Power Loss Possible Valve Float
Dec 9, 2009, 05:38 AM
#1
Evolving Member
Thread Starter
iTrader: (4)
Join Date: Dec 2004
Location: Northern Virginia
Posts: 154
Likes: 0
Received 0 Likes
on
0 Posts
Power Loss Possible Valve Float
I've been struggling with an issue for quite some time, and haven't been able to figure it out. Please, help.
The problem: A sharp dip in tq/hp drop after 4000 rpm, slight recovery, then a deep drop after 5000 rpm. The power loss seems to happen mostly in those spots.
According to my Evoscan logs; AFR (11.5 after peak boost), timing, knock, boost, and airflow are all reporting normal. According to Evoscan's power and tq numbers everything is working fine. I didn't notice this issue until I used Jack of All Trades's VDR spreadsheet, which plots RPM vs time.
I'm noticing the power loss is less dramatic with less load, and sometimes it's not as severe as others (illustrated in pic below.)
My mods:
2.3L stroker
ARP L19 headstuds
Headgames head
PTE 1000cc injectors
Aeromotive FPR and fuel rail
HKS 272/272 cams
Evo VIII turbo w/10.5 hotside
BC valve springs and retainers (assuming that's what they are: I had my head redone, thinking this might've been valve float. My exhaust valve seals were bad, so I had all the seals replaced. The valve stems were shaved since they were a bit too long. 3-angle valve job for fitment, and I had the springs measured 80#@1.57" 190#@1.15".)
This issue has been happening through numerous different settings. Cam gears were changed (+2,-1; 0,0; -4,-1), ROMs were changed 96940011 & 96530006, MBC & ECU controlled boost, swapped out stock turbos, swapped out ignition coils with COP and vice versa, swapped out MAFs, swapped out JDM MAP sensor, swapped out my cat for a test pipe.
Boost leak checks, cylinder compression checks, and cylinder leakdown tests all come back good.
I've ordered a set of Kelford 272 cams in case it might be my HKS 272s going bad from the valve springs being too stiff or my valve stems being too long.
I'm at a loss at this point. Any advice would be appreciated.
Graph is using Mustang Dyno simm with smoothing factor of 1.
Blue/Red: 24.5 psi
Green/Yellow: 21 psi
The problem: A sharp dip in tq/hp drop after 4000 rpm, slight recovery, then a deep drop after 5000 rpm. The power loss seems to happen mostly in those spots.
According to my Evoscan logs; AFR (11.5 after peak boost), timing, knock, boost, and airflow are all reporting normal. According to Evoscan's power and tq numbers everything is working fine. I didn't notice this issue until I used Jack of All Trades's VDR spreadsheet, which plots RPM vs time.
I'm noticing the power loss is less dramatic with less load, and sometimes it's not as severe as others (illustrated in pic below.)
My mods:
2.3L stroker
ARP L19 headstuds
Headgames head
PTE 1000cc injectors
Aeromotive FPR and fuel rail
HKS 272/272 cams
Evo VIII turbo w/10.5 hotside
BC valve springs and retainers (assuming that's what they are: I had my head redone, thinking this might've been valve float. My exhaust valve seals were bad, so I had all the seals replaced. The valve stems were shaved since they were a bit too long. 3-angle valve job for fitment, and I had the springs measured 80#@1.57" 190#@1.15".)
This issue has been happening through numerous different settings. Cam gears were changed (+2,-1; 0,0; -4,-1), ROMs were changed 96940011 & 96530006, MBC & ECU controlled boost, swapped out stock turbos, swapped out ignition coils with COP and vice versa, swapped out MAFs, swapped out JDM MAP sensor, swapped out my cat for a test pipe.
Boost leak checks, cylinder compression checks, and cylinder leakdown tests all come back good.
I've ordered a set of Kelford 272 cams in case it might be my HKS 272s going bad from the valve springs being too stiff or my valve stems being too long.
I'm at a loss at this point. Any advice would be appreciated.
Graph is using Mustang Dyno simm with smoothing factor of 1.
Blue/Red: 24.5 psi
Green/Yellow: 21 psi
Last edited by MadMsheen; Dec 9, 2009 at 05:41 AM.
Dec 9, 2009, 09:42 AM
#2
Just FYI I have my BC springs set to 93lbs of seat pressure with HKS 272s and have no issues so far all the way to 8600 rpm. 80lbs of seat pressure sounds low for those valve springs. I am not sure if that would cause float at only 4k rpm though, that sounds like it could be something else. It sounds like something was not installed properly.
Last edited by fre; Dec 9, 2009 at 09:45 AM.
Dec 9, 2009, 09:57 AM
#3
Evolving Member
Thread Starter
iTrader: (4)
Join Date: Dec 2004
Location: Northern Virginia
Posts: 154
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for the response.
I'm going to try swapping out my BOV to see if that's the issue. I would think if it was the BOV leaking, I would see my BoostErrorCorrection acting strange, but I've had this issue prior to switching over to ECU controlled boost. It's worth a try.
