Big dip in A/F on dyno while tuning
05-29-2004, 02:58 AM
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Big dip in A/F on dyno while tuning I have a TT 427, and when we try to dynotune i get a 7 degrees knock @ aprox 4000 RPMs, and also have a big dip in A/F ratio on this point.
My theory is:
less timing, same amount of fuel and air going in, gives me a situation with less efficient burn prosess and A/F get fatter ?
Does this make sense ?
I have 14-16 degrees spark advance in this area, still getting knock, could it be a false knock generated by turbos rapid spooling up (ceramic BB) ?or something else ?
Her is a summary of my pull
427 TT with auto on Dynojet 248c
RPM A/F HP TQ
3000 11,6 289 506
3100 11,6 343 582
3200 11.6 404 663
3300 11,4 478 760
3400 11,4 543 838
3500 11,2 587 881 knock starts
3600 10,8 624 911
3700 10,4 659 935
3800 10,1 689 952
3900 10,0 702 945
4000 10,0 690 906 knock peak 7 degrees (15-7=8 degrees)
4100 10,3 646 828
4200 11,0 657 822
4300 11,6 671 820
4400 11,9 687 820
4500 12,1 695 820
4600 12,2 696 796
4700 12,2 699 782 knock ends
4800 12,1 702 769
4900 12,0 708 759
5000 12,0 707 743
5100 11,9 709 731
5200 11,8 702 709
5300 11,8 705 698
5400 11,8 704 685
5500 11,8 704 672
5600 11,8 669 627
5700 11,9 687 633
5800 11,9 678 614
5900 11,8 673 599
6000 11,6 662 579
6100 11,5 664 572
6200 11,3 658 557
6300 11,3 656 547
I have low timing 14-16 degrees, so a 7 degrees kncok leaves me with 8 degrees total timing :-)
My plan is to have a smooth even A/F with low timing, a bit rich, then start
to increase timing back up until knock accurs, then back off some...
Boost rises QUICKLY with my new turbos, shoots to 15 psi, then drops off and hold steady 13 psi
God i love the cold dense weather in Norway (sometimes) :-)
TIA
My theory is:
less timing, same amount of fuel and air going in, gives me a situation with less efficient burn prosess and A/F get fatter ?
Does this make sense ?
I have 14-16 degrees spark advance in this area, still getting knock, could it be a false knock generated by turbos rapid spooling up (ceramic BB) ?or something else ?
Her is a summary of my pull
427 TT with auto on Dynojet 248c
RPM A/F HP TQ
3000 11,6 289 506
3100 11,6 343 582
3200 11.6 404 663
3300 11,4 478 760
3400 11,4 543 838
3500 11,2 587 881 knock starts
3600 10,8 624 911
3700 10,4 659 935
3800 10,1 689 952
3900 10,0 702 945
4000 10,0 690 906 knock peak 7 degrees (15-7=8 degrees)
4100 10,3 646 828
4200 11,0 657 822
4300 11,6 671 820
4400 11,9 687 820
4500 12,1 695 820
4600 12,2 696 796
4700 12,2 699 782 knock ends
4800 12,1 702 769
4900 12,0 708 759
5000 12,0 707 743
5100 11,9 709 731
5200 11,8 702 709
5300 11,8 705 698
5400 11,8 704 685
5500 11,8 704 672
5600 11,8 669 627
5700 11,9 687 633
5800 11,9 678 614
5900 11,8 673 599
6000 11,6 662 579
6100 11,5 664 572
6200 11,3 658 557
6300 11,3 656 547
I have low timing 14-16 degrees, so a 7 degrees kncok leaves me with 8 degrees total timing :-)
My plan is to have a smooth even A/F with low timing, a bit rich, then start
to increase timing back up until knock accurs, then back off some...
Boost rises QUICKLY with my new turbos, shoots to 15 psi, then drops off and hold steady 13 psi
God i love the cold dense weather in Norway (sometimes) :-)
TIA
Last edited by Rune; 05-29-2004 at 03:19 AM.
05-29-2004, 12:50 PM
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Maybe you have more boost overshoot than you
think, and the excess cylinder pressure is pushing
you into knock? If you have a lot of air volume
in front of the throttle you might ought to take
a look at this, try rolling the throttle on slow, to
see if it's a tip-in pressure spike problem?
think, and the excess cylinder pressure is pushing
you into knock? If you have a lot of air volume
in front of the throttle you might ought to take
a look at this, try rolling the throttle on slow, to
see if it's a tip-in pressure spike problem?
05-31-2004, 12:17 PM
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Originally Posted by jimmyblue
Maybe you have more boost overshoot than you
think, and the excess cylinder pressure is pushing
you into knock? If you have a lot of air volume
in front of the throttle you might ought to take
a look at this, try rolling the throttle on slow, to
see if it's a tip-in pressure spike problem?
think, and the excess cylinder pressure is pushing
you into knock? If you have a lot of air volume
in front of the throttle you might ought to take
a look at this, try rolling the throttle on slow, to
see if it's a tip-in pressure spike problem?
05-31-2004, 03:04 PM
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05-31-2004, 04:03 PM
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Originally Posted by jimmyblue
Did you do anything to suppress the Cat Overtemp
function? Do you even have cats left, to protect?
A sudden enrichment at 4KRPM or so is COT's
"calling card".
function? Do you even have cats left, to protect?
A sudden enrichment at 4KRPM or so is COT's
"calling card".
Thanks for the hint !
Rune
10-25-2004, 04:04 PM
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i'm having the exact problem on my supercharged ls1.
i always see knock no matter what i do around 4000 rpm and my A/F gets very rich in that area too.
i took my timing down to 14 deg. and max allowed kr is set at 4 deg.
could this be something related to on eof the burst knock tables ( not sure which one , but i was told the computer sees a difference in airflow and if it is big enough it will pull timing because it assumes its knock or something) . is this true?
any suggestions?
i always see knock no matter what i do around 4000 rpm and my A/F gets very rich in that area too.
i took my timing down to 14 deg. and max allowed kr is set at 4 deg.
could this be something related to on eof the burst knock tables ( not sure which one , but i was told the computer sees a difference in airflow and if it is big enough it will pull timing because it assumes its knock or something) . is this true?
any suggestions?
