Car starts making hella power then...
12-04-2003, 08:05 PM
#1
HELP! Car starts making hella power then... it just lays over. Will get dyno graphs up soon.
Its a big cam, with SLP maf. Thought maybe the MAF was off in the midrange, but the mafflow rate differences seem to widen as you go up the hrt range so theoretically it woudl get wackiest at the top end not just the mid range.
The torque curve is pulling HARD at 3000 (beating out any other cam only car weve dynoed) peaks at 3500 then starts a slow downslide to about 4500. Then it climbs slowly to 5000, where it planes off and then decends in a normal manner. The car held onto 350 lbft as long as any G5XX cam, and made 395 hp at 6300 thru cats and a full catback, but the midrange was like 50 lbft off.
Not injector i wouldnt think because it regains it at high rpm (duty cycle of 98% peak but many cam cars weve done are that high. not preferable, but they dont lay over) Dont think its valvetrian if it floats valves or collapses lifters at 4000 it should regain by 6300. Slipping clutch? Wouldnt think that would magically start grabbing at the exact same point every run either.
here is a screenshot of the EFILive log
Its a big cam, with SLP maf. Thought maybe the MAF was off in the midrange, but the mafflow rate differences seem to widen as you go up the hrt range so theoretically it woudl get wackiest at the top end not just the mid range.
The torque curve is pulling HARD at 3000 (beating out any other cam only car weve dynoed) peaks at 3500 then starts a slow downslide to about 4500. Then it climbs slowly to 5000, where it planes off and then decends in a normal manner. The car held onto 350 lbft as long as any G5XX cam, and made 395 hp at 6300 thru cats and a full catback, but the midrange was like 50 lbft off.
Not injector i wouldnt think because it regains it at high rpm (duty cycle of 98% peak but many cam cars weve done are that high. not preferable, but they dont lay over) Dont think its valvetrian if it floats valves or collapses lifters at 4000 it should regain by 6300. Slipping clutch? Wouldnt think that would magically start grabbing at the exact same point every run either.
here is a screenshot of the EFILive log
Last edited by GrannySShifting; 12-06-2003 at 10:50 AM.
12-04-2003, 08:09 PM
#2
Notice in the third chart, the puslwidth actually lessens in the midrange. Every other car gets largest p/w there, because obviously peak fuel demand is at or slightly before peak torque.
This cars torque curve mirrors the pulsewidth graph (yellow), and the hp curve mirrors the dutycycle curve (green)
I noticed MAF kinda layed over but it made less power there so that kinda makes sense. I think thats more of a result not a cause, as motor making less power consumes less air.
I dont understand why the pulsewidth would actually drop there, if anything level off???
Oh yeah air/ful doesnt SHOW lean, actually i have it at 12.6-12.8 then at 3500 down to 12.0 trying to see if it needed richening up (before i noticed the pulswidth) no affect on power. As a side note, I picked up 50 ftlb in the low end (2500-3300) and 15-20 hp past 5500 but in the area 4000-5000 the first and last pull were within 8 hp, no gains richer/leaner less/more timing. no knock whatsoever anywhere. If it was THAT lean it should knock id think especially seeing as i had 32 degrees in there at one point.
Only thoght i have is to richen the car up until the p/w graph looks like id expect, and then see what kinda power the car is making
This cars torque curve mirrors the pulsewidth graph (yellow), and the hp curve mirrors the dutycycle curve (green)
I noticed MAF kinda layed over but it made less power there so that kinda makes sense. I think thats more of a result not a cause, as motor making less power consumes less air.
I dont understand why the pulsewidth would actually drop there, if anything level off???
Oh yeah air/ful doesnt SHOW lean, actually i have it at 12.6-12.8 then at 3500 down to 12.0 trying to see if it needed richening up (before i noticed the pulswidth) no affect on power. As a side note, I picked up 50 ftlb in the low end (2500-3300) and 15-20 hp past 5500 but in the area 4000-5000 the first and last pull were within 8 hp, no gains richer/leaner less/more timing. no knock whatsoever anywhere. If it was THAT lean it should knock id think especially seeing as i had 32 degrees in there at one point.
Only thoght i have is to richen the car up until the p/w graph looks like id expect, and then see what kinda power the car is making
Last edited by GrannySShifting; 12-04-2003 at 08:22 PM.
12-06-2003, 10:55 AM
#5
TECH Fanatic
What kind of exhaust setup do you have on the car?
There is no KR and your timing tables look good. Only thing I see that is strange is that there is a significant difference between your B2S1 and B1S1 readings, it is odd that they are not more similar. Looks like one bank is leaner than the other???