If the BOV doesn't fix the issue, I'm going to a more thorough leakdown test. But possibly the skirt of the pistons could be expanding and dragging against the cylinder walls at high pressure, which I might not see on the leakdown.
I'm going to try swapping out my BOV to see if that's the issue. I would think if it was the BOV leaking, I would see my BoostErrorCorrection acting strange, but I've had this issue prior to switching over to ECU controlled boost. It's worth a try.
If the BOV doesn't fix the issue, I'm going to a more thorough leakdown test. But possibly the skirt of the pistons could be expanding and dragging against the cylinder walls at high pressure, which I might not see on the leakdown.
Dec 9, 2009, 10:07 AM
#4
Thanks for the response.
I'm going to try swapping out my BOV to see if that's the issue. I would think if it was the BOV leaking, I would see my BoostErrorCorrection acting strange, but I've had this issue prior to switching over to ECU controlled boost. It's worth a try.
If the BOV doesn't fix the issue, I'm going to a more thorough leakdown test. But possibly the skirt of the pistons could be expanding and dragging against the cylinder walls at high pressure, which I might not see on the leakdown.
I'm going to try swapping out my BOV to see if that's the issue. I would think if it was the BOV leaking, I would see my BoostErrorCorrection acting strange, but I've had this issue prior to switching over to ECU controlled boost. It's worth a try.
If the BOV doesn't fix the issue, I'm going to a more thorough leakdown test. But possibly the skirt of the pistons could be expanding and dragging against the cylinder walls at high pressure, which I might not see on the leakdown.
Last edited by fre; Dec 9, 2009 at 10:09 AM.
Dec 9, 2009, 10:12 AM
#5
Evolving Member
Thread Starter
iTrader: (4)
Join Date: Dec 2004
Location: Northern Virginia
Posts: 154
Likes: 0
Received 0 Likes
on
0 Posts
I actually had my head redone about a month ago. Cylinder walls were clean. And the piston tops were undamaged. I tracked the power loss issue all the way back to 2/15/2009.
I think the stock spring pressure is 63#@1.575, so I'm unsure why 80#@1.575 would cause a problem, especially running as mild a cam as the HKS 272s.
I think the stock spring pressure is 63#@1.575, so I'm unsure why 80#@1.575 would cause a problem, especially running as mild a cam as the HKS 272s.
Dec 9, 2009, 11:06 AM
#6
Well, this is going to cause a dropoff in power somewhere in the picture.
The graph is just a basic thumbnail sketch that doesn't reveal specifics. Please post a log of the entire 100% TPS area, showing:
TPS
2-byte load
Airflow (Hz)
Ignition Advance
Knock Sum
Boost (if you are set up to do this)
WGDC
That should get us started.
The graph is just a basic thumbnail sketch that doesn't reveal specifics. Please post a log of the entire 100% TPS area, showing:
TPS
2-byte load
Airflow (Hz)
Ignition Advance
Knock Sum
Boost (if you are set up to do this)
WGDC
That should get us started.
Dec 9, 2009, 11:43 AM
#7
I actually had my head redone about a month ago. Cylinder walls were clean. And the piston tops were undamaged. I tracked the power loss issue all the way back to 2/15/2009.
I think the stock spring pressure is 63#@1.575, so I'm unsure why 80#@1.575 would cause a problem, especially running as mild a cam as the HKS 272s.
I think the stock spring pressure is 63#@1.575, so I'm unsure why 80#@1.575 would cause a problem, especially running as mild a cam as the HKS 272s.
Having said that, I still don't believe that is your issue, because you are dropping at only 4k rpm which is way too low for valve float, unless something is just completely installed wrong somehow. I don't believe a 13lb difference in seat pressure would cause that.
Trending Topics
Dec 9, 2009, 11:51 AM
#8
Evolving Member
Thread Starter
iTrader: (4)
Join Date: Dec 2004
Location: Northern Virginia
Posts: 154
Likes: 0
Received 0 Likes
on
0 Posts
Ted, I'm currently at work, but I'll try to get a log up when I get a chance.
fre, you make a good point about the stock springs. I'll check with the head shop to see if that could be a possible issue.
fre, you make a good point about the stock springs. I'll check with the head shop to see if that could be a possible issue.
Dec 9, 2009, 12:04 PM
#10
Also, I wouldn't go replacing your cams unless you can visibly see that they are worn. I put these valve springs in a few weeks ago, so I will probably need more time with them to see if they have an adverse effect on the cams. My friend used a similar setup in his talon without issues, though, so I don't expect to have any.
Dec 11, 2009, 05:42 PM
#15
Yea I asked the same question in the other thread he posted that in. No info on what car it was in or what conditions it failed under is not helpful. Any part can break with enough abuse. The retainers also look different than the ones I have. The ones I have are silver metallic, which makes sense for titanium. Those retainers in the picture look more bronze, unless it was discolored from the failure somehow.