390 carb question

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Dec 12, 2002 | 04:23 PM

althoffaaron

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From: USA

390 carb question

I am overhauling my 390 for my '76 4X4. I want to acheive at least 350 Hp on the overhaul. Currently it has a 2 barrel carb. I'm upgrading to a 4 barrel with the overhaul. I have decided on a edelbrock performer intake, but I can't decide on the carb I need. I have a manual transmission so I'm going with a double pumper Holley. I'm not sure if I should go with the 750 or 650cfm. I've been told that 750cfm is a waste for what I'm trying to do. I've also been told that a 650 is not enough carb for the big blocks. I'm putting in a mild cam. I want a nice idle and a good power from 1-5000 rpm. Would the overstock cam make me need the 750 or would the 650 get the job done? Also do I need to upgrade to headers and dual exhaust right away or could that wait? Any advice is appreciated. This is the first big block I've done.

Dec 12, 2002 | 05:25 PM

Ratsmoker

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From: Missouri

390 carb question

Here is what I would recommend. Ditch the performer and go with the RPM. For a cam I would recommend the crane 343901. I would not recommend going with the double pumper. You may want to look at the holley street avenger 670. That should give you a very streetable 325HP. You will need to do a little bowl work on the exhaust and add CJ exhaust valves to hit 350HP or more I would think. It all depends on your compression too. If you want to run 9.5 - 10:1 and depend on premium fuel you should hit 350HP without the exhaust work. Definitely go with headers and dual exhaust. Stock manifolds are good for stock engines and that is about it.

Dec 12, 2002 | 05:51 PM

lee

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Joined: Jul 1999

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From: Lacey, WA

390 carb question

Hi,

Rat has it "Right on". Only thing I can ad is if you do alot of 4-wheeling that puts your truck at large angles as in hill climbing you may want to also consider the Holley 670 Truck Avenger. It is designed for 4x4's.

As for the Headers, If you get long tube conventional headers place them in the engine bay before you drop the engine in. Once the engine is installed you will probably have to jack the engine over on it's side to install/remove them.

Hey Rat, You PCS'ed yet?

Lee

Dec 12, 2002 | 06:50 PM

Ratsmoker

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From: Missouri

390 carb question

I agree about the truck avenger. It is supposed to be great for the inclines. I already PCS'd. I'm at work right now.

Dec 12, 2002 | 10:22 PM

althoffaaron

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From: USA

390 carb question

I would like to go with the street avenger but it has a vacuum secondary. Everyone I've talked to so far has said that doesn't work well with a manual tranny. The vacuum is too sporatic. That is why I've narrowed it down to the double pumper.

Dec 12, 2002 | 10:35 PM

Ratsmoker

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From: Missouri

390 carb question

I don't know who told you that but it is completely false.

Dec 13, 2002 | 08:44 AM

William

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Joined: Feb 2000

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From: Sun River St. George

390 carb question

Well good! I think 650 cfm is plenty and a carburetor built for 4x4 trucks is likely a good thing. 350 HP may not be important as high torque at low RPM. Camshaft selection is critical on this application. I believe a true dual exhaust with crossover pipe and stock log manifolds will be fine for this truck. Spend extra money on the highest quality internal engine components you can find. I like Silvolite 1130 pistons and moly rings. Balance everything including the weight of the rings and inserts. Get a high volume oil pump, use ARP fasteners do all the oil mods we keep talking about. Since it is a 4x4 consider a FT 10 quart oil pan, long pick up and I would use a windage tray if you are flogging off road and up hills. Build the bottom as strong as you possibly can and later you can add headers if you must. I think a big crossflow radiator is more important than headers but whatever. Keep compression down around 9.0 or 9.5 to 1. Save the warm air stuff so you can actually drive this truck when your done. There is other stuff I would do before headers, like a 100 amp one wire alternator and one of those new batteries that don’t leak when you tip them over.
William in Atlanta :-)