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View Full Version : Is 770 CFM too much for a 304?


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craigparrish
07-14-2004, 08:39 PM
I found a great deal on a holley 770 truck avenger. I've got a 304 .040 over with an edlebrock performer cam/intake. pistons are mild TRWs. The rest is pretty much stock. What problems will I get from the 770 CFM? Should I stick with a 670?

jeepsr4ever
07-14-2004, 08:45 PM
:!:

craigparrish
07-15-2004, 07:28 AM
:!:

Is that a vote for or against the 770?

jeepsr4ever
07-15-2004, 07:53 AM
yeah, thats a little much my friend. But as we all know it depends on you jet size

tufcj
07-15-2004, 08:26 AM
I'd say it's a little too much, even for a built 304. If it has vacuum secondaries, and is jetted properly, it could work. The bigger the primaries are, the more sluggish the throttle response. Small primaries make high flow and crisper throttle.

I've actually used 390-450 CFM carbs on 304s, and they worked very well. I only used a 650 on my built 360, and sometimes that was too much carb. Bigger is definitely NOT better when it comes to carbs.

There are formulas to calculate needed airflow, I'll post if I can find it.

MNTrailBoss
07-22-2004, 09:54 AM
I have the smaller Truck Avenger on my 360. Plenty of carb for that engine. Probly only makeing 195 - 200 HP with it anyway.

rollen dean montoya
07-22-2004, 09:01 PM
might try going with either a 570 or 600 cfm max. just my 2 cents
worth
later, rollen :lo1l:

thigh19
09-11-2004, 04:53 PM
It really only depends on what you're planning to do. I ran a 780 holley on a 304 with a tunnel ram, wild cam, headers on a mud bogger and could have used more carb. My 401 didn't like the 600, but really woke up with a 750 on my J10. I look at it this way, the engine will only flow so much, start big and jet down. Cheaper than going from carb to carb and easier too. Just my 2 cents.

jeepsr4ever
09-11-2004, 08:43 PM
Just to clear things up 700cfm is just the max air flow not the fuel amount going to the carb however if you run a large jet size and the primaries bores allow too much air in you will never get a idle without stumbling. I would run a 600 or 650 (DP) tops......BTW any updates on this one?

Lifted79CJ7
09-11-2004, 10:43 PM
I have a brand new Edlebrock 600 cfm (ran it on my 401 for 20 minutes) with an off road needles and seat kit already installed that will be too small for my 401. I originally bought it for my 304, but ran across the 401 for a good price, so decided to rebuild it instead. Wanna trade? Not sure what those are worth, but just a thought.
Jack

Goose
09-12-2004, 01:26 PM
I'll probably catch heck for saying this but Iv'e never let fear or good sense guide me.. I wouldn't trade 1 edelbrock for 3 holleys..I used holleys for years on drag cars and they work great at WOT but for street/off road manners uh-uh..Im sure the "avengers" are improved but..

But I would add my vote 770 is much more carb than you want on a 304 or actually a 360. I forgot where I found this but they dyno'd several engines for max airflow at about 6500 to 7000 rpm and If I remember right the 350 chev pulled 590 cfm and the 396 was 620..

For what it's worth.. :-|

Mudrat
09-12-2004, 04:39 PM
I had a Holley 650 DP on a warmed up 304 and it ran great (intake ported/polished, headers, 3 angle valves). But 650 would be the MAX I would take it - a 600 would probably be better if jetted right and you didn't get really wild with the cam.

Mudrat

milocj
09-12-2004, 04:46 PM
I used to have access to lots of Holleys from boats that we did warranty work on. I must have tried 6 different versions from 600-750cfm on my old 1972 Bronco with a pretty healthy 351W and nothing worked as well as the standard 600 vaccuum secondary model. One or two of the 750's did better for WOT, but the driveability was terrible.

That being said, if you're going to be wheeling and using it as a daily driver I would go with the Edelbrock and add the off-road needles and seats. I've used these on that Bronco and two CJ's with slightly beefed 304's and they are the best (imho) for all around driving and off-roading. The Holley 600 worked a little better for stoplight to stoplight racing, but the Edelbrock was much better in the rough and for average street driveability.

