Erratic dyno curves
02-05-2003, 09:22 AM
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Erratic dyno curves I have a 2002 Z28 M6 with Hooker LT's, ORY, SLP Loudmouth, LS1 Motorsports lid, K&N, and new Granatelli 6.0 MAF. I dyno'd the car a few days ago after a few LT1's and some 98-00 SS's went, and I notices that while their torque/hp curves were relatively straight-lined curves, my torque looked like somebody's heartbeat! The HP curve was a little zig-zaggy, but not nearly as bad as the torque. I pulled 344.5rwhp/366.8 tq, and the 2 met right at 5000 rpms. A friend of mines 01 T/A's sheet looked like mine also, but he doesnt have headers or ORY.
Any guesses as to why my curves werent as smooth as the other LS1's there, which basically had the same mods? Could it perhaps be the different cam or something??
Any guesses as to why my curves werent as smooth as the other LS1's there, which basically had the same mods? Could it perhaps be the different cam or something??
02-05-2003, 09:53 AM
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Re: Erratic dyno curves I know some dyno's have a smoothing option on the dyno chart. Maybe smoothing was off when your graph was displayed. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> This has happend to me before. The graph was spikey from start to start. Can you post a pic of your dyno graph? Your peak numbers look great!
02-05-2003, 10:30 AM
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Re: Erratic dyno curves Because you followed other cars on the chassis dyno whose torque curves were smooth, I would concluded that the dyno was working correctly as well as the data collecting and display along with any smoothing method. I would say that it is your car that is causing the jagged torque curve, possibly knock retard.
Next time you go on a dyno, hookup a scanner and record your own data, if you are allowed.
Right now, you could go out on the xway with a scanner and check for KR under WOT conditions.
Next time you go on a dyno, hookup a scanner and record your own data, if you are allowed.
Right now, you could go out on the xway with a scanner and check for KR under WOT conditions.
02-05-2003, 11:04 AM
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Re: Erratic dyno curves The KR was my guess...Any way to fix that? I'm new to the LS1's, so I dont know alot about the computer stuff yet. I'll scan the dyno sheet later on tonight and post it, if I have time. Thanks!!
02-05-2003, 02:30 PM
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Re: Erratic dyno curves Mine just turned 7K miles. Like I said, the 98-00 were smooth, but my 02 and another 01 were erratic-dont know the mileage on the 01.
02-06-2003, 12:44 AM
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Re: Erratic dyno curves My car was dyno'ed last weekend as well. Same thing happened to me. 2 LS1's before smooth curve, mine looked jagged and unsmooth. But took it to the track and ran 13.4 stock.
The dyno guy said I might need to switch my plugs out...havent tried it yet. Car has 50k on it, how many miles on yours?
The dyno guy said I might need to switch my plugs out...havent tried it yet. Car has 50k on it, how many miles on yours?
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02-07-2003, 12:03 AM
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Re: Erratic dyno curves Poor combustion is usually what causes a jagged dyno graph.
1) Bad ignition: If your sparkplugs or ignition system is weak it can cause this
2) Detonation: Your computer playing tug-o-war with the timing. Detonation can usually be seen as a definitive drop of ~5hp, then its gets jagged.
3) Too Rich: If you are running with too much fuel combustion suffers. This is usually the one that I see and deal with.
Good Luck,
Kevin
1) Bad ignition: If your sparkplugs or ignition system is weak it can cause this
2) Detonation: Your computer playing tug-o-war with the timing. Detonation can usually be seen as a definitive drop of ~5hp, then its gets jagged.
3) Too Rich: If you are running with too much fuel combustion suffers. This is usually the one that I see and deal with.
Good Luck,
Kevin
02-07-2003, 07:52 AM
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Re: Erratic dyno curves Thanks Kevin!
Really good information.
Just had my A/F checked out on a dyno...was fine.
Plugs probably need changed
How would I know about the Detonation? LS1Edit/ATAP I am assuming. Anything noticeable to the 'naked eye'?
Thanks!
Really good information.
Just had my A/F checked out on a dyno...was fine.
Plugs probably need changed
How would I know about the Detonation? LS1Edit/ATAP I am assuming. Anything noticeable to the 'naked eye'?
Thanks!
02-07-2003, 09:15 AM
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Re: Erratic dyno curves If the detonation is bad enough, you'll actually hear it. It sounds like somebody just threw a bag of marbles into your engine.
The best way to monitor it though is through a scantool watching Knock Retard. Knock retard is an indication that the engine knock sensors are seeing detonation.
The best way to monitor it though is through a scantool watching Knock Retard. Knock retard is an indication that the engine knock sensors are seeing detonation.
