Knock sensor and idle concerns

Moderator: Hooter

Postby delco » Fri Mar 09, 2007 8:23 am

It is actually better to place the MAF after the supercharger/turbo as if it is in the inlet tract before the supercharger it is a restriction to flow.

Superchargers are not designed to suck but to pressurise air , any slight inlet restriction hurts their efficiency

When on the other side it is under pressure so it can flow a lot more air than it could if it was under atmo pressure. Also it can account for the air density change depending on your intercooler eficiency as well as not having the HUGE issues with blowoff air not being measured.

The part throttle blowoff is a huge problem on a superchaged car ( not so much a issue with a turbo as airflow is related to exhaust flow ) that has airflow related to rpm , part throttle on a supercharged car running moderate boost will always have the bypass/blowoff valve venting

The main reason people pushed for mafless on the intercooled V6 motor was the bypass valve is in the manifold so it is impossible to place the MAF after this bypass so it causes huge issues in drivability , placing the MAF on the inlet has issues as well since there is so much pipework that the pcm sees a lag from when it sees the extra air to when the engine actually gets it creating another divabilty headache.
Posts: 31
Joined: Wed Aug 03, 2005 4:21 pm

Postby Davo » Thu Mar 15, 2007 7:09 pm

ok, thanks for all the replys guys. I've been running my setup without a blow off valve and MAF on the charge side directly before the butterfly for 8 months now. What I have found is yes it does work reasonably well on the charge side BUT, you need to move it away slightly from the throttle body mainly because being so close to the TB means it's not a smooth flow of air passing through so mainly while idling for extended periods of time the flow requirements and actual readings go out of wack. 2nd problem i've found is the heat comming up from the exhaust eventually heat soaks the MAF aluminium body causing a lower than normal PMT value, which leans mixtures out slightly. If I was to start again I would have put the MAF 1/2mtr or so away from the TB and heat. Now the standard 65mm MAF is running out of range at 3600rpm! i've bought a 75mm unit and put it on the intake side of the charger (yet to be plugged in though). Another thing is i'm in the process of fitting and plumbing back 2 bosch blow off valves after the MAF including crankcase vacuum line. 1 valve is fitted now but at 4500-5000rpm + I can hear reversion so it really needs another valve. With reference to the air temp sensor (MAT or IAT) i've seen upwards of 100deg C (on the burnout pad, yes I give it hell!) so the metal unit holds up to this punishment just fine and it has a threaded section whereas the plastic unit would have to be held in with silicone and maybe a hose clamp some how. The reason for going to so much trouble is I need that damn blue plate to keep the cops happy :( I've purchased a chassis ear to find the ignition limit, then I want to know how to see what the knock counts are so I can set them in the table. What path do I use : LIST-MAIN- ???
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Joined: Sat Nov 18, 2006 11:23 pm
Location: Cairns, Queensland


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