1998 Z71 Build

[Awest623]

This was mine when I first swapped more than 7 years ago. L31 with a factory GM LT4 cam, 1.6 rockers, shorty headers and the TB lip removed. If I remember for my startup tune all I did was remove the VATS, set the Park/Neutral switch to None, bumped up the High octane spark map and idle spark map about 4°. Was running stock VE and MAF tables at the time. Ran so smoothly even after a cold start.

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When I first started tuning WOT. Still had 100% of the torque management in the tuning and ran 0-60 in about 9 seconds. 3 ton van with 3.42 gears.

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I had to bump up the base idle airflow by 30% and base idle spark to 28 degrees to get mine to idle good. She does great now. HT383 cam with 1.6 rockers

 

[L31MaxExpress]

I had to bump up the base idle airflow by 30% and base idle spark to 28 degrees to get mine to idle good. She does great now. HT383 cam with 1.6 rockers

I setup a histogram to average the MAF reading vs coolant temps of the base idle airflow table. Cold start on the coldest morning at that time two days in a row. Let the engine warm up in Park the first time. The 2nd time I shifted into Drive as soon as it fired and let it warm up. The average values are what I put into the tables. Idled perfectly after.

For my 25% underdrive pulley I had to adjust the a/c idle torque table. Worked really well multiplying the stock table by .75. Stopped the engine from surging when the a/c compressor cycled.

 

[L31MaxExpress]

What injectors did you go with? The 36 lb/hr upgrade spider?

 

[Awest623]

I setup a histogram to average the MAF reading vs coolant temps of the base idle airflow table. Cold start on the coldest morning at that time two days in a row. Let the engine warm up in Park the first time. The 2nd time I shifted into Drive as soon as it fired and let it warm up. The average values are what I put into the tables. Idled perfectly after.

I was curious on how to properly do it. Thanks, I'll give it a try next time I get the chance

 

[Awest623]

What injectors did you go with? The 36 lb/hr upgrade spider?

48lb upgraded from Wynnjammer. Was gonna get the 36lb but wanted to have plenty of headroom for the Whipple. I know I would be better off with a marine intake but I haven't found one with the right throttle body mounting pattern in months. And I don't wanna go with an aftermarket intake and end up having to get rid of A/C.

 

[Supercharged111]

Throttle body mounting pattern? What am I missing?

 

[L31MaxExpress]

I was curious on how to properly do it. Thanks, I'll give it a try next time I get the chance

Generally speaking it is better to overshoot it a little. For the area of the map below the startup I added about 20% to the coldest temp and interpolated the values up to the coldest value recorded. Then for warmer temps I simply flat lined the highest value recorded. Figured the PCM could subtract a little air if needed if the engine ever ran hotter than normal.

 

[Awest623]

Throttle body mounting pattern? What am I missing?

The marine intakes came with both an electronic throttle body and a normal throttle body. The electronic one uses a 4 bolt mounting pattern and is completely different.

 

[L31MaxExpress]

Throttle body mounting pattern? What am I missing?

The new ones use a 4 bolt DBW throttle body. Similar to the last few years of the 4.3.

 

[Awest623]

Throttle body mounting pattern? What am I missing?

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[L31MaxExpress]

I am running a 383 now. I have the dual plane MPI intake and a 1200 cfm 4bbl throttle body on mine. 4" spectre carb bonnet and a 100mm maf housing with a LS3/LS7 cartridge MAF.

Even with a ~525 hp 383 the mileage is suprisongly good until I get into the secondary throttle plates. I have PE set to activate right where the linkage picks up the secondaries.