Question about my dyno
Thread Starter
Teching In
Joined: Oct 2003
Posts: 33
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Question about my dyno Here is a link to my original results thread:
https://ls1tech.com/forums/dynamometer-results-comparisons/194316-do-these-numbers-sound-right.html
On my dyno sheet, the horsepower fluctuates at the top of the power band starting at about 5500. It goes up and down rapidly in about 5-10HP bumps from 5500 to the rev limiter. Any idea as to what is causing it to fluctuate?
Mods are in my sig.
Thanks in advance.
https://ls1tech.com/forums/dynamometer-results-comparisons/194316-do-these-numbers-sound-right.html
On my dyno sheet, the horsepower fluctuates at the top of the power band starting at about 5500. It goes up and down rapidly in about 5-10HP bumps from 5500 to the rev limiter. Any idea as to what is causing it to fluctuate?
Mods are in my sig.
Thanks in advance.
On The Tree
Joined: Nov 2001
Posts: 157
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From: DFW,TX
Could be valve springs. My 2000 Z28 did that very thing at 4500 miles. By 7500 miles it would lose 45 RWHP at 5600 RPM's and shoot back up at 5800 RPM's on the dyno. I could actually feel it in 2nd and 3rd gear. I replaced them with 01 LS6 valvesprings (this was in Jan 2002) and it was a clean kill. Problem gone 
Thread Starter
Teching In
Joined: Oct 2003
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Would there be any other symptoms if it was valve springs? The fluctuation isn't near that much.
My tuner said that some cars do this and it's nothing to worry about. You can't feel it at all in the car when driving it.
My tuner said that some cars do this and it's nothing to worry about. You can't feel it at all in the car when driving it.
If you can post the graph, that could help. My first guess just reading the first sentence of your post was valve float. We've seen it alot, stock springs with stock heads and cam and all the bolt-ons. If you have the graph, post it up, and we'll go from there 
-Matt-
-Matt-
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Dyno Graph..
Originally Posted by Baluchitherium4
Here is a scan of the dyno sheet:
Thanks in advance.
Thanks in advance.
Good luck...
Tony M.
Thread Starter
Teching In
Joined: Oct 2003
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Originally Posted by Tony Mamo @ AFR
It looks to be either valve float or "Knock Retard"....or both for that matter. You would have to use a scanner (Tech II , Predator, etc.) that would record real time data during the run to verify whether you are getting knock retard. I'm leaning towards Knock retard because serious valve float usually causes a very sudden drop in power easily recognizable on the dyno graph (although can start to be a little "choppy" similar to your graph as it starts to lose valve control, then a very sudden drop off as the loss of valve control becomes more pronounced).
Good luck...
Tony M.
Good luck...
Tony M.
On The Tree
Joined: Nov 2001
Posts: 157
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From: DFW,TX
Well mine started like yours and progressively became worse to the point it would loose 50 RWHP. I have not heard of an 01 or 02 doing this. It is always 98-00 LS1's. I believe it is due to the higher lift cam of the 98-00 (.500 I/E). It can weaken the stock springs if the engine is run hard often. I noticed my problem started after I hot-lapped my Z28 at Ennis and ran 7 quarter mile passes almost back to back.
I'm the guy that tuned his car. When he was making his runs, it never had any knock.
Some of you guys could be right, maybe the springs are getting weak. I've seen this before on other cars, even some cammed cars with better springs but after looking at his graph again, maybe it is a little much.
Dale, once you get that cam, you'll need new springs anyways. get that car to the track!!! Does your old graph show this?
Some of you guys could be right, maybe the springs are getting weak. I've seen this before on other cars, even some cammed cars with better springs but after looking at his graph again, maybe it is a little much.
Dale, once you get that cam, you'll need new springs anyways. get that car to the track!!! Does your old graph show this?
Thread Starter
Teching In
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No, the old graph doesn't show this at all.
What doesn't make sense is that it only does it between 5500 and 6000 and not above 6000. I would think it should be doing all the way to the limiter.
Bill, do you have a scan of the car that dyno'd after me? You said his did it a little also. Could the dyno be vibrating since it's a mobile dyno? Probably not, but I figured it might be worth bringing up.
I was back to the track yesterday. I ran a 12.81@109 on street tires with no change in air pressure.
I don't think I'm going to worry about it until it's to the point where I can feel the power fall off. I should have a cam in it before then anyway.
What doesn't make sense is that it only does it between 5500 and 6000 and not above 6000. I would think it should be doing all the way to the limiter.
Bill, do you have a scan of the car that dyno'd after me? You said his did it a little also. Could the dyno be vibrating since it's a mobile dyno? Probably not, but I figured it might be worth bringing up.
I was back to the track yesterday. I ran a 12.81@109 on street tires with no change in air pressure.
I don't think I'm going to worry about it until it's to the point where I can feel the power fall off. I should have a cam in it before then anyway.
