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Old 08-11-2019, 12:07 AM
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eschaider eschaider is offline
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Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4.6
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Some how I missed this thread when it first started. Couple of thoughts on the self tuning and knock protection.

Self Tuning

My experience has been that as Bob (Moore) and Olddog have already said / implied the self tuning leaves more than a little on the table tuning-wise compared to the results a skilled tuner can provide. However, it can easily get you up and running tuned well enough to allow you to finesse the tune to what you need should you want to take a shot at the job. Alternatively it gets you running well enough to drive the vehicle to your tuner to have him finish the job.

By far the MAF (Mass Air Flow) based systems provide the most consistent tune across all environmental conditions, altitude, temperature and barometer. The reason auto manufacturers use MAF based systems is it allows their vehicles to meet the strict emissions targets anywhere in the country or world for that matter.

A Speed Density system can be easier to tune because it is volumetric efficiency (Ve) based and infact you tune it by manipulating the engine's apparent Ve across the Fuel Ve Table. The task is not particularly difficult but if you change anything that affects Ve you end up retuning the engine. Additionally if you go to altitude or sea level the tune changes again because of engine Ve changes attributable to altitude driven air density changes. If you change cams, carbs, manifolds, mufflers etc the engine Ve changes and a retune is required.

With the MAF based system the MAF measures the actual mass of air in Kg/hr, g/sec or what ever your particular system uses to gauge the air mass entering the engine. Once the ECU knows the air mass it can calculate the fuel volume required from the AFR or lambda commanded in the tune. You can change anything you want on the engine and the MAF will accurately measure the air mass and the ECU will calculate injector pulse widths required to deliver this fuel volume.

The MAF is an extremely important component of the MAF based EFI system. Because of that you need the best you can get. Pro-M offers that MAF. The 5 minute YouTube video here => MAF Signal Quality shows you what is possible.

DIYATOTUNE (<=clickable) HAS JUST ANNOUNCED A Plug and Play (PnP) version of their MS3Pro system that uses a stock Ford OEM engine harness and all the OEM sensors so you don't need to buy high dollar EFI manufacturer GM sensors and connectors at elevated prices. The Ford harness is easily available from salvage yards or new from Ford. The systems even come with a base tune that is good enough to drive to your tuner or begin to tune yourself if you are so inclined.

By transplanting the Ford harness and sensors to your engine and changing the engine displacement in the ECU, to what ever you are running, the system suddenly becomes specific to your engine.

Because there are so many different MAFs available, the system is delivered as a Speed Density system. It is easy to add your MAF xfer function and convert to a MAF based system. As a nice extra attraction available at no extra cost is that they also support an improved model of the OEM returnless fuel system allowing you to run big power pumps w/o pumping big fuel volumes around at boulevard causing speeds.

Knock Protection

The MS3Pro has a lot of engine protection features built in that you can choose to use if you want. One is knock protection. It actually does pull back on a cylinder by cylinder basis and then roll timing back in until it "hears" the characteristic sonic signature of knock. Once it hears the sonic signature it pulls back just far enough to avoid knock. It does this on a cylinder by cylinder basis in real time.

There is actually another knock detection and suppression system that is even better. It is the J&S Electronics (<=clickable) family of knock detection and suppression systems. J&S has been doing this stuff since the early 90's (possibly earlier) for the Turbo Buicks.

The J&S system identifies the knocking cylinder so quickly that it interdicts the detonation event before the next ignition event, in real time and on a cylinder by cylinder basis. Like the MS3Pro ECU it pulls back a programmable amount of timing at the first detection of knock. ON each subsequent ignition event it comes half way back and listens for knock. When it detects the second knock signature it falls back to the last safe ignition advance for that particular cylinder.

The J&S product(s) do this in real time, on a cylinder by cylinder basis even at peak engine rpm. They offer systems for distributor, coil on plug, coil near plug and just about any configuration you can imagine and for any type of engine n/a, supercharged, turbo charged, nitrous etc.

If you run a boosted engine and you do not use knock detection / suppression technology it is only a matter of time before you kill your engine.

Parting thoughts 14.7 AFR was for pure gasoline. If as most of us you get 10% ethanol gas at the pump the ethanol changes the stoich point to 14.08 and richens the max power point correspondingly. For boosted engines it will move the max power AFR from 11.7-ish to approximately 11.2-ish. Especially on boosted gasoline engines you will want to go slightly to the rich side and moderate your timing expectations.

Closing Thoughts

The eight stack system is not impossible but, it is difficult to use in a MAF based system because you need to seal the stacks to a single air box that draws the air through the MAF. Not impossible but the air box must be air tight or unmetered air will enter the engine and screw up the injector pulse width calculations.

A Speed Density system will be a breath of fresh air on an eight stack system because it does not use a MAF. That makes it very easy to use the eight stack system without hiding it under some type of air box.


Help them do what they would have done if they had known what they could do.

Last edited by eschaider; 08-11-2019 at 08:07 AM.. Reason: Spelling & Grammar
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