I have a pretty good idea how to build up my 390 engine, except I'm still pretty undecided on the type and size of carburetor, and the type of headers. Can anyone provide advice.

I plan to port my D2TEAA heads and install 428 CJ valves, L2291F Pistons, Crane 343801 Cam, Performer RPM Manifold, Oil Mods, and Headers.

What Carb should I use. I don't race, I just want it street fast.

What headers and exhaust system? I would like great performance without being loud.

 

A 600cfm carb is plenty big for a FE.
You just absolutly can't live without them, use shorty headers, duals on a daily driver will do better than a single.

The long tube can make a 15 min starter change out extend to 6 hours. I know, and that is after I put the second one in, in a three week period.
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In the cool still quiet of night, you can hear chevies rusting away.

 

I had a engine built similar to yours and a 750 vacuum secondary will be perfect, I've tried a 600 in the past and its too small on a 390 except a bone stocker w/ single exhaust. 2.5" dual exhaust with a X pipe works really good. I use hedman headers but I don't like them.

 

I can recomend Stans headers. Get them ceramic coated and put in an H or X pipe between your duals. This will aid in performance and also decrease noise somewhat. I also recomend a 750...600 cfms are fine on stock 390s but I feel are inadequate on built up ones.

 

To determine carb size, you need to determine the maximum amount of air your engine will need, and then get a carb that will provide it. The formula is:

(displacement in cubic inches) x (maximum rpm) x (VE)
------------------------------------------------------
3,456

VE refers to volumetric efficiency, or how efficient your engine is at pumping air. A stock engine may have a VE of 75% (0.75), where a full race engine with tuned headers ported & polished heads may even slightly exceed 1.0 (due to scavenging and the like). With the setup you described (CJ valves, headers, etc.), it would be reasonable to assume a VE in the range of 0.90.

Your max rpm is a matter of guessing and desire. I'd guess that you wouldn't want to run that setup much over 4500 rpm, but we'll use 5000 just to be conservative.

Thus, (390 ci x 5000 rpm x 0.90 VE) / 3,456 = 508 cfm. In other words, your engine will swallow 508 cubic feet of air per minute when running at 5,000 rpm. If your carb is rated to deliver that amount of air, it's big enough. Even with 95% VE and a 5500 rpm redline, your air demand will only be 590 cfm.

That's why most guys say a 600-650 cfm carb is plenty big for even a "built" 390. The fact is that adding a bigger carb not only doesn't give you any more power if your existing carb is big enough, it will hurt you. Plenty of dyno testing has confirmed that too big of a carb kills throttle response and mileage without adding any power.

 

[updated:LAST EDITED ON 14-Dec-01 AT 06:34 PM (EST)]Did you know that you are supposed to multiply your answer after that formula by up to 150% for a dual plane and 130% for a single plane?

 

FE, if this surprising information is true (and I'm not saying it isn't), why did some big FEs come with 480cfm carbs?
Eric

 

it was mostly 390's with 5500RPM powerbands, the really hot engines got the 3 2 barrel set up which was what? 800+CFM? I'm guessing on that, I'll assume 250 for the outboard and 275 for the inboard carb or the holley for cobra jets which was 735 CFM, the 427's got dual 600's or a single 780cfm also most hop-up reccomendations reccomended swapping the small carb for the CJ carb as THE first mod dynoing as a 17 horsepower increase over the stock 390 GT carb. ( http://www.woodyg.com/fairlane/finfo/390stage1.html ) Also it's interesting to me at least to note that I've been told the 352 got the big carb and the 390 got the smaller one for some applications. And another reason may have been that the cars were also passenger cars, the smaller carb would have better throttle response and better milage since the stronger the vacuum signal you have the better you can tune your carb for economy or performance

 

oh yeah, the pic is from the back of a edelbrock catalog, and I have no idea on this but I'll assume that the biggest engine to use the 480 was the 410 merc and it was a torque engine more than a horsepower engine

 

Barry Grant had a good carb article in Car Craft a few months back and said the math formula for carb sizing is worthless.I put a 830 annular booster carb on for fun in place of my 750 and my 390 ran better below 3500rpm than with the 750, go figure.

 

Thanks to all of you. You guys are great. I wrote this comment late last night and thought I would just look tonight to see if possibly one person might have responded. And holy cow 9 responses.

Building this engine is pretty easy with all you guys.

I never saw that carb. formula before, that's great. It would appear that the formula supports a 750 CFM. And so far I have never heard of a personal complaint about having too large a carb. So I'm leaning that way.

What is the most relyable brand: Edelbrock? Holley? Also Brands of Mufflers?

 

unfortunately the most reliable brands are the aftermarket for holley, they set the carb up the way you want but are usually $$$pendy your best bet would be to tell the companies your engine, cam specs etc.. and then let them pick the one best for you and set it up. you may need to find a good core or two at swap meets of get the proform carb body from summit... and a bunch of small parts from the junkyard or something.

 

I have found Holley the best carb,summit usually sells the 3310 750 for under $200 and they run pretty good right out of the box.I've tried a edelbrock and it was a POS , even after I spent $100 on jets,rods and kits it would not run right. The older holleys are better than the new ones,if you can rebuild carbs and tune them ,then a used one would be ok , but you will spend just as much as a new one.

 

427FE
I have not heard of the added 30% to 50% factor. Here is a site that I just found seems to have a lot of useful "fill in blank" calulators that you mind find useful. Even notice a section for flow bench results, didn't ok at it yet. It might be for the other guys stuff. Check it out.

DirtySideDown

http://www.prestage.com/

 

>I have found Holley the best carb,summit usually sells the
>3310 750 for under $200 and they run pretty good right out
>of the box.I've tried a edelbrock and it was a POS , even
>after I spent $100 on jets,rods and kits it would not run
>right. The older holleys are better than the new ones,if you
>can rebuild carbs and tune them ,then a used one would be ok
>, but you will spend just as much as a new one.

Boy, that was exactly my experience with the edel pos. It seems most guys like them, but I couldn't get mine to run right even with buying the $ jet kit. I'll stick with Holleys, thank you. The new ones are fine, supposedly you won't have a powervalve blow out on with them. Oh, and while overcarbing your engine will cost you performance (i.e. an 850 double pumper on a mild 302...yea, seen it), I've yet to find a built big block that won't benefit from a 750cfm. You usually don't need any bigger than that, except for Jowiliker...I think he needs a 1000cfm Dominator on his FE