5.7L Sonoma going to the dyno soon.

[Rinkrat456]

After 2 years of being a trail-only truck, my '96 GMC Sonoma is finally hitting the road again for daily driver status. I fired it up this past weekend after not running for 3 months while I fabricated a flat bed, upgraded to true dual 2.5" exhaust, made a snorkel while relocating the IAT to a cool spot and swapped to an electric fan . The next 2 weeks will see quite a few tuning changes I hope. I'm curious what you guys think I'll make for power. On Oct 12 I have an appointment to see how close my tune is and figure out what the truck can do.

Here's the build list for the drivetrain:
-'00 Vortec 5.3L block bored to LS1 specs.
-Speed pro cast aluminum OEM replacement LS1 pistons, flat tops
-241 LS1 heads, port matched intake/exhaust runners, milled for 10.3:1
-LS6 "yellow" OEM springs, 206/212, 259/265, .515"/.522", 112lsa 110icl 38* of overlap
-Truck accessories, truck intake, truck MAF and throttle body
-Sanderson S10-swap shorty headers, 1-5/8" primaries 2.5" collectors
-True 2.5" dual exhaust, Magnaflow mufflers
-Tuned by yours truly, see attached

This all goes through a 4L65E I built with mostly OEM parts, stock truck torque converter and NP241 manual transfer case. This was a 2wd frame and is now an off-road truck, converted with a high pinion 8 lug front D44 and rear GM 9.5" 14 bolt SF. 4.10:1 ring and pinion turning 35" all terrain tires.

I was really hoping for 385-400lb-ft of torque at the wheels and 330-350rwhp. Think I'm far off? I hand-built this engine to be extremely DD friendly and to turn 35-37" tires like they're not even there. The preliminary tune is set up for 26-27 degrees of timing at WOT and 91 octane. I will eventually run MAF/SD hybrid tune after I get the VE and spark dialed in.

[Rinkrat456]

BTW, I welcome any and all criticism on the tune. This is a tune that I have probably spent 100 hours putting together and I have not yet uploaded this version to the PCM. The stock tune was a mail order garbage tune from ******* which allowed the truck to run, but left much to be desired. I feel I have pulled the best ideas from a bunch of different platforms (truck gen III and car gen III engines) to put together a 'perfect' tune for this particular Sonoma's 5.7L.

I've looked at this tune so many times it wouldn't surprise me if I missed something so please feel free to dig deep and pull the tune apart before I upload it.

[mecanicman]

Back the timing off. Get your fuel sorted/confirmed first. I have used those pistons before, they are fine when your tune is on but they will not take any knock.


Edit:Not sure if you have done any 3.8L v6 stuff, but I would put the pistons in the same category. If the tune is on they will take a lot of power. It the tune is off and there is knock, it goes very bad very quickly.

[Rinkrat456]

No experience with the 3.8L's shy of helping a friend replace his coil packs in his Monte Carlo.

Are the speed pro hypereutectic pistons stronger or weaker than OEM LS1 pistons? I ask because I borrowed the WOT cells from an LS1 spark table I tuned over the summer that was basically the same engine as mine but with a bigger cam and an LS6 intake. That engine experienced zero KR with a similar spark map...which is what led me to believe I could re-use it for my build. I could definitely be wrong though, especially since my "truck-style" 5.7L builds almost two-thirds more cylinder pressure.

I've got timing set to 26-27* around WOT, what would you back those cells down to?

[Rinkrat456]

mechanicman, are you suggesting I back the timing off during the tuning process and start bumping it back up after VE/MAF is done? I ask because I just looked at a '99 Vette I tuned a few months ago, and in comparing it's stock high octane spark table I found it commanding 27-29 degrees! I did not catch that the first time I did a read-entire. Is this because the Vette weighs so little and my truck so much?

[mecanicman]

My expieriance with those pistons is they are not as strong as stock. If there is no knock they are fine, but they will take less knock then a stock piston.

Yes, back the timing off for tuning. Once fueling is correct you can start putting timing back in. This is the method you should use for any vehicle you are tuning, but if you dont want to pop a head off to see a rod dancing in the hole all by itself and shattered piston in the pan, this is especially important.


I am sure the weight/load of a truck compared to corvette has a bearing on the timing. I always pull it down to a safe level for tuning, then bump it back closer to what I expect it to be and adjust based on dyno feedback form there. I dont believe starting with a table from something else is the safest way to go.

[Rinkrat456]

See attached high octane table for an ideal "post tune" spark table and see also the low octane table for the "in tuning" table based off your suggestions.

What I always hoped for in this truck was an extremely responsive feel to the gas pedal any time I'm over 2k rpm...which is why my initial thought was to give it as much advance as I've typically seen 241 heads take. It's a daily driver, so when used as such all part throttle driving below 3,000 should feel pretty timid but if I were to ever stomp on it to enter PE I really want it to wake up and it should...it's got all the gearing necessary to turn 35" tires in a 4800lb truck.

Edit: Speaking of PE...how does it look btw? That's another part of the tune I focused a lot of attention to. My intention was 12.75:1.

[mecanicman]

If you want the most out of your timing, adjust it on the dyno. Well I can say those numbers are close, the dyno will tell you where it should be. Also, flat numbers like that are not generally what would be ideal. The timing will climb, then flatten out or even decrease, then climb some more. If you watch a scan after the fueling is tuned and you have made a run, you will see the maf max out and be flat, then start to decrease. You can also view injector duty cycle the same way. This area is where your cylinder fill is at its highest and will require the least timing. The areas on either side of it can take more.

[Rinkrat456]

Interesting theory in what you just said...take a look at the Corvette's high octane table again.