Ok i been holding back on asking this but im going to ask it now cause i have seen noone post about doing it, everyone talks about porting the intake for more air power and better temps. What is really being over looked and alot don't know that it can be done most the people who has been around any type of racing knows this alot of people over look the 20 to 30 more horse power they have seying on top of the motor looking at them carburetors can also be ported this is mostly done with the edelbrocks and holleys carbs. That is one trick that nascar motor builders do not let out of the bag when it comes to asking them how they get the performance they get from there motors porting the carbs are one of there most use performance tricks. I know this first hand and have seen it first hand as my dad at one time was a motor builder for a nascar team afew years ago call no names. But you will be shocked at what results you can get form a carb with biger jets and being ported. And it's not hard at all to do you can set right at the table you eat at and doit does anyone here port there carbs or know of doing it.
Have played around with this before on Holley 4150 carbs. Milled off choke horn and polished the venturi bores but thats about all. Cannot say they ever got close to 30 hp increase. Nascar engines use high dollar, high flowing heads and manifolds so a bit of grinding here and there might benefit them. Normally the air fuel mixture is calculated by the mfg for its different models and tested on a flow bench. If we attack there original design on the kitchen table, we can actually lose that very critical atomization and air flow so that the engine (a big air pump) will lose hp or become intolerable to drive. Most of us running mild modification engines are better off to just run a factory carb and tune it to our engines with jetting, squirters, and some pump cam changes. One carb out there has replaceable venturi's which I assume would be similiar to porting. In case you can get some secrets on this porting from dad, pass it on. Never to old to learn new tricks.
I think I may have picked up a couple of hundredths when I did mine, but I changed a few other things at the same time so not sure.
With the right tools it can be done on the table but you have to be very good with math and stuff like that but the work is a internal no choke or venting.
Wrong Idea Nascar rules only allow certain carbs, hence they must tweak them for more power. For any motor that you build that is not restricted it is far easier to purchase a larger carb than to try and modify what you already have. There is also much more to porting a carb than simply more airflow. You must be concerned with booster signal and a host of other factors. Once you change these things if affects every aspect of the carb and then you have to change other things like air bleeds, booster size etc which require lots of dyno time or track tuning, both of which are expensive. When it comes to carbs spend the money and buy from a respectable builder like quick fuel, carb shop, davinci, pro system etc. They build according to your combination and they literally are bolt on and require no modification.
I agree with my Louisville brother. For the average racer/cruiser, buy the carb you need and tune it. I know I could not afford to try to "port" on my carb only to screw it up and have to buy another.......there is plenty of other places to pick-up 30 hp without me trying to tamper with a $600+ carb. But it is a neat techinal part of speed that often gets over looked.......the fast Nascar guys are the ones that do it best. And again, there is so many things that each NASCAR team to has to run that are so similar... that things like porting carbs, mixing their own special fuel and running a pneumatic rear spoiler are things tried to gain that little edge, that extra .01 of a second. very neat topic.
My family has been in the nascar field since part of the day fl raceway was still part sand. Bur any type racing can be fun it's all in what the driver makes of it.
I've never personally heard of carb porting, I have thought about it some though but after talking to alot of carb builders, it's not a good idea. You would end up screwing up the venturi taper which is what draws the fuel out. I'd say that if 99.99999% of people take a grinder to there carburetor they are gonna really screw it up!! To port anything properly for more air flow you would need a flow bench and an assortment of precise measuring tools. My carburetor cost $1,000.00 and I can have just about any size I need from 650cfm to 1150 cfm, because it has removeable venturi sleeves. The only "accurate" way that I know of to increase cfm on a "typical" carburetor is to shave the throttle shafts and use the small "button head" screws to attach the butterflies. I've been told that it should increase by 15-35 cfm+- I've performed this operation on many holley carbs. If it has a choke you can mill the choke tower off for a little increase in flow....
