Im just wondering why Stromberg 97's became so popular over 94's or 81's and other 2 barrel carbs. I have read that 97's have a higher cfm rating, but with a multicarb setup is the extra cfm needed? What benefits do they have in multicarb setups? Are they easier to tune? Better driveability? The reason I am asking is Im building a flathead for the street with plans of a multicarb setup (3 carbs maybe even 4). I have noticed the obvious value of 97's is a good bit higher. I did a search for this and did learn a good bit, but didnt really find what I was looking for. Thanks in advance for any input and help.
It is kind of traditional to use the 97's, especially the large logo, mostly for the looks, you can get the CFM you need from 94's or other 48's, 81's too. The 81's are more desireable and more a lot more expensive because they are harder to find. Hot rodders like the look of the 97 style, with the accelerator pump and rod, etc.. You can use the 94's or 59's or any 3 bolt 2BBL with about the same overall effect and the 94's usually cost a third or half of the Strombergs. I like both Holley's and Strombergs and they are easy to rebuild and dress up and give you a lot of options on a build.
It's true they do look better but you better know what intake your going to use as well. Some intake were just made for the 97's ,like a 4x2 for a flatty,6x2 for a redram hemi. Were the 94's etc were just a bit too long and don't fit. So if spacing is not a problem your Golden
I was going with 97s till.....I bought 4 matched 94s in GREAT condition for $300!!!! I then sold 2 un rebuilt 97s for over $300!!! and I get more cfm out of the 94s. Stromberg guys will tell you "they are not strombergs" but Holleys have been around and used for a long time.
this has much more to do with the 97's ease in setting up for multi-carb applications vs. the 94. 94's have power valves that dump too much fuel when getting a weaker manifold vacuum signal, vs. 97's which have power jets that are mechanically operated. an engine only produces so much vacuum. more venturi area = less effective vacuum at each carb. plugs can be purchased to block off the power valve circuit in a 94 but this obviously eliminates the power circuit and makes the carbs harder to tune in a straight, non-progressive linkage setup, creating a potential dead spot. multi 94's are best run in a progressive setup with the primary carb running the power valve, and careful selection of the vacuum value of the valve will be required. 94's also have a higher cfm rating and this must be taken into consideration for your selection of carbs for a multi-carb setup as well
What continentaljohn says is true about the spacing on some manifolds - Edelbrock Flathead 3x2 to name one, designed for Strombergs only. The main thing about Strombergs vs. Holleys is the ease of tunability you get with Strombergs; they don't rely on vacuum for enrichment like Holleys - which can be an issue if you have any kind of cam - but rather a mechanically actuated powervalve that can be tweaked simply by changing the stroke of the pump rod on the "S" or "W" balls. In redneck terms, the pump rod signals the powervalve, by way of the accelerator pump, telling it when to come to the party and how much beer to bring. Jet changes are a snap too. Simple is good.
94s can look as good as the 97s. Here's a photo of my 57 Ford with 3 Chrome 94s on a 312 engine.---TwoChops
Zig Zag,I'm going to disagree with your vacuum theory.It's been my experience with reasonable multiple carbs(like two carbs) that the vacuum seen by the intake manifold under the throttle plate remains the same as for one carb.What does change is the air velocity through the venturis.Additional venturis slow the air flow and reduces the venturi vacuum signal seen by the main jet circuit.Now my experience is not with Strombergs but manifold referenced power valves, so I may be full of shit .If so tell me
i bow to your superior definition Tony, much more eloquently stated than mine... yes, when the throttle plates are all closed the vacuum signal is no different than a single carb setup. the air velocity thru each carb drops respectively because of the increased venturi area. vacuum = negative pressure velocity = volume
81's were the V8-60 stock carb. They have smaller venturis, and are a lot more rare. Smaller acc pumps too.
Throttle closed vac will be about the same, but is irrellevant to the PV's, which feed through the venturis. Issue is that vac drops off very quickly with more carbs opening, and sometimes PV's will thus be open all the time the venturis are working. Most applications will need PV's that open at a lower Vac than stock, so they operate as intended, only at large throttle openings.
Good post on a contriversal topic....... The 97 uses a mechanical power valve that isnt affected by the vacuum making it the choice for the multiple carb guys. The vac operated valves on a 94 are a bit harder to tune , especially years ago on multiple carbs. I dont think its the number of carbs used ,as much as MOST change the camshaft as well as the carbs. The so called BIG camshafts (increased lift and duration) are the vaccum killer and must be delt with. Bruce a question ? Most of the 94 power valves are rated at 4-5-6-7-8-9 etc , i have always thought that was inches of manifold vacuum. Are you thinking venturi vacuum could equal 6-9 inchs of vacuum??
what kind of car are you putting the motor in that might help make up your mind. if you goung to run 3 carbs with prgressive linkage you cant beat the price of 94's with plugs for the pv on the outer carbs, early ford hotrods just dont look right with 94's (to me) later do?
