Thanks , Carl, I had some tough times this summer and just did not take the time to visit. I'm too ornery to get run thru ANY processing plant!!!

Ohhh.....

 

Over here tough times also with this bad back 24/7 and fighting SSD.
Hang in there to see what else they can throw at us.

 

Have you ever Dynoed a 428 By Chance Gary???? Better go check out Jay Browns post on is mild 428 that he built and made the most power and TQ with a 950 Holley. I do believe he used a 750 and a 850 in his test. And you Don't need to pull 8,000RPM to get the power out of an FE!

So have you post any of your FE Builds on this forum??? And if so did you give all the specs and what you did to get it there??? I would love to see what you have contributed to the people that love there FE's........

Buy the way My 11to1 428 with a solid roller cam has 220psi of cranking pressure and you are going to tell me that a 750 is TO BIG....... Your out to lunch Dude.......and stick to being a book worm! JMHO

 

Thank you Baddad457. Sound like you have some real world experience.....Books are not everything!

 

Getting a little testy are we? YOU are the one that called BS. Nobody is saying your 428 isn't HOT, I have no doubt it is, that wasn't the discussion, so git your panties out of your crack!I have been racing FE's since they came out! Y blocks before that. I don't really care what your cranking pressure is. It is not relevant to what the engine will flow, only to compression and horsepower and frankly with a lot of overlap in the cam it can go down! Flow is a matter of displacement, restriction and rpm ONLY. Good induction, big valves, smooth passages and good exhaust help the restriction, but you still have a displacement of 428 cubic inches and a four cycle engine. That means you can only move 214 cubic inches of air on each revolution of the crank shaft. There are 1728 cubic inches in a cubic foot which means 214/1728 per revolution of the crankshaft. With the right set up you can get a little ram effect due to velocity.(If you look at a lot of racers from the 60s you will see a little hole drilled in each header pipe an inch or two from the flange. This allowed the tuner to adjust the jetting by looking at the exhaust flame.) A carburetor is only efficient at one point which equals max venturi vacuum with wide open throttle Once the venturi gets too big the air velocity starts to drop below nominal and you don't get good mixing of air and fuel. If you put a blower on an engine you can change the physics otherwise you can't put 10lbs in a 5lbs sack.

 

Where does 214 cubic inches of air in one crankshaft revolution come into conflict with a carb that's flow rated at 750 cfm ? (that's at a 1.5"HG drop) It doens't mean it's going to flow that sitting on top of any certain motor, only one that would pull that amount of vacuum at WOT with that size carb sitting on the intake. Put a smaller carb on and although it's rated to flow less, it'll actually flow more, due to the stronger vacuum pulling air thru it. Bolt a 600 cfm carb on a 500 cubic inch engine and it'll pull more than 600 cfm thru it at WOT.

 

I think we are in total agreement on that. I am not questioning what a carb will flow at rated vacuum. I am stating what an engine will suck in and blow out the exhaust if it has no carb at all. It will flow less efficiently with any restriction on the intake or exhaust side. The flow the engine will produce is dependant on the rpm and the displacement. In a PERFECT world a 500 cubic inch engine will move 250 ci per revolution (that works out to about 144cfm/1000rpm). Any restriction will cause the pressure differential to go up and velocity to go up Exactly as you say it will. At least until you exceed the sealing capability of valve guides or rings and start sucking major oil (seen this happen a few times) The problem is when you get too BIG a carb on the engine you LOSE velocity thru the venturi. This will cause the venturi vacuum to drop and result in poor fuel delivery at WOT, puddling in the manifold also comes along in severe cases. Going the opposite way you will get higher differential and higher manifold vacuum resulting in higher velocity at WOT. The problem you get into there is reduced rpm capability due to throttling. The old Y block 312 heads actually had a restriction cast into them to increase the velocity at low to medium speed for improved driveability. We used to run a 70 degree reamer into the port to get rid of it before we ported them. I get the feeling Wes thought I was trying to discredit FE engines and his in particular. I am not, I cut my teeth on Ford engines. I was merely answering a question about a carb for a 390 which would be over carburated with a 750 at normal street or off road rpm ranges. I appreciate the fact that you have kept the conversation logical and left the big emotion out of it. I love to discuss and even argue, but Flame turns me off.

 

Sorry Greg but your math cam out wrong! If you are going by the book. You need to give your RPM's. So for my 428 X 6,200RPM=2,653,600. Then 2 X 1728=3,456 then divide the 2 #'s that you came up with is 767.824 CFM required to do the job (assume 100% efficiency)! So your 214CFM is waaaaaay off from 768 CFM's required by Holley.......Need to brush up on the ole Holley book Bro....

 

And you stated this as well "A 750 on a 390 (or 428) is over carburated under about 8,000 rpm."

Sorry Greg but this became a sore subject if you read the past post. Then out of the blue.....You pop in saying things not quite right either. So ya I took it the wrong way and it wasn't the right thing to do by any means or say. And I don't know ya from Adam nor do you know me (or maybe you do know me LOL)! But I'm having a bad day and you caught me at the right time so to speak LOL. No harm, No foul

 

The only problem with Holley's sizing formula is it has no correlation to the flow rating of the carb. So it should only be used as a guide in picking a carb. I recall Car Craft dyno testing a Mopar 440 (or maybe it was a 383?) with several intakes and carbs, it turned out a tunnel ram with two 750's on top still managed to show a restriction at the topend (of about 1"hg), even though by the formua, one was suficient. In short, you don't know how much any carb will flow, until you actually bolt it on the motor, on a dyno and actually measure how much air the motor moves thru it.

 

I don't disagree with ya on that one bit. Flow does have a lot to do with it! I know a guy who runs a 311 Ford (little 302 punched out). Has state of the art heads runs 13to1 with a mid 600" lift cam (solid roller). Make 640HP @7,400 RPMs. They tried a few cabs on it and the 950HP Holley came out on top for max HP and TQ!

I realize that the Holley book is just in general and nothing beyond that..... But thanks for the classification on that!!!

 

I wasn't aiming at you Wes. There are others here that seem to use that formula as THE gospel on what works and what doesn't. After running smaller carbs than I used to pick, I find these better suited for street duty. I think a 750 is perfectly sized for a 390, but a vac. sec would be my choice for the street over a DP simply due to being able to tailor the sec. opening point.

 

I know that you weren't aiming at me LOL. I hoped that I didn't come off harsh??? I'm totally on your side on the subject! A 750VS would work for most people and no doubt about it .

 

:-x22 :-x22

 

Wes,
I don't mean to belabor this, but lets talk apples and apples. What I said was 214 cubic INCHES per revolution not 214 CFM. That is correct. A 4 cycle engine is a 720 degree cycle so you only get half the intake flow every rev. There are 1728 cubic inches in in a cubic foot so you get 214/1728 cfm per revolution or .124 cfm per revolution of the crank. Multiply that by 6200 to get 768 cfm (more or less a RCH). You are right and so am I. I guess I didn't spell it out clearly. I sure didn't mean to get on your bad side. I love 428s and from your signature line you have a sweet one!