Hey fellas, I have a couple questions about 97 tuning. My set up is this: Basically stock flathead v8 with a 4-71 blower and 2 97's. Before the blower I was getting great milage, but now not so much. The car runs really well, but is not yet 100%. My theory is with the virtually nonexsistant vacuum signal due to the blower, the power valves are enriching most all the time. I know it is very common to block off the power valves on Holley carbs on low vacuum setups, and then jet up 4-6 sizes to compensate. I have not heard of anyone doing this with Strombergs. Is there any reason why I shouldn't try this? If anyone does have exprience with this, is 4-6 jet sizes a good place to start (like with a holley). Also, I rigged up an O2 sensor, so I am sure it is over rich. I made up a cheap and simple way to do this and will tell you about it after I take some pictures of it. Thanks Crusty
Stromberg power valves are purely mechanical, and are pushed open when the accel pump bottoms out... Vacuum issues here: You still have vac between blower and carb anytime engine is drawing more than the throttles are open for, just as always...but numbers may be different. Downstairs, you have vacuum when blower is not boosting, which I think is much of the time at light throttle openings.
Issues...is air draw at very low throttle now enough to screw up delivery through off idle system?? What's different now? Carbs are upstairs not pressurized, but something has changed. Carburetion may be a bit small for blower notor, but I don't think radically enough to overload venturis to point of dysfunction. And--you cannot functionally make up for power valves through main jets except at full throttle. Engine will be too rich to make power at lower throttle, and rings will wear out in as little as a few hundred miles with seriously rich mixture!
So your saying blocking them and jetting up would make no difference? Maybe the main jets are my problem, I still feel like that big air pump (blower) is "****ing" the fuel out of the carbs with all the increased air that is moving through there.
How do plugs look, and are any different from others?? Are pumps on summer setting? Pump shot may be an issue some of the time here.
Yeah, I was expecting that. But it REALLY decreased, just looking to get the most bang for my buck out of it.
You might be getting the same issues as experienced with tunnal rams. The large plenum and smooth draw thru the carb makes the mixture richer. The flow in a regular manifold pulses and the carb has to be set richer as the fuel flow does not catch up to the air flow. I would put some 42 or 43 jets in and see what happens.
More draw might actually improve mileage, or at least control--it would get the engine running on the venturis lower in the RPM range, and out of the poorly controlled off idle system...problems would only arise as venturis were overwhelmed and pulling substantial vacuum at full throttle. I suspect main variable may be somehow in effects on off-idle circuit...or entirely external. What are you using for aircleaners?? Most hotrod air cleaners are ****.
Thanks everyone that gives me some ideas to toy with. Flatdog, I'm going to try a few things and call you if I get stumped again.
What are you using for fuel management eg fuel pump regulator ??? If all you did was add the blower I would suspect a lean condition. What is your final drive ? All of these can effect how the carbs react When adding a blower.
Hello..Bruce is correct about the Power Valves, "machcanical"..What type of fuel pump are you using, are you setting the pressure to the 97s at 2.5 psi..Also the needle in the power valve can be bad and open at all times....Lots of Flatheads with blowers and running great.. Duane.
I got rid of my 97's 97's are leakers and don't flow much air they had enough meat in the castings so you could bore out all the fuel p***ages to run alky -nitro and you could put in an adjustable jet system like for idle adjustments i like to use carter wcd 2 barrel carbs much better design. used on 30 's gm to 70's amc. 1 3/16 venturi balanced float chamber. metering rods adjustable outside the carb body. My brother had 4 on his hemi dry lakes car so i put 3 on my t bucket worked good on both cars retired ford engineer
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