i have a 383 stroker with camel hump heads and a duel carb weiland tunel ram intake and i have two 1406 edelbrock carbs on the shelf and i dont have enought money to get better carbs at the moment and the edelbrocks are to big so i was thinking of rejetting them but to what? i also was looking at brackets for my alternator but i need to know if i have a long water pump or a short water pump its a stock water pump

 

You don't rejet carbs to make them smaller. You rejet carbs to get the proper air/fuel mixture.

Those carbs won't flow more than the engine can use, so you'll probably be okay - even though you are running a tunnel ram, and even though you are running dual carbs, and even though you're running Edelbrock carbs.

 

but i am running the orginal electric fuel pump and wont it flood it self out cuz they are 600cfm each thats 1200 in to a small block to me that seems like thats to much fuel

 

Years ago when I had a 383, I ran a single 850 on it.

CFM is the amount of air going into the engine, not fuel. The carb is jetted to give the best air/fuel mixture. The pistons going down in the cylinders can only suck in so much air. While a larger carb can make more power because it allows in more air to mix with the fuel, there comes a point when going even bigger doesn't help. Two 600's is acually better than one 1200 Dominator. The smaller butterflies will be more responsive.

Your 600's would be fine for a race engine but on the street, a couple of 450's would be better especially for the small engine. Two 600's would be better on a street BBC.

The 600's will run OK but fuel mileage on the highway will be lower but not by a whole lot. You'll probably notice less power and less mileage with city driving. Stop and go driving will have no bottom end torque. A tunnel ram is for top end power, 4000+ rpm. They suck below that and that's where street driving always is. I'm not familiar with Edelbrock carbs. Driving around, you'll only be using the primaries. It won't be until you put your foot right to the floor that the secondaries will open and really suck the fuel into the engine.

I ran dual 850's on my 540. I now run dual toilets with injected alcohol that flow 1800 CFM each.

Your water pump will be a long pump. Without knowing more about the engine, everything else is a guess.

 

i never rejetted a carb before so what size jets would i need to make it 450 cfm

 

You get a 450 cfm carb, you CAN NOT rejet to change the CFM.

 

As stated, you don't rejet to change the CFM. You jet to obtain the correct air/fuel ratio for your set-up. Go to the Edelbrock website. They have instructions for tuning their carbs.

Again, the carbs won't be too big. Think of them as two 300 CFM carbs with an extra 300 CFM flow each available if needed. They will not allow flow beyond what the engine can use. If you have one-to-one linkage (which is probably what you want with a tunnel ram), the responsiveness won't be as good as it would with smaller carbs, but, it won't be a killer (above and beyond the fact that you've got a race-only intake on the engine). If you went to a progressive linkage (and I'm really not sure how well that works on a tunnel ram), with the rear carb as primary, it will act like a single carb under street driving conditions.

As far as fuel supply, get a return-style regulator such as the Mallory 4309. Adjust it for 6 psi to the carbs.

A stock '85 water pump will be the long style.

 

See the thing about CFM in relation to carbs is where there rated at say 600 CFM thats under some specific test parameters to give you a means to compare carbs. The actually CFM flow rate will be dependent on things like RPM trottle position dissplacement ect. Now comming back to the real world situation CFM is a volume moveing at a specific speed to give you a flow rate. The volume is determined primarily by the geomety by the carb itself but what determins the air flow velocity? The velocity is related to the amound of vacuum produced the piston travaling downward and the flow rate of the parts connected to it. So for example say you had a constant CFM flow rate you could have a huge carb that will yeild a low air velocity or a smaller carb running at a higer air higher velocity. In the end although the flow rates are the same they will have very different charateristics. The lower air velocities will in turn cause things like less throttle responce not as good fuel atomization maby hesitation in extreme cases. So in clonclution although thoes carbs will physically work youde be better off with some smaller carbs i think.

 

Velocity flow rates for carbs, heads etc are measured at 28 InHg vaccum. Head flow numbers can look more impressive if rated at 25 InHG so everyone tries to use 28 as a standard.

A carb rated at 600 CFM will only flow that much at WOT and at high rpm.

CARB CFM Required = Cubic Inches x Max RPM's / 3456 x VE%

Very few street engines will reach 100% or higher volumetric efficiency. A typical street engine may only run at 75%. A street engine normally stays well below 5000 rpm but may peak out to around 6500 depending on camshaft etc. VE is at engine peak HP. Since we don't know your cam specs or operating range of the engine, lets guess.

CFM reqd = 383 x 6500 / 3456 x 0.8
CFM = 576

Now at 100% VE, you would need a 720 CFM carb. At 100% VE and spinning the engine to 7000 rpm, you will only need a 775 CFM carb.

So why do so many people put a 750 on their 350's when they only need a 600? GM knows this as most Q-jets were 600-650 CFM. The larger CFM will allow more air fuel into the engine and make more power but the larger CFM also gives a flatter power curve until the carb(s) CFM exceeds the engine's demand for air and fuel. At that point, the engine just can't pull in any more air and a larger CFM carb can't feed more fuel. Carbs work off a venturi effect. Air gets sucked through a venturi which sucks fuel out of the float bowl. The faster the air travels, the more fuel gets sucked into the engine. Larger carbs need the higher rpm or larger displacement engines to keep the right amount of suction going through the carb. WOT at 3000 rpm isn't going to suck as much air through the carb as WOT at 6500 rpm.

Now these rating are at the maximum flow of the carb and at maximum rpm of the engine. Cruising around below 3000 rpm, you're not going to be feeding 1200 CFM into the engine from the 2 carbs. The engine is only going to pull in enough air to fill each cylinder. If the proper air/fuel mixtures are set, the engine will chug along as if nothing is different. Going to WOT is where you'll really notice a difference or at higher rpms where the engine is sucking in more air.

I've seen a 434 race engine in an altered with two 1250 dominators on it. The engine also spun to around 8000 rpm and being a race engine, it's hard to over carb it.

 

Lucky for you, you have the old fuelie heads. They flow like a clogged toilet, so you shouldn't need a lot of carburetor bore.

Also lucky for you is the fact that the AFB/Edelbrock uses a barometric secondary air valve, and if set up properly, shouldn't admit more air than the engine can handle to avoid bogging and the poor venturi vacuum as Stephen described.