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140/164 Series General Forum for the Volvo 140 and 164 cars |
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Modifying a Stromberg 175 CarbViews : 2527 Replies : 13Users Viewing This Thread : |
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Aug 30th, 2021, 20:17 | #11 | |
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Location: Saskatchewan, Canada
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Your dyno guy may be suffering from 'digital EFI think' where it would be easy to tweak specific cells in a fuel map to push that AFR from 13.4 up to 13.7 around 5000 RPM. I suspect the Stromberg doesn't have that ability to adjust fuel delivery at 5000 RPM wide open throttle without having some knock on effects at lower RPM. Your AFR does seem to be excessive at around 2200 RPM; but, if part throttle AFR at 2200 RPM is good then wide open throttle AFR at 2200 RPM may not be an issue. On the matter of potential modifications to the Stromberg to improve flow, you might want to consider mapping the manifold air pressure during a dyno run. New MPX 4250AP MAP sensors are fairly inexpensive (about $35 Cdn); but, a salvaged MAP sensor from just about any car will likely fit the bill (our local pick and pull salvage yard had a flat $5 charge for any sensor pulled from a wreck). The sensors almost universally have a 0-5 volt linear output and you can usually find the slope calibrations on line. With a 5 volt power supply, an analog input data logger and the sensor you can record your actual static manifold pressure during engine operation. If your manifold pressure is running just 3 or 4 kPa below atmospheric pressure during peak RPM wide open throttle conditions there is probably nothing to be had by beating your self up fiddling around with the Strombergs. Last edited by 142 Guy; Aug 30th, 2021 at 20:20. |
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Aug 31st, 2021, 21:44 | #12 |
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The richness at about 2.2k showing badly on the AFR graph is mirrored slightly on the torque curve. The needles might like a bit of extra meat there but probably makes the car feel lively too. Good set of curves. Smoothing the bridge would I think reduce the atomisation at lower revs and that isn't good.
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Sep 1st, 2021, 07:29 | #13 | |
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The idea of the porting post bridge is to make the air flow easier the same as at the front of the carb with stub stack at the entrance. It's opening up the area at the outboard side of the piston. Tapering the lower front and rear edges of the piston is suppose to improve throttle response. There definitely is extra Hp to be had with more carb.
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Sep 1st, 2021, 14:12 | #14 |
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Years ago I rounded the front of the pistons on my B16B. Didn't notice any difference. My comment about keeping the bridge sharp was because at that point the fuel is being sucked from the jet so having the smooth airflow changed to "rough" helps the atomised air in the inlet manifold. It doesn't want to drop out of atomisation onto the walls of the manifold. This can happen with the alloy manifold as it runs cooler than the cast iron one. The GT one piece is the best of all of the various one and 2 piece setups. The alloy inlet looks cool but it may be too cool at times!
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