general help with carbs

Scooby5.0Doo · Dec 11, 2005

ok im finally looking to start to put my 79 togeather. the crank i want to get for it and boreing it 60 over puts me right at 421cid so i was wondering what size carb i should run with it. im also shooting for close to 10-1 compresion ratio any help would be apricated. im not sure if i want to keep the 2v head and just put larger yeah i said larger valves in them. end goal of the car is to make it close to 10.90 so also keep that in mind

74courier · Dec 11, 2005

so are you asking what size carb you should run? you really shouldnt need anything bigger then a 650cfm carb for that size of a motor. youll just have to fine tune the jetting to get it to run in its sweet spot for your combo

Scooby5.0Doo · Dec 11, 2005

im not very good at matching carbs with set ups yet but my freind just had a crate 350 and he had a 650 on that. i will have more then a liter more displacement then he had and a higher compresson ratio not sure if that stuf matters to much. i i was thinking i was going to need more the a jetted 650 but like i said before i do not know much about mactch carbs with motors

Darkness · Dec 13, 2005

It all depends on what kind of flow you can get out of the heads and intake. For that size of a motor you could go with an 850cfm but if your heads and intake dont flow crap, then an 850 would over kill and give you bad throttle response.

Scooby5.0Doo · Dec 13, 2005

ok thanks paul so it come down to what the intake and the heads can do but a 650-850 is what i will now look for.

loud 95 · Dec 14, 2005

What Paul said is certainly correct. Lord knows I have seen too many SB 350 Chevy motors with holley 750 carbs and owners who complain about sluggish throttle response. I would not go any larger than a 750. I would recommend a Demon, personally. Their carbs are awesome and are under rated for what they actually flow. If you want, you could consult my friend and ex-college room mate Alex. He has tons of aftermarket carb experience and has sold hundreds to people. PM me if you want his number. Remember, he is a fellow Cleveland owner, who will be building and very similar carbed motor!

white 89 GT · Dec 14, 2005

.060 over is crazy, but you need a 700 or 750 cfm
road demon 725 would be a good start.

ddonaca351 · Dec 14, 2005

If youre going more than 30 you should have it sonic checked (C had some core shift problems), not real bad, but they are out there.... 60 is pretty optomistic.

(imho) a 750vs square bore would be good.

DD

Scooby5.0Doo · Dec 14, 2005

as i do more and more research im finding that what i measured that could be taken out and still have cylinder wall and then parts that i can buy i think ill just stick to 30 over i could still get a 418 out of that but i would have lots of cylinder wear so ill probly settle with a 408.

loud 95 · Dec 14, 2005

Scooby5.0Doo said:
as i do more and more research im finding that what i measured that could be taken out and still have cylinder wall and then parts that i can buy i think ill just stick to 30 over i could still get a 414 out of that but i would have lots of cylinder wear so ill probly settle with a 408.

Alex is going with a 408. He will probably get rid of his two-valve heads, as he knows that he would upgrade to some aluminum castings after a while. So you're going all motor? Alex will probably hit his with a 200 shot of nitrous...but I don't think he'll have the car ready for a while .

ddonaca351 · Dec 14, 2005

Scooby5.0Doo said:
as i do more and more research im finding that what i measured that could be taken out and still have cylinder wall and then parts that i can buy i think ill just stick to 30 over i could still get a 418 out of that but i would have lots of cylinder wear so ill probly settle with a 408.

Hey Scoob' look man, before you get alllll crazy on...
(loud booming deity like voice) "I MUST HAVE 400+ INCHES...."
realize that for 1700 bucks, you can get a nice all SCAT, all forged, 393/6 stroker kit. And it wont drive the oil controll ring clear out the bottom of the rist pin.
(check strokerkits.com, flatlander racing, CHP, network54.com, etc....)

Now like I just mentioned over in Classics, for a comperable idea of what a 393 inch C runs like in a stang, envision or take a ride in a 396 powered camaro.

But anyhow... just a few pennies from the cheap seats.

OH, and before I get down off the soap-box since I know youll ask soon anyhow, Blue Thunder makes a great intake for the C, or the new Edelbrock can be ported to match 4v heads. If you have 2v heads, there are several good outfits down under that make good intakes, mostly single plain, but on a big inch C thats not such a bad thing... 2500-7K

DD

84Gt350 · Dec 15, 2005

You will need at least a 750 and an 850 will work if setup correctly. Back when I had my car tuned at Blood we swapped the 650 for a 750HP and gained 18 HP. They had to change some internal bleeds to get the throttle response perfect but the power is worth it.
Plan a dyno session to get the ignition curve and mixture set.

Dan

Scooby5.0Doo · Dec 15, 2005

i found this general formula on what size carb to use
cid times peak hp rpm divided by 3456 times V.E.= cfm let see 408*5500/3456= 650 then times volumetric effiency. most stock cars are round .75-.80 but i plan on havein slight head work and a ram air system so 1.2 is not out of the question, gets me a 780 cfm but if i want to make peak power at 6000 rpms ill need an 850 just to get me close to what i will need. research is wonderful

TheRedBlur · Dec 15, 2005

try to stay away from bread and rice.

stock50LX · Dec 16, 2005

Uhhh, If you plan to rev the thing over 6 K and you are going to race it, you better get a 1000 CFM carb. I know that puts me in the minority and may test my credibility, but I stand by it.

Post on Hardcore 5.0 and see what you get.

Scooby5.0Doo · Dec 16, 2005

the 1000 would be more for safty over anyhthing else. the a/f ratio you know. i will keep that an option in my head as i think where i want my peak power to be at. and thanks for everones imput. i really have no idea how much air will be forced in with the ram air but if i over rev to only 6200 as i go out the back end at 110-125mph (should be a good range) and the V.E. is 1.3 instead of 1.2 the cfm's needed jumps to 952

ddonaca351 · Dec 16, 2005

Scooby5.0Doo said:
the 1000 would be more for safty over anyhthing else. the a/f ratio you know. i will keep that an option in my head as i think where i want my peak power to be at. and thanks for everones imput. i really have know idea how much air will be forced in with the ram air but if i over rev to only 6200 as i go out the back end at 110-125mph (should be a good range) and the V.E. is 1.3 instead of 1.2 the cfm's needed jumps to 952

To exceed more than 100%ve for more than a very narrow rpm band is pretty optomisitc on a street driven car (imho) but a 780vs holley or equivelant (like mine ) should work pretty well I would thnk.

Oh and scoob' if you do run a holley, I have (quite litteraly) boxes full of float bowls, secondary diaphrams and housings, squirters, cams, jets, etc, etc, and also etc...

For what its worth....

Dave-

OHHHHH, I also have an 850 dp I might be willing to part with.

Scooby5.0Doo · Dec 17, 2005

i dont plan on driving this car much on the street. and with the ram air im thinkin on useing at the top end you never know. and i will keep that in mind about the holley stuff. its always good to have a selction of tunin parts even if it is a carb

TheRedBlur · Dec 19, 2005

I thought you can only exceed 100% volumetric efficeincy with boost!

Scooby5.0Doo · Dec 19, 2005

what do you think ture ram air does

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