Interesting info on B3702 Injection timing

[Gelf VXR]

The reason I bring this up is I was amazed to see how a slight movement of the injector firing event affects idle, AFR, idle load, and throttle response. You also immediately notice things like, your AFR getting leaner on the gauge, but the exhaust smelling like unburnt fuel. So far, adjusting the event so as to yield the richest idle mixture (the most burnt fuel at a fixed pulse width) seems to get me closest to optimal with everything else.

I was considering the the exhaust valve timing when cold, if the valve is open later, then perhaps the timing should be retarded in line with the difference from the stock cam. For example the stock cam closes 6 BTDC, my cam closes 1.5 ATDC, so I might need to retard 7 or 8 degreeswhen cold??

[Goldfinger911]

I was considering the the exhaust valve timing when cold, if the valve is open later, then perhaps the timing should be retarded in line with the difference from the stock cam. For example the stock cam closes 6 BTDC, my cam closes 1.5 ATDC, so I might need to retard 7 or 8 degreeswhen cold??

Hmm. Thats what I was thinking. Regarding cold running... when my car starts up... the tune does retard timing and it sounds very mean out the tail pipe. The AFR is rich, but very stable. I have always wondered about this when cold.

Wait... what stock cam has the EVC at 6 deg BTDC? I thought the stock LS1 EVC was 10.5 deg and the stock LS2 was 8.5 deg BTDC?

Mine is a bit more challenging to tune for; 242/248 .612"/.617" 112+2 LSA 110 ICL.

[eficalibrator]

So far, adjusting the event so as to yield the richest idle mixture (the most burnt fuel at a fixed pulse width) seems to get me closest to optimal with everything else.

In the context of tuning large overlap cams, with an emphasis on throttle response and idle control, this should work fine. (It may negatively effect emissions) Keep in mind that any previous VE or MAF mapping done in the reversion sensitive region will probably need to be revisited now that you have a cleaner wideband signal.

[Gelf VXR]

I heard back from the garage carrying out my cam and head install today, they said the idle is smooth. This is stock LS2 and tune with LS7 injector calibrations with L92 heads, comp 216/229 cam.

One interesting difference I noticed with the injector calibrations for the injector timing when you add the ECT + RPM advance tabes, from 0 to 1020 rpm. Apart from that identicle.


The LS7 calibration has 20 to 65 degrees more advance than the LS2.

[LS1_Dragster]

Another interesting fact:

The WBO2 showed 1.3% richer then the previous run. The first time I changed the tables a few weeks ago it showed more like 5% richer afterwards. Since it showed a smaller percentage maybe it's closer to optimal now. When I get a chance again in the future I will up it again. If I remember right it max's out at 8.0ms.

It would be interesting if someone else could back up this data at the strip....

Lee

[dfe1]

The reduction in ET is impressive, but I've found that it is often difficult to correlate some modifications to improvements in elapsed times. On the other hand, mile per hour is typically a very reliable indicator of horsepower. What I find particularly impressive about Lee's results is the improvement in mile per hour-- a 1.3 mph improvement from changing injector timing is HUGE, as is 3 miles per hour resulting from injector timing and mixture changes. That kind of mile per hour improvement indicates that definite horsepower increases should show up in dyno testing

[GAMEOVER]

This thread is very interesting!!!

[redhardsupra]

wouldn't injection timing be very dependent on valve events? i know that most OEM calibrations do injection against a closed valve, but if the timing wasnt important, they wouldnt have the table for it, would they?

[dfe1]

wouldn't injection timing be very dependent on valve events? i know that most OEM calibrations do injection against a closed valve, but if the timing wasnt important, they wouldnt have the table for it, would they?

I really wonder about that. Seems logical that it would be, and Lee's testing seems to prove that. Someone should do a bit of testing with an engine that has a stock cam and see if results are similar. It may well be that GM decided to trade off some power for improved emissions numbers.

I don't know if this is relevant, but when GM switched from batch to sequential (for the 1994 model year) the engineers stated that there wasn't much difference in power. The switch to sequential was primarily a result of the need to improve emissions and economy. I was somewhat doubtful at the time, and have become more so over the years. I don't know that they were "mis-speaking" as much as the computers of the day may not have had the capacity to alter injection timing. It may also be that the engineers were basing their comments on little or no comparative testing. If they were chasing emissions, they probably didn't look at power. Sounds strange, but on at least one occasion, when I asked about results outside the operating range of the program focus, I had engineers say, "I don't know, we didn't test there". Be interesting to do a back-to-back batch-to-sequential test and see what the power difference is.

[exploder]

anything new on this subject...has anybody else tried this?