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Dynamohum Dynamohum is offline
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Join Date: Jan 2008
Location: Midland Ontario Canada
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Originally Posted by 911st View Post
As to timing:

Could add MSD with boost retard.

We can also use the fuel quality switch on the ECU.

There is also the brown wire jumper at the ECU.

One could also move the timing sensor at the flywheel.

Suck v blow throught.

Turbos do not like restriction in the intake to the turbo which makes a blow through a positive.

However, there is temp sensing at the AFM. With heat it pulls back timing and fuel. This may or may not be a concern if we get enough fuel w pressure or injectors.

On the 944T Porsche did a suck through. I think that was up to about 270-300hp.

I think the early BMW M5's used the same size AFM and the euro was good to about 310hp.

I suspect the AFM on the intake is more restrictive.

Also turbo's pass oil. As such with a blow through there will be some coating of the AFM with a blow through.

One of the issues with the 3.2 system is after about 170hp the AFM bottoms out. After that it is a referance system. Not sure what would happen of we bottom it out at 3500rpm with a turbo.

This is part of the reason I was thinking we would probably have to tighten the spring on the AFM.

As Jim noted, loosening the AFR spring lets the motor go fatter earlier so that is something to think about.

Over on the 944T board there is a pretty cool product they are using. It converts the system to a Mass Air Pressure system using an interface computer in place of the AFM.

Seems pretty tunable and gets rid of the AFM restriction. I believe is also allows playing with the timing via the temp signal.

Having said all that Protomotive's Vacuum Sensing (now offered through dealers like S Car Go) is something to consider. Especially of big HP is a goal. He adds a TPS to the throttle body and a MAP connection so the AFM is eliminated (somewhat like the RUF Yellow Bird) It was about $2k and he gives you a program so you can burn your own chips.
I like the idea of the MSD boost retard MSD Boost Timing Master Ignitions -
It gives you up to 15deg of adjustable timing retard, which is great and not to pricey.
So how much retarded timing do we need while under boost from the stock maps?

Problem with using the fuel Quality switch on the ECU is that it affects the full range of the maps and ideally we just want to pull timing under boost, leaving idle and off boost cruse alone.
Also I don't know if we can get enough retard from this, the max I'm seeing is -2.79deg of retard. That said if used Position #6 on the fuel quality switch seems to best option with +6.3% of fuel and -2.79deg of timing. The Motronic Web Site Go to the left hand side and down to the FQS fuel quality switch button. Lots of Motronic info on this site.

Re: moving the timing sensor at the flywheel, would change the full range of timing, you could do the same by rotating the distributor, but that's not to our benefit. To maintain good drive ability, ideally we only need adjustment during boost.

I think JFairman and you are onto something with the output from temp sender.
I'm not sure how much they actually pull back or what this is capable of -3deg? Can this be confirmed? and by which temp sensor, the one on the cyl head or in the AMF?

more later
Thank You for your time, Paul. We do because we can.
87 911 3.2 (Turbo conversion, build in progress, Thermal Barrier Coatings, High Pressure Dry film coatings) Modified heads, boat-tailed case, ARP hardware, OBX Header, 930 clutch disk, G50 Trans
89 5.0 Mustang convertible (For Sale)
Old 01-27-2010, 07:28 AM
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