3rd gen in cmc2 progress update

[Den341548534727]

x2

[camaro_1le]

LT1's are better

[cozog1548534733]

X2

[Lady in Nomex]

Hard to beat a good running LT1! I also like L98s (third gen 350), but they are maybe too torquey? I can't remember why we are not using those.

[Den341548534727]

Carburetors don't have a "limp mode"

[cmc38camaro]

We all have our favor induction systems and we could debate the advantages and disadvantages for a long time. Personally I'm fond of direct injection and forced induction, what are the chances of getting it added to the 2011 rules update?

 

In an earlier post I mentioned I was going to lie to the ECM about water temperature on my 305 TPI CMC2 engine and see if it had any impact on the partial throttle lean backfire condition. It did.. it eliminated the partial throttle stumble and exhaust backfire.

 

The theory behind this experiment is that the ECM runs in open loop mode and on a richer fuel table until reaching operating temperature. I inserted a 1000 ohm resistor in place of the coolant temperature sensor. The value was chosen because it was something I had laying around and was in the right range. It provided a 122 degree water temp reading to the ECM.

 

This experiment did not observably impact idle or WOT performance, but is not the complete solution either. The next problem is a lift throttle backfire. I suspect this is the result of the high fuel pressure I'm having to run on the 19# injectors. Had I been thinking this past weekend I would have connected the vacuum to the fuel pressure regulator to see if it made the tune better or worse. Next on the test agenda is 24# injectors.

[cmc38camaro]

I tried the 24# injectors running at 43 PSI this weekend at Buttonwillow. For the practice session I reconnected vacuum to the fuel pressure regulator and reconnected the intake water temp sensor. The results were mixed, the partial throttle stumble returned, but there were no lift throttle issues. For the qualifying session I disconnected the intake water temp sensor and plugged the resistor back in. This combo did the trick, the car is now running the best it has since modding it for CMC2. Later in the day on the dyno the car did 262/320. These numbers are identical to those measured at the Nationals. The difference in driveability is night and day however, I can use the throttle as intended rather than using it as a switch.

 

The one area where I think further improvements can be made in the tune are in the area of throttle repsonse. I'm running at TDC to get down to the required power levels and this makes for lazy throttle response. My plan for next season's certification dyno run is to go back to the stock 1.5:1 stamped rockers arm and to dial the timing up. This should be a fair trade as I have measured 10-12 HP gains in dialing up the timing.

 

Finally after many experiments and too many dyno pulls this is a competitive engine package.

[durburz]

that's great news mike congrats.