Better to be Overcarbed or Undercarbed?

[Kingofthehill]

I keep being told im overcarbed... i have a fairly modded 440 and layed down 577hp on the dyno and the carb is a race demon 1050. The other day at a buddy's house he kept insisting i was way over carbed... telling me how bad it was, its gonna leak through the rings and get in the oil, and myabe one day get a low boom in the bottom end????...

anyhow.. we took the vaccum secondaries 750 holley off his 440 coronet and insisted we put it on mine and take it for a spin..

all i can say is that it felt GOOD.... now this is the butt dyno but it did feel better, especially at idle and off the line... but this could also be due to the tuning on mine..

anyhow... am i over carbed?

i have a 650 NIB that i could throw on, but i know that will be too small.. but is it better to be too big or too small?

JOe

[345Dart]

Phone this number in Oregon 503-627-0728 talk to Don
Whatever he tells you - buy new or modify RD.
You are overcarbed with a 1050 RD - unless you plan on running WO all the time - your buddy is correct.

[B1owner]

Originally Posted by Kingofthehill

The other day at a buddy's house he kept insisting i was way over carbed... telling me how bad it was, its gonna leak through the rings and get in the oil, and myabe one day get a low boom in the bottom end????...

JOe

Well, you could stand a smaller carb. But if you planning on making more horsepower in the future, (ie: low deck 499, 511) , the 1050 will come in handy. As far as "leaking through the rings", this is where your buddy is misinformed. The proper term that he is reffering to is washdown. Washdown will not happen with a bigger carb generally because you run the chance of running too lean if anything with overcarburetion. Understand that the common misconception is that a big carb "dumps" alot of fuel into an engine. But in reality, too big venturies lead to low vacuum and consequently not enough fuel gets pulled from the boosters. An engine has to "suck" fuel from the carb and a good analogy for overcarbing would be, say,like trying to drink soda from a straw 2 inches in diameter.

[72Challenger]

Overcarbed, if it is tuned as closely as it can be gotten, will give you the best possible max HP numbers on a dyno, and (usually, but not always) the best dragstrip times.

Other than that, there is nothing good about it. You get much better throttle response, low and mid range torque, and gas mileage with a smaller carb. As you found out, driving around on the street these are much more important characteristics. You would probably notice the drop off in top end with a 750 if you get on it a lot, because it is definitely too small to feed 577 horses, but it would have great drivability. An 850 would probably be your best all-around choice.

As for your buddy's contention that you will leak fuel past the rings and blow up your motor, as long as the 1050 is jetted correctly this won't happen. Likewise, even a 750 could be jetted too rich. This is a tuning issue, plain and simple. That said, it will be easier to correctly tune a properly sized carb than the monster you're running now.

[PistolGrip440-6]

Well, based on you power level im going to take a shot in the dark and say you rev to around 7000-7500 rpms. A 1050 is certainly too large and must be a big peice of bogging equiptment, but a 750 is probably too small, and definately is if you rev to 7500 rpms. Anyway, alot of people who dont put on big carbs get real conservative with them to get rid of bog, but I would say you need an 800 or 850, depending on hopw high you rev. I reccomend Holley, Im not an experienced engine builder or anything but theyve led the industry for years and I dont care what people say about the Barry grant carbs. Anyway, I would get a double pumper and you shouldnt have any bog problems. Your friend might try to convince you to get vaccum secondaries though, but I say vaccum secondaries are for under 400 hp and for the front and rear carbs on 6 packs.

[Kingofthehill]

Im hearing what everyone is saying and trying to figure this all out for myself.. but i was wondering the advantge of this carb then?

This one is the Race Demon RS version wich says the sleaves are changeable to make it a different size carb....
http://www.barrygrant.com/demon/default.aspx?page=18
http://www.performancedepot.com/prod...08243ce3d8faf5
anyone know of a good book, or place online that gets deeper into this? i would love to know if i can put a smaller sleve in there and make it equivelent to a smaller carb?

does this make any sense? hahahaha... im so damn confused... i didnt buy this carb, it was on the car already.. but its out of the box tuned...

Thanks

JOe

[dave571]

1050 race demon is way too big. We are all in agreement. Although i will say, with an A body like that, the motor will be more forgiving with a bigger carb, than a heavy ruig with SB

I run a 750 mighty demon on a 440 that makes over 500 hp (needs to, to run a 3800 pound car/driver into the 11's)

Resleve it down to 800 and give it a shot.

The smaller carb will give better throttle response. Feels way better on a street car. Difference is usually only seen on a dyno.

I don't think the "can cause damage" argument is realistic. Not if jetted right.