No...venturi vac is pretty small, and here there's half the flow, as well. I'm saying that with multiple carbs, vac will drop quickly because more holes are opening, and this can tip in the power enrichment too early in main circuit operation, especially on smallish engines. I think 2 factors pushed 97 popularity...as noted above, multiple Strombergs will do fine just bolted on, while 94's need tinkering, and second, racing image...racers almost always used Strombergs in early days, not just for simplicity in general but because fuel use was very common, and only the Stromberg is readily converted for alcohol or nitro. Rodders on the street wanted to emulate the hard core racers, just as more modern rodders chose Holley 4's rather than Q-jets.
Ah, but it does have to do with the # of carbs - because vacuum "seen" by each carb is total vacuum divided by # of carbs. So if you've got 15" at the manifold, the most each carb will see is about half that. Yes, those are rated in "Hg. I don't think that's what Bruce was saying, but I'll let him explain it. How I look at it is the PV are held closed by high vacuum and open under low vacuum. Where they open is the number on the carb. You want to start tuning from about half the vacuum seen by each carb. If you had a single carb & 15" of manifold vacuum, I'd start at 7.5 PV. If you have the same 15" manifold vacuum & two carbs, I'd start at 3.5 PV. If you've got a big cam in there (you're right, it does affect vacuum & hence, PVs), I might start out at 3 or maybe even 2.5"
Venturi vac (usually called V drop or V signal) has only indirect role here. PV is actuated by manifold/ported va direct from under the carb. It will start off about same as engine with one car, will drop more rapidly that single carb and so kick in PV early. Venturi signal determines here when venturi will actually start drawing in gas. This is gas from main jets and from power valve if it is open...venturi signal will be essentially divided by number of crbs, will reach a useful point later/at higher RPM than a single carb installation, increasing the importance of the role of the off-idle/transitional gas delivery circuit downstairs. As long as there ain't enough venturi drop to draw in gas, it actually doesn't matter what the PV is up to, but generally you don't want it already open when venturis start working.
I don't know everything, but I do know that if you are trying to tune the engine, and your multi-carb set up is not just a show job where it opens both, all, or two period....it's not for the backyard hobbiest. Granted you can buy linkage to make it work progressive and such, but to actually know when and where and position of the fulcrum and all that crap you need some experience. I don't have any, but been around a few fools in my life that tried to pull performance out of a multi-carb set up on V8s of various makes. If you are running more than two carbs buy a book, or find someone who knows. Just my take on the stuff.
Agreed...... However just for the sake of discussion lets add the position of the throttle plates. Three carbs with closed throttle plates would ( in my thinking) ALL see the same 15 inches ( or so) of vacuum below the throttle plates. Its only when we open up the holes so to speak that it would divide. Right ??? Then the volume of vacuum ( or pressure as some would say) would change.
Ran an experiment on a 386ci flathead I built for my hiboy a few years back. I installed thin alum. plates between the end two 81's and the manifold and also blocked off the fuel inlet fittings and ran a Stromberg 48 in the center as the only operating carb. Nice crisp throttle response. Maybe a bit under cfm req. at the upper range but it really let the torque from the stroker come through. If you like to twist your flattie that's a different matter. Finally felt a little guilty not using those neat little 81's at all so went to a progressive but then had to play with the idle all the time. Looking good is easy..running good....
Ok, so I know I'm a few minutes late to work here, but I think this thread deserves a little attention since it was helpful to me and my 94 that has to run at temperatures between -45 and -20 F this week (yeah Fairbanks is warm). It is important to know that manifold vacuum is not "divided" no matter how many carbs or holes you have. If the manifold reads 11" mercury, then all the carbs will see 11". This is what the power valve will experience. -Big cams will lower vacuum. --Multiple carbs will see the 11" disappear faster as you open up the throttle plates. Venturi vacucuum is not really related to manifold vacuum. It can be thought of as venturii velocity. This works on a principle that says as you INCREASE THE VELOCITY through a converging-diverging nozzle (venturi or funnel like thing) YOU WILL LOWER THE PRESSURE. So the multiple carbs will see the VELOCITY "divided". Usually requiring fatter (richer) jets. Venturi vacuum should be ignored unless you are designing carbs, jets will take care of your needs. What has been said about power valves being half the manifold vacuum reading is correct for most people. Buy a vacuum gauge!!!! To recap - manifold vacuum is not divided. -multiple carbs will cause vac signal to go away faster with multi carb. -multi carbs will usually [require] changing jets depending on the linkage type. (a primary/secondary could allow you to have a mostly stock center carb for small throttle openings -- if the outer carbs are shut). Check your plugs for color!!!
"Carb King" in a post was saying that even in the most efficient multi carb set up (2X4) that due to inefficientcies such as linkage the most you'll get is 80% of rated CFM, 2 500s = 1,000 less 20% = 800 CFM. The more carbs you have the greater the inefficientcy. 4, 6, or 8 carb set up will be down quite a bit
I believe 97's were more popular was that they were older and therefore cheaper in the junk yard when Hot Rodding became popular after the war.. Also you could change the accelerator pump stroke to control the amount of gas discharged when the gas pedal was depressed. 81s were off V-60s and much smaller also scarcer
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