Valve float on a datalog

Adger Smith · 10-03-2013, 01:13 AM

I've never had a blown engine float valves and seen AF ratio change. I have seen one with too little spring pressure that had blower pressure keeping the intake valve open too long. It was blowing the valve off the seat. It acted like the cam was too big. The intake did finally close, but way late and it made no power and did some stupid surges. With a large valve and 12 lbs boost you had better have way more spring than you think is normal. Do the math 12 PSI x area of the backside of the valve... that just gets you started back to holding the valve on the seat... I just did a little quick math and with a 2.2 valve you need a min of 46 additional lbs just to hold the valve on the seat. That is over your traditional seat pressure.

Kirk Morgan · 10-03-2013, 07:53 AM

I believe your O2 would show a big difference because of a incomplete combustion. Its been a long time since i have used a gas analyzer, but there would be alot of oxygen going out the headers.

Kirk

Chris Hill · 10-03-2013, 10:31 PM

I'll agree with Adger on this one.

My gut says AFR won't change during valve float.

The valve train would be noisier when valve is bouncing off its seat.

Adger Smith · 10-03-2013, 11:26 PM

It's not valve float, but the intake valve blown off or held off the seat by intake pressure before the cylinder pressure pushes the valve shut on the compression cycle. Then normal combustion takes place. I should have been more clear on my comment about 02 readings. I've never had any 02 sensors on an engine that had this problem, so I don't know how 02's would respond. I do think they would be normal because the problem with the valve off the seat occurs during the compression event & before combustion, not during overlap. It is Ex Valve Float during overlap that will mess so much with 02 readings.
I think Ed was on somethng with the A/F ratios. I've seen the same thing with a BB blown gas engine I did quite a lot of development work on. I called it Fat when it made good/best power.
My thoughts are you might be looking at two problems. Intake spring pressure and being lean. Don't be shy to address both or others. It is human nature to look for one problem, not a couple. Good luck
One other thought: What is the timing curve look like when & after the boost comes in?

dart440 · 10-04-2013, 08:37 AM

Thanks for your help. The timing is at 20 degrees and steady when it happens. I will try richening up next time. The valve spring info makes alot of sense, and agrees with what my go-to guy was suggesting. Guess I'll be ordering up some springs soon.

Dave

buzzinhalfdozen · 10-04-2013, 02:29 PM

Ok, 20 degrees of timing with 12 PSI of boost? Again I'm certainly no expert on boosted engines but seems high to me, certainly at 12.5 AFR, have you ever looked at the plugs on this thing? While I'm all in on the weak valve spring theory, maybe as Adger had eluded to you have a few issues instead on merely one. BTW is this a new engine, I mean fresh engine and have you spoken to the engine builder? Who engine controller are you using? Joe

dart440 · 10-04-2013, 02:44 PM

The plugs look good. The engine builder.....that would be me! Yes its a fresh build

Mike Taylor 3601 · 10-04-2013, 08:51 AM

I'm no expert on boosted stuff,or anything else as far as that goes,but in your description you said 5800 was like hitting a wall, I would check springs first. n/a engines will act like that if intake valves are leaking,blows compression back up runner,basically blows fuel back up runner,messes up carb signal,etc
usaully they will get a certain rpm and act like has a governor,had one once on dyno would get to 6500 and shut off like you killed ign.
If you are blowing valves open could act the same as leaking valves.
I'm gonna say that if valves are blowing open you could add fuel and A/F ratio would probaly not change like it should,it probaly would'nt richen as much as it should.
Mike Taylor 3601

10-03-2013, 01:13 AM	#1
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Valve float on a datalog I've never had a blown engine float valves and seen AF ratio change. I have seen one with too little spring pressure that had blower pressure keeping the intake valve open too long. It was blowing the valve off the seat. It acted like the cam was too big. The intake did finally close, but way late and it made no power and did some stupid surges. With a large valve and 12 lbs boost you had better have way more spring than you think is normal. Do the math 12 PSI x area of the backside of the valve... that just gets you started back to holding the valve on the seat... I just did a little quick math and with a 2.2 valve you need a min of 46 additional lbs just to hold the valve on the seat. That is over your traditional seat pressure. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 10-03-2013 at 01:24 AM. Reason: sp

