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Old 02-04-2022, 10:14 PM   #15
Evansa22

 
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I've heard the window for injection is between exhaust valve closing and intake valve opening, is this correct? Same source says 5* before e.v.c. to account for computer latency is close to ideal. So you'd be looking at aeound 352.8. Just my guess
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Old 02-05-2022, 07:02 AM   #16
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Originally Posted by Evansa22 View Post
I've heard the window for injection is between exhaust valve closing and intake valve opening, is this correct? Same source says 5* before e.v.c. to account for computer latency is close to ideal. So you'd be looking at aeound 352.8. Just my guess
Window of injection is between EVC/IVO (depending on overlap of cam) and IVC. That said, your start of injection can typically start 5* before IVO for the reason you described. Spring isn’t far away so I’m looking forward to documenting the SOI impact on power with some dyno time in the near future.
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Old 02-05-2022, 06:36 PM   #17
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Sweet! Like to see new data added to the mix
Guess I had gotten it mixed up because I didn't think it made sense to stop at IVO but thought that is what it said. Thanks for the info
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Old 02-05-2022, 08:05 PM   #18
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Sweet! Like to see new data added to the mix
Guess I had gotten it mixed up because I didn't think it made sense to stop at IVO but thought that is what it said. Thanks for the info
Yeah, it needs from approx 5 degrees before IVO to 5 degrees before ignition. That’s your window and why we keep IPW under ~6 ms or so.
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Old 02-08-2022, 09:55 AM   #19
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Yeah, it needs from approx 5 degrees before IVO to 5 degrees before ignition. That’s your window and why we keep IPW under ~6 ms or so.
True but advancing SOI allows for longer IPW's. For example, My brother's C7Z seems to tolerate IPW's up to 7.5ms before things start to get wacky. Now I didn't leave it that way of course, but it seems custom cams with advanced SOI can tolerate longer pulse widths. First thing I notice when fueling goes south is the wideband will start to show rich when it's really not. Bring the IPW's down and the AFR reading will show leaner even though the engine really richened up. What you are seeing is wasted fuel going out the exhaust causing a false rich reading. Also can cause "fuel knock". My car with stock cam doesn't like anything over 6.5ms. And if you leave the SOI stock values you could likely start to see some issues above 5.8-6.0ms.

SOI main purpose is to get the fuel injected on time for complete combustion. I do believe there are some gains in power to be had but it's not huge. Interested in your results this coming Spring.
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Old 07-12-2022, 08:47 PM   #20
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Just to circle back to this, when I hit the dyno the other day we baselined the car using 330 SOI at WOT. We then changed SOI to 350 and blended in the change and picked up *28 WHP*. We then tried 370 SOI and the run was identical to the 350 SOI run. So that was good data. We then put it back to 330 again and sure enough, lost 27 WHP. So that 350-360 range most tuners use worked well in my case.

IPW didn’t change (in the 5.0 range at E42 for those runs), but the exhaust richened up when advancing the SOI to 350/370. So, I’m not sure what to think about that yet. No change in knock readings regardless of SOI.

Hope that is good data for my fellow Camaro6 pals.
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Old 07-13-2022, 09:13 AM   #21
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I believe what you found is optimal injection time for max power @ 350. Further advancing the SOI to 370 is richening up the AFR due to the longer injection window? In theory that should allow you to pull some fuel and reduce fuel system demand.

Great info!!
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Old 07-13-2022, 09:31 AM   #22
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I believe what you found is optimal injection time for max power @ 350. Further advancing the SOI to 370 is richening up the AFR due to the longer injection window? In theory that should allow you to pull some fuel and reduce fuel system demand.

Great info!!
Thanks! My tuner, Josh Pearl of Performance Dyno, was a good sport and gave me a hour of dyno time on the house so that we could both experiment with SOI. It was good stuff and eye opening.

So what’s clogging my brain is: is 370 actually richening it up? If the amount of fuel is the same that got sprayed in, and the IPW didn’t change, why is it richer? I feel like I’m missing something. If IPW was different then maybe that would be a clue. Maybe 350/370 just gave it more time to burn in the chamber?
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Old 07-13-2022, 03:34 PM   #23
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Originally Posted by Joshinator99 View Post
Thanks! My tuner, Josh Pearl of Performance Dyno, was a good sport and gave me a hour of dyno time on the house so that we could both experiment with SOI. It was good stuff and eye opening.

