CFM Requirement for 289

[StudeRich]

quote:
Originally posted by 65cruiser (On another post)
What size carb would I need for an install like this? Recommendations?
Addedfor a four barrel carb added to a 194 Chev. 6)
Dick Steinkamp's reply:

Looks like in the 250-300 CFM range... (From here

http://www.4secondsflat.com/Carb_CFM_Calculator.html

Wow! this is interesting ![:0] what I found from this site (if I did it right) is that a 289 with 83% volumetric efficiency (VE), (considered normal for stock engine) at the normal redline of 5500 RPM, requires ONLY a 381.7 CFM Carb.![:0]

If you had 100% VE such as an R2 might have with Supercharging, []you still would need only 459.9 CFM's at 5500 RPM! Of course, like the detail instructions say: there COULD be many other things that enter into the equation. [^]
OR, if you had a fair flowing set of heads with big valves, fully ported and a R1 or better Cam and unsupercharged. If you were real lucky you might get in the 90's VE and STILL not need over 500CFM!

Looks like the 500CFM "Economy" Edelbrock AFB clone, is more than enough!




StudeRich
Studebakers Northwest
Ferndale, WA

[PackardV8]

FWIW, the 600 CFM Edelbrock/Carter is the most common loss leader advertised by speed shops. Not much reason to pay more and/or special order the 500 cfm. I learned this the hard way. The 500cfm actually cost me $50 more and all the difference is in the primaries. Go with the 600cfm if it is the better deal.

One thing to watch - the 600cfm can come in either economy and power calibrations. Get the economy calibration for a normally aspirated street car and the power calibration for supercharged or race use.

PackardV8

[60Lark]

I was standing at Ted Harbit's table at the Omaha meet and heard him tell someone that he recommended using the 600 cfm carb on a 289


Studebaker Fever
60 Lark
51 Champion
Phil
Arnold, Missouri

[Mike Van Veghten]

The statement "the difference is in the secondaries" is completely wrong. It's actually in the primaries. A different booster is inserted into the primary venturies. It's a big "plug" of sorts!

That said, as you have seen by looking into the "calculations" (good for you by the way!), a stock non performance 289 that will be used as a normal drive around town type car will most definatly run better with a well tuned 500cfm carbueter. Now if you have a hot rod with 3.70 gears or more and a R2 (or more) cam, and play at the drag races or such, the 600 may be a little better choice.

I've tried both, with and without spacers (over the 1/2" required for a bolt pattern change!). In all my playing with a Lark and a stock 259. The 500 produced much better low speed performance...up to about 50mph, where the 600 starts to run about even. The 600 will run better at higher freeway speeds, but as I said, the around town power WILL suffer somewhat.

You have to be realistic with the way you drive when you choose a carburetor.

Sorry to disagree with the bigger is better thought...but...
I guess most guys are just prone to that statement...!

Mike

[1956 Hawk]

Here is the difference between the 500 and 600cfm carbs:

http://good-times.webshots.com/photo/2432343970089385702geZMJr

David

[Mike Van Veghten]

Yep...see above...

Just a note for you "big" carb. guys....Barry Grants, Street Demon series carburetors has a 525 cfm, vacuum secondary carb.
So you get a big hot rod looking carburetor and big cfm.
I've never used one myself so I can't comment on how well they work, but they seem to be selling well.

May be worth a try.

Me....I'm gonna use two 390's on a home made cross-ram. I just can't decide on vacuum or mechanical secondaries! Vacuum would probably be the best, but I've always had good luck with the mechanical types..???
The car will be sort of a 50% / 50%.....street / weekend race car / mule for testing heads!

Mike

[N8N]

Speaking of carbs, I remember a long time ago someone posted that they had been in contact with a knowledgeable carb guy and was going to post some "baseline" rod/jet combos for common aftermarket carbs on a Stude V-8. I don't remember seeing the results of that post...

anyway, I'm a bit of a newbie when it comes to a carb, so I could use said info. I'm using a 650 CFM AVS on an R1, simply because I got a screamin' deal on it (the 500 CFM version would have cost me quite a bit more.) Anyone got any combos that work? I realize I will probably have to tune it in some more, but I'd like a place to start. I think it is likely currently a bit rich.

nate

--
55 Commander Starlight

http://home.comcast.net/~njnagel

[hank63]

The thing to remember about cfm, is the air flow. The bigger the cfm, the higher revs are needed to get the right air flow velocity. A big cfm might give more power, but you'd need to have the revs up to benefit. Too big cfm will be a pain at low engine revs, bad fuel economy and no power gain. There was a formula for it, but I have long since forgotten it. Perhaps the racing people can help out.
/H

[PackardV8]

Hi, Mike

FWIW, back in the bad old days, a race-prepped Holley 390cfm with mechanical secondaries and dual accelerator pumps was the best all-around carburetor I ever ran on Ford 289-302" and Buick 215" engines. I redrilled one Holley base plate to bolt directly onto the Rochester bolt pattern on the Buick. (Have to check to see if that also will fit an early Studebaker manifold.) It actually turned better 1/4mi times than the 600cfm vacuum secondary carbs. When a Holley 390cfm is set up with four-corner idle, it works especially well on a single plane or tunnel ram manifold when the engine has a strong cam.

