I am planning on converting my stock 2bbl manifold to an aluminum 4bbl intake. After doing some research on this site, I have found the EDL-2105 at Summit Racing.
Is the EDL-2105 a good match to my stock 390? Just as info, I rebuilt the 390 last summer. Also, what 4bbl carburator is a good match to the 390/aluminum intake? What other factors do I need to look at?

Thanks in advance,

Chris

 

The Performer manifold is a good stock type replacement for stock to mild performance use. A Holley 600 cfm vacuum secondary or an Edelbrock 600 carb would work well. If you have an automatic trans make sure you get a carb with the Ford kickdown linkage on it.

 

I used a Holley street avenger 770 on my aluminum intake with a 390 engine and I love it.

 

I havent been able to figure out so far why you guys seem to like a 600cfm carb on your 390's ?? When I first bought mine back when...and I put the 428 intake on it and the C4AE-G heads and Headers..I put the Holley 750 on it with Vac.secs. and an electric choke and never looked back??

Russ

 

Well, Russ, I suggest that because according to Holley a stock 390 will only need 573 cfm at 100% volumetric efficiency. Typically, a street engine will rarely be more than 85% efficient which calls for 487cfm at 5000 RPM. Holley suggests a 600 cfm vac sec carb for stock to mild builds, for more performance upgrades they go to the 750-770 cfm carbs.
I ran a 650 double pumper on my 390 before the 428 was slipped in. I got 12 mpg and could pull a 3 horse gooseneck trailer( about 7-9K lbs) without any problems.

 

Ok Putt I can understand that...But it only takes, a set of headers on a stock motor to improve Air flow...all a motor is ...is a fuel powered air pump...when ever you increase air flow..you have to increase fuel flow to try and keep a 14 to 1 ratio...

For those who are following this (14parts air to 1 part fuel) and if you change Intake's the only limiting factor would be the heads..a head upgrade..and more fuel... Cam change more fuel...

Russ

 

I agree with Putt. The problem with too big a carb is you lose torque on the low end. One of the things that makes torque is Air velocity. the smaller the opening, the faster the air travels through it, so a smaller throttle body means the air must travel at higher speeds to get through it.
No amount of opening up the heads or exaust is going to make a diffrence on the 100% volumetric efficancy number. Thats the most air the pistons can push, regardless of breathing. I trust Putt's numbers more than these, as they account for combustion chamber diffrences, and pressure, but for ease of refrence, these will work.

a 390 engine is 390 cubic inches. The air stays in the piston through 4 strokes, or 2 revolutions, so every 2 revolutions, it pushes 390 cubic inches of air. or, 195 inches of air per revolution. at 5000 revolutions per minute, its pushing 975,000 cubic inches of air. there are 1,728 cubic inches per cubic foot, so that means the motor is pushing 564 cubic feet per minute. Thats Max CFM, the only way to improve that number is make the motor larger, or compress the air with a supercharger or turbo.

With really good flowing intake and heads, and a free flow exaust, you still aren't going to get up to 564 CFM on the motor, infact, using Putt's number of 85% volumetric efficancy, most 390's in stock form won't move more than 500 CFM.

 

While this is all true, a 390 wont move more than 564cfm at 5000rpm, there's more to it than that. Carburetors are rated with a specific pressure drop across the carb. I think 4 barrels are rated at a 1.5" pressure drop, and 2 barrels are rated at a 3" pressure drop. There needs to be some vacuum in the intake to get the air moving. So you can improve performance with a bigger carburetor, assuming you can keep the air / fuel ratio correct. This is also why the 700cfm electronic fuel injection I'm running on my 390 outperforms the 600cfm vacuum secondary Holley carburetor I tried on it for a while. For one, the intake manifold vacuum is lower at WOT, and for two, it meters fuel more accurately.

 

Well any time you change runner length and runner diameter...a carb spacer, air cleaner etc. its time to retune...it all has an effect on the carb.... I have always used a rule of thumb....what ever stock was..with nothing else changed, I would go up 100cfm.. and then lean it out if needed....but I have always run my cars and truck a little rich...to save on the Valve's too...

Russ

 

I was unaware that how much air was flowing thru a carb would change the fuel to air ratio. If the power valve is open and you are at 3000 rpms or 5000 rpms the f/a ratio should not change as long as there is enough air flow to pull fuel through the system. This is why a vacuum secondary carb is good on the street, it keeps the engine from over carburation (to big of hole which slow air flow).

 

Bear..But not everyone is running a holley....and thats also the reason why the performance carbs come with a 4 Idle circuit....and either do not run a power valve..or have a dummy valve...to get the crab to run off the circuits.

And you can take a power Valve in a carb and put it on a flow bench..and a 6.5hg maybe 6 or 7...any other time your changing a power valve your just guessing..Unless you have it on a flow bench..you can get close...But not on the Nats A$$...

Unless you get lucky...

Russ

 

Every carburated boat engine (not two strokes) out there does not run a power valve and on a true race motor I never ran one. I am well aware of how a power valve works, all I was saying was that if the power valve was open the the f/a ratio would stay consistant. The reason for a power valve on a street motor is the same reason vacuum advance is used on dist.; fuel economy. But f/a ratio in a carb is controlled by jet size and bleed holes and has nothing to do with the air flow thru it or the engine under it.

 

Thank you for the help and the great information.

Chris

 

good job guys I think you scared Chris. But he's right you all share good points. I personally wouldn't over jet. I say you don't need more than 600cfm for your type of build.

Madmike33

 

I appreciate the help. I will use a 600 cfm carb with the intake. I have no intentions of building a high performance engine. The only upgrades I have done so far have been rebuilding the engine from a 360 to a 390 and a dual 2.5" exhaust system. I may go with headers in the future, but all of the headers I have seen say they will not work with the Camper Special trucks.
Its a '73 F250 by the way.

Chris