What CFM for 383? (1 Viewer)

[4x4 Station Wagon]

I searched CFM 383 on mud with no luck. Please hook me up with a thread you know of that might help me. I have a 383 stroker with a RPM air gap manifold. The motor is claimed to be 410 hp and 420 lb torque which ?? it only has 9 to 1 comp with 76 CC Heads that have 1.6/2.02 SS Valves and Flat top pistons
The cam is a .480/.480 -230/230/110. the motor does have the capabilities of RPM's with good vavle springs, screw in studs, guide plates, good bolt kits, balanced, etc. but I dont plan on winding it that hard. Infact I threw 2" ramhorns and a walkers crossover pipe on it since I only plan on usnig about 4500 rpm's of it for the most part and thought I would sacrifice HP for a bit of torque. My problem is when I use all the CFM calculators they tell me at 6500 (which is what the intake is rated at on the high end) the motor will need around 650-680 cfm pending the efficiency. Everything I read and am told so far says no way it will be flat on the top and to go with a 750 and 700 minimum . I am currently looking at a Truck avenger holley which leaves me with either a 670 or a 770.

Any help would be appreciated.

 

[craptabulous]

i would go with the 670 for a drive around town go off road land cruiser .

if you want to go drag racing in a nova i would go with the 770 .

or a properly built and tuned q-jet , im sure i will get bashed for that but if they are set up right and don't have a leaky throttle shaft they are awesome , plus there max flow is 800cfm . i still can't believe how clean the tail pipe is on my cruiser with the q-jet and no cat .

if i remember right my buddy only has a 750 double pumper on his 455 i think the 770 is over carbing a 383 .

 

[copasspupil]

The 650 is correct. Personally I'd opted for a 650 speed demon myself. I love both of mine. Barry Grant makes a very nice carb. My mustang is a 347 stroker with a paxton that makes 626 hp. I use a 650 mighty demon for it. They are very easy to instal and tune if you know how to do it.

There is guy on Ebay that sells reman. speed demons for really inexpensively.

 

[4x4 Station Wagon]

Great advice thanks to both. I actually had a quadrajet and was going to throw the normal tricks at it to make it crisper but then I realized I had the whole square bore vs. spread bore thing going. I know I could use an adapter plate but I have seen dyno results that show it hurts. I fit into the driving around category rather than the drag racing so 670 should do it. I was actually looking at a reman from Holley but I will check out the speed demon reman for sure!

 

[oldracerguy]

670 TA

I have been down this road already. I have a mildy built 383 that is supposed to be around 400 hp. I had the 770 truck avenger on it and it would fall flat on it's face at around 4,000 rpm. I replaced the HEI ignition with a DUI, tried adjusting the floats, jets, timing, etc. It was driving me nuts! I tried a vacuum sec 600 Holley on it and it that I had on the shelf and it ran awesome. Everyone told me to run a qjet. I love Holleys because they are so easy to tune and the new truck avenger had all of the off road tricks already done to it. I spoke to Holley tech several times and finally got the guy that runs the tech department. He about blew a nut when I told him I was trying to get the 770 truck avenger to run with my motor combo. He said it would never run right with that carb. They already sent me a new metering plate, assortment of secondarry springs, etc., before I talked to him. He told me the truck avengers are underated for CFM and I would never get the 770 to run right in my motor. He said it is way too much carb and was designed to be run on a big block or better.
I boxed up my 770 and he sent me a brand new 660. Holley has great tech support and treated me very well. I mounted up the new 660 and it runs awesome! I also talked to Jim at Downey and he has a great tech article on their site regarding the mods needed to make a Holley run for off road. The Truck Avenger already has all the tricks done to it.
I have a hill in my back yard that lets me test my carb while I idle up it in low range. The 770 would stall trying to climb, the 600 Holley pulled nice and idled right down and never stalled, the new 660 Truck Avenger also idled right down and runs great. I am very happy now and can fine tune the Holley if needed with easily accessible parts and tools. Make sure you get the newest 660 truck avenger that is the #3 model, not the #1. They had issues with the early builds. Go with the 670 and you'll be happy.

I also run my motor with a targeted rpm of around 4,500. However it spins up to 6,000 rpm with no issues and still has low speed manners that make it perfect to off road. I am running the Edelbrock Performer series intake with a 278/282 cam. I am also running block hugger headers.

 

[maximum destruction]

ya'll will probably laugh at this suggestion but have u considered a 500 cfm 2 barrel holley? it has way better low end throttle response than a 4 barrel, u could actually get a little gas mileage out of it, & it will fit u're intake because it's a 4 barrel casting w/out the rear venturi's. i ran 1 on my dirt late model for 2 season's due to carb. restrictions. the engine was 410 ci.. keep in mind she was on alky but the only difference really was larger jets. she would carry the left front tire 6in. off the ground coming out of the turns. just some food for thought.

 

[marks69cruiser]

Go with the Holley Truck Avenger! I hear nothing but great things about this carb! Holley Performance Truck Avenger Products

 

[marks69cruiser]

There is a cfm diagram on that web link.

 

[Bret]

I would lean toward the Q-jet, has good road manners and work very well off road bone stock. I don't know crap about the avenger, it may work just as well. With a QFT (Holley style carb) it runs like a scalded dog on flat ground, the second you are off camber/uphill/downhill it would stumble and die. All the extra power didn't work so well when I just needed it to run.

that and in a pinch I can swap it out at Autozone if it dies, may not be perfect, but it will get me home.

