[radz28]

I've been playing with an 85mm upper, with no other changes, and am trying to figure out some inconsistencies I'm wondering if anyone else has seen or has thoughts they could share on...

Just a quick recap on the combo': stock exhaust & long block, 2650, 103 TB/ snout, RFBG, bigger H.E., port injection, and stock lower with a switch from a 90mm upper to an 85mm

I started playing with this little pulley upgrade, and am seeing fueling inconsistencies at WOT. I knew I'd need to watch for more fueling, but I thought it would, mostly, be at the top of the MAF CURVE. I did make some FUEL PUMP changes to try to control the initial pressure spike ([6970] BASE FUEL PUMP DUTY CYCLE) when the DSX LOW SIDE kicks in, but they were really small changes, and LSFP never came below anything close to 70-psi. The HSFP/LSFP was fine on my first test drive, though I was a little lean as I came to redline. The MAF showed only a couple percent LEAN of commanded, so I only really added that few percent toward the top end of the MAF curve. Then - on a day 12-degrees cooler (cooler day was about 76*), a little fatter MAF at the top end of the scale, my IPW went completely nuts, but starting as low as around 2800RPMs (16ms and 620psi) and was completely bonkers through 6500RPMs (9ms and 1400psi), where it was working back toward commanded, but was still way higher than the 5.1ms and 2900psi (and what I've been consistently seeing) I was seeing from the warmer day. RAIL PRESSURE/IPW dropped and was stupid high on the cooler day, and was very confusing. I didn't really change my PORT INJECTION MAF CURVE, so I didn't shift fueling from DI to PI, or vise versa.

I remembered an LMP video where Alec was talking about a build he was tuning. He made a comment on how opening up the snout from (something like) a 103 to a 112 (or a size about that) DROPPED some fuel demand from the run with the 103, and no other notable changes (tune-wise or mechanically). I started wondering if I'm experiencing the opposite, in a way, because of driving the blower harder in cooler air. I know it's not significantly cooler, but maybe I was on the ragged edge before (in the 88* heat), and coming down to 76* was enough to throw my fueling off, because of being on the edge of having a safe balance between the DI and PI. Again - there were no really other notable fueling changes that I made between the runs. It was mostly temperature and a slight MAF adjustment (added a tiny bit more fuel) in the E92. I know the hit was a, kind of, low RPM, but it was also doing it a 3500RPMs, too, in other hits on this, same, drive.

Outside of retarding the cam another 2* with the last test drive (the one with the crazy HIGH PRESSURE issues), some small DRIVE DEMAND changes (THROTTLE BLADE was acting fine), there was nothing that I thought would cause a drastic change like this. The AIRFLOW MODEL didn't seem to be crazy or anything, as I was seeing a spread of around 4% between MAF/VVE/DYN at WOT. TIMING didn't change much, but I did eliminate the COT/PE modifier and just commanded a flat total that equaled the same amount among the BASE and ALCOHOL tables. I think I heard sometimes changing timing can change fueling a bit, but I don't have a dyno to confirm if that was right, or I just heard wrong. Tune-wise - I think those were most of the total changes I made between the two tunes.

As far as cam timing - I'd read RETARDING the cam (raising the values in the tables) was beneficial to air flow until it came to the point to where one would start getting KNOCK. I'd just found a post on HPTuners where it was said that was beneficial for AFTERMARKET cams, and an OEM LT4 cam would prefer to be advanced, which is where my tune has been. I've played with this a little in the past, and have seen some tunes where it goes either way in a combination like mine. It FEELS like the power comes in stronger and faster with the cam slightly ADVANCED over stock, but I don't know if that's placebo. I've also seen MAF AIR FLOW increase, slightly, RETARDING the cam a little... What am I missing?...

Does anyone have any comments they'd share, or some insight into what I am not seeing? Anything's welcome. I know I could be completely off, but I'll be darned if I can come up with anything else that makes sense.

Thanks for any and all!
Chuck

[Megahurtz]

There is a very steep slope once you're out of fuel pressure/injector. That's where there is a recommendation to stay under 6.0 ms on the DI side. Because at that point, a drop in air temp alone can cause the injectors to drain the rail and then it never recovers and you are spraying low pressure through DI and it spray up until spark and then boom, you can damage the motor. You changed the pulley too sooooooo that's even more demand. It could have put too much strain on the low side but that is a bit surprising. I've run even the original DSX low sides to support more power. Now we use the upgraded 320's from DSX. Maybe the high side draining was just too much for the DSX low side to overcome. Maybe the low side part of the tune isn't optimal?

