7.4 timing curves

[Schurkey]

The L29 cylinder heads won't need more than 30--32 degrees for best power. Perhaps not even that much.

Best economy is another story--but--because the chambers are fairly efficient, I don't think you're going to want the high-40s, low-50s even with the part throttle electronic "vacuum advance" adding advance.

A dyno would tell the tale. I bet ~40--42 is all you'd need.

 

[Supercharged111]

I got audible knock at 32 degrees here in CO under load with 91 octane. Was hoping just for a max of 40. I do wonder if shorty headers and larger front pipes would help it tolerate more timing.

 

[ZRoe]

I got audible knock at 32 degrees here in CO under load with 91 octane. Was hoping just for a max of 40. I do wonder if shorty headers and larger front pipes would help it tolerate more timing.

What are you using to measure and adjust timing? Are you tuning a 411 swapped truck?
I hope I didn't throw the OP off with my statement about the electronic advance being different via cheap OBD2 scanner vs. proper mechanics scan tool with respect to the black box.
I'll check mine again but I thought my OBD2 via torque and BlueDriver both gave me wonky readings for timing. When I say wonky I mean retarding timing not advancing. I felt like the OBD2 reading was the amount the computer was compensating not the actual timing.

I really appreciate the information either way, I don't mind being wrong and I'm happy to find people that can teach me something.

Sent from my moto e5 supra using Tapatalk

 

[Christian Steffen]

If your CMR is set at 0 you are limited to 42 maximum by physical limitation of the distributor. Anything beyond that will cause misfiring.

This is definitely true. I helped another member on here that had a 0411 truck that was misfiring. Luckily he bought hp tuners so we could see the tune, his tune was commanding into the 50s with the max timing set at 45 (it definitely saw up 42-43 command), and misfired like crazy. We pulled it back a few degrees and all the misfiring went away. Also makes perfect sense considering 360/8=45.

 

[Supercharged111]

Welll ****, I think my cmpret is around 12 on the dually. But if it knows what cmpret is, doesn't it just compensate for it automatically? My 1500 had a cmpret of 30 until I changed the distributor gear and still managed to advance around 40.

 

[Schurkey]

Welll ****, I think my cmpret is around 12 on the dually. But if it knows what cmpret is, doesn't it just compensate for it automatically? My 1500 had a cmpret of 30 until I changed the distributor gear and still managed to advance around 40.

Unless the rotor alignment is so bad that the spark is jumping to the wrong plug wire terminal, or to ground through contamination on the inside of the cap, I believe that the cam retard makes no difference in the running of the engine.

At least, the service manual for my '97 is saying approximately that--the cam sensor is used to determine which cylinder is misfiring, and that's all.

My '97 doesn't run right, and the cam retard is 29 degrees off--so I guess I'll find out how much better it runs just by aligning the distributor. This will happen soon after it warms up. Today and tomorrow are expected to be ~ -30F overnight ,and the truck with snow plow is too long to fit in the garage.

 

[Christian Steffen]

Welll ****, I think my cmpret is around 12 on the dually. But if it knows what cmpret is, doesn't it just compensate for it automatically? My 1500 had a cmpret of 30 until I changed the distributor gear and still managed to advance around 40.

Just to be clear, in my post above I was referring to the above 42* part. I don't have any experience with cmp causing issues. Max timing has always gone where I told it to.

 

[Christian Steffen]

So on the topic of timing curves though, here are a few.

489, 9.6 cr, 270hr cam, headers, exhaust (mine)
86 *F, 91.5 kpa, 4000 rpm, 277 g/s (South Dakota)

You must be registered for see images attach

stock computer, stock engine 150k, no cats better muffler, occasionally kick a little kr

You must be registered for see images attach

9.1 cr rebuilt engine with comp 270hr cam, headers, exhaust
85 *F, 92 kpa, 4000 rpm, 237 g/s (South Dakota)

You must be registered for see images attach

stock truck with 130k, 91 octane, occasionally kick a little kr
56*F, 96 kpa, 4000 rpm, 239 g/s (South Carolina Tuned w/ different WB)

You must be registered for see images attach

 

[Supercharged111]

What airflow are you seeing?

 

[Christian Steffen]

What airflow are you seeing?

Well I tuned the maf on all of these to dial in fueling with the wideband, so we'll have to take it with a grain of salt. I closed my laptop for the night, but I'll update the previous post with airflow of what I still have logs of in the morning.