So what’s clogging my brain is: is 370 actually richening it up? If the amount of fuel is the same that got sprayed in, and the IPW didn’t change, why is it richer? I feel like I’m missing something. If IPW was different then maybe that would be a clue. Maybe 350/370 just gave it more time to burn in the chamber?
Less went out the exhaust valve?
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Old 07-13-2022, 05:11 PM   #24
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Less went out the exhaust valve?
Running the SOI up too high actually increases the risk of sending fuel out the exhaust since at 370 SOI you’re damn close to the EVC event, if I’m correct in my understanding. I really can’t explain it, since longer SOI has nothing to do with the actual combustion event, it’s just time to spray the fuel. So if I’m spraying the exact same amount of fuel… what the hell lol? Maybe Ted or Mike (TooHighPsi) can explain it?
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Old 07-14-2022, 01:00 PM   #25
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I thought increasing SOI starts the injection time earlier not later? Aftermarket cams typically allow to start injecting fuel earlier due to the increased valve events?
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Old 07-14-2022, 05:01 PM   #26
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I thought increasing SOI starts the injection time earlier not later? Aftermarket cams typically allow to start injecting fuel earlier due to the increased valve events?
It does, which pushes your injection start time into the Exhaust Valve Closing event if you get carried away. Let me see if I can find the great diagram I saw on HP Tuners Forum… I thought that did a great job explaining it…but I still don’t fully grasp it.
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Old 07-15-2022, 04:59 PM   #27
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Josh, your thoughts of earler are in the right direction. When it comes to DI with SC we want as much window as possible to inject fuel (as this is normally our limitation to power) and we want as much time for that fuel to try and reach a homogenous condition with the air before it burns.

Remember - SOI is not when the injector opens - it's when we "ask" it to open. Hence, it should get earlier with higher RPM, not because it's actually happening earlier, but due to mechanical limits of the injectors that we need to account for.

All of my testing was done with a stock LT1 camshaft back in 2015, but since PD camshafts have similar overlaps, I wouldn't expect any differences. We ran dyno pulls increasing SOI at 5 degree incements on the engine dyno (not chassis) from stock settings until power flatlined, which happened with SOI at about 360-365 at 6500 rpm. (lower at less RPM of course) Also note that changing SOI does not change your fuel flow, only a change to PW can make that happen. While there are settings for EOI they aren't a hard limit, stretching your PW to longer than your allowed injection window will inject fuel outside this window.

Below are my "safe" settings for PW while staying withing the window (also based off rpm)

Engine RPM MAX PW (ms)
2000 20.0
2500 16.0
3000 13.3
3500 11.4
4000 10.0
4500 8.9
5000 8.0
5500 7.3
6000 6.7
6500 6.2
7000 5.7
7500 5.3
8000 5.0
8500 4.7
9000 4.4

Preferably I like to stay within those ranges - but on DI only I'll admit to pushing a bit past this in the quest for power.

So, in short - if you're pushing the limits, I've always found increase in power when SOI is early and correct for that RPM, which in part lies the solution and the problem (finding that exact number).

Since we now run port and full E85 on our cars, importance of these DI SOI settings drops a bunch and I leave most of the DI fuel settings as stock. We keep enough PW on the DI to maintain all the knock benefits that it offers, then provide a nice homogenous port fuel charge to make as much power as possible.

Hope that helps!
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Old 07-15-2022, 06:21 PM   #28
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Quote:
Originally Posted by toohighpsi View Post
Josh, your thoughts of earler are in the right direction. When it comes to DI with SC we want as much window as possible to inject fuel (as this is normally our limitation to power) and we want as much time for that fuel to try and reach a homogenous condition with the air before it burns.

Remember - SOI is not when the injector opens - it's when we "ask" it to open. Hence, it should get earlier with higher RPM, not because it's actually happening earlier, but due to mechanical limits of the injectors that we need to account for.

All of my testing was done with a stock LT1 camshaft back in 2015, but since PD camshafts have similar overlaps, I wouldn't expect any differences. We ran dyno pulls increasing SOI at 5 degree incements on the engine dyno (not chassis) from stock settings until power flatlined, which happened with SOI at about 360-365 at 6500 rpm. (lower at less RPM of course) Also note that changing SOI does not change your fuel flow, only a change to PW can make that happen. While there are settings for EOI they aren't a hard limit, stretching your PW to longer than your allowed injection window will inject fuel outside this window.

Below are my "safe" settings for PW while staying withing the window (also based off rpm)

Engine RPM MAX PW (ms)
2000 20.0
2500 16.0
3000 13.3
3500 11.4
4000 10.0
4500 8.9
5000 8.0
5500 7.3
6000 6.7
6500 6.2
7000 5.7
7500 5.3
8000 5.0
8500 4.7
9000 4.4

Preferably I like to stay within those ranges - but on DI only I'll admit to pushing a bit past this in the quest for power.

So, in short - if you're pushing the limits, I've always found increase in power when SOI is early and correct for that RPM, which in part lies the solution and the problem (finding that exact number).

Since we now run port and full E85 on our cars, importance of these DI SOI settings drops a bunch and I leave most of the DI fuel settings as stock. We keep enough PW on the DI to maintain all the knock benefits that it offers, then provide a nice homogenous port fuel charge to make as much power as possible.

Hope that helps!
GREAT stuff and very helpful. I think we settled at 365 SOI so I feel much better about our decision. Thanks again!
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