victor25

Believe I understand how your Alpha system works after re-reading the thread. My question is this then. For centrifugal supercharging, instead of using the pressure sensor in the black box, couldn't you just use an external pressure sensor between the supercharger and the throttle body. Then it would make the correction for boost just as if you went from high mountain elevation to death valley. That's like a 4 to 6 pound swing isn't it?

John Speake

The sensor (2 bar) would have to be located after the throttle body.... to measure true engine vacuum/boost.

We are working on such a variation of the Alpha-N for supercharged and turbocharged applications.

victor25

If the Map sensor was used as the primary source of data, then yes after the throttle body for sure. But I was thinking of it as a variable on your current NA setup with low boost. Do you know what I mean??

victor25

BTW ... Do you know why the throttle response on the 83, 84 is sooo much quicker than that the S4's are. Those cars really sounded great when you blip the throttle. They just bark!! Every S4, GT, and GTS I have dealt with has a slow throttle response, and that gasp for fuel when you hit the throttle. Is it the because the MAF is slower in response compared to the barn door? I would imagine your Alpha system cures that, yes?

John Speake

I don't think I fully understand you..... but here goes.

The map sensor measures atmo pressure to use as one of the airmass compensation parameters, combined with airtemp. That sensor air intake is accessable with ALpha-N. In fact Jim Corenman has fitted a tube to it which is located insude his airbox, so that if the pressure there is different to true atmo, then that is taken into account. SO that sounds the same as you are wanting ?

John Speake

The MAF sensor in an LH/MAF equipped S4 (S3) is much faster acting that the flappy type of AFM. (think upgrades for 911s, 944s etc)

A MAF is very fast. 20mS response time IRC. The flappy meter has to much slower due to the mass of the flap.

A well calibrated MAF is essential for good throttle response. ALso, have you tried experimenting with the acceleration enrichment of an S4 with your Sharktuner ?

I can't see that ALpha-N MAF-less is going to be an advantage over a MAF based system, but I 've not compared them back to back. Jim Corenman, having tried both on his GT could advise his opinion.

I would stick with the MAF system.

Mongo

Hey John, is this still in testing, or is production imminent?

I have stepped away for a while and didn't see any of the news yet on it. I will go back, digging through the pages of this thread as well.

John Speake

The MAP based system for TS and turbo systems is still in development.... other things got in the way. But we are now picking it up in ernest again :-)

Speedtoys

John: I will find myself in Cambridge again in the next # of weeks.

I wont forget to bring my MAF this time.

John Speake

OK ! Look forward to seeing you again :-)

jcorenman

This ^^^ was unexpected but true. When I swapped the working-fine-but-aging MAF in our '88 S4 (stock tune) for a JDS-rebuilt MAF, the transient throttle response was much improved.

But also, tuning is a big part of the equation. Besides transient fuel-enrichment (the "acceleration pump") there is also static and dynamic ignition timing that plays a large part. For example, the stock idle timing for a 87+ EZK is only 5-6 deg advance, where most 'hot rods" are tuned in the 10-12 deg range at idle. That seems to make idle less stable (another topic completely) but also improves the engine response from idle (the "throttle blip" that Victor asked about), as does optimizing the timing map and reducing the transient-retard.

Certainly the 20ms lag of the MAF is nothing, but the Alpha sure seems to respond quicker than the MAF. Again, a lot of it might be tuning, but driving the car the general impression is that the throttle pedal is more directly connected to the engine (which it is, in a sense).