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Fast951 Fast951 is offline
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Join Date: Jan 2003
Location: Atlanta
Posts: 181
I developed a WI system for the 951, I also experimented with WI on my type IV 914 supercharged engine. WI works, however unless you tune for it, you will actually lose power. Once tuned properly, addressing ignition and AFR, the results are respectable. As a example, on my 914 supercharged air cooled engine (converted to EFI running a Motronic system), I was able to increase the ignition timing anywhere from 8-10 degrees while under boost. This alone raised the power!

All this is nice and dandy, however there is a huge risk. Unless the WI + Engine management are working as a system, things can go wrong very fast. There are a few things that will cause a WI system not to operate properly or to fail. Unless you can catch and handle the fault, you can hurt the engine. This what most WI suppliers don't tell you.

Let's assume you advanced the timing 3-4 degrees (probably more), you raised boost by a few psi and leaned the mixture some (all over what is safe to run without WI). If any component in the WI system fails you mast capture it, be able to reverse to a fail safe state (lower boost, lower ignition, richen mixture back to a safe level). Some of the possible failure points on a WI system: power loss at pump, damaged pump, clogged nozzle, stuck solenoid, clogged filter, lost in line pressure are possible problems. Based on this information, you can imagine the complexity of a fail-safe system. If you track your car, the chances to recover from a error must be done without user intervention, there is no time act fast enough (electronics react much faster than me).

On a CIS engine, there are not many things that can be switched to fail-safe mode other than boost. So if you add WI safely you can just raise boost (as it's the only variable that can be controlled electronically). Not being able to alter ignition and AFRs, renders the use of WI a bit useless.
When using a multi-nozzle system, failure areas get a bit more involved. What happens if one nozzle clogs up? There is nothin on the market to detect this fault condition.

Ideally you want the engine in addition to monitoringthe WI system. If you have a Intake Air Temp in the intake and a EGT in the exhaust, monitoring both and triggering a alarm when things are not fine will be another layer to protect your engine.

A WI system on a 930 will be great. I plan on adding one once I'm done converting my 930 to EFI (using the Motronic, MAF & Wasted Spark). Both WI and Engine management will be integrated to handle the possible failures.

As a alternative for WI for the 930, a intercooler spray bar will help. Keeping the intercooler cold raises its efficiency and indirectly makes more power.

Lots of claims and marketing behind various WI systems on the market. Research every system! It's easy to design and sell a WI system. However designing a truly fail-safe system is not simple, and will cost a bit of $.
Old 02-06-2009, 06:40 PM
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