i have a 91 rs with a 350 that currently has 305 heads and is tbi, iam ditching the tbi and doing a carb setup. iam also installing 350 ported and polished heads, a mild comp cam, long tube headers. i know i need a intake, and hei dizzy. but dont know what size is good for this setup?? please help

 

what are the specs on the heads and cam?
vacuum or mechanical secondaries

i say 670 street avenger vacuum sec. for the street.

 

iam still not 100 percent on the heads and cam spec. a buddy of mine has them iam picking them up this weekend. some guy was telling me a holley 750cfm double pumper would do it but seemed a little over kill to me

 

Without knowing anything about the heads and cam, I'd say a 650 double pumper.

 

Holley says a 600 which should be pretty close, most people over carb their motors making them less efficient.... go here it is pretty cool...

http://www.holley.com/applications/C...bSelection.asp

I am running a HP4150 750dbl pumper on my dart block 355ci mighty mouse motor and it is highly modified.

 

good deal, thanks alot

 

Holley is conservative with their recommendations, both for size and type. Too many magazine mechanics out there that think a 1050 Dominator is the hot ticket for their stock 305.

650 double pumper, assuming you aren't talking about winding it to 7000 RPMs.

 

Magazines only print dyno charts, not driveability or fuel consumption stats.

 

i wonder why everyone is recommending a double pump? did i miss some info?

 

here is something to think about...
a 390cfm 4bbl and a 850cfm 4bbl will flow the same cfm at part throttle. although the 390 may be a 50% throttle and the 850 at... we'll say 20%. carburetors are rated a max flow. if you go vacuum secondary i doesn't hurt to get a little bigger carb. then the secondaries open when the engine needs it. i would recommend a 750 vacuum secondary

 

i agree with what he said. although im no master mechanic! lol but for a street car. i would say a 670 street avenger vacuum secodaries. or maybe anything with that quick change for the secondaries. thats what i got

but it would be better if we had the specs for heads and cam.
best of luck to you!

 

The 390cfm will be more responsive(higher velocity in the venturis) to throttle input. I think this is more important on a street driven vehicle than peak output which is used maybe 5% of the time.

I'm not reccomending a 390cfm for a modded 350, just saying that being a little conservative will be rewarded by a more responsive throttle input.

 

well i have a stock 305 engine in a 92 rs. headers-no cat-magnaflow. dizzy-edelbrock performer intake. holley 4160 600 cfm carb. have it jetted down some and have it running damn good. so in my mind as others have stated and some help from 57kid. i have it running kick but. i would say a 650 to 700 cfm.

 

They're rated at a particular pressure differential, nothing to do with max flow at all. You could put 10,000 CFM through a 1 bbl "100 CFM" carb

Vacuum secondaries are for heavy trucks, and people who buy carbs that are too big. A properly-sized double pumper offers better performance.

 

so 650 or 650 double pump? to many choices

 

carburetors are measured on a flow bench at wide open throttle at something like 29"mercury. they are not measured by forcing 10000 cfm through them.

 

4bbl carbs are rated at 1.5 inHg, and 2bbl at 3.0 inHg. At 29 inHg, you probably would get 10,000 CFM. There are variations between manufacturers on whether that's "wet" or "dry" flow as well.

The point is, flow ratings are not "maximum" at all.

 

i must be thinking about cylinder heads.

 

650 is the right size like apeiron said, vac sec or dp? how much gas money do you have? lol! i'm not kidding! double pumpers require much more foot finesse to get even close to vac sec. mileage.
seriously though, i see you have a 700r4 auto, unless you have a 3000 stall converter or higher i'd stick with the vac. sec.
on the other side, if you race from a roll, nothing snaps your neck like a d.p.!
i don't know if it's still a problem or not, but the street avengers used to have a bad problem with the fancy plating. the inside of the fuel bowls would corrode and leave a pile of chips laying in the bowl. that can really mess up the needle and seat assembly and clog the tiny internal passages in the metering blocks and main body. i would stick with something like jegs # Holley #510-0-80783C universal 650 vac. sec. in the original finish for 350 bucks new, or about a hundred used plus a minimal rebuild kit, and add the good stuff like quick adjustable vac spring housing later.
unless you have some pretty huge heads that carb will allow a 350 to spin damn close to 7000 rpm, IF the rest of your combo can handle it.

 

Only when you overcarburate. A properly-sized DP will get very comparable mileage to a VS, and better throttle response. That's regardless of transmission type, too. If you don't have too much carb, or a lead pig of a vehicle that takes forever to get up to speed, you don't need the self-sizing properties of a VS.

 

here is a video of me racing a 4th gen with a 800 cfm DP (4780). it wouldn't have looked so bad if my transmission was working properly. just look at the launch. http://www.youtube.com/watch?v=dmsrKWhcZBk

 

i agree with what you'er saying apeiron, i was talking more about keeping your foot out of a double pumper if you want to save gas.

 

its like choosing manual or auto transmission. do you want to be in complete control or let the car decide?