It reminded me of a video I made a while back... LOL
Carburetor cfm calculator
- Thread starter Dan the man
- Start date
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Because it’s stupid to worry about that when the carb is close to proper size for the task at hand which in this case is not WOT performance. It’s a secondary minor at best concern if at all.
What most people are looking for in there daily driver or mile hot rod is drivability first (response and mileage if that idea of mileage even makes the grey matter!) and good WOT second.
The amount of vacuum drop achieved is not of any real concern for most applications unless maximum results are your thing. The difference in a 1.5 to a 1.7 is a few hp at best. Something you’ll never feel and be very hard pressed to see at the track with a street driven seldom seeing the track car.
This, by you;
Is out of wack and dangerous to follow. This will for certainly lead to a poor performance tire not e in each class you listed. Been there, done that, seen it tested, seen it dyno’d, heard it from seasoned fellas.
Even @ 0.5 for a race engine is boarded line in some case, if not out right crappy. Full blown take no prisoners exempt from my descriptions above.
These are also not cfm ratings but pressure drops in the engine.
LMAO! I love being told I’m going to drown my engine and wash the rings off!
Morons!!!!
Morons!!!!
CFM calculator says a 318 @ 5400 rpm's on the street should use 422 cfms. So I did the right thing and multiplied it by 3 and went with 1200 cfms 
CFM calculator says a 318 @ 5400 rpm's on the street should use 422 cfms. So I did the right thing and multiplied it by 3 and went with 1200 cfms
Must have to calculate the E.T's with a sundial
CFM calculator says a 318 @ 5400 rpm's on the street should use 422 cfms. So I did the right thing and multiplied it by 3 and went with 1200 cfms
I know the feeling…. My buddy Mike couldn’t help himself. He just had to lay hands on it. So I said go for it, I’ll film a little….
360/.030, Comp 294S, Edelbrock heads, 1-3/4 headers, same intake as yourself, twin 600 AFB’s.
I love multiple carburetortion! (SP!)
Not all People might not be looking to get every last hp but I imagine they at least want 80% when they spend $500-1000 swapping from a 2 bbl to 4 bbl.
Difference between 650 and 750/850 might not be much but from the formulas 390-450 cfm for a stock ish 360 to what 600-650 cfm most people would put on they would want that hp gain. But picking for a mild combo really ain't that hard I bet most would agree 600-650 cfm for small block maybe some would say smaller for a 273 and 750 for a big block. It's all the other cases where this stuff becomes an issue especially when wanting a good balance of max performance and driveability.
As for the 3 ratings, my main point was there should be 3 stock, performance and race the vacuum numbers I quickly picked weren't the point, the ones if they did do that should work with that formula and help get people a little closer in the ballpark.
Well, for less than 500.00 into a 318 2bbl, including timing chain and freeze plugs, using 2.76 gears and stock converter, it's goal was to run with a factory stock '73 340 auto with 3.21's in a Duster, and it did it.
Was there any noticeable throttle response loss from one to two 4 bbl's ??
I'm guessing not really
Actually, it feels more responsive because I'm working both primaries on both carbs. However, it never scratched (chirp the tire) before between the 1st and 2nd shift, but you can certainly hear it in the video. Again, the carbs will only flow what the 318 will pull. As with any engine.
The HP Holley's are rated at 2"Hg, so a 950 has 830 at 1.5", 1000 is 866 at 1.5".True but a 440 runs fine with manifolds but headers are better for power, bet it would run fine with a with a 2 bbl at a cost to power, put a 750/850 on a stock 440 picks up a decent amount of power. Bet if you put a 390 4 bbl on a 440 would work better than people would think, My cousin Late Model 372 pulls strong to near 7000 rpm with a 500 cfm 2 bbl, carbs are pretty flexible. People could use the formula but they would be short changing themselves in power especially in a performance situation but they would definitely not worry about over carbing
I think carbs should come with 3 cfm ratings the conservative 1.5 hg for stock and maybe add something like 1 hg for performance and 0.5 hg for race.
Multi ratings are pointless, the only thing that determines the capability of a carb is at what flow rate it can maintain a standardized depression, that is how one can compare carb to carb. That doesn't compare quality of signal, metering, enrichment, etc. That job is up to Us, We use the products & evaluate them in the real world, and it's possible to bolt on 3 different 750's and have totally different performance/driveablity/efficiency characteristics...which one is for You & Your package? I know of a Guy that owned a machine shop that became so frustrated w/a Eddy Perf on His son's car, He took a hammer to it. Yet a friend of mine put a street TR w/2 of 'em on top of a 350 I did a set of camel-back heads for, only a Comp 280 Mag cam w/1.6 rockers, ran fine. 2 cammed 350 chebbies with over 9:1 squeeze, 750 on RPM & (2)500's on Eddy Street TR. Many variables there, and I have more of those, like a 440 GTX w/a 2x4bbl "low" intake w/2 600 Perf and it coughed and spit every time He nailed it. The pump shot didn't cover it, wasn't My project, but you could hear the weighted flaps snap open then back when it coughed. Yet again a member here had a pair on a smaller mill that worked for them.
