[radz28]

Originally Posted by JSH

Mine's now at 370/175. 370 makes sense, but the 175... not so much. Here's a graphic to study on rainy days.

Ben Charles posted that like 10-years ago, lol. He helped me on my tune early on, and it ran GREAT. That graphic might be specific for the cam he was doing these SOI/EOI tests on though. Just be careful with what you're referencing, is all I'm saying.

What doesn't make sense about the 170*? Why did it drop so much? If that's what you're asking, it could be because you pulled SOI back such that the ECM has to inject that far toward the compression side. Some might say that might work, but is on the edge, but others may say to put SOI back up some degrees.

It is my understanding, ideally - you want EIO to not drop below 180*. It is my understanding that EIO is about where the highest efficiency is; that you could also hear it in the tone of the exhaust. I've heard it in my exhaust, I believe: it sounded a lot more staccato - that is, the pulses were a lot more separated from each other, whereas when EIO was lower (and the WB showed a false RICH) and probably spraying into compression, the individual pulses were very muddy, if that makes any sense.

At least that's what I've gathered.

[JSH]

It would be nice to have a few days at the track to see if it matters much for ET.

Originally Posted by radz28

Ben Charles posted that like 10-years ago, lol. He helped me on my tune early on, and it ran GREAT. That graphic might be specific for the cam he was doing these SOI/EOI tests on though. Just be careful with what you're referencing, is all I'm saying.

What doesn't make sense about the 170*? Why did it drop so much? If that's what you're asking, it could be because you pulled SOI back such that the ECM has to inject that far toward the compression side. Some might say that might work, but is on the edge, but others may say to put SOI back up some degrees.

It is my understanding, ideally - you want EIO to not drop below 180*. It is my understanding that EIO is about where the highest efficiency is; that you could also hear it in the tone of the exhaust. I've heard it in my exhaust, I believe: it sounded a lot more staccato - that is, the pulses were a lot more separated from each other, whereas when EIO was lower (and the WB showed a false RICH) and probably spraying into compression, the individual pulses were very muddy, if that makes any sense.

At least that's what I've gathered.

[Joshinator99]

Originally Posted by JSH

Mine's now at 370/175. 370 makes sense, but the 175... not so much. Here's a graphic to study on rainy days.

It does make sense because your EOI has to be done before your ignition timing advance. So IVC, then injection EOI, then spark, then EVO.

[SOCAL.M6.ZLE]

My SOI maxes out at 385... safe to assume you deduct the flex fuel advance to find the accurate number?

[Megahurtz]

You guys need to remember with DI spraying too early will just send fuel out of the exhaust valve. The goal is to get as much fuel into the combustion chamber in the spray window. There is no drop in power if you spray a little past 180 (BDC) because the piston speed is slower right after BDC and with aftermarket cams and boost, the intake valve is still open and assisting fuel mix with air in the chamber.

But if you really want to know what SOI And EOI window you car likes, put it on the dyno and test or take it to the track and test.

[JSH]

Here's my cam card. This is my first DI car, so everyone on this thread has more experience than I do, but I believe this card tells me how to set SOI. But then I found this table from DSX. I assume all of these PID are available in HPTuners.

[Megahurtz]

If translating to SOI/EOI numbers in the ECU. Basically, that cam card says your Intake Valve opens at roughly 366 SOI and closes at roughly 130 EOI. On the exhaust stroke the exhaust valve is still open until about 2 degrees after TDC(358 SOI). Now that is at .050 lift so its not the exact position, but it is about where it starts to matter.

Another thing to remember is the velocity of the air charge and how it moves in the engine/valves/combustion chamber. Air is elastic. So there isn't a firm line of when you should start injection, at least not definable by looking at a cam card. This is where the dyno comes in. But my comments in this thread are still accurate and true.

Example, if you're exhaust valve is still open until 2 degrees past TDC (358 SOI) but you start injecting fuel at 380 SOI, you're spraying fuel for 22 degrees of crank rotation where the exhaust valve is open during the exhaust stroke. Some of this fuel will just fly out of the exhaust port. As long as EOI is not dropping to the point of causing incorrect mixing of fuel and air, which will be seen as a loss of power on the dyno, you don't need to back SOI up where it throws fuel out of the exhaust port to bring the EOI higher than 180.

As a GENERAL rule. SOI of 370 or less and an EOI of 160 or less is perfectly fine on stock cam LT4. This even translates to cammed cars but that is where you need to start testing on the dyno to see if the airflow characteristics of the setup prefer an earlier SOI or not. It all depends on the air velocity and how it behaves since air is "elastic" in nature.

