951 MAX chips installed
09-20-2006, 05:44 PM
#31
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Originally Posted by rberry951
My only point was specific to the open/close time of the exhaust valve at high rpm, where you won't really have as much load, but a factor of that open/close time not being long enough to expell all the gas around the valve area. What you are talking about here is purely load/backpressure. When you have the wrong turbo sizing to an extreme that exhaust is trying to push through at a VOLUME that the turbo can not flow it ends up pushing against it, creating HUGE backpressure and hence going back into the cylinders.
But what you're stating in that scenario is correct, but if your turbo is matched size wise to your displacement that won't be an issue unless there are other exhaust restrictions. In either case, no matter what the reason for the exhaust not getting out, you risk a lean condition and detonation.
Regards,
Russell
But what you're stating in that scenario is correct, but if your turbo is matched size wise to your displacement that won't be an issue unless there are other exhaust restrictions. In either case, no matter what the reason for the exhaust not getting out, you risk a lean condition and detonation.
Regards,
Russell
Hmmmm.........me thinks this post was subtely aimed in my direction........
if someone did have a turbo too small for their displacement what precautions should they take to limit the backpressure issue?.....or can they?......limit boost??.....shift way before redline?
BTW - Did you see the post by Turbotim from SFR on the new Turbonetics turbos coming out? What do u think of those?
09-20-2006, 05:51 PM
#32
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Hmmm, I’m still not coming to the same conclusion…
If there is an excess of pressure in the exhaust, say 30psi, and because of the high RPM (less time) not all the exhaust is expelled, there is a resident pressure in the cylinder, say 10psi. Now in the intake you have a positive pressure of 15psi. Assuming that the intake valve has enough duration (remember the same limited time at high RPM is true for the intake). With the intake valve open the pressure is simply going to normalize between the two (intake and cylinder).
Regardless of the exhaust backpressure, the cylinder pressure can’t be any higher then the intake charge. (I know about inertial supercharging for intake design, but trying to keep this simple)
The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
Rogue
If there is an excess of pressure in the exhaust, say 30psi, and because of the high RPM (less time) not all the exhaust is expelled, there is a resident pressure in the cylinder, say 10psi. Now in the intake you have a positive pressure of 15psi. Assuming that the intake valve has enough duration (remember the same limited time at high RPM is true for the intake). With the intake valve open the pressure is simply going to normalize between the two (intake and cylinder).
Regardless of the exhaust backpressure, the cylinder pressure can’t be any higher then the intake charge. (I know about inertial supercharging for intake design, but trying to keep this simple)
The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
Rogue
09-20-2006, 06:22 PM
#35
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Originally Posted by Andial951
Hmmmm.........me thinks this post was subtely aimed in my direction........
if someone did have a turbo too small for their displacement what precautions should they take to limit the backpressure issue?.....or can they?......limit boost??.....shift way before redline?
BTW - Did you see the post by Turbotim from SFR on the new Turbonetics turbos coming out? What do u think of those?
if someone did have a turbo too small for their displacement what precautions should they take to limit the backpressure issue?.....or can they?......limit boost??.....shift way before redline?
BTW - Did you see the post by Turbotim from SFR on the new Turbonetics turbos coming out? What do u think of those?
Did you ever talk to Dave Lindsey about your engine/turbo combination? From what I've heard from him and others here the consensus seems to be you need a different turbo all together. But I'm not the best person to tell you 'which' turbo to buy, maybe an engine builder that doesn't sell turbos would be less biased than someone who wants you to buy their turbo or their favorite turbo. Are the people that designed/built your engine still around? Did they have any input on what turbo matched it best?
I did see the turbos Tim posted for SFR, but I don't have the technical expertise in turbos to comment on what they can do or can't do.
Regards,
Russell
09-20-2006, 06:26 PM
#36
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Originally Posted by Rogue_Ant
Hmmm, I’m still not coming to the same conclusion…
If there is an excess of pressure in the exhaust, say 30psi, and because of the high RPM (less time) not all the exhaust is expelled, there is a resident pressure in the cylinder, say 10psi. Now in the intake you have a positive pressure of 15psi. Assuming that the intake valve has enough duration (remember the same limited time at high RPM is true for the intake). With the intake valve open the pressure is simply going to normalize between the two (intake and cylinder).
