EOIT with a larger cam

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L31MaxExpress

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My LS3 cartridge MAF placement is less than ideal but I really have little choice. From 8,000 hz and beyond my MAF flow table is straight out of a GM 525 HP LS3 and below that it has small changes to improve fuel trims. My MAF is literally shoehorned into the air inlet at the end of the 90" bend coming off the airbox and nearly wedged between the oil fill tube and firewall.

What GM has to say about MAF placement.

Mass Air Flow (MAF) Sensor
NOTE: It is critical that the MAF sensor is mounted per the instructions below. Vehicle performance and/or driveability may be affected if it is not mounted as recommended. The mass air flow sensor must be installed in the induction system using the supplied MAF sensor mounting boss. The induction system should be 4 inches in diameter and have a minimum straight section 6 inches in length. Mount the MAF sensor in the middle of the straight induction section, ensuring that the middle of the mounting boss is at least 10 inches from the throttle body.


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yevgenievich

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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.

On my after a bend maf, I had to get a straightener thing. It would bounce really bad especially at idle. There had to be a very drastic change in the maf table just to get engine to run when I initially moved the maf to after a bend
 

L31MaxExpress

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On my after a bend maf, I had to get a straightener thing. It would bounce really bad especially at idle. There had to be a very drastic change in the maf table just to get engine to run when I initially moved the maf to after a bend
Mine drifts 3-4 cells at idle and 2-3 cell running at moderate engine speeds. Usually 1-2 cells at WOT. My temporary soultion is just running in speed density or I have also run it with dynamic blend 100% of the time. That being said I am happier with the way it runs in speed density then trying to use the turbulent data from the MAF at all. Using speed density to run it has really given me some miles of datalogs to really dial in the VEs. With any luck the straightner thing will fix the MAFs signal as I have found these systems heavily bias toward the MAF for most accurate fueling.
 

L31MaxExpress

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Getting closer all the time with the tune on this thing. Hopefully some of these screenshots help some of you out there with really bad tunes be able to spot them before they do engine damage.

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I have the Timing map pretty close to what it likes. The values in the lower left side of it are only used on a WOT stomp from idle. In a typical factory tune these values are as retarded as -12* or 12 ATDC and will make the engine feel lifeless on a WOT stomp from Idle. The higher values help the throttle response to get the engine up on the converter. The lower values at 1,400-1,600 rpm are to allow for timing value necessary for lugging the engine down to 1,400 rpm with the converter locked. WOT from a stop the engine blasts up the rev range so quickly it does not miss the slightly retarded timing between 1,400 and 1,800 rpm. Even on the runs on the engine stand this engine like 16* initial timing and was most responsive with that timing value through 1,500 rpm where the centrifugal advance started to advance.

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L31MaxExpress

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Saxon PC 100mm 6:1 MAF flow straightner has arrived and it is installed. Testing will soon start with it.

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L31MaxExpress

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Made a short test run with it installed and the datalogger going. MAF signal is far more stable now. Engine runs smoother all around. The straightner has the MAF reading higher gms/sec now. Its a bit rich now but consistent. The short term fuel trims no longer oscillate 6-8% from the MAF signal drifting. Seems much happier all around. At steady throttle and rpm it had as much as a 200-300hz float to the sensor and it is now 20-30hz.

PS-I was once a MAF de-screener. I don't recomeend it seeing the huge difference it can make.
 

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Ran 250 miles in it again, just under 19 mpg. I could leave the tune as is but have a few tweaks here and there I am still working on. I was able to get a little more timing in it at cruising speed on flat roads which made it more responsive and smoother. The note of the cam has definately come out now that I have it idling at ~725 rpm warm. Its most noticeable with a cold engine when the oil is thick though.

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L31MaxExpress

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MAF straightner and the fine tuning has definately resulted in a better running engine. Its also dropped down into the 50s and 60s here the past 2 days. Drove 200 miles this morning without having to use the ac. The clutch fan is not having to engage either to keep the engine cool. Best fuel mileage I have seen so far. I drove 200 miles without breaking 2,500 rpm and did not even hit PE once. Cruise set at the 70-75 mph speed limit for most of the trip, averaged 19.7 mpg. I am going to throw a 205F thermostat into it before my return trip to get the engine up to ~210F. The increased heat will cause the PCM to pull ~2° of timing which I am not going to change since I am so close to the knock threshold anyway on the tuning. About to see if I can break 20 mpg without using lean cruise. Lean cruise was worth ~2 mpg on the 350 with the same gearing and the 383 makes the torque to better utilize it. My next experiment is Ethanol free 93 octane. A station local to me sells it, but it is $0.40 a gallon more than E10 91 octane. Thats $12 more per tank. The ethanol sensor is reading 8.9% ethanol currently. In theory the straight gasoline should be a little better on fuel efficiency especially since I should be able to put a little more timing into it. The break even point on the non ethanol fuel would be +2 mpg. At $4 vs $4.40 gal thats 10%.
 
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L31MaxExpress

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On another note. My charcoal canister had come apart internally. Probably from sitting non running with fuel in the tank. The charcoal had made it up to the purge solenoid and blocked it off. I changed the canister with a new one, changed the purge solenoid and blew out the lines. With 30 gallons of fuel giving off vapors sitting a day or two, when the LTFTs become active at 140°F and the purge valve opens, the fuel trims on both banks will drop 5-10% for about 5 minutes before tappering off. My fuel mileage around town slightly increased having a functional vapor canister. So much for the old thinking of deleting it and venting the tank. I have seen multiple LS swaps on the GMT400 chassis with the EVAP system basically deleted. Why smell up your garage or shop or dump the hydrocarbon fumes into the outside air when you can burn those vapors?
 

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I was unable to find a Vortec specific 205F thermostat. That being said it now has a balanced flow, high flow Murray 195F in it. Too early to tell but I did drive it 80 miles today. 30 miles in speed density mode making some VE corrections. Then 30 miles in MAF only dialing in the MAF table. Then I re-enabled the blended fueling mode with the MAF taking over completely ar 1,600 rpm. The VEs were a little lean under throttle and rich on over-run. The MAF was a little rich everywhere. With both the MAF and Speed Density working in unison the engine is seamlessly smooth.

Tailpipe is starting to look a little funny now. Its so clean of soot, the moisture from cold starting it is starting to rust it.

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