Cam bucking and MAF vs SD
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Cam bucking and MAF vs SD Has anyone noticed an improvement in low-speed cam surging/bucking just by switching from MAF to SD?
I just stumbled on a post where someone theorized that bucking stems from the MAF signal getting unreliable due to flow reversion, and if that's the case then I'd expect that switching to SD should help a lot.
Conversely, if switching to SD hasn't helped, then I'll just focus on timing changes.
I just stumbled on a post where someone theorized that bucking stems from the MAF signal getting unreliable due to flow reversion, and if that's the case then I'd expect that switching to SD should help a lot.
Conversely, if switching to SD hasn't helped, then I'll just focus on timing changes.
You need to have your VE tables tuned properly even when running a MAF. You have to disable the MAF to do this, so the answer to your question will become readily apparent while dialing in the SD portion of your tune. Your results will depend on exactly what cam and intake you are running, as well as your MAF placement. Once you exceed a certain amount of duration, Alpha N may be the only way to really smooth out idle instability, although a cam that large is generally not used in anything resembling a street car anyway.
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Mostly just first and second gear, under 2000 RPM, with light throttle. Maybe third gear too but it's smooth in 4th-6th at any RPM.
It's just standard low-speed / low-load big-cam stuff. The cam is 239/251@114+4, in a 454, but the low-speed behavior is pretty similar to when I had a 232/234 @ 112 cam with the stock LS6. This one just stays rough until a couple hundred RPM higher.
I'm probably going to try reducing the spark advance first as I've seen a few posts saying that helps a lot. The VE table needs work too though.
This thread was mostly just to help me decide which one to focus on first.
It's just standard low-speed / low-load big-cam stuff. The cam is 239/251@114+4, in a 454, but the low-speed behavior is pretty similar to when I had a 232/234 @ 112 cam with the stock LS6. This one just stays rough until a couple hundred RPM higher.
I'm probably going to try reducing the spark advance first as I've seen a few posts saying that helps a lot. The VE table needs work too though.
This thread was mostly just to help me decide which one to focus on first.
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From: Florida
im pretty sure the oem algorithm favors using the map sensor at low rpm (below 4000rpm) and then switches to 'high speed' mode which is effectively 'maf mode'
what does your inlet piping/maf look like? do you have a honeycomb ahead of the maf?
getting the ve table dialed in should make a big difference. you can also log your maf hz and see how noisy it is.
what does your inlet piping/maf look like? do you have a honeycomb ahead of the maf?
getting the ve table dialed in should make a big difference. you can also log your maf hz and see how noisy it is.
Mostly just first and second gear, under 2000 RPM, with light throttle. Maybe third gear too but it's smooth in 4th-6th at any RPM.
It's just standard low-speed / low-load big-cam stuff. The cam is 239/251@114+4, in a 454, but the low-speed behavior is pretty similar to when I had a 232/234 @ 112 cam with the stock LS6. This one just stays rough until a couple hundred RPM higher.
I'm probably going to try reducing the spark advance first as I've seen a few posts saying that helps a lot. The VE table needs work too though.
This thread was mostly just to help me decide which one to focus on first.
It's just standard low-speed / low-load big-cam stuff. The cam is 239/251@114+4, in a 454, but the low-speed behavior is pretty similar to when I had a 232/234 @ 112 cam with the stock LS6. This one just stays rough until a couple hundred RPM higher.
I'm probably going to try reducing the spark advance first as I've seen a few posts saying that helps a lot. The VE table needs work too though.
This thread was mostly just to help me decide which one to focus on first.
Most if not all bucking can be removing by decreasing spark from the low RPM/Spark Airmass cells (Base High/Low Octane) and properly adjusting your fueling tables. This is the case with most "big" camshafts, at least for me.
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How many grams per cycle do you all see in cruise? I'm asking because I want to make sure I'm adjusting the right region of my timing tables.
Also because I don't have a logging parameter for grams/cycle so I divided MAF (grams per second) by RPM/60 (revolutions per second) and divided by 2 again (two intake strokes per revolution since there are 8 cylinders) and I want to make sure I'm getting this right. Basically I seem to be getting about 0.45 - 0.55 grams when it's running smoothly, so I plan to reduce timing for lower airflow and 1200-1800 RPM.
Thanks!
Also because I don't have a logging parameter for grams/cycle so I divided MAF (grams per second) by RPM/60 (revolutions per second) and divided by 2 again (two intake strokes per revolution since there are 8 cylinders) and I want to make sure I'm getting this right. Basically I seem to be getting about 0.45 - 0.55 grams when it's running smoothly, so I plan to reduce timing for lower airflow and 1200-1800 RPM.
Thanks!
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Verdad Gallardo Thread Starter
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I took a 2 degrees out at 0.52 and 4 degrees out at 0.44 and lower, drove it around tonight, and it helped quite a bit.
So I took another 1-2 degrees out for the next iteration, will try it tomorrow.
So I took another 1-2 degrees out for the next iteration, will try it tomorrow.