A conservative goal and operation is better served with a like choice. Of course a 750 pumper will get You a better 60ft time, if You've got enough pump shot to cover the air stall, they always produce the best times. For a cruiser with occasional romps, how will one affect plug condition/life & mileage? Just sayin'.
They do publish those, the problem is booster size/design affects flow & signal independent of the other 2 parameters, what You say is correct if You are staying within the same brand and design of carb.
I feel like your back pedaling.
Not all carbs are giving this information out.
I think they should though. But that might add confusion.
racerdan80
Well-Known Member
@1Badcolt , my 318 currently is stock internally. D453 headers into duals, msd ignition with 2 med springs, 10 degree initial with 20 mec for 34 total. Eddy performer. Higher stall converter, about 2800-3000. 3.23.-1 gears with 26” tires. The street avenger carbs like my 670 has an adjustable secondary by changing springs. I can open it early with the lightest, or restrict it to about 50 percent with the stiffest. On a fairly worn 318 I still had great throttle response and decent mileage about 17-18 at 60-65 mph. All around good carb and very tuneable
That's a right purdy little motor.
Really what other better test do you need than on a drag strip with back to back runs within an hour of each other. So this is not misleading at all, these were actual experiences on track not some controlled test (what like a dyno?) which is no way more reliable than real life track situations.
We are obviously talking about performance here as I mentioned previously, its rather obvious not a stock street car that will rarely or never see 6k+ rpm. As it happens I was still using my 850DP with a 50cc front pump on the 340 for street driving at that time and there was a noticeable improvement even at the stall speed of 3500 rpm but I didn't have 2.76 gears a .420" lift cam with a 600cfm carb, stock manifolds and converter. And if you can tune twins and have the right combo they WILL outperform a single in most cases, probably by another 2 10ths.
Dartswinger70
Well-Known Member
I like the drag strip or open it up on the highway test myself, only you behind the wheel will know if its running strong or not. Numbers and calculations mean something to those that are into numbers and calculations.
Pretty respectable mileage
Dan the man
Well-Known Member
I'm sure that most on here know what I'm wanting to do with the car I get. From what I've read, if I go from a 2 barrel to a 4 barrel that the edelbrock performer intake wouldn't be worth the effort. Also, the rpm's that my engine would be operating in most of the time wouldn't a 600 cfm be plenty for a 318? Cylinder heads, doesn't the smaller ports make good power in the low to midrange area? Would cylinder heads with 170cc intake runner's be to big for a mild 318 or are they okay? Cam, single or dual pattern grind? I'm wanting good throttle response and acceleration with good torque in the low to midrange. I'm not worried about doing major upgrades later as I'm 62 years old and don't care about racing anymore. I'm wanting a cruiser that's fun to drive and has a little extra zip. When I first said that it's a budget build, I do have amount planned for the car and engine modifications, gears, and a good exhaust system. If the cylinder heads wouldn't be cost effective to get them redone, then what would be a good choice for a set of heads? I figured that I could build a engine whether it's a 318 or a 360 to perform well from off idle to around 5,000 rpm's. I appreciate all the help, advice etc, but I truly don't think that I need tunnel ram or a blower to reach my goal.
Dan the man
Well-Known Member
I was thinking, would it be a good idea to get cam specs first and then select the rest of the combination, as the compression ratio, tire size, gear ratio, stall speed converter, intake manifold all need to coincide with each other in order to get the best performance from every performance dollar spent. I'm wanting to get this right the first time, LOL
After the basic idea of what I want to do comes to mind, it’s camshaft contemplation time.
The Performer intake isn't totally worthless. It's a bit better than stock and aluminum, too. I've seen some on 11 second cars. lol For a stock to relatively moderate build, they're a good choice. If I didn't have an intake at all, I'd honestly probably look for something different, but if I had one, I wouldn't go out of my way to replace it.
Page 4 ... you lost me back about 3 stop lights ago, you turned left? Opening post, we were talk'n 360? I read this ^^^ this morning, and we are working with a stock 318 2bbl? Ok, whatever it is that you are trying to do for whatever car, just get an eddy performer intake with a 600 eddy carb and electric choke. That should cover all the basis even if by the time I catch up and were talk'n 383 in a C - body !!! LOL Good luck !
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