EOIT with a larger cam

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L31MaxExpress

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I downloaded the spreadsheet and revisited something I messed with years ago on the 350 vortec when I had a mild cam in it. I have calculated the difference and adjusted the EOIT to ensure that the injectors do not spray fuel until the exhaust valve is nearly closed. With the overlap the 383s cam has it was pulling fuel out of the exhaust valve and smelled like a 60s 2bbl 390 Ford truck even though it had high flow cats. Now the exhaust has zero noticeable smell. The fuel trims were fairly neutral before around -2 to -5%. I have not altered the VE or MAF tables yet to remove the extra fuel, but the fuel trims are removing it. I am working on dialing in part throttle shift points and running timing loops to optimize the part throttle timing at all rpms and loads I will see. I have been using a roughly 1 mile long, 6% grade that has a climbing lane on a minimally traveled country road I drive through to really load the engine at part-throttle from a standstill to highway speeds. I have not checked the fuel economy yet, but with fuel trim reading indicating the PCM is pulling more fuel nearly everywhere it has to be somewhat better. Here are snap shots from 10-75 mph, holding 75 mph uphill, then holding 75 mph on flat land after the climb.

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L31MaxExpress

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I really like the behavior of the stock diameter custom built converter in this. It stalls about 2,800 rpm and when it is unlocked at moderate acceleration behaves much like a CVT. The transmission shifts through the gears but the engine hangs at a near steady rpm. It is always a bit weird getting accustomed to a converter.

In this test run I also found I pushed the spark timing a bit too high at cruising speed and the engine responded with a couple of seconds of pining. I was actually beginning to wonder if the knock sensor was even working. The only time I had seen it register any knock retard was when it smacked the fuel kill a few times. I dropped the timing back to 34* from 38* where it pinged and it has not done it again. For all the flak I caught for building this engine at 11:1, I was expecting the PingMaster3000 and it simply has not been the case at all. It tolerates more timing than the 9.6:1 350 with iron Vortec did allowing it to run closer to MBT. The 350 was extremely octane limited and I had to really watch the timing on it to prevent detonation.

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L31MaxExpress

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Much respect.

EOIT = Exhaust Open, Injector Timing?
End Of Injection Timing but what is really being more importantly changed by altering the settings is Start Of Injection Timing. By moving the EOIT at lower pulsewidths like idle and lower rpm part-throttle it moves the Start Of Injection Timing.

The idea is to move the EOIT until the fuel trims reach the maximum negative value. At that point you are keeping as much fuel as possible in the chamber and burning fuel as efficiently as possible. At high duty cycle and high rpm it does not matter much as the duty cycle will be high and the injectors spraying say 60-100% of the time. However there is a good bit of improvement to be found when you are at Minimum to say 40% duty cycle where you run 95% of the time. Even at ~2,800 rpm at 1/2 throttle I was still under 50% duty cycle.

With a cam that has minimal overlap like a stock cam and the stock exhaust manifolds, GM typically sprays atomized fuel on top of a closed intake valve for vaporization. When you put a cam in that has more overlap and combine it with strong scavenging from headers it becomes more benificial to inject the fuel after the exhaust valve is nearly closed so that the overlap can still help pull the fuel into the chamber but only allow a minimum amount of fuel pulled into the exhaust. If you were to spray fuel on the back of a closed intake valve, when it opens the overlap merely pulls some of that fuel through the chamber straight into the exhaust system. Hope my explination helps.

I know less fuel is getting into the exhaust now because my cats have dropped nearly 100°F in temp at idle.
 
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L31MaxExpress

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I am thankful a few guys using HP Tuners figured out how it all works and created formulas in the form of an Excel Spreadsheet. Basically one only has to put the stock GM values from the PCM into it, the stock cam EVC and the new EVC and it spits out revised values to test as a starting point. Then fine tune from there.
 

yevgenievich

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I am thankful a few guys using HP Tuners figured out how it all works and created formulas in the form of an Excel Spreadsheet. Basically one only has to put the stock GM values from the PCM into it, the stock cam EVC and the new EVC and it spits out revised values to test as a starting point. Then fine tune from there.
Which spreadsheet is that? I need to get my e38 ecu dialed in better and could use some ideas.

Looks like good work on tuning that motor.
 

L31MaxExpress

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Which spreadsheet is that? I need to get my e38 ecu dialed in better and could use some ideas.

Looks like good work on tuning that motor.
Thanks! Still running a bit fat, but working on leaning it out again. I am working on the VEs with each trip I drive it. I need to order and install a Saxon PC MAF flow straightner for the 4" MAF. The MAF is immediately after a bend and needs some flow straightning as the signal bounces around a bit. Not a huge problem since I am dynamic blending the airflow until 6,500 rpm which is above fuel kill. However with the flow straightner the signal will be cleaner. Cleaner MAF signal equals steadier and more accurate fueling.

GenIV is a bit different.

Check out this thread.

 
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