I'm curious how much improvement people have actually found (dyno and/or track results) from going from a properly running carb to a custom carb built for their specific combination. I'm not talking about replacing a piece o' crap carb that wasn't running well in the first place, but swapping something that's reasonably tuned for somebody's "special" carb and seeing quantifiable gains as a result.

My hypothesis (or is it a theory?) is the typical person sees at best 5-10 HP, unless you're talking about switching from some under-carburated deal or going from a basic 4150 to a 4500 on a combination that can really use the extra CFM. In that case I'd guess going from something like an 850 to a 1050 gets you 20+ HP, if the intake isn't a restriction.

Am I wrong? Got any examples that really prove some carb specialist brought out the beast in your ride from a basic carb swap? I'm all ears...

my personal opinion is that more good carburetors have been ruined from people "improving" them than anything else. imho i buy a new (proper) carburetor for the application then just make the necessary minor adjustments. unless you're talking books, braswell, davinci (all BIG $$$$) or the like i stay away from modified carburetors.

Few years back I tried 3 custom carbs on a well sorted out 416 combo
I had ran the car with a 1025rs race demon for quite a while.
I tried a 750 and 1000 cfm pro systems 4150 carb and a 1100 pro systems dominator.
The dominator was a couple or three hundreds better than the race demon, and the two 4150 carbs were tenth to tenth and a half slower.
I bought the dominator and sold the race demon thinking I could get even more out of the custom dominator than initial testing showed. I never did.
I suspect a real well tuned and sized. carb won't be beat by much if any

I can only share going from one custom carb to another. On my 860-HP 9200-9400 RPM 412" SBF, I switched from a Pro Systems Dominator to one of Dale Cubic's at CFM (Cubic Flow Modification). I don't have my timeslip anymore, but it was significant. Keep in mind the motor was dyno'd with the Pro Systems carb and ran well, but it did pick up with a change to Cubic. Luck w/Cubic? Nope, his stuff is that good.

Reading this with interest, probably going to put the 950 HP on my Dakota this winter, I was thinking about sending it out to Jesse Bigs first.

Here's my impressions....

If you have a well sorted out carb, and its close to optimal for the application, air/fuel is just that, air & fuel. Spending big money on a custom unit thinking you left Hp on the table to be had isn't likely. The engine still wants the same A/F ratio unless you changed somthing else or your carb has a restrictive choke horn or another issue. The only way it make more hp is getting more air and fuel in togather.

Now, lets say you have a new engine, and no carburator, a custom one will get you a lot closer out of the box a lot quicker from my experience. Then its worth it because your not spending as many TNT sessions finding the correct A/F and squirter shot for your combo.

Now as far as carburator sizing vs. HP, there is an article titled "Tall Tails" by Steve Dulcich that does away a few of the myths, but in his test, low end was limited to 3200rpm or above...With the big carburators making more power in the upper rpm, but not sustaining anything below 2600rpm...This is where I learned the advantage of annular boosters. They make a large carb effectively 200cfm smaller in responsiveness. If you want a big carb for the max hp, and you want good low end for driveabliilty, then you need a carb that offers annular boosters, and is bigger than what you currently use without being too big.

I used this to run a 800cfm annular quick fuel carb on my mild 360 street engine. It actually took a little bit of time with the efi to achieve the same results at the drags.

Also note, this is before the new SV1 style carb as well...

http://www.moparmusclemagazine.com/parts/engine/mopp_0111_demon_carburetor_dyno/viewall.html

I don't usually see much difference in the "pro" carbs and the ootb carbs at the track. ASSUMING that the ootb carb is correct for the application and a reasonable amount of track tuning is done.


For street cars though, I have seen some pretty dramatic improvements in idle, light throttle response and cruise. Tayloring the part throttle transitions for each individual engine seems to be a lot more difficult than getting the WOT mix right.

All I'm looking for is WOT...With the stock PCM and my cam I've gotten pretty good at brake stalling my truck onto the trailer at 4K RPM..

Everyone around me runs away though...

Anyone that truly thinks a WELL BUILT custom carburetor does not make more power than a "dialed in" box carburetor has never used one.
I have spent enough time tuning several different ones to see a real difference.
After several days with A/F and egt readings dialing in different carburetors,I bolted on a Dale Cubic that was not built for my combo and saw decent gains.
The next best I saw was an SV1 with A little tuning.
There is way more to it than just air and fuel ratio. Droplet size,proper for the fuel and rpm range comes into play.
I don't claim to have all the answers,just sayin'!
Keith

The only way these carb gurus can make a carb RIGHT
for your engine is to have a wet flow bench with a
bell on it.... I did carb flow work (for a short time)
before I started the injection work at Chrysler...
if they dont have that equipment its their BEST GUESS

I have two street cars, one with a prosystems carb built for the motor and the other one has a 950 ultra HP.
The prosystem carb was much closer out of the box, it is still to rich but at least you could ajust the idle mixuture and the car is more driveable.
Sure you can spend 500 dollars on a WB[I did] and you can dial in the out of the box Holley ultra HP to work just as good as a custom carb after you spend more money on air bleads power valve restrictors, pumpcams, squirters and jets.
Do I think a custom carb will be faster than a well tuned holley, no I do not but for the average guy I think a custom carb is the better way to go for a street car.
Now I know that some of you guys think that I just bought the wrong Holley carb for my car, well the holley tech told me the carb should work great right out of the box.