Kids, I'm putting together six 97'S on a Drag Star intake for my Nailhead motor. These motors love lot's of fuel and I don't mind running all 6 carbs but I would like to hear from anyone that has run six Strombergs........Do you run 2 carbs, four carbs or all six? How 'bout the main jets, did you block the power jets, progressive linkage?.............I did a search re: stromberg 97 and found lots of great info on these carbs but I need more information on tuning six of 'em! Thanks Uncle...............The motor is a 364, very stock.
The last 6x2 rig I did went as follows: Two center carbs with .045 mains and # 65 powervalves; four end carbs, using progressive linkage, .043 mains with # 69 powervalves. You want to go skinnier on the end powervalves to prevent bogging when the 4 slaves come to the party. The old thinking was to remove the chokeplates for more flow. Not true. They're there for a reason, to provide a smooth airstream over the open ends of the discharge jets for proper atomization. Stromberg's love unrestricted air gathered from a still source. If you use scoops, turn them to the rear. All idle speed and idle mixture settings are done off the two center carbs. The idle circuits in the four end ones can be disabled simply by turning the mixture screws all the way in snug, assuming you have nice tight throttleshafts and bushings. Since you didn't give specifics, like displacement, altitude, cam etc, these suggestions are just a good starting point. If you want to be married to your carbs, just fuggedabout progressive linkage and run them straight . Have fun!
Uncle Max, do you think the engine is going to run fat.. 1.5 CFMs per CI, figures about 550 CFMs, his 364 "very stock"..??????????? I'm thinking block off the two center ones and run the smallest jets and power valve on the four outside ones.. 6x150CFMs is 900 CFMs, thats a lot of fuel for a "very stock" engine.. ?????????????????????????????????????????????????????????????????????????????? Duane.
I was told to do the same, run four and block the two centers. What size jets and powervalves would I need, running a 322 nailhead.
Bolt just the bases to the manifold...that way you can dial in the linkage, insuring all carbs open at the same time....of course, that depends on how many you plan on opening at a time.... If progressive, you're gonna want the secondary throttle blades sealing tight in the bores without sticking upon opening. Personally, I'd hook 'em all up direct, and leave the stock jetting in 'em as well. Dial in the linkage.....then a few runs and check the plugs. That'll tell ya what the motor wants. Good luck and post results.....6x2's rule when running good.
The 6x2 I was talking about is on a 327 Chevy, Duntov cam with fueler heads. He's near sea level on the East coast and checks in with me from time to time telling me how well it runs. CFM requirements are one thing, but the volumetric efficiency of any particular motor plays an important part too. Usually, the motor will only pull as much CFM's as it needs - there's plenty of guys running around with 500 CFM Holley 4 barrels on flatheads, when in fact, on paper a healthy flathead, according to your formula, only requires 300 or so CFM's. Then of course, everything changes at WOT, but who really drives with their foot all the way in it, all day everyday? Lean is mean, but dummy carbs remind me of toupees.
engine is going to run fat...900 CFMs, thats a lot of fuel The carburetor capacity does not provide any fuel - it provides air. The engine + your jetting choice determines how much fuel. If the carbs are too big the original jetting won't be enough fuel. I'm guessing, but the center 2 are probably what the manufacturer intended, and may have better mixture distribution than the end 4. They will certainly have better low speed part throttle response and gas mileage. I agree that all 6 are more than the engine needs - the easiest cure is to set the progressive to use only the center 2 until 2/3 throttle, so you only have 300 CFM unless you want it. I disagree on intake though. Forward facing scoops do cause turbulence (called buffeting) at the air horn in some carbs, so this may be a problem at higher speeds. Still air is definitely what you want, however, running the scoop backward will cause a vacuum in the carb above the throttle at higher speeds - not what you want. Although not stylish, a box containing all the air horns with a single big filter is the most effective - there's just no way it doesn't look like a coffee table.
And on the insufficiency of gas with too much air...note Max's method blocks only the idle port, not the off-idle, on secondaries; this is a potential help in getting across the bog when too many throats open. The off-idle circuit is all you have working for you for significant periods of time on a heavily over carbed engine. The jets are delivering nada or only part of their capacity as long as there is not enough air moving through the carbs to create a decent pressure drop in the venturis!
With some of these "secondary" carbs I've gone so far as to enlist the help of couple of ladies in sensible shoes (dikes) and nip the ends of the idlejets and bend them over - the jets, not the ladies - creating a plug. And, in some cases have been known to add a small piece of 3-M tape, between the base, gasket and idlejet passage. Trouble is, I can't tell a whole lot of difference from just turning the bleedscrews in snug. I'd go back to the dyno, but I broke the chain drive.
As you can see, the carbs are set directly over the ports in the heads. I'm sure the center two carbs could be run alone, but it looks like distribution of the air/fuel will suffer.
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