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fredmeister fredmeister is offline
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Join Date: Oct 2002
Location: Baltimore, MD, USA
Posts: 2,235
how to adjust VDO boost gage

I have a VDO boost gage in the clock hole location that reads a little low. It is teed into the brake booster line as per standard practice.
I verified this against my LM-1 gage that is picking up a sigmal off the recirculating valve housing or after the outlet of the intercooler above the throttle plate.
When the boost on LM-1 says 13.5psi the VDO gage reads 0.75 bar on the needle or about 10.8psi. Only explanation I have for the large discrepency is pressure loss across the wide open throttle or VDO gage inaccuracy.
My question does anyone know how to rest the needle on the VDO gage by indexing it a little to match the LM-1 reading which I assume is dead nuts?
I don't want to send it away to Hollywood Speedo to get charged for this....want to do it myself.

Second question is how much pressure drop should be expected before and after throttle plate considering the source of my signals to each gage as described above?

1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 03-11-2009, 12:28 PM
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