DR

Flott,

>Dave, I can now see why you are using a dummy MAF. You need to have the exact same volume of >air coming from both intakes since one side is not being monitored at all.

Correct, I did have a lot of experts tell me this was not necessary, but I wanted to be absolutely sure it was the same, PLUS I wanted to have the visual balance of the 2 MAFS. As a goofy side note it continues the "Twin" theme.. Twin Screw, Twin Throttle Body, Twin MAFS, Twin Air Intake System and Twin IC Radiators..:-)

> The fabrication of the intake and making one side as identical as possible to the other is crucial.
>I bet you probably even measured the length of the two air tubes to make sure they are precisely equal as well! Very nice work.

Yes, both sides are made from identical parts and fabricated/assembled here.

DR

Flott,

>One other thing, Dave (and John would have to build it, I guess):
>Did you ever give any thought to using two MAFs and desiging a "black box" >that wold read both voltages, average them and send the averaged voltage >signal to the LH and EZK?
>Dave, that is probably more complex than need be but wouldn't it provide a >more accurate air monitoring circuit?

I have had such a black box for over 6 months and my testing showed it didn't work as well as the new setup. Plus, I didn't get the side effect of having more MAF capability to enable additional power in the future. Also it didn't still drive and feel like a stock 928 which was very important for me. On top of that having a 928 specific programmer like the ST made a lot more sense than an aftermarket generic black box that doesn't give a fraction of the control over all of the original LH system like the ST does (which programs the 928 computers like the factory did when they developed them).


>Also, couldn't you then substiute newer (less expensive or more reliable) MAFs for our 20 year-old-engineered stock ones?

Tried that also (many different MAFs), the only thing that made the 928 feel like a 928 (within my capabilities and knowledge) was a stock 928 MAF.

>All that would matter is that the final, average voltage signal that comes out of the black box is compatable with our computers, right?

That is what I thought 3-4 months ago. But I felt starting with the factory settings and MAF and tweaking the LH to accomodate the increased airflow, fuel and power was much more simple and effective than starting from scratch with something totally new. Plus down the road when I am pushing up roses the 928ers will still be able to get the proper replacement engine management components they may need since they are stock replacements.

John Speake

[QUOTE=Flott Leben]John,

Am I correct when I state the following (very simplified, I know):

1) the MAF merely sends a voltage out to both the LH and EZK based on the air flow it sees across the hot wire, then:

a) the LH receives this voltage and based on the fuel map on the EPROMS decides how much fuel to supply (duration and width of pulses) and

b) the EZK receives this voltage and based on load (throttle body position) and a set timing mapping scheme decides how much to retard timing?

I know there are probably other sensors involved in the process but is that generally it?
>>>>>>>>>>>>>>>
Hi,
That is correct in general terms. The LH processes the MAF voltage (this requires some clever and precision processing). It uses this "load" voltage on then fuel maps, and also passes this load voltage to the EZK where it is directly used on the ignition maps
>>>>>>>>>>>>>>>>>>>>

Questions:

Does the EZK use EPROMS to set its timing mapping scheme based on MAF (and other sensors) voltage?
>>>>>>>>>>
Yes
>>>>>>>>>>>>>

If you can reprogram both the LH and EZK to react to the MAF voltage according to new mapping schemes, it doesn't matter what the voltage input from the MAF is, all that matters is what the LH and EZK are programmed to do with that certain input voltage, right?
>>>>>>>>>>>>>>
Effectively, yes. There are limits of course.
>>>>>>>>>>>>>>>>>

So, with Dave's dual throttle body set up, only half the air is traveling over the MAF hotwire and therefore sending only half the voltage signal. But the LH and EZK will interpret that voltage as twice the air and adjust accordingly. Therefore, the intake can supply up to twice the stock MAF’s normal air capacity and the system can still handle all the monitoring functions. Wow!! Hats off to you, John and Niklas, for producing these devices. You have made so much possible with use of the stock LH, EZK and sensors. All you need is new EPROMS.
>>>>>>>>>>>>>>>>
Well, you need to tune a car with the ST to produce the EPROMS. As there are variations between cars, then the best results will always be obtained with a custom Sharktune.

Regards

Flott Leben

Thanks, Dave and John. I think I've gotten a better understanding of how the systems work.

