Wednesday, December 22, 2004

Fuel Injectors

I heard from Marren on Monday. They tested my original fuel injectors, then cleaned and rebuilt them and tested them again.

After servicing, they strive for less then 2% deviation between richest and leanest. Bad news, my injectors deviation was just over 10% - skewing to the rich side. Which means that one of my 38 Lb/Hr injectors was flowing over 41 Lb/Hrs.

I also learned that my injectors are made by Lucas. As in "Prince of Darkness" Lucas.
Marren does not have good things to say about Lucas injectors in general, saying that they have a typical deviation of 5-8% even when new and my 10% is typical of older injectors. They strongly recommend replacing them with Bosch injectors, offering a "drop-in" replacement for my Lucas injectors. Bosch typically has a deviation of 2%. Sounds good.

The problem is that the custom ECU software in my car was developed for Lucas injectors. Not just any Lucas injectors, but my 8 Lucas injectors. Bosch are a different design and have a different opening and closing pattern, and a different spray pattern than Lucas injectors. In stock applications the difference may be minor, in a 10.8:1 CR, 6.6 PSI forced induction application the tolerances are a bit tighter and a small difference can cause total melt-down.

The fuel system in my car was originally designed by Dinan Engineering and includes a higher volume fuel pump, adjustable Fuel pressure regulator, lots of braided steel lines, and the injectors. I spoke with them at length about the differences between Lucas and Bosch in terms of static and dynamic flow characteristics, spray pattern, and interoperability. Dinan stands behind their choice of Lucas injectors, claiming the Lucas "Disk" design is technically superior to the Bosch "Pinltle" in terms of opening speed and spray pattern. That said, they felt the a 10% injector to injector deviation is a "bad thing" in a forced induction application.

In addition to Dinan, I also spoke with a number of professional BMW racers, Turner Motorsport, BimmerWorld, EvoSport, and every single one of them recommended Bosch, many stating they would never, ever use any Lucas part in any race car.

There is a lot of conflicting information about this topic, making the decision quite dificult. I finally decided to buy a set of 8 blueprinted and flow-matched Bosch injectors, and hang on to the old ones just in case.

I should have them in a couple of days and will let you know how they work.

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