Hib Halverson

That is correct.

The E99 lacks the ability to control 16 injectors. As ZR1 production will end somewhere between 2500 and 3000 units and there will be no future need for an engine controler capible of running 16 injectors, developing a specific PCM for the LT5 made no sense from a cost standpoint. The solution was the ZR1's fuel injection control module (FICM) which controls the 8 port injectors.

As for "tuning" ZR1s, it's one thing to have the financial means to ship an E99 to HPTuners and have them do their hardware change to remove the encryption, but it's another thing to actually "tune" a ZR1. Right now, my opinion is there is way too much marketing flim-flam surrounding the ability to "tune" LT5s. Plus, there are a lot of folks who can afford HPTs hardware mod, as well, as buying the necessary credits to make cal changes but there are few out there who actually have experience tuning a "decrypted" E99 in a productive manner which also leaves some durability on the table. My guess is the learning curve will be steeper than many know because, even someone able to afford HPTs removal of encryption would likely find the cost of replacement LT5s quite high.

One problem is that the direct injection side of the engine is near max'ed out from a fuel supply standpoint. Like the LT4, the LT5's DGI uses the biggest high-pressure fuel pump available for an OHV V8 configuration. Anyone with a goal of 1000-hp or the goal of running the car on E85, is going to have to address fuel supply because, while 1000-hp LT5s or those running on E85 can make more power, use of E85 requires a lot more fuel flow. Katech has done 1500-hp from the LT5, but they did that using their belt driven high-pressure pump and a non-OE engine controller. Some may suggest a solution might be more fuel out of the secondary PFI, but can only happen if HPT's decrypt. mod allows calibrators access to the FICM and if the secondary injection is capable of more useable fuel flow.

While, right now, I'm the last guy who can afford HPT's hardware mod, but I have used the beta versions of HPTuners Scanner application to log data from an LT5. One interesting observation I have is that once the PCM is in power enrichment and then decides to enable the PFI, the system runs the port injectors at high duty cycle, and backs off the direct injection and appears to use DI pulse width to control the air:fuel.

Another observation which I expected was the PE starts at about .86-lambda but richens to .80 at higher engine speeds.



In the lower pane, blue is bank 1 primary pulse width. Red is bank 1 secondary PW. Purple is commanded EQ ratio reading in lambda.

So, it's possible that those looking for more performance, could start with calibrating the GDI to provide more fuel once the PFI is enabled, but then...there will be that fuel supply limiting high-pressure fuel pump.

My bottom line is that having the capability to tune an LT5 is one thing. Actually doing it sucessfully will be far more complex than many believe.

Pizz

Hey Hib, where'd all that fuel system knowledge come from? Excellent write-up

0DSX Tuning

Luckily some of us having knowledge about and access to things most don’t have.

HPT has a fraction of what’s actually there mapped out. The reality is most can’t or don’t know how to do anything with much of it anyway, but a few of us are capable of going the distance so to say.

What you’re seeing with richening up is catalyst overtemp protection which was the primary reason port fuel was added. GM calls it “exhaust protection”, and the ability to control when it happens and how much the FICM contributes is what separates the men from the boys.

Hib Halverson

It comes from a combination of 1) a briefing on the LT5 I received in December of 2017 from V8 Chief Engineer Jordan Lee, Assist. Chief Eng. John Rydzewski and supercharger engineer Scott Halsall and 2) logging data from my LT5 over a period of a couple of weeks.

The briefing was for an article I wrote last year for Corvette Magazine.

Well, I agree...kinda sorta.

According to what Lee and Rydsewski told me in the briefing, the PFI exists becasue the GDI was "max'ed out" at 650 hp. The initial goal was to "beat the Hellcat" and that required 700+ horsepower. The extra 105-hp comes from the PFI. Admittedly, some of that extra fuel is going to cat protection along with providing the rich air:fuel that supercharged engines "like". That said, my logging clearly shows when PFI enables, it PW goes from zero right to 5.5-ms and the GDI PW decreases. That tends to refute the idea that the GDI is max'ed at 650-hp but I sure as **** am not doing to disable the PFI to find out for sure.