Since you have to the too high PSI, I would recommend shifting more fuel to the port system. I would aim for in 70F weather, the DI side injectors are no more than 5.2ms at redline. Then push the rest of the fuel to the 2HPSI side. This will give you room for colder weather on the DI side.

Most people push the DI side to the edge to support Flex Fuel even when they add meth. Basically I'm recommending that you back the injectors down to the 5.0-5.2ms range and then lean on the Port Side(or meth side).

[KingLT1]

Since you have port why are you adding fuel with the DI system? I agree with Jason that you should remove enough fuel from the DI system so your IPW's are around 5.2, then compensate on the Port side to hit target AFR.

[radz28]

Originally Posted by Megahurtz

There is a very steep slope once you're out of fuel pressure/injector. That's where there is a recommendation to stay under 6.0 ms on the DI side. Because at that point, a drop in air temp alone can cause the injectors to drain the rail and then it never recovers and you are spraying low pressure through DI and it spray up until spark and then boom, you can damage the motor. You changed the pulley too sooooooo that's even more demand. It could have put too much strain on the low side but that is a bit surprising. I've run even the original DSX low sides to support more power. Now we use the upgraded 320's from DSX. Maybe the high side draining was just too much for the DSX low side to overcome. Maybe the low side part of the tune isn't optimal?

Since you have to the too high PSI, I would recommend shifting more fuel to the port system. I would aim for in 70F weather, the DI side injectors are no more than 5.2ms at redline. Then push the rest of the fuel to the 2HPSI side. This will give you room for colder weather on the DI side.

Most people push the DI side to the edge to support Flex Fuel even when they add meth. Basically I'm recommending that you back the injectors down to the 5.0-5.2ms range and then lean on the Port Side(or meth side).

Thanks Jason!!! I think I got all that.

I'm on the same page, for the DSX, because I purchased the 320-upgrade, and I've created the situation where the LOW SIDE comes down to about 72-74psi, because initially - it banged-off at 90psi, and stayed there, lol. I've been playing with that from the beginning to try to maintain a lower-to-mid-70s pressure (I thought that would be okay in comparison to the COMMANDED OEM PRESSURE). I'm not arguing (just to be clear), but shouldn't 72psi be okay to support the DI and PI? I'm showing at least that in my logs. If that's wrong, I'm happy to accept that, and bump it back up. I'd thought that was an okay strategy for that...

I've been using a similar strategy to what most people do, as you have pointed out. My logic (right or wrong - I'm obviously NOT a calibrator/tuner) was the DI was the best at optimized fueling (as BTR's DI vs PI demonstrated, lol), so while I've been able to stay around 5.1-5.2ms, I know that was kinda' close to the limit (fortunately - my PI has CLOSED LOOP control that was keeping the car pretty RICH in this area) it seems like is accepted. Even my current revision, not yet tested, continued this trend, in that I started pulling fueling from the E92 PE table and shifted the load toward the PI CONTROLLER's PE table (the REFLEX that 2HIPSI sells, too). In case this needs to be said - I'm a dingus that's not lowering the MAF curve to allow for the PI to bring fuel in - I've altered the DI INJECTORS [33355] to pull fuel for compensation so my TORQUE MODELS stay the same (even though I've played with VTT/VVE/DD already anyways). ANYWAYS...

I was wondering if the cooler air, being more dense, could (in theory) make the blower work slightly harder, too (rotors beating the denser air through the blower), which could just add to a greater load the smaller upper would, increasing the demand for more fuel that I was already at the edge of. It kind of makes sense in my brain, but you (and many other here) would know better than I.

I'd probably making something out of nothing, and just needed to hear that I wasn't going to find what I was looking for in that iteration. I will continue to pull the fuel load off the E92 and shift more to the PI. Thanks again, and for all the information you share here, and in the other Community. I've learned A LOT from what you've shared.

[radz28]

Originally Posted by KingLT1

Since you have port why are you adding fuel with the DI system? I agree with Jason that you should remove enough fuel from the DI system so your IPW's are around 5.2, then compensate on the Port side to hit target AFR.

I, think, I was also trying to find the limits with the DI. I know they're pretty low, and this tank is at more than 75% E', so knew to pay attention. After BTR's video (referenced in Jason's response), I was just trying to balance that optimal DI, and I must have been right on it with that 90mm, because until now, I haven't seen this behavior from the fuel system.

I, honestly, was hoping from confirmation from BOTH of you, lol. And THANK YOU for coming in and setting me straight. You guys see this all the time, and it helps collection your guys' knowledge.

Thank you Joe for taking more time to help me, as usual.