I’m getting my stock LT one machine for a 383 stroker and I need help with the tune so I can drive it to get it Dino tune. I went with the LT for hot cam with 1.6 roller rocker arms and I’m not sure about the timing. Does anyone have a basic tune for this? I’m putting in #42 injectors and a walbro 255lph fuel pump. My heads are stock other then new springs for the new cam.
Last edited by lyonheart; 10-13-2020 at 04:43 AM.
Meh, call me a redneck, but just change the cylinder displacement and leave stock timing for now until you can tweak it on the dyno. Add the characterization data for the injectors (flow rate, short pulse adders and voltage offsets), and leave everything else the same as before (especially your intake and exhaust configuration). I'm sure someone smarter than me will chime in but that's what I'd do.
Thank you. I didn’t know if it would mess anything up if I tried to start it. I have tuner cat and I can change injector size and cylinder displacement. I haven’t got the motor back yet so I have plenty of time to mess with tune.
I try not to dump a bunch of gas past the rings or overheat the catalytic converters and you're fine. Stock timing tables will be safe for now.
I’m not running a cat.
Call me conservative, but I would back off the whole timing table atleast 4° if not 6° for a startup tune. With the displacement change the compression ratio will likely change as will the dynamic compression ratio and cylinder pressure. Better to kill any chance of detonation than hammer bearings, break ring lands or shatter pistons.
I built an 11:1 383 for my Express van and backed off the timing 6° from the factory Vortec 350 for startup and break-in. Then once I had the rings seated and the fueling close tuned for MBT. Also during intial break-in you will have some oil getting into the cylinders which will drastically decrease the available octane making detonation more of a possibility. I ended up making peak power at only 27° of timing on 93 octane and 31° on E85. With a tight quench distance and a good piston design timing requirements are also often less than a factory engine.
Last edited by Fast355; 10-15-2020 at 08:52 AM.
Thanks for the info. So just high light the whole chart and minus 4 degrees in the spark table and the extended table
well, what's the specs on your motor?
Bore is 0.030" over.
What dish on the piston (in cc)?
What head gasket?
Are the pistons at zero deck or 0.025" down in the bore like factory?
Which cylinder heads? (Aluminum or iron)?
My builder has not gotten back with me yet but I’m pretty sure it’s a stock bore so he will go 30 over. As for the pistons I don’t know. I’m using felpro head gaskets and bolts for the head. If there is something wrong with that I would like to know now. As far as heads they are the stock aluminum and my builder called comp cam as order the beehive springs and hardware to fit the lt4 hot cam.
Everything I listed will affect the static compression ratio of the motor. You NEED to know all of that, plus your cam specs, to get a good sense of what the spark tables will likely look like. More cylinder filling means less timing needed because a more dense mixture burns more quickly. Higher compression will also mean you need to run less timing or higher octane, or both.
My cam with the 1.6 roller rockers will be .525 & .525
Duration @.006 cam lift. 272. 281
@ .050 cam lift. 219. 228
Lobe centerline 109. 115
Lobe separation. 112
As far as every thing else I will know more tomorrow because I’m going to see my builder. I’m sorry it takes so long to get back to you I’ve been working 12 hrs days and there’s not much time to do anything else.
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