What is a good dyno chart?
Racer
Joined: Oct 2001
Posts: 442
Likes: 2
From: San Clemente CA
Re: What is a good dyno chart? (ElDiablo)
Hi,
I would like to get more info on this subject so I'll start with what I think you can tell from the shape of the dyno curve.
The 1st curve below shows a "good" dyno curve. This doesn't mean that the values are high but that the engine seems to be running well at its current tune. This curve shows both the published Chevy data as well as my first dyno run. Notice that the curves are smooth and continuous with the absence of any sharp discontinuities. The slightly higher power at higher rpm's is due to the intake mods.
This next curve shows an issue as you can see by the big dip at high rpm's. I have heard that this could be from "spark retard" but it looks like valve spring surge to me. Whatever it is, you would need to fix this up before spending too much time running near this rpm because you won't be going very fast and/or you may be in danger of breaking your engine.
The next curve is a little more interesting in that you can see several dips at various rpm's. I have heard that this is a symptom of a poor computer tune for the setup. Even if the peak numbers are good, this current setup is demonstrating "area under the curve" problems.
The next curve has a certain humpyness which I thought could be the knock sensor chasing a low octane issue.
So what do you dyno experts think? Have I got any of this right? What would bent pushrods look like?
Thanks,
Steve
I would like to get more info on this subject so I'll start with what I think you can tell from the shape of the dyno curve.
The 1st curve below shows a "good" dyno curve. This doesn't mean that the values are high but that the engine seems to be running well at its current tune. This curve shows both the published Chevy data as well as my first dyno run. Notice that the curves are smooth and continuous with the absence of any sharp discontinuities. The slightly higher power at higher rpm's is due to the intake mods.
This next curve shows an issue as you can see by the big dip at high rpm's. I have heard that this could be from "spark retard" but it looks like valve spring surge to me. Whatever it is, you would need to fix this up before spending too much time running near this rpm because you won't be going very fast and/or you may be in danger of breaking your engine.
The next curve is a little more interesting in that you can see several dips at various rpm's. I have heard that this is a symptom of a poor computer tune for the setup. Even if the peak numbers are good, this current setup is demonstrating "area under the curve" problems.
The next curve has a certain humpyness which I thought could be the knock sensor chasing a low octane issue.
So what do you dyno experts think? Have I got any of this right? What would bent pushrods look like?
Thanks,
Steve
Melting Slicks
Joined: Mar 2001
Posts: 3,258
Likes: 61
From: League City TX
Re: What is a good dyno chart? (SNW Vette)
Please explain, Valve Spring Surge.
My 01 had some Valvetrain trouble, please search for my thread for details. It included a slightly bent intake valve after missing a shift.
It has been 6 months since I dynoed and I'm now seeing a simlar dip at 5500-5600 RPM (very much like the curve you posted).
I just Auto-Tapped. I did three log files and saw 0 knock retard. Next I plan on looking at total timing to see if it is just retarding timing across the board.
My 01 had some Valvetrain trouble, please search for my thread for details. It included a slightly bent intake valve after missing a shift.
It has been 6 months since I dynoed and I'm now seeing a simlar dip at 5500-5600 RPM (very much like the curve you posted).
I just Auto-Tapped. I did three log files and saw 0 knock retard. Next I plan on looking at total timing to see if it is just retarding timing across the board.
Racer
Joined: Oct 2001
Posts: 442
Likes: 2
From: San Clemente CA
Re: What is a good dyno chart? (Closer_2001)
Hi,
Valve spring surge happens when the spring vibrates at its natural frequency causing the spring to stop following the motion of the valve. The spring uses all of its energy to sit there and kind of ring. The interesting thing about spring surge is that you can regain control of the valvetrain by raising the rpm’s at which time the engine will not excite the natural frequency of the spring and things get back to normal.
This loss of valve control is different then that which is caused by weak springs that do not have enough pressure to follow the cam motion. This is “valve float” which is when the valve/spring combination can not accelerate as fast as the cam would allow during closing. The engine loses Hp very rapidly after floating the valves and never recovers with rpm.
Isky says that the spring could be seen lifting off of the head during a surge event. They test for this condition using a Spintronics machine that motors the cam & head configuration while looking at the valve train with a strobe light or high speed photography.
The natural frequency of the spring is a function of its geometry and material properties. For the same spring rate, a lighter spring has a higher frequency. This also means that it is running at a higher stress level. That is one of the reasons you see such exotic metals used for springs. Straight wound springs may use a flat damper in an attempt to raise the total spring system frequency. Dual springs also use an interference fit to add damping. Chevy uses a conically shaped spring on the LSX engine which has a different frequency for each coil size in the stack. The lack of a damper reduces friction and heat at the spring.
A broken damper or inner spring and overheated springs can cause a spring to surge that was OK earlier. If you think your springs where hurt, why not change them out for a new set from Chevy for ~$100. The '02's have a little more rate which would give you an increased margin.
Any spring/cam manufactures out there that can give us some info or test data?
Steve
[Modified by SNW Vette, 10:06 PM 1/19/2002]
[Modified by SNW Vette, 10:07 PM 1/19/2002]
Valve spring surge happens when the spring vibrates at its natural frequency causing the spring to stop following the motion of the valve. The spring uses all of its energy to sit there and kind of ring. The interesting thing about spring surge is that you can regain control of the valvetrain by raising the rpm’s at which time the engine will not excite the natural frequency of the spring and things get back to normal.
This loss of valve control is different then that which is caused by weak springs that do not have enough pressure to follow the cam motion. This is “valve float” which is when the valve/spring combination can not accelerate as fast as the cam would allow during closing. The engine loses Hp very rapidly after floating the valves and never recovers with rpm.
Isky says that the spring could be seen lifting off of the head during a surge event. They test for this condition using a Spintronics machine that motors the cam & head configuration while looking at the valve train with a strobe light or high speed photography.
The natural frequency of the spring is a function of its geometry and material properties. For the same spring rate, a lighter spring has a higher frequency. This also means that it is running at a higher stress level. That is one of the reasons you see such exotic metals used for springs. Straight wound springs may use a flat damper in an attempt to raise the total spring system frequency. Dual springs also use an interference fit to add damping. Chevy uses a conically shaped spring on the LSX engine which has a different frequency for each coil size in the stack. The lack of a damper reduces friction and heat at the spring.
A broken damper or inner spring and overheated springs can cause a spring to surge that was OK earlier. If you think your springs where hurt, why not change them out for a new set from Chevy for ~$100. The '02's have a little more rate which would give you an increased margin.
Any spring/cam manufactures out there that can give us some info or test data?
Steve
[Modified by SNW Vette, 10:06 PM 1/19/2002]
[Modified by SNW Vette, 10:07 PM 1/19/2002]