Additionially, my data logging shows quite a bit of inconsistency as to at what point the PFI enables. It is true that there is a "band" of rpm in which it might turn on, but there seems to be no set RPM at which that happens. I could learn more about that if I had a chassis dyno to run on a lot, but for now, I use an uphill stretch of four-lane highway in fourth gear in my ZR1 8-spd. I'm at about 125 at the rev limiter. I tried fifth gear but the speed at the rev limiter was too high for that section of road.

I wanted to comment on the axle shaft issue. Though I'm sure there is a point where axle shafts will break, there was not a lot of discussion of that in my interview with those guys back in late '17. What they did say was that the weak link is transmissions, ie: the 8L90 8-spd auto and the TR 6070 7-spd manual. I was told that they set 715-lbs/ft torque as the safe limit and beyond that they broke a lot of clutches and transmissions. In fact, they also blew-up one of GM's engine dynos as well. In fact, one of the reasons the ZR1 was delayed was in early testing, the LT5 destroyed GM's highest capacity engine dyno and a new, more stronger unit, had to be acquired. Also there were problems with exhaust temperature. Initially, they has some problems with melting exhaust tubing. First, they tried a water-cooled exhaust out of the dyno cell but they ended up with Inconel tubing which had to be freakin' expensive. Anyway, they set a torque limit at 715-lbs/ft. and let the horsepower number go "wherever" between peak torque and a 6600 rpm rev limit. That, of course, turned out to be 755@6400 and Jordan Lee told me they never had engines make less than that, but they did have engines which made more.

Finally...fuel quality. Pay close attention to what the '19 Track Prep Guide says. The engine needs a min. of 93-oct fuel and, based on my testing at near sea level with 70°F IAT, even with 93-there will be some knock retard. I was only able to run detonation free with a mix of 1:1 91-oct and 100-oct fuel (works out to about 95.5-oct) and that's with the rich commanded EQ ratio. GM says 100-oct. unleaded is required for max. performance when tracking on warm weather and I totally believe that.

NicD

Hey, stop sharing stuff like that! I finally got HPT to add that table in the latest beta so I can pull fuel for various things without disabling PI. Funny enough the car will fuel just fine when it's stock without PI and cat overtemp on.


As for what Hib said about tuning the E99 vs the E92, it's really much of the same minus the port injection aspect of it. Once you figure that out you are good to go, but from what I've seen around here people still haven't figured out the E92 so I guess that's not much of a stretch.

0DSX Tuning

I should post a screen shot of my user defined parameter list just to stir the pot. Haha. There's actually a couple significant ones that should be in the general release... but I've grown tired of doing things that help the collective because I generally end up getting forgotten for it while others get YouTube hits and Facebook likes from it.

NicD

LOL I've seen it but no don't post it online. I've submitted a few things to HP Tuners for this stuff and they are still working on some of the others but yes they definitely need to add some more tables because their current ones don't really do much related to the PI fueling. We've already figured out work arounds for various things that they haven't added yet but it would be nice to do it the way it was intended. I'm just blown away that the port injection doesn't reference fuel pressure, how stupid for such a critical variable.

0DSX Tuning

“Environmental control” is what that’s called. Don’t measure the value... control the operating condition. What’s really strange is the ECM assumes 400kPa in the rail when it actually runs 500kPa. I have to tap into my secondary CAN bus to log some direct values from the FICM before going further.

Once I can come up for air from other work, I’m going to modify my FICM to use an actual pressure sensor. I’ve got it 90% figured out.

JHEBERT

I have experienced this myself several times on this forum and others, not that I want any recognition but when people argue with you 10 years after the fact it can get under your skin. I still have BIG shops flame me when I tell them they need the lash cap for the fuel lobe cam or they are urinating in the wind and mushrooming the fuel pump pushrod using a fuel lobe cam and no lash cap.