I can't remember what the CFM ratings are for them, but anything around 650 should be enough. The 2 barrel idea might be worth looking into as well. It does seem a little unnatural putting a little carb on a bad-ass 383 though...

 

[dargreg]

I,ve had some issues with Holley ,Alot more with the Q jet and hardly any with the Edelbrock series.Holley is a lot better to tune and probubly your best bet .DO NOT go any bigger than 670 .This is lots of experiance talking.Good luck

 

[Brian in Oregon]

I had a Holley 670 Truck Avenger on my 350 in my FJ40.

Never again.

Yes, it made LOTS of power once you got it rolling. The problem was, it had no low end torque, and you had to slip the clutch A LOT to try to move slowly. And the gas mileage sucked.

I switched to a QuadraJet, and it made a huge difference. It does not make as much gross HP as the Holley. But it is far more streetable and the gas mileage is 20% better. Because of the small primaries it gets down and lugs. I've been able to make second gear starts on hills whereas the Holley required first gear burnouts or excessively slipping the clutch. I've even lugged up hills as a test in third gear that the Holley could not do except in first gear.

If you insist on a Truck Avenger, and you're not going over 4500 rpm at the most (I don't go over 4000, and 3000 is cruising speed) then you certainly DO NOT need a 670 or 770 cfm carb, because you are not running high RPM at WOT (Wide Open Throttle). If I ever went back to a Holley Truck Avenger, I think I'd opt for the 470 cfm. It will be more suited to running up to 4500 rpm, and provide better low end response. Check your cfm charts and you'll see.

The only thing the Holley 670 TA did, aside from sheer power, was fire right up and run decently out of the box. But that's because it's jetted so friggin' rich. And it's not a carb that likes to be jetted down, at least not on the primaries. I've tried, and found as the jet size goes down, the performance falls flat, and it quickly becomes a miserable piece of crap, backfiring and bucking. You better be happy with the primaries out of the box, because you really can't go down more than one jet size. On the other hand, the secondaries were jetted with 89's, and when I got on it, I could see black smoke coming out of the tailpipe. I was able to drop the secondaries by ten (!) jet sizes, going to 79's. It still sucked gas, but not quite as bad.

Now, take the above with a grain of salt. My 350 is a bone stock, Plain Jane. I don't have a big cam in it.

I'll tell you what. I see you are in Oregon. If you are near Gresham, I'll be happy to loan you the 670 Truck Avenger I had on my Land Cruiser. Then you can see if you like it without having to spend $400+ for one. In fact, if you really like it, maybe we can work out a trade or something.

 

[dargreg]

Once again the 670 is almost to big.As Brian has said its a little over fueled however he is bone stock and your not and will be grabbing the fuel at idel with more overlap Its really up to you for choice and performance.I personally would stick with the Holley.You have to take a course to tune a Q jet as far as im concrned ,they are good reliable carbs though I just have had bad luck and poor fuel milage.I think for what tou want 650 cfm is ample.Your choice of carbs.

 

[fieldsken1]

gee i hope a 670 is not to big for a midly built 350 this sucks

 

[Brian in Oregon]

Once again the 670 is almost to big.As Brian has said its a little over fueled however he is bone stock and your not and will be grabbing the fuel at idel with more overlap Its really up to you for choice and performance.I personally would stick with the Holley.You have to take a course to tune a Q jet as far as im concrned ,they are good reliable carbs though I just have had bad luck and poor fuel milage.I think for what tou want 650 cfm is ample.Your choice of carbs.

I didn't have to tune my QuadraJet. Found a used one off of an 1980's Corvette and slapped it on. Works just fine. While vette motors have more performance than my stocker, by the 1980's they were also designed to run leaner, so it's worked out well. But yes, you pretty much have to be happy with your Qjet "as is", because they are not fun to tune.

BTW, one other issue I found with a Holley on my FJ40. When out of the trail, and even in normal every day driving, I rarely opened up the secondaries. This tended to cause the secondary needle to stick shut, and combined with the fuel boiling out, the engine would flame out. I've never had that problem with a common bowl design like the Qjet, or the Edelbrock, which while it has two bowls, shares them on the sides, not front and rear. I recall replacing the rear needed and seat three times while running my 670 TA, because of sticking.

BTW, I have another 670 TA on the 454 in my 71 Chevy pickup, with 4.10 gears. The secondary jets are so large that if I take off WOT, by the time I hit second gear the engine bogs because the secondary fuel bowl ran out of fuel. The needle and seat in the primary along with the fuel transfer tube are inadequate to fed that much flow. Since it is not an off road truck, I've been tempted to install center pivot bowls with dual inlets to get around this, but at 6 mpg I'll probably wind up with a Qjet on it as well, or maybe dig up my 700 cfm Edelbrock.

 

[copasspupil]

I have a 635 Carter 4v you can have. It came with mine but am gong fuel injected. It probably needs to be cleaned is all. Just pay for shipping.

 

[HunterMcC1]

If you go to Holley's website they have a calculator based on CID and max rpms that will give you the amount of CFM's your motor needs...

 

[albee]

Their is a good review of differet offroad carb's that has been linked here a few times, I cannot find it.
I had a holly 650cm on a 383. It ran great on flat ground, but got 8mpg. Same carb on a 400 sbc with the same result.
Put a rebuilt quadra jet on the 400 and it now gets 12mpg. The big change the q-jet made is I can run my junk and any angle. It did lose a few horspower, but still cruises 50mph at 2200rpm's.
good luck

 

[cmiller114]

Call Barry Grant Inc. 706-864-8544.
I have similar motor with a little more compression and cam. They fixed me up right!