Dave, I didn't mean to abandon the ST or your tuning process. I meant that the black box would be added to your system, but with dual, working MAFs. Both MAfs would send their voltage signals to the black box which would do nothing more than average them out and send that averaged signal to the LH and EZK. This way any discrepencies from the non-monitored intake (of your system) would at least be accounted for in the averaging process (of the dual, working MAF system). The LH and EZK would still need to be tuned with the sharktuner to produce the desired fuel and timing along the air flow voltage range because the voltage would still be 1/2 what it normally would be for that amount of airflow. I can see how your system is simplier. I was just thinking that if we used modern MAFs that give off a signal in the same voltage range as our MAFs we might be able to get more dependable and accurate MAFs and MAF readings. Just thinking out load.

John - Understood. That is why Andrew's SC car did not run very well (if at all) with his stock LH EPROMs and ran lean with Dave's EPROMS tuned for Dave's SC 928. The best results will always be with sharktuning and remapping the fuel map on each individual 928 onto the EPROMs. Your system also provides one huge advantage off the bat - fuel delivery does not need to be controlled mechanically by a rising rate fuel pressure regulator. Dave is able to maintain close to stock pressure and control the injectors through the LH based on a properly calibrated fuel map, as was meant to be. What were your thoughts on the averaging method of the black box? Any real advantages or just a waste of time? Also, do you sell the EPROM burning equipment with the ST?

928autobahndreamer

Especially if DR is going to go after it with a plasma torch!!!

DR

Bend over while I get my torch ....

ew928

So with dual MAF's, one could theoretically be on the road and have a running
spare MAF if the active one chooses to go beyond LH's compensation limit.
Cool.

Double the pleasure, double the fun.

From college physics: To alleviate friction, Use lubrication.
Someone get Andrew "twice screwed" Olson a tube of Anti-Seize.

Ernest (NYC)

FlyingDog

This from the man who threw a hose at me for standing behind him while he was screwing Andrew's shark...

Flott Leben

Dave, if you are serious I can send you down my copy but at the stage your are at you are probably way past that book's level. What might help is a Bosch manual on LH and EZK mapping, if it exists.


Ernest, I thought about that, too. On Dave's system you have a nice compartment set up for a spare, good MAF. The only problem is that a hot engine bay with air flow running through it is probably not the best place to store one of those $400+ babies.

Bill Ball

I like this as it would compensate for differential filter flow if that happened.

DR

In all the craziness I forgot who that was... just be glad it wasn't a crowbar :-)

Thanks for being a good sport, but when I saw your shadow right behind me I just couldn't resist!!

Flott Leben

Exactly!! Thanks, Bill. That is one important variable - say a leaf or three is sucked up one of the tubes and clogs that filter or one filter gets dirtier than the other for some reason or any number of other things that could result in uneven flow between the two intake tubes.

DR

Flott,

>Dave, if you are serious I can send you down my copy

I am serious, I have purposely not read anything like that because I prefer to come to my own conclusions from my direct experience/testing. Heck, come to think of it I don't think I have ever seen one of the Supermodel kits installed in a 928 in person until this weekend.

>but at the stage your are at you are probably way past that book's level.

No way I can be compared to someone like that. I am still learning everyday, but as I have said before I prefer to learn by doing and not reading. This has always worked better for me as I am not bound by what others say will or will not work.

>What might help is a Bosch manual on LH and EZK mapping, if it exists.

That would be very helpful as I still have a lot of learning to do, but John has been very forth coming in his ST manuals and with "therapy" via e-mail and phone calls , thanks again John! I have also learned a lot from the guys here on Rennlist and wish to thank everyone for sharing their information and experiance here on this forum. It benifits all of us in so many ways.

DR

Which would be the same effect when your MAF(s) starts to degrade as it will over time. This is why we supply A/F gauges and include the Adjustable Regulators so anyone can easily compensate for these variances in A/F ratios at WOT without programming knowledge. At idle and during normal cruise the computer will take care of such variances just like they do on a stock 928 (up to a certain level). Also with the clear tubes you will easily know if you have trash in your filters.

Flott Leben

Okay, Dave. You got it. Expect a little present or two late this week/early next week. I figure you need a week to recover from SITM anyway, right?