Hi All:

I am in the process of tuning in my 383 TPI with no egr. I am on my 9th chip burn and am finding that with no EGR the motor does not like any additional advance as you decrease load. I knew of this phenomenon, but didnt realize how significant the effect of no egr was. My motor is built with a small 204/214@050 cam with 112 lobe separation with 5 deg advance so I have VERY good low rpm cylinder filling due to early intake valve closing. I started with a stock 350 camaro speed density spark table and have been steadily taking out advance in the part throttle region. As an example, at 50 kPa 1800rpm the stock camaro table has about 28 deg advance and I am currently using 17deg and getting some knock retard. If you look at the 1800rpm line on the Camaro table when you go from 100kPa to 50 kPa the advance increases by 20 deg!! In my motor, the advance increases just a few degrees. I know this where the motor wants to be as performance gets better and better everytime I take a few more degrees out. My motor specs are: stock TB, ported plenum, stock runners, ported factory base, Edel RPM alum cylinder heads, 9.6:1 KB HypEu pistons, 5.7" rods, GM 400 crank. THis motor may seem mild to some, but it is in a 79 Jeep CJ7 which sees alot of offroad use so I wanted strong low end torque(which I have!!!)
Thanks for any inputs you fellow tuners may have!!

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Dave Zelinka

 

The engine will always tell you what it wants, just go with that. Never try to tune to numbers that you want.

Might be needing some addition fuel. You have to work things back and forth.

 

Thanks Grumpy! I always appreciate hearing your responses. I think I am on the right track, just hope others will share their results. My BLM's are getting REALLY close too. So glad I invested in PROM burning equip and a Diacom setup. Don't really see how to get a motor dialed without it!! One tuner in town wanted $300 to change my idle speed!!!

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Dave Zelinka

 

You are discovering a lot that I also discovered when I was doing "tests" of my EGR et al. I was debating of removing my EGR and realized that it allowed me to run my longer spark advance and gave much better gas mileage with minimal loss of part throttle response.

I then made various changes to keep my EGR functioning longer. I changed the minimum temperature to its lowest value and then later modified the code to change the test from the MAT to Vehicle speed. This is due to a "surge" I felt in part throttle when starting. After much testing and mucking around, I finally got my EGR to function the way I WANT and yield excellent driveability and gas mileage.

If their is any way you can retain your EGR, do it. But if you DO have to blow it away, I found doing a lot of "mountain driving" road tests, having Diacom capture the knock counts and tweak the spark with the VE tables eventually eliminated it - when I thought I wanted to eliminate my EGR. I have really found your fuel and spark need to be played with in unison.

 

Wow Glenn, that is EXACTLY what I am doing! I have a good long hill right near my house and do most all my testing/tuning there. I find I can maintain about any MAP value I want and pull the whole rpm range by manually shifting. I have a vacuum gauge in my dash so I just use that to set the engine load. In other words, I make one run with my accel set to get say 15" vacuum, then do another run set for say 10" vacuum and then one for 5" vacuum. I then review the Diacom and see at what rpm and MAP the knock retard initiates and by how much.
One question though..... Since I am in closed loop for all this testing, why is fuel so critical?? The ecm is keeping me toggling rich/lean since my throttle position is no high enough to go into open loop. I have been fine tuning my VE tables based on the diacom data, shooting for between 122 and 128 is my goal as I heard that it is better for overall driveability to have BLM's on the low side..... Do you agree??? Thanks

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Dave Zelinka