Valve Float on a Stock Engine? (Dyno graph inside)
Thread Starter
Drifting
Joined: Jan 2000
Posts: 1,660
Likes: 9
From: Charlotte, NC
Valve Float on a Stock Engine? (Dyno graph inside)
Mods are intake, exhaust, and shorty headers. Stock the car made 301-rwhp.
I took the car to get dyno tuned by Alvin at PCM For Less in Mooresville, North Carolina (good guys and I think he did a pretty good job on the tune - notice the A/F ratio).
I recently installed a set of BBK shorty headers, prior to the tune. While I had everything apart, I also installed a set of GM Performance plug wires and NGK TR55 plugs. This was on a 75k mile engine so I thought it good maintenance stuff to do.
Take a look at the upper rpm fallout I'm getting on the before/after dyno graph below:
Alvin suggestd that I try lowering the gap on the sparkplugs. While I can certaintly give that a try, I'm was also wondering, on a 75k mile engine, if its possible the valve springs are a bit tired and possibly I'm getting some float? Any suggestions?
I took the car to get dyno tuned by Alvin at PCM For Less in Mooresville, North Carolina (good guys and I think he did a pretty good job on the tune - notice the A/F ratio).
I recently installed a set of BBK shorty headers, prior to the tune. While I had everything apart, I also installed a set of GM Performance plug wires and NGK TR55 plugs. This was on a 75k mile engine so I thought it good maintenance stuff to do.
Take a look at the upper rpm fallout I'm getting on the before/after dyno graph below:
Alvin suggestd that I try lowering the gap on the sparkplugs. While I can certaintly give that a try, I'm was also wondering, on a 75k mile engine, if its possible the valve springs are a bit tired and possibly I'm getting some float? Any suggestions?
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
What are the dates between these dyno's? Is it before - after?
If there is a period of time between pulls, it could be the valve springs, however they seem to recover which would be more indicative of a harmonic. I wouldn't hesitate to slap in a set of LS6 springs for $55 though. If this was thew same tune session, a valve train issue would appear on both curves and you should look elsewhere for the problem.
If there is a period of time between pulls, it could be the valve springs, however they seem to recover which would be more indicative of a harmonic. I wouldn't hesitate to slap in a set of LS6 springs for $55 though. If this was thew same tune session, a valve train issue would appear on both curves and you should look elsewhere for the problem.
Last edited by vettenuts; Apr 17, 2008 at 03:24 PM.
Thread Starter
Drifting
Joined: Jan 2000
Posts: 1,660
Likes: 9
From: Charlotte, NC
Harmonic being an issue that occurrs at only a certain rpm?
Looking at the above graph, I didn't feel like they really recovered before the rev limiter kicked in.
Its pretty hard to swap out springs, isn't it? Don't you need special tools or something? I'm trying to determine if this is something I could handle myself.
Looking at the above graph, I didn't feel like they really recovered before the rev limiter kicked in.
Its pretty hard to swap out springs, isn't it? Don't you need special tools or something? I'm trying to determine if this is something I could handle myself.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
They aren't too difficult to swap with the correct tools, but that us key. I am just confused that if these two dyno graphs were done during the same tuning session, the valve springs "may" not be the problem. You should see a similar drop at the same RPM on the other curve, although there is some evidence of a little drop off at 5,500 in run 1. Since one is run 1 and the other run 8, do you have plots of the in between runs? Was there any knock retard?
Thread Starter
Drifting
Joined: Jan 2000
Posts: 1,660
Likes: 9
From: Charlotte, NC
I believe there was but I'll have to check. Hopefully he can email me the other charts.
The tuner thought perhaps it was my sparkplugs and suggested that I gap mine a little bit closer (colder).
The tuner thought perhaps it was my sparkplugs and suggested that I gap mine a little bit closer (colder).
Race Director
Joined: Oct 2002
Posts: 16,477
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From: Gone
CI 6-7-8-9-10 Veteran
St. Jude Donor '03
Per factory literature, an (internally) stock LS1 HP peaks at 5600rpm, which your graph seems to agree with.
I'm not sure what you were expecting, but f you want that hp curve to continue on upwards beyond 5600, you need a bigger cam (and better springs).
Just because stock redline is 6200, doesn't mean it peaks there. The stock engine goes noticeably flat long before that point, just like your graph shows
I'm not sure what you were expecting, but f you want that hp curve to continue on upwards beyond 5600, you need a bigger cam (and better springs).
Just because stock redline is 6200, doesn't mean it peaks there. The stock engine goes noticeably flat long before that point, just like your graph shows
Last edited by Y2Kvert4me; Apr 17, 2008 at 10:25 PM.
Team Owner
Joined: Mar 1999
Posts: 22,025
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From: At the beach in little Rhody
I think he is concerned about the amount and slope of the dip, I am thinking it might be a tuning issue but based on the two lines its not clear.
However, if you are concerned about the valve springs, the LS6 springs are cheap and it certainly won't hurt the motor to install them.
However, if you are concerned about the valve springs, the LS6 springs are cheap and it certainly won't hurt the motor to install them.