Regardless of the exhaust backpressure, the cylinder pressure can’t be any higher then the intake charge. (I know about inertial supercharging for intake design, but trying to keep this simple)
The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
Rogue
If there is an excess of pressure in the exhaust, say 30psi, and because of the high RPM (less time) not all the exhaust is expelled, there is a resident pressure in the cylinder, say 10psi. Now in the intake you have a positive pressure of 15psi. Assuming that the intake valve has enough duration (remember the same limited time at high RPM is true for the intake). With the intake valve open the pressure is simply going to normalize between the two (intake and cylinder).
Regardless of the exhaust backpressure, the cylinder pressure can’t be any higher then the intake charge. (I know about inertial supercharging for intake design, but trying to keep this simple)
The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
Rogue
I remember reading a post about it a while back while browsing around, let me see if I can find it and if it contains a better explanation.
Regards,
Russell
09-20-2006, 06:32 PM
#37
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Just think of a VE map.... the higher rpms usually have a lower VE, meaning less air in the cylinder... the highest cylinder pressure (from simple intake and exhaust pressure) should be at the highest VE.
Rogue
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09-20-2006, 06:33 PM
#38
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Originally Posted by rberry951
LOL! What was subtle about it?
Did you ever talk to Dave Lindsey about your engine/turbo combination? From what I've heard from him and others here the consensus seems to be you need a different turbo all together. But I'm not the best person to tell you 'which' turbo to buy, maybe an engine builder that doesn't sell turbos would be less biased than someone who wants you to buy their turbo or their favorite turbo. Are the people that designed/built your engine still around? Did they have any input on what turbo matched it best?
I did see the turbos Tim posted for SFR, but I don't have the technical expertise in turbos to comment on what they can do or can't do.
Regards,
Russell
Did you ever talk to Dave Lindsey about your engine/turbo combination? From what I've heard from him and others here the consensus seems to be you need a different turbo all together. But I'm not the best person to tell you 'which' turbo to buy, maybe an engine builder that doesn't sell turbos would be less biased than someone who wants you to buy their turbo or their favorite turbo. Are the people that designed/built your engine still around? Did they have any input on what turbo matched it best?
I did see the turbos Tim posted for SFR, but I don't have the technical expertise in turbos to comment on what they can do or can't do.
Regards,
Russell
I was previuosly preoccupied with trying not to be a part of a military coup that recently took place........you might have heard about it..........anyway needless to say I am not in the country but will speak to Dave when I get back.......he has always been helpful in the past.
Andial is still around and I suppose that would be a good start.
You didnt answer my questions about how to take precautions against the backpressure issue......unless of course there is no answer.........
09-20-2006, 06:39 PM
#39
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Originally Posted by Andial951
Russell,
I was previuosly preoccupied with trying not to be a part of a military coup that recently took place........you might have heard about it..........anyway needless to say I am not in the country but will speak to Dave when I get back.......he has always been helpful in the past.
Andial is still around and I suppose that would be a good start.
You didnt answer my questions about how to take precautions against the backpressure issue......unless of course there is no answer.........
I was previuosly preoccupied with trying not to be a part of a military coup that recently took place........you might have heard about it..........anyway needless to say I am not in the country but will speak to Dave when I get back.......he has always been helpful in the past.
Andial is still around and I suppose that would be a good start.
You didnt answer my questions about how to take precautions against the backpressure issue......unless of course there is no answer.........
The only suggestion I would have is to keep your boost really low (~12psi) until you can change turbos. Dave mentioned venting it via the bung for emissions, you'd have to run some sort of tube from there to keep the exhaust out of the car though. I really don't know much else you can do, that is why I suggested speaking to those more knowledgeable than I.
Good luck over there...
Regards,
Russell
09-20-2006, 07:33 PM
#40
Originally Posted by Rogue_Ant
Just think of a VE map.... the higher rpms usually have a lower VE, meaning less air in the cylinder... the highest cylinder pressure (from simple intake and exhaust pressure) should be at the highest VE.
Rogue
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Evidence would suggest that you are 100% correct!!!
09-20-2006, 10:39 PM
#41
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Originally Posted by Rogue_Ant
Just think of a VE map.... the higher rpms usually have a lower VE, meaning less air in the cylinder... the highest cylinder pressure (from simple intake and exhaust pressure) should be at the highest VE.
Rogue
Rogue
09-20-2006, 11:46 PM
#42
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Rogue - I agree with your line of thinking.
ST - I'm not sure what side your on. You replied to Russell "I agree with you". I wasn't sure if that was to his explanation (which I found hard to believe) or to his statement "I don't know everything".