The cam and heads make the power on any engine. The carb only needs to keep up.(that said, I hope to someday have a motor mean enough to move up to the 850 thermoquad. I have been missing out on real performance....LOL)

345dart's advice to call Don at FBO is the best advice you could take right now.

www.4secondsflat.com

Like Don (or not) he is extremely knowledgeable with demon carburetors. undoubtedly he has installed more demons on mopars than anyone.

Perhaps a copy of his tuning guide would be a good purchase also.

[Kingofthehill]

so with the 1050 i have, i can sleeve it to a...

675
750
775
825
975

(Pretty cool )

im thinking 775? at 100bucks for a set of sleeves for a certain CFM, i hope to make this choice once

JOe

[PistolGrip440-6]

I would go 825, but thats just me..... I dont know much about the Barry Grant carbs because I dont care for them, but im assuming a race carb from them would HAVE to be mechanical secondaries. Is it a double pumper? If so, then I would definately go 825.

[DartGT66]

Change it to a Thermoquad, you'll get more power and better fuel economy + all the other good things in the world

Like said above, 1050 may be on the big side for your engine. However, if it's tuned correctly, you propably won't gain anything making it smaller. If it works, I wouldn't bother. Peoples assumption that a big carb means more fuel, is nonsense. A carb, wether it's big or small, tries to keep the same A/F ratio. The boosters get slightly worse signal in a "too big" carb, because of the smaller air velocity, but with a good carb that shouldn't make much difference.

[451Mopar]

To be short "It all depends on...."

For fuel mialage, and low to mid RPM driving, a smaller carb usually works good, but will restrict air flow at high RPM, which will cost you some peak power.

For Racing, and on a big engine, you need a big carb to get the most power.
I believe the owner of a carb shop here runs a small block chevy 350 with a 1050 Dominator on it. He clams it makes the best power when tuned correctly.

And that is the real point, having a carb that delivers the correct amount of fuel through out the RPM level and with different engine loads.
This is why the newer race carbs have so many replacable and adjustable parts, but you need a dyno to really set the carb up.

Anyhow if your making close to 600 HP, your 1050 carb sounds about right.
I had a 850 DP on my 451 stroker that makes a bit less power, and when I switched to a 1,000 CFM pro series carb the engine ran way better throughout the entire RPM range. I believe this is because the pro-series carb matched my engine better. The real tale was when I chassis dynoed the car, and the A/F ratio was nice and flat throughout the RPM range of the Dyno pull.

[slepr1]

Is there a formula to find which size carb for your needs? I too have been told I'm over-carbed. I went from a 750 holley vac.sec. to a 850 holley dbl.pumper and the gain was noticable enough.

[dave571]

An 850 holley isn't too big for a warmed up 440.

There are formulas out there. Use google, or try some math.

Your engine will use it's displacement in air(440 cid), every 2 rev's.

a cubic foot of air is 1728 cid

So at 6000 rpm a 440 should use 768 cfm at 100% volumetric efficiecy.

It gives you a ball park.

It does become obvious why smaller motors don't need 850's etc.

[bigiron]

Talk to the BG boys if you are going to resleeve that carb... I own two RS type Demons and I am told if you make a large size change you MAY need to change more than just sleeves... We talked about it once... but can't remember what all needs to change...

I like the Idea of those carbs, I just haven't had that much luck with mine... But I finally got someone that is willing to make things right with them, so we will see if they are what they are cracked up to be...

With all that being said... a Race Demon is exactly that... it may not give you the best performance on the street.. in any size. The Speed or Mighty Demon might be a better choice for your combo... although I would (at this point) still buy a Holley... just a better company to deal with... but size does matter... I would stay as close to the 800 to 850 cfm range as I could...

Here are some numbers from Demon to think about...

Here are some flow numbers off of a few Mighty Demon carburetors so you can get an idea. The WOT number at 1.5” Hg will be with an average A/F ratio of about 12.5:1.

650 Mighty Demon at 1.5” Hg will flow 753 CFM Wet (Air and Fuel)
750 Mighty Demon at 1.5” Hg will flow 920 CFM Wet (Air and Fuel)
825 Mighty Demon at 1.5” Hg will flow 982 CFM Wet (Air and Fuel)

The wrong carb choice really sucks in that... you can spend alot of money thinking bigger is better (or whatever) and leave ALOT of performance on the table.

After reading about the TQ... I have decided to play with them a little... My brother has about 20 of them, he told me to come get them if I want them.. so I am going to get some rebuild kits and freshen a couple of them up and see what all the Hoopla is about... That may not be a bad route to go on your combo... My understanding is that these carbs are 800 cfm... but I don't really know anything more than that about them.... I've always been a square bore kind of gu