have an o2 sensor to analyze the a/f ratio and recalibrate the air bleeds as well? As I stated earlier, I was surfing the net and found a reference to this subject and was wondering if it was worthwhile. There was a book available called home porting the holley carb, and although I was skeptical, I was also interested in how the holley can be optimized from it's out of the box state.

This is sort of the same thing. I 'de-ported' my Holley 3-bbl by machining and installing aluminum barrel inserts the size of a 600cfm carb. Replaced the original 78 jets w/ 54s. Left booster venturis, throttle plates and air bleeds the same. Thing works great, I have great throttle response, tuned throughout the range perfectly w/ Edelbrock O2 sensor. Been driving it off-&-on since I did the work in '72. The ultimate spread-bore carb!

My recomendation is get an ebaY cheapie Holley, an Edelbrock O2 sensor, a big tub of epoxy putty, a $14 Harbor freight die grinder w/ carbide bit and start cutting and pasting until you get what you want. Then if the prototype carb is too chewed up to use, get a good carb and do the final mods on it for your final runner. Folks will tell you that you are a total idiot for trying this but stop and think where Edlebrock, Wieand, Iskendarian, B&M, Ed Roth, and the rest of the gang would be now if they had taken that advice!

Here is a web site on porting

that's the spirit!
I have seen some of the dominator style carbs with interchangable venturis as your picture depicts. Very interesting mod to the carb. Would not be the first time people questioned my sanity! After all what the heck's sensible about building 500 horse engines in the first place?! Thanks for the link.

Hey Ratlover,

I once polished the inside of a Quady with Scotchbrite and u could could feel the difference no worries, all i did was to smooth everything out, didn't remove anything but dust.
Not long after i aquired a Holly3310, did the same and havn't looked at another Quady since.

Its pretty hard to go wrong if long u only polish and blend.

I call it the PoorMans Airram

Cheers RobbieRat

Hey guys I would say go for it..carbs can be picked up for cheap at swap meets or from a friendly guy at the auto wreckers..If ya mess it up so what..consider it the cost of education..The ole guys figured this out and made their own flow benches and such..

And really investing some time into your education does give results..

Just the thought of this day..

__________________
I have tried most all of it and now do what is known to work..

9 out of 10 times you will ruin a perfectly good carb. If you have the money to burn, buy the right carb. The guys in the old days didn't have the products of today to choose from.

http://www.qksltwo.com/tb.html is a good link, but it's for porting throttle bodies, which operate under the same laws of fluid dynamics as carbs do, but with no concern for fuel passages and stuff, since TBs are on injected engines.

In case you're wondering this after viewing the link, yes I did have (and like a lot) the early pre-96 Saturn coupes. Those things are go-karts for the road.

Here's the results of the first of my two carbs I cut the choke horn off of and polishes the bore. Took 5 hours from start to finish using a hacksaw, die grinder and sandpaper. Man, were my fingers sore! Next step is to epoxy the holes and have downleg boosters installed. Thought I would post some photos for your perusal. The second two photos were taken during removal of the stock boosters and in the last pic the new downleg boosters aren't swaged in yet. I just wanted to check the positioning in the venturi. They're about .250 further down in the venturi from where the stock boosters were. I was told by AED that they should improve flow and increase signal as well as better atomization from the step in the booster venturi's body. I hope it all means more torque, throttle response in low/mid range and hp on top end.
Any comments?

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I like it.

Throttle bodies flow dry, carbs flow wet, different theories are involved. If you're going to port a carb, learn about things specific to carb porting, I'm not sure trading ideas back and forth between the two systems is a very good idea.

K

just completed a 4175 carb porting for a mopar 360cid with a torker2 intake. I got to say it was worth the time. if you are gonna chuck it in and buy something else what the heck give it a try. the only worry is too lean a mixture but you will know that by the exhaust smell. now my carb is a spread bore and 650cfm and I have a buddy with a flow meter who tells me I am at 712cfm which gives me plenty of room to play with as my 360 will only suck 585 at best. the real diff is off throttle response. low end off the line is like nothing else and I have tried several other carbs since predator, holley square bore, demon,. I have to say the best launches are with the otherwise stock holley ported.

How did you swage the new boosters in? Old holleys are common for loose boosters and I know this operation can be challenging at times. Just curious how you're going to get them good and tight. Bob