I keep seeing all this stuff about injection timing. Is it really that important?

[dpuckett]

In a word, yes. The timing can have a HUGE effect on performance, to the good or bad.

The spec for the CPL (Control Parts List) 804 engines is 1.4mm plunger lift @ #1 TDC. Now, usually, your engine is within spec, but the timing pins can be off by up to 5 deg, which will wreak havoc with any adjustments, if that is used for the tell all, end al TDC. I use it for a guide to get me close, then use another method to find true TDC.

CPL 1351 (91.5-92) and CPL 1379 engines have a spec of 1.25mm lift @ TDC. THis is due to the cooler charge air coming in as a result of the intercooler. Emissions related- cooler air, coupled with slightly retarded timing, makes for cooler combustion, lowering NOx emissions) These engines (along with the CPL 804, nonIC- just not as much) can benefit from advancing the timing to about 1.5-1.6mm lift, depending on your preferrences and altitude (higher needs a little more).

But you CAN go too far with the advance, too. I wouldnt go any more than about 1.7mm, esp if you have a mid to high performance engine. The reasons are numerous. First, if you go beyond the optimum timing, you get pre-ignition of a sort- the fuel charge is trying to burn while the piston is still coming up. This makes for a harsh knock, and can reduce MPGs, power, and bottom end torque. It also increases cylinder pressures dramatically; raising the risk of head gasket failure and other risks I'm sure others here have more experience with. It is best to run at the lowest timing spec you can get livable performance and economy from in order to maintain the longevity and reliability of your engine.

Some aftermarekt performance injectors have a higher pop off pressure, which will have the same effect of retarding timing. This necessitates a higher static (initial) timing spec.But the same ideology of higher timing and potential engine damage applies.

Daniel