1967mustang

so i guess a 4bbl650 holly is way to big for my 289. so i was wondering if everyone could tell me what size carbs they are personly using

thank you

Arcticspook

Edelbrock 650 on my 302

67mustang302

570cfm on my 302. Carb size really depends on the application. A 400hp 302 driven on the street can get by just fine with 600cfm, but a 9 second drag car with a 302 is gonna need a lot more carburetor than that.

Displacement* RPM / 2820 or 3456(3456 is the typical number used for calculating, but a more modern carburetor with better boosters can generate more metering signal with less vacuum so you can run a slightly larger carburetor, 3456 with a typical carb, or a good aftermarket carb use 2820) * VE.

So, in your case 289 * 5,000(peak hp with a stock replacement cam approx) / 2820(assuming you use a good carburetor) * VE(in your case with stock heads and a flat tappet cam, no better than 80% or 0.80) 289*5,000/2,820*0.80= around 400cfm or a titch over. In other words, your engine won't really be able to pump any more than around 400cfm of air, so there's no need to go bigger, all it does is reduce metering signal.

In my case it's 307*6,000/2820*0.90(aftermarket heads, roller cam etc, it might be a bit higher like 92 or 93% at best)=around 590cfm, I went with 570, so the carburetor may be slightly restrictive, but only for the last 100-300rpm. Any carb WILL move more air than it's rated at, since it's rated to flow a given CFM with a given vaccuum, so more vaccuum = more cfm moved.

1967mustang

see mine stock 289 block with 302 heads.. everything stock. this just coming to a surprize to me that my carb is way to big. i allways had this carb on there so i just thoght that how driove i eman wasnt a huge turd but i guess littol slugish. so i see everyone so far thinks 650 is too big.

rmodel65

ive got a 670 street avanger on my 302 way too large, but it was avaliable since my cleve is dissasembled im gonna try getting a 4100 from advance since i have a core carb

1967mustang

oh allright 67mustang302

that calculation makes sence i didnt read that till now... so i should shoot for buy like 450. that should make my throttle alot SNAPPyer, so me running that 650 didnt hurt just made it a turd?

390bigblock1

800cfm edelbrock on my 390.

67mustang302

You could tune the 650 and make it better, but the throttle response and power, especially at lower rpm, is always going to suffer to some extent. A stock 480cfm carb would work just fine. If you wanted to spend money on a good carb you could get something like a 525 Demon, a tad large but well within the range of tuning. But with a basically all stock 289 there's not much point in spending a chunk of money on a performance carburetor. A stock 4bbl is fine. The Autolite 4100 "1.08" is around 480cfm, and Autolites are very nice carburetors, they have annular discharge boosters so they atomise and vaporize fuel quite well. A stock 480cfm carb would work very well on your setup, and they are a very trouble free carburetor as well. Save the 650 for when you build the engine up later with heads, cam etc.

And just to give you an idea of what kind of power a smaller carb can make, the NASCAR Busch series guys are running 358 cubic inches and turning around 6,500rpm and making about 500-600hp. And they're doing so running only 390cfm carbs(rules restricted). Granted, it's restrictive to a large degree, but the power is still being made.

my77stang

hell i would almost trade you for my 570, send some pics over of what you have and maybe we can strike a deal.

see my avatar

1967mustang

man 67mustang302 thx man ur helping alot, now that i am thinking about i i still have stock carb but just 2 BBl and i liek the 4bbl so ill look into diff carb, so if know anywhere with cheeper carbs. i can rebuild them even if i had too.liek what is the autolite # equal to the holly # you know what i mean what are equal to each other. wht size carb should i be looking for. i wish i woulda suscribed to this site along TIME ago. i kinda want another holly i never had a problem with them but autolite i herd good things too