There are lots of Holley 390cfm carbs for sale on eBay, but buyer beware, because many have been used in race cars and some of them have truly bizarre modifications which make them questionable for street use.

Have been out of the Holley business for many years, but I have a couple of 390 bodies and maybe enough parts to build them up. Will be fun to see if I still remember how.

thnx, jv.


PackardV8

[Challenger]

Well, in my little ol' opinion, carb sizing is theoretical, or practical. Theoretically, plugging in the inputs for a 289 Studebaker would indicate the use of a carburetor rated at about 500 cfm. In reality, carburetors in excess of that are used very satisfactorily. There was a kid running around town here with a 750 Holley on a 4 cylinder Chevette for several years, and he claimed it ran great. I don't see why a 600/650 cfm Edelbrock or Carter AFB-style carb wouldn't work fine. That seems to be the consensus, anyway.

[Thomas63R2]

For those who really want to go big there is this thing they call the "Flying Toilet" http://www.killerrons.com/toilets.cfm

A 750 VS Holley on a Chevette will never open the secondaries, so it will still run but why would anyone be taking tips from a kid racing around town with a Chevette?

When in doubt you should always run the smaller carb, especially for a street car.

Thomas

New Stude guy! Long time hot rodder
'63 Avanti R2 4 speed with interesting plans

[Challenger]

Well, the point is thomas--that even if you use a theoretically too-large carburetor, it probably will perform satisfactorily, anyhow. Because, as you said--the engine may not generate enough airflow to open those secondaries. So, why pay more for a 500cfm rated carburetor, when you can readily buy a 600 for less money? It may limit the performance of a large cid more to undercarb it, than to overcarb a small engine. Carburetor sizing on hiperformance engines is more critical when using competition-style carburetors with mechanical secondaries.

[1956 Hawk]

I had an 800CFM Edelbrock on my R2 for a while. Power wise it wasn't any better than the 600CFM. Drivability wise, unless I tuned it to run super rich on crusing it would have horrible throttle response. My dad is running a 500CFM on a 259 without any problems.

If there is enough interest I could convert my 600CFM to a 500CFM to see what power difference there is on a R2.
David

[Mike Van Veghten]

Challenger -

Boy you opened up a can-o-worms with some of those statements!!

The "runs great" statement. As opposed to what?
Does the guy "really" know what is GREAT?

Since many will install a part...any part, and have nothing to compare it with, (or compared the original two barrel!) if it makes more noise or a different sound...power is "mistakenly" associated with sound.

Or...they may not have taken the time to properly sort out a new tuneup that will best go with the new parts, may in turn think a part "doesn't help!

Another one..."satisfactory"... Who really wants "satisfactory"? I know I don't like just satisfactory! To buy a new 600 carburetor because it's cheaper....thAn a 500 (to me anyway) is a joke. So save for one more paycheck and do it right!

But you are correct to some extent about theorecical sizing. BUT...the difference between the minimum and maximum CFM rating isn't that big...especially on a street car.
People spend most of the time pulling away from signals or stop signs at what...maybe 1500 rpm? Who needs a carb. that makes great power at 5000rpm...when 95% of their driving experience is below 3500rpm?

Another thing, you want to see how a larger carburetor will run on your engine? Install a 1.00" thick open spacer under your existing combination. Open spacers add plenum space which in turn "slow" the signal from the cylinders to the venturies the same way a larger carburetor will.

But alas...I guess it "is" the American way...bigger is better.

Mike

[63Avanti]

Back in the late 70's a big fad was to up on BIG carbs on cars to "go faster" Car and Driver spiked that fad with an article with calculations, likely the same one you used, combined with some devastating Dynometer sessions. Bottom line, "small is better."

They did find one, and only one, exception to "small is better." If you are hauling white lightning down back roads being chased by "rev'ner's" then oversized may keep you out of jail. Then again, isn't that the way NASCAR started????




Terry, North Texas
1963 Avanti R2, 63SR1065
(in stage 1 resto "Project A")

http://sterkel.org/avanti

1985 Kubota L2202(Diesel)
2000 VW Jetta GLS
1999 Toyota rice burner