Leaning out at high RPM right before shift points

[Worthog]

At the track yesterday, I finally got a chance to try out the LM-1 on race gas and high boost. On my first run I just left everything at street levels (17psi, 45 psi fuel) and got a nice pig rich 10.5:1 AFR all the way down the track. As I kept turning up the boost, I hit a best of 12.18 @ 112mph @ 23psi with no knock in third(except a couple of degrees on the shift, and a bunch of knock from the launch) and an AFR around 12.2:1 or so I turned it up to ~25psi. This resulted in my AFR starting to slowly climb after 4,500 RPM to a not so happy 13.8:1 by 5,000 RPM and detonation. Under 4,500 RPM it was a nice flat 12.5:1 or so.

My guess on this problem is that my 6 year old Walbro 307 is getting a bit tired and not able to keep up with demand at high RPM/high boost levels. I was also thinking that maybe i just need to richen up the top end of the fuel map, but I'd think the leaning out would show up no matter what the boost level is if that was actually the problem. I'm interested on what everyone else's take on this is.

I can post the LM-1 datalog if anyone is interested.

I also saw a big lean spike when the TCC locked up, and was wondering if that's normal?

 

[BoostKillsStres]

Well, like you said you could add more upper RPM fuel in the chip and work the boost back up to that level and see if it helped since your certainly at full boost well before 4500 RPM as far as boost to the FP regulator. If you had a 12.5:1 A/F before that RPM point, then the pump should be good for the rest of the run unless your already seeing much larger commanded inj pw at that point in which case the pump probably can't keep up. What kind of format is the log file in? Post a link if you don't mind.

 

[Worthog]

Here's a link to a screenshot of the log, I can post an excel file also. The boost is off a psi or so too high for some reason, and I apparently was wrong about my AFR #'s

Log picture

 

[ijames]

Did your boost creep up in third gear that last run? I'm thinking that as you leaned it out the egt's started rising, which put more energy into the turbine which raised the boost if your wastegate didn't keep up, which leaned it out, which made the egt's rise, which ... . From my reading 12.2 is getting agressively lean on a TR; it seems most of the conservative FAST guys stay between 11.5 and 11.8. Finally, is the bypass valve shimmed in your 307 pump? If you are running 45 psi base pressure and 25 psi boost the pump needs to do 70 psi and a standard 307 starts bypassing between 65and 70 psi. Most vendors shimmed the spring, but are you sure your is?

 

[Eric Stage I]

Bluetops are all done at 23psi with "normal" fuel pressure and race fuel, with a combo like yours. I rarely see anyone go past that without leaning out.

Also, the red line in your chart, at ~97%, is that inj duty cycle?

Eric

 

[Worthog]

Boost is the green line, TPS is the red line, RPM is black, and AFR is purple.

I think the pump is from APE, so I don't think its shimmed. From some reason I was thinking a normal 307 would hold good pressure until 75psi or so.

The AFR got lean on the initial spoolup spike and when it creeped up a PSI in second gear right before the shift. It didn't creep in third for whatever reason, but it still leaned way out by then.

The injectors aren't quite maxed yet, but they're pretty close. Guess its time to just do 50s and a 340.

 

[onefastgn]

55's and chips

I had about the same combo I ran low 12's.Be carful you are about out of Injector.I have a set of 55's and chips for sale for $225.00.Just thought you might want to know.