Based on the output of the SOI calculator image, the output would say start spraying at 326 SOI and stop spraying at 27 EOI which would be 5 degrees before the spark plug ignites if you want 22 degrees of timing. This is completely wrong and will damage your engine if you actually tried to run this duration.

[radz28]

JSH - IMHO - just let a calibrator get this done for you. There are 2 that always try to help, and JRE jumps in, too.

[Joshinator99]

Originally Posted by Megahurtz

You guys need to remember with DI spraying too early will just send fuel out of the exhaust valve. The goal is to get as much fuel into the combustion chamber in the spray window. There is no drop in power if you spray a little past 180 (BDC) because the piston speed is slower right after BDC and with aftermarket cams and boost, the intake valve is still open and assisting fuel mix with air in the chamber.

But if you really want to know what SOI And EOI window you car likes, put it on the dyno and test or take it to the track and test.

Yep, dyno will definitely tell the tale! Here was my post from 2 years ago after specifically playing with SOI only on the dyno:
https://www.camaro6.com/forums/showp...3&postcount=20

[JSH]

Originally Posted by radz28

JSH - IMHO - just let a calibrator get this done for you. There are 2 that always try to help, and JRE jumps in, too.

My current tuner has never tuned SOI. My shop owner has built and tuned many lt4s also never tuned for SOI. He didn't know what it was. I sent a log to my previous tuner, and he returned and said that SOI of 393 was too high. He sees actual hp gains by dropping back to 380.

Both the previous tuner and King had SOI set at 378 to 380. Jason here I believe thinks that 370 is a better number for me. And Josh is saying that 360 works best for him. I need to make some laps and establish a baseline and then try 360-370-380-390 and see

[JSH]

Originally Posted by radz28

It is my understanding, ideally - you want EIO to not drop below 180*..

It's probably pretty close to 380/ 180 right now, versus 393/203 untuned

[Megahurtz]

Originally Posted by Joshinator99

Yep, dyno will definitely tell the tale! Here was my post from 2 years ago after specifically playing with SOI only on the dyno:
https://www.camaro6.com/forums/showp...3&postcount=20

I'm not surprised by those results.

Originally Posted by JSH

My shop owner has built and tuned many lt4s also never tuned for SOI. Didn't know what it was. My current tuner has never tuned SOI. I sent a log to my previous tuner and he came back and said that SOI of 393 was too high. Both the previous tuner and King had SOI set at 378 to 380. Jason here I believe thinks that 370 is a better number for me. And Josh is saying that 360 works best for him. I need to make some laps and establish a baseline and then try 360-370-380-390 and see

King isn't wrong for letting SOI start at 378. I am not wrong for suggesting 368. I suspect you will find no discernable difference between the two on the track.


I actually theorize that spraying at 380-390 when running ethanol could assist with cooling the exhaust valves but I have no way of actually knowing. Some of the earlier Corvette Z06's seem to back SOI up more than you have commanded in the ECU but only sometimes. The Camaro LT4's don't seem to do this. I've always wondered if it was a hidden table or logic in the ECU to perhaps "cool" the exhaust valve by spraying and the end of the exhaust stroke (SOI of 380+)

[JSH]

Originally Posted by Megahurtz

I'm not surprised by those results.

I've always wondered if it was a hidden table or logic in the ECU to perhaps "cool" the exhaust valve by spraying and the end of the exhaust stroke (SOI of 380+)

Is exhaust valve temp an HPT PID?

I see people at 390 on stock cams with no overlap, and people discussing valve failures with SOI at 400-440. On big aftermarket cams with overlap, I'm seeing most at 370-380/170-180.

[Megahurtz]

Originally Posted by JSH

Is exhaust valve temp an HPT PID?

I see people at 390 on stock cams with no overlap, and people discussing valve failures with SOI at 400-440. On big aftermarket cams with overlap, I'm seeing most at 370-380/170-180.

no PID for that, I mean the exhaust valve temp being cooled by ethanol evaporation by spraying when the exhaust valve is still partially open. I'm not suggesting this is correct or good or accurate. It's just a thought I had about I wonder if it actually does anything or is beneficial. I also wondered if it cooled the cats a little too. I have NO working theory or proof of this thought.

SOI at 400-440 is VERY bad on DI. You're literally dumping raw fuel into the exhaust stroke and probably at some point at WOT you will have a continuous flame from the exhaust tips as the hot exhaust mixed with raw fuel hit oxygen rich air.


360-380 SOI is fine. 160-180 EOI is fine. Fit the spray window in where you minimize spraying fuel out of the exhaust port and minimize spraying too far into the compression stroke.