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Thanks Chaps.
On to today’s ramblings…
As said before, the last drive out I had was a very gentle 16 mile cruise just to make sure everything was ok in the engine bay, but I did have one very small blip of boost, just to check I had not over done the waste gate preload.
You are looking at the yellow trace here.
So cruising at around 62MPH, 3200RPM, ~74 Kpa and 34% TP
Hit the throttle up to 75% at which point the Corrective Realignment Automation Processor took over control of the car, calculated I was too close to the nearside bank and did its normal overcorrection to the offside.
Being brave (ish) I held my ground until peak boost – A whole 4MPH faster…
Anyway, looking at the logs to work out why boost rose quite as quickly as it did, I notice that during cruise before the blip, it was actually reading ~116Kpa pre intercooler.
Not only that, but on cruise I had 112Kpa of pre turbine back pressure.
So, my theory:
I have a cheap Chinese recirculating dump valve installed, which is currently plumbed in so that post compressor pressure cannot push it open, so it relies solely on Plenum signal pressure to suck it open.
I have been out to the garage and tested the DV with a syringe.
The valve opens under vacuum at 50Kpa, so anything above 50Kpa MAP and the valve is tight shut.
Coming back and looking at various other parts of the log, this does seem to compute – 50Kpa and below Pre intercooler pressure reads at atmosphere
55 - 60Kpa I start to see slight Boost at both pre and post intercooler and slight exhaust pre turbine back pressure.
So on the one hand, I have boost being produced even when cruising, which seems to help with boost build when needed, but on the other hand, it means I have pre turbine back pressure which I assume will hurt both full economy and power.
So if I adjust the dump valve to a very weak setting, say opening at 95 Kpa, will this have the effect of:
a) Reducing pre turbine back pressure and giving better economy and more power off boost?
b) Allowing the turbo to be more free running and assisting with spool up?
c) Partially bypass the compressor housing when off boost and reduce flow restriction in the inlet tract.?
This will be the next thing to play with once the sun comes back out to play.
Edited by Graham T on 18th May, 2019.
’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189
Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675
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