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1979-1993 & 94 Conv [Subscribe to Daily Digest] |
As SDP notes, you should gain at the high end. Here's how I understand Jetronic; someone correct me if I've got it wrong.
Up until somewhere north of 4000 RPMs, Jetronic measures air with the AMM and adjusts fuel injector pulsewidth accordingly. Now, Jetronic doesn't know about your 24# injectors, so more fuel than it thinks it's squirting is actually being squirted. The O2 sensor, in the meantime, is sniffing the exhaust and letting Jetronic know how things are smelling - rich or lean. Most likely, it's reporting a rich mixture because of the larger injectors; Jetronic, in turn, trims injector pulsewidth to compensate. This is called "closed loop" operation. There is only so much Jetronic can compensate (I have read here that it is ~25%), so you can't simply throw on any old larger injectors all willy nilly (whatever willy nilly means).
Above a certain RPM, Jetronic ignores AMM & O2 inputs and uses pre-set fuel delivery values (the "fuel map") that are encoded in its ROM chip, i.e., Jetronic switches to "open loop." Because there is no O2 sensor compensation at these RPMs, you get to enjoy the benefits of the larger injectors.
Larger injectors won't give you the low end power increases you want (I would install the 24# injectors anyway). Turbo cars, with lower compression ratios, are inherently sluggish off-boost. To compensate, you could modify your vac advance timing capsule (search the performance board) for an improvement in off-boost performance or get a different turbo.
With the turbo, you have two factors to contend with: boost threshold and lag. Both are determined by the turbo's design - basically, the larger the mass of the rotating components, the higher the boost threshold and lag. Boost threshold is the point at which the turbo has spooled fast enough to begin generating boost; lag is the time between boost threshold and full boost. An analogy might be the time it takes a jet engine to generate enough thrust to move the plane (threshold) and to generate maximum thrust (full boost).
A smaller turbo such as the Mitsu TE05 installed on later c900s, with lower rotating mass, will reach the threshold at lower RPMs, and spool up to full boost faster.
posted by 65.101.15...
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