10-03-2013, 07:53 AM	#2
Kirk Morgan Member Join Date: Jan 2009 Posts: 230 Likes: 1 Liked 80 Times in 44 Posts	Re: Valve float on a datalog I believe your O2 would show a big difference because of a incomplete combustion. Its been a long time since i have used a gas analyzer, but there would be alot of oxygen going out the headers. Kirk

10-03-2013, 10:31 PM	#3
Chris Hill Senior Member Join Date: Jan 2002 Posts: 655 Likes: 8 Liked 244 Times in 26 Posts	Re: Valve float on a datalog I'll agree with Adger on this one. My gut says AFR won't change during valve float. The valve train would be noisier when valve is bouncing off its seat. __________________ Chris Hill https://ihmusedparts.com

10-03-2013, 11:26 PM	#4
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Valve float on a datalog It's not valve float, but the intake valve blown off or held off the seat by intake pressure before the cylinder pressure pushes the valve shut on the compression cycle. Then normal combustion takes place. I should have been more clear on my comment about 02 readings. I've never had any 02 sensors on an engine that had this problem, so I don't know how 02's would respond. I do think they would be normal because the problem with the valve off the seat occurs during the compression event & before combustion, not during overlap. It is Ex Valve Float during overlap that will mess so much with 02 readings. I think Ed was on somethng with the A/F ratios. I've seen the same thing with a BB blown gas engine I did quite a lot of development work on. I called it Fat when it made good/best power. My thoughts are you might be looking at two problems. Intake spring pressure and being lean. Don't be shy to address both or others. It is human nature to look for one problem, not a couple. Good luck One other thought: What is the timing curve look like when & after the boost comes in? __________________ Adger Smith (Former SS) Last edited by Adger Smith; 10-03-2013 at 11:32 PM. Reason: sp & thought

10-04-2013, 08:37 AM	#5
dart440 Junior Member Join Date: Sep 2012 Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	Re: Valve float on a datalog Thanks for your help. The timing is at 20 degrees and steady when it happens. I will try richening up next time. The valve spring info makes alot of sense, and agrees with what my go-to guy was suggesting. Guess I'll be ordering up some springs soon. Dave

10-04-2013, 02:29 PM	#6
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: Valve float on a datalog Ok, 20 degrees of timing with 12 PSI of boost? Again I'm certainly no expert on boosted engines but seems high to me, certainly at 12.5 AFR, have you ever looked at the plugs on this thing? While I'm all in on the weak valve spring theory, maybe as Adger had eluded to you have a few issues instead on merely one. BTW is this a new engine, I mean fresh engine and have you spoken to the engine builder? Who engine controller are you using? Joe __________________ Joe Buchanan SS/BX 3117

10-04-2013, 02:44 PM	#7
dart440 Junior Member Join Date: Sep 2012 Posts: 7 Likes: 0 Liked 0 Times in 0 Posts	Re: Valve float on a datalog The plugs look good. The engine builder.....that would be me! Yes its a fresh build

10-04-2013, 08:51 AM	#8
Mike Taylor 3601 VIP Member Join Date: Oct 2008 Location: Somerset,Ky Posts: 1,372 Likes: 354 Liked 307 Times in 103 Posts	Re: Valve float on a datalog I'm no expert on boosted stuff,or anything else as far as that goes,but in your description you said 5800 was like hitting a wall, I would check springs first. n/a engines will act like that if intake valves are leaking,blows compression back up runner,basically blows fuel back up runner,messes up carb signal,etc usaully they will get a certain rpm and act like has a governor,had one once on dyno would get to 6500 and shut off like you killed ign. If you are blowing valves open could act the same as leaking valves. I'm gonna say that if valves are blowing open you could add fuel and A/F ratio would probaly not change like it should,it probaly would'nt richen as much as it should. Mike Taylor 3601