--Brian Morris
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ST - I'm not sure what side your on. You replied to Russell "I agree with you". I wasn't sure if that was to his explanation (which I found hard to believe) or to his statement "I don't know everything".
--Brian Morris
89 951
09-21-2006, 01:10 AM
#43
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St is maybe trying to be politcally correct these days
Rogue,
I also agree with you.
Although: "less time to expell exhaust" is more of a function of the camshaft profile than the actual RPM. But, I guess, you could argue that the stock cam doesn't do good at higher RPMs, so there's some truth to the statement.
The main reason exhaust doesn't expell correctly is because of the exhaust pressure in the cross-over pipe. Fix that, and exhaust remaining in the combustion chamber won't be a problem regardless of what RPM or what camshaft.
The question was asked about what can be done to alleviate this exhaust backpressure tendancy. Well, the main thing is that us turbo guys have to realize you can't have high Rpm power coupled with instant, out of the hole response in lower displacement turbo engine. If you don't want any lag, buy a mustang or a vette. So, all you boost happy enthusiasts, get rid of your restrictive exhaust housings and pay attention to all pressure drops in your intake, from the air filter (usually too small), all the way to your intake manifold.
Rogue,
I also agree with you.
Although: "less time to expell exhaust" is more of a function of the camshaft profile than the actual RPM. But, I guess, you could argue that the stock cam doesn't do good at higher RPMs, so there's some truth to the statement.
The main reason exhaust doesn't expell correctly is because of the exhaust pressure in the cross-over pipe. Fix that, and exhaust remaining in the combustion chamber won't be a problem regardless of what RPM or what camshaft.
The question was asked about what can be done to alleviate this exhaust backpressure tendancy. Well, the main thing is that us turbo guys have to realize you can't have high Rpm power coupled with instant, out of the hole response in lower displacement turbo engine. If you don't want any lag, buy a mustang or a vette. So, all you boost happy enthusiasts, get rid of your restrictive exhaust housings and pay attention to all pressure drops in your intake, from the air filter (usually too small), all the way to your intake manifold.
09-21-2006, 01:53 AM
#44
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LOL! ST was agreeing that I don't know everything, heh...
Seriously, if I knew everything I'd be sitting on a yacht in the Caribbean somewhere and not sitting here talking with the likes of you people!
Rogue the reasons you state for lift of course are right, I can't find the article I had read but attempted to state why higher rpms. I was just trying to convey it, but you state that everything being equal the remaining pressure in the cylinder will be equalized by the intake. And this is true. You also state that
"The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
" Also true. Backpressure being produced by a restrictive exhaust component and /or "less than ridiculous" boost. Well all I am adding to that is that at higher rpms that exhaust valve 'becomes' that restrictive component, and coupled with greater than 15psi of boost 7K rpm will eventially lift the head, if something else doesn't break first...
If you're into boost then most anything you do with a stock engine is just a stepping stone on your path to building a better engine. You know you're gonna kill it, so have fun doing it and save up your money for a race engine and suspension.
Regards,
Russell
Am I making any sense yet?
Seriously, if I knew everything I'd be sitting on a yacht in the Caribbean somewhere and not sitting here talking with the likes of you people!
Rogue the reasons you state for lift of course are right, I can't find the article I had read but attempted to state why higher rpms. I was just trying to convey it, but you state that everything being equal the remaining pressure in the cylinder will be equalized by the intake. And this is true. You also state that
"The only reason a head will lift is from Detonation or Pre-Ignition, which can be a direct result from excessive exhaust back-pressure (or ridicules boost pressure)
" Also true. Backpressure being produced by a restrictive exhaust component and /or "less than ridiculous" boost. Well all I am adding to that is that at higher rpms that exhaust valve 'becomes' that restrictive component, and coupled with greater than 15psi of boost 7K rpm will eventially lift the head, if something else doesn't break first...
If you're into boost then most anything you do with a stock engine is just a stepping stone on your path to building a better engine. You know you're gonna kill it, so have fun doing it and save up your money for a race engine and suspension.
Regards,
Russell
Am I making any sense yet?
09-21-2006, 02:08 AM
#45
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It is hard to agree on some of this terms that are the cause for internal engine damage Like "lifting the head"," blowing the HG". The true is that running countinous high RPM ,like 7K all the time it is bad idea on the stock engine. I think most of us can agree to that. Regarless of the cause, it is BAD.
Regards,
AL
Regards,
AL