There is no KR and your timing tables look good. Only thing I see that is strange is that there is a significant difference between your B2S1 and B1S1 readings, it is odd that they are not more similar. Looks like one bank is leaner than the other???
12-06-2003, 11:58 AM
#6
Restricted User
iTrader: (9)
Join Date: Sep 2002
Location: Sierra Vista, AZ
Posts: 7,603
Likes: 0
Received 0 Likes
on
0 Posts
That dip in timing from the 1st table all the way down is mirrored in every one of your parameters. Looks like the timing drops down to about 9*, that will definately put your power band in a hurt locker.
Charlie.
Charlie.
12-06-2003, 08:20 PM
#7
Timign never was below 26 degrees maybe you got the wrong graphed line?
Or possibly your talking about the dip at the end? Only where I let off it does that, and it was making 394 hp at that point bak on track again.
The exhaust is Jethot longtubes, 3' Y pipe with cats at the time (two 3' cats) and a corsa catback.
No more cats next time and thru a cutout
I shoudlve used a different example for the last graph. The last graph was of another car with a normal torque curve and a normal pulsewidth graph (BPW) His one O2 was fried, so I put the car in open loop, cleared the LTrims and dynoed the car to those results
This car is frustrating I do this for a living, and have never seen a torque curve like that. Done probably 200 LS1 cars before this is funky.
Or possibly your talking about the dip at the end? Only where I let off it does that, and it was making 394 hp at that point bak on track again.
The exhaust is Jethot longtubes, 3' Y pipe with cats at the time (two 3' cats) and a corsa catback.
No more cats next time and thru a cutout
I shoudlve used a different example for the last graph. The last graph was of another car with a normal torque curve and a normal pulsewidth graph (BPW) His one O2 was fried, so I put the car in open loop, cleared the LTrims and dynoed the car to those results
This car is frustrating I do this for a living, and have never seen a torque curve like that. Done probably 200 LS1 cars before this is funky.
Trending Topics
12-07-2003, 11:58 PM
#11
sensors of varying quality, etc. happends ALOT on LT1 cars. Unless your talking about the last graph, which was another car, with a dead o2
Bottom graph is a DEAD STOCK program. Noticed gain at 3000 rpms
Bottom graph is a DEAD STOCK program. Noticed gain at 3000 rpms
Last edited by GrannySShifting; 12-08-2003 at 08:39 PM.
12-10-2003, 09:10 AM
#13
Seen a lot of dynosheets with a power dip starting at 4000rpm and recovering above 4500. My suspicion is that it's related to the header/exhaust system. Adjusting fuel and spark in the affected area doesn't seems to make the dip go away. I think the issue is more on the mechanical side (ie. intake or exhaust length tuning). Working with one of the finalists in the last 2 Engine Masters competition, we've seen headers make enormous differences in torque curves and affect the shape of the curve. The higher the specific output of the engine, the more sensitive to intake and especially exhaust tuning. Studying the scan log everything appears to be pretty normal. Was the AFR steady throughout the run?
I have an SLP MAF on my 2000 SS and have had to recalibrate the entire MAF table including the shape of the curve. I don't know who checks the calibration of these units, but they're definitely not consistent with factory calibration. I'm trying to setup a labscope on my flowbench to build a proper caliration table for each MAF.
Keep us posted on your progress.
Richard
I have an SLP MAF on my 2000 SS and have had to recalibrate the entire MAF table including the shape of the curve. I don't know who checks the calibration of these units, but they're definitely not consistent with factory calibration. I'm trying to setup a labscope on my flowbench to build a proper caliration table for each MAF.
Keep us posted on your progress.
Richard
12-10-2003, 02:56 PM
#14
Richard, i think that a high percentage of dyno graphs that have that dip are due to the factory style timing tables that incorporate a timing dip at peak torque, Im guessing to keep them out of detonation.
Lots of guys just add 3 degrees across the board, whiel it may make some gains, still keeps the timing dip intact. I think 95% of the cars weve tuned leave sans dip
Lots of guys just add 3 degrees across the board, whiel it may make some gains, still keeps the timing dip intact. I think 95% of the cars weve tuned leave sans dip
12-11-2003, 08:40 AM
#15
Originally Posted by GrannySShifting
Richard, i think that a high percentage of dyno graphs that have that dip are due to the factory style timing tables that incorporate a timing dip at peak torque, Im guessing to keep them out of detonation.
Lots of guys just add 3 degrees across the board, whiel it may make some gains, still keeps the timing dip intact. I think 95% of the cars weve tuned leave sans dip
Lots of guys just add 3 degrees across the board, whiel it may make some gains, still keeps the timing dip intact. I think 95% of the cars weve tuned leave sans dip
Richard