Lifted79CJ7
09-13-2004, 12:20 AM
OK, after listening to you guys, sorry man, keeping the Edel!! So do you guys think 600cfm will be OK with a warmed over 401? So what happens after I tap out the max the carb can produce...for example a 600 cfm carb vs a 750 of the same brand/type/style? Does the power band just drop off?
Jack

Goose
09-13-2004, 03:11 AM
Well IMHO Unless your going to spin that 401 awfully tight (over 6 grand) I don't think your gonna run out of airflow..you might have to fatten the secondary metering up a bit, But I would bet with a step up spring kit (to open the secondaries quicker) and a little fatter rods/jets in the secondaries you will be fine..We are running a 1406 600cfm on a 69 ranchero with a warmed up 390 and it is plenty.. 12.58 et at sea level (when it will hook up!)

The easiest mistake to make with an engine is over cammed and over carbed (of course stock bites but bigger aint always better) and the best money spent for offroad is ignition and exhaust..Just my opinion.

Mudrat
09-13-2004, 10:00 AM
We are running a 1406 600cfm on a 69 ranchero with a warmed up 390 and it is plenty.. 12.58 et at sea level (when it will hook up!)

The easiest mistake to make with an engine is over cammed and over carbed (of course stock bites but bigger aint always better) and the best money spent for offroad is ignition and exhaust..Just my opinion.

12.58!!!?? Man what a dog :shock: J/K :wink:

My dad want's me to rebuild his early 80's Ranchero - 6cyl F/I He wants it a good looking stock rig nothing hot.

OBTW agree withthe stage one off road kit - ignition, headers and maybe an intake.

Mudrat

Lifted79CJ7
09-13-2004, 10:49 AM
Well, so far I have collected a bunch of edelbrock stuff to run together:
Performer Intake
Performer Carb w/ off road needles and seat kit
Performer Cam
Performer Valvesprings
plus lots of other little goodies here and there...
I figured they must be matched for each other, so why not?

Goose
09-13-2004, 11:11 AM
That will be a good combo. The edelbrock stuff is pretty good.

My 360 has a edelbrock Torker on it (kinda wrong choice for a j-10 but the engine was in a gremlin I used to race) with 10.5-1 the 600 edel carb headers and port matched..And a cam that I just flat cant identify.. I originally built the motor 10 years ago and I don't have a clue what Cam I put in it when I put it in the J-10.. but since it works so well I left it alone when I had it apart this week.

Man I wish I could find another Gremlin..It was like a fuel altered with doors, always sideways :!: :!: :t:

FrankNB
09-13-2004, 11:28 AM
In light of all that's been said in here.. what about throwing in a Q-jet on that intake? They seem to come in two flavors, 750 or 800 cfm.. The 750 came on 305s, so I don't get it anymore.. why are the the recommended CFM rating from Holley type carbs to Rochester type carbs so different? I put an 800 on my 360 with the rods for a 5.7litre, paired with the 8600 Summit cam rated at 1500-4500rpm.. I have a little rough idling @ and under 900rpm, it idles best around 1000... any reason, I mean from my research the 800 came on the 5.7 and up so I should be good.. I don't mind the rough idling, but I'm just trying to make sense of it all..

jeepmonster
09-13-2004, 03:03 PM
Quadrajets have very small primaries and the sceondaries will only open in response to what the engine airflow dictates, so the airvalve above the secondaries may not ever fully open, if the carb is too big. On modified engies the carb size formulas are not very reliable.

Goose
09-14-2004, 03:14 AM
Well I would agree on the quadrajet..It is an excellent low buck option to the edelbrock..it has one flaw for offroading ..the metering well (in the middle by the aircleaner stud) serves as sort of a vent if you get it bouncing or at wierd angles, fuel will slosh out here and down the primary bores..but! there is a trick little precut sponge that you can find on the stock racer sites that fits snugly in this well and while it doesnt completely cure the problem it slows it down..but as for the cfm ratings the Q-jet is almost an "automatic" carb along the same lines as the edelbrock and the carter AFB, the amount of airflow will dictate how much secondary response and or fuel you get..so you can get away with overcarbbing (geez is that even a word?) :shock:

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