Refresh951's Hybrid Ultra Stroker Build
02-01-2013, 12:24 AM
#182
Rennlist Member
Thread Starter
103 mm
Yes, ARP. 87 ft lbs is what I used on my 2.85L. It is a number I came up with after looking at a lot of documented builds and subsequent results. I am running lower CR (8:1) in hopes of keeping peak cylinder pressures reasonable and avoid excessive head flex. I believe 100 flbs is pretty much the absolute max without block inserts. My goal was to achieve the best clamping force without risking pulling out block threads.
Yes, ARP. 87 ft lbs is what I used on my 2.85L. It is a number I came up with after looking at a lot of documented builds and subsequent results. I am running lower CR (8:1) in hopes of keeping peak cylinder pressures reasonable and avoid excessive head flex. I believe 100 flbs is pretty much the absolute max without block inserts. My goal was to achieve the best clamping force without risking pulling out block threads.
02-01-2013, 12:29 AM
#183
Rennlist Member
Be interested to hear Michael’s perspective on solid lifters…especially on a street car. From what I understand, they require quite a lot of regular adjustment. I’ve not had any direct experience with them though.
02-01-2013, 12:50 AM
#184
Nordschleife Master
A lot of BMW's require valve adjustments every few thousand miles (solid lifters too), but from what I've read over on their forum, its more of the precaution. They are very rarely out of adjustment.
02-02-2013, 01:01 AM
#185
Rennlist Member
I don't believe solid lifters have any business on the street. They're a strong candidate for the track, though, since they allow a more aggressive lobe profile. And with these radical profiles, the lifters and lobes take a pretty good beating. I wouldn't expect them to last very long on the street. That said, there are some pretty serious profiles for hydraulic lifters these days, so why go solid?
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
02-02-2013, 01:56 AM
#186
Rennlist Member
Thread Starter
I don't believe solid lifters have any business on the street. They're a strong candidate for the track, though, since they allow a more aggressive lobe profile. And with these radical profiles, the lifters and lobes take a pretty good beating. I wouldn't expect them to last very long on the street. That said, there are some pretty serious profiles for hydraulic lifters these days, so why go solid?
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
Great info! Thanks so much for sharing your knowledge and experience.
02-02-2013, 02:16 AM
#187
Drifting
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Michael:
I do respect your expertise and opinion, but your statement is quite generalized. I agree if you were to have a daily driver with solid lifters, it would not be a wise choice, but for a novelty car that might get 1,000 miles a year put on it, why not? Not to mention the I have something you don't factor!
I do respect your expertise and opinion, but your statement is quite generalized. I agree if you were to have a daily driver with solid lifters, it would not be a wise choice, but for a novelty car that might get 1,000 miles a year put on it, why not? Not to mention the I have something you don't factor!
02-02-2013, 08:57 AM
#188
Rennlist Member
I don't believe solid lifters have any business on the street. They're a strong candidate for the track, though, since they allow a more aggressive lobe profile. And with these radical profiles, the lifters and lobes take a pretty good beating. I wouldn't expect them to last very long on the street. That said, there are some pretty serious profiles for hydraulic lifters these days, so why go solid?
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
Here's something to consider: The 2-valve engines are RPM limited by valve spring seat pressure. I have a stronger inner spring I use with the Porsche outer that allows MUCH higher RPM. How high? It will likely take you beyond wherever the power falls off (which is a function of the cam profile). The 4-valve stuff works fine with stock springs as long as you have enough spring travel before coil bind. I've taken hydraulic cams to 7700 RPM on the dyno with stock springs and big cams. I have an alternate spring that's used with larger lift cams, but still figure a max of 7700 with the hydraulic. I'll take the solids to 8000. They'll go higher but there's other limiting factors in the engine.
02-02-2013, 09:28 AM
#189
Rennlist Member
Michael:
I do respect your expertise and opinion, but your statement is quite generalized. I agree if you were to have a daily driver with solid lifters, it would not be a wise choice, but for a novelty car that might get 1,000 miles a year put on it, why not? Not to mention the I have something you don't factor!
I do respect your expertise and opinion, but your statement is quite generalized. I agree if you were to have a daily driver with solid lifters, it would not be a wise choice, but for a novelty car that might get 1,000 miles a year put on it, why not? Not to mention the I have something you don't factor!
02-02-2013, 12:55 PM
#190
Rocket Scientist
Rennlist Member
Rennlist Member
Agreed.
One other thing I would mention is that cylinder pressure is what causes head lift. What I mean by this is that compression ratio, to a specific level, by itself, will not initiate head lift. It is a part of cylinder pressure, coupled with boost pressure. Compression and boost will dictate cylinder pressure (among other things but in an effort to keep it simple). That means that if you run less compression, you can run more boost. In my opinion, I would raise the compression ratio a small amount (9:1 ish) in an effort to increase the response of the low end. By doing this, you must lower your boost pressure. However, this doesn't change when head lift becomes an issue because it's based on both compression and boost. This change in compression just allows for a more responsive engine. Then you can control your peak torque timing curve to avoid head lift. Once the engine has passed around 5500 rpm (based on the specific engine), you can ramp up the timing to a pretty extreme level. If you have RPM based boost, you could also raise that as well.
One other thing I would mention is that cylinder pressure is what causes head lift. What I mean by this is that compression ratio, to a specific level, by itself, will not initiate head lift. It is a part of cylinder pressure, coupled with boost pressure. Compression and boost will dictate cylinder pressure (among other things but in an effort to keep it simple). That means that if you run less compression, you can run more boost. In my opinion, I would raise the compression ratio a small amount (9:1 ish) in an effort to increase the response of the low end. By doing this, you must lower your boost pressure. However, this doesn't change when head lift becomes an issue because it's based on both compression and boost. This change in compression just allows for a more responsive engine. Then you can control your peak torque timing curve to avoid head lift. Once the engine has passed around 5500 rpm (based on the specific engine), you can ramp up the timing to a pretty extreme level. If you have RPM based boost, you could also raise that as well.
02-02-2013, 01:15 PM
#191
Rennlist Member
Thread Starter
Agreed.
One other thing I would mention is that cylinder pressure is what causes head lift. What I mean by this is that compression ratio, to a specific level, by itself, will not initiate head lift. It is a part of cylinder pressure, coupled with boost pressure. Compression and boost will dictate cylinder pressure (among other things but in an effort to keep it simple). That means that if you run less compression, you can run more boost. In my opinion, I would raise the compression ratio a small amount (9:1 ish) in an effort to increase the response of the low end. By doing this, you must lower your boost pressure. However, this doesn't change when head lift becomes an issue because it's based on both compression and boost. This change in compression just allows for a more responsive engine. Then you can control your peak torque timing curve to avoid head lift. Once the engine has passed around 5500 rpm (based on the specific engine), you can ramp up the timing to a pretty extreme level. If you have RPM based boost, you could also raise that as well.
One other thing I would mention is that cylinder pressure is what causes head lift. What I mean by this is that compression ratio, to a specific level, by itself, will not initiate head lift. It is a part of cylinder pressure, coupled with boost pressure. Compression and boost will dictate cylinder pressure (among other things but in an effort to keep it simple). That means that if you run less compression, you can run more boost. In my opinion, I would raise the compression ratio a small amount (9:1 ish) in an effort to increase the response of the low end. By doing this, you must lower your boost pressure. However, this doesn't change when head lift becomes an issue because it's based on both compression and boost. This change in compression just allows for a more responsive engine. Then you can control your peak torque timing curve to avoