Join Date: Jun 2007
Location: Los Lunas, NM
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1st question: My boost gauge at full boost reads ~9psi, however, the datalog at the dyno said my set up produced 10.94psi. I am at 5000ft elevation which calculates to ~2psi loss of boost. Does this mean that my boost gauge is 2psi off (low) of what is actually being produced? Disregard that peak boost number that was a temporary spike that probably lasted a tenth of a second. Boost osculates a little due to it being a large four cylinder engine. Every time an intake valve opens the boost pressure drops a little. My graphs have always been a little wavy. The graph is showing you are making 8-8.5psi.
I am in the process of installing a Megaquirt 3 (big thanks to the help of Kurt). When i start tuning, I want to run lower boost around 5psi to start. I currently am running an older style 38mm Turbosmart WG using an older Tial 8psi WG spring. The WG I am using has a larger diaphragm than the newer more compact TS WG's and uses a diaphragm for the larger 50/60 WG's. Does this mean that I need to also use a spring from the larger 50/60 WG? And will the psi ratings transfer directly to being used in the older style 38mm WG? I don't know this one. Bigger diaphram should be able to push on spring harder than a smaller diaphram. You have the larger diaphram so probably need a spring for that size diaphram. You may have trouble with boost creep trying to keep it at 5psi it may creep up to 8psi anyway because the wastegate may not be able flow enough air around your turbo to keep boost that low.
3rd Question: My AFR gauge at full boost reads 10.8 @ 4500rpm (pre cat) where the dyno's meter that was inserted into the tailpipe was reading much higher. Does the AFR sensor placement make that much of a difference? I agree with atheworld0. Your wideband should be much more accurate than a tailpipe sensor. Just being behind the cat makes a tailpipe sensor read about 0.5 leaner. If you have any leaks in the exhaust that would let in fresh air it would read even leaner.
It looks like it's running really good!
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