hopefully this helps someone(s)

Ok, don’t laugh or stick your nose up at this yet. That’s the disclaimer.
So I decided to ask chat gpt what my specific injection timing should be in hp tuners for my summit ghost cam. Figured what the heck, worst that could happen is I’d get a nice laugh. It actually asked me a bunch of details and I provided detailed answers and then it provided me with a detailed answer on the numbers I needed to plug in. And it explained to me the effect of what the numbers did. Pretty cool. Anyways, I plugged those numbers in and cranked the car. I could immediately tell a difference (at first I thought it was in my head) at idle. I blipped the throttle a few times after it warmed up and it “seemed” more responsive. It always get a lean pop if I stabbed it too quickly. That was gone. Btw, I’ve messed with transient, the VE till my fingers were sore (just exaggerating there lol) and other things I’ve tried and could never get that intermittent lean pop to go away. But now, it’s gone. this was just testing in my driveway. I was excited to drive it to work today. I drive this car every day pretty much. Especially lately. I’m well tuned in on the little quirks it has. Well let me tell you, my tip in hesitation is gone. It idles better. Cruises better with no bucking at 1200rpm, locked up in overdrive. It accelerates (not wot) more effortlessly. And smoother. It cruises smoother. It all around sounds quieter and smoother. The indicated instant fuel mileage has gone up. Idle fuel consumption is the same, but it sounds like it no longer struggles.

below are my before settings and after settings. The car is a turbocharged 2004 GTO with a 5.3

here’s my before numbers. (Injection timing > Boundary is 6.5 for before and after but later on I changed to 6.3 but have not reflashed yet)

the way I got these numbers is a spread sheet or calculator that I came across for figuring this out. Guess it wasn’t quite right for me.




and here’s after

 

For comparison using EOI, a 6.5 boundary and a 6.22 injection target works out to ~361 deg EOI. A 6.5 boundary and a 5.6 target is ~305 EOI so you are just spraying more fuel on the back of the intake valve with your after settings and it's likely vaporizing the fuel better with the hot intake valve. Most P01/P59 operating systems end up commanding around 300 deg EOI when fully warmed up from the factory. GM is really aggressive on the older Gen3 stuff on putting fuel on the back of the intake valve especially at colder temperatures where it really helps, not so much going forward with the Gen4s. Gen4s delay it quite a bit more from the factory especially when warmed up.

What injectors are you running and what is your idle pulse width? That will play a big role along with accurate injector data, personally I would have thought that 361 deg would have been more "on target" so to speak than 305 with your cam but injectors have a pretty large say in what works well for each combo.

 

im running deka 80’s. My inj pulse width at idle is around 2.0 to 2.1. I’ve seen 1.9 and it consumes less fuel but it seems to wander back to 2.0-2.1 after a while. My trims have because wonky and I’ve been fighting them for weeks. Gpt even told me that my trims would do this if my injection timing wasn’t right, without me mentioning it. I’m gonna log it on the way home to see.

 

Putting fuel on the intake valve should keep it cleaner.

 

it should decrease fuel mileage tho, shouldn’t it? It’s definitely increased my efficiency.

 

If it bounces off the valve and atomizes into the air mixture, it should burn more efficiently. It might not be enough of a flow difference to notice a change in overall mileage.

 

Oh damn, OK throw it all out the window. SD 80s are DIRTY down low and the available data for them also sucks. I'm going to say what is working for you is only working for you because of those injectors. Put something else in there and everything would change for sure.

 

eventually I’ll be going with a bigger injector, those are just cheap and they work good enough for the boost bug to bite, and make someone want more. I’ll be going to e85 and I’ll have to switch to something else. GPT did mention I should put the values in the injector offset vs battery voltage vs kpa vac, straight across. As in all the same numbers.

8v 1.23 all the way across
10v .85 “ “ “ “
12v .60
14v .43
16v .30


actually looking at it, from 12v and up, they are the same all the way across from 15kpa and up.

I had mine inj pulse at .593. It said put at .9.

 

Well the big problem is that they are so completely non-linear below ~1.7 ms, and with another break point at 2.4 ms, that you will never get fueling to be accurate at idle or light part throttle and the standard deviation on these things can be upwards of 25% at 1.3 ms. It's nearly impossible to even flow match these injectors because of that. Continental themselves claims the minimum pulsewidth on the SD80s is 1.322 ms and that's literally just to get away from the gigantic swings at lower pulsewidths. Those voltage offsets aren't terribly far off from the actual datasheet but it's the non-linear nature of those injectors that ruins it. Just do yourself a favor and upgrade to a modern injector based on the EV14s like ID or FIC.

 

I set my EOIT to start spraying after the exhaust valve closes at normal operating temps. I left it closer to factory settings during warmup. So far I have seen no reason to change it back. This is with a 226/230 @.050" on a 113lsa cam and FIC (clinic) 1000cc injectors in the original GTO 5.7.

 

That's generally a good target with cams that have some overlap in them.

 

The stock EOIT for my '02 C5 is 5.55, so it sound like you changed from a delayed injection target to something very close to stock.

Like Nic D said, delaying EOIT is pretty common for setups with lots of overlap, but that cam has relatively little (2 degrees at .050) so it kinda makes sense that stock EOIT works better.

 

Keep in mind that stock Gen4 ECMs are up in the high 300s/low 400s and those have no overlap at all... my point being that his problems aren't related to EOIT and are more so caused by the SD 80s that he is running. His current EOIT settings are essentially covering up the deficiency in those injector's low pulsewidth characteristics so to speak.

 

if it’s covering up the bad characteristics of these injectors and helping it drive better, I’m ok with that.


I had more drive time yesterday (about to head to work in it in a few minutes) and it’s fixed loads of quirks I’ve had. I had a stutter it I hit it from a stop more than 50% throttle, it felt like a Convertor lockup judder, but that definitely wasn’t the issue. I could never get anything to show up in my logs that led me to the problem. It went away after doing this and like I mentioned before, it’s much more peppy out of boost. And it gets in boost quicker it seems like.

 

No doubt but the title of this thread is Summit Ghost cam injection timing and your EOIT settings are working for you because of your injectors, that's the only point I'm making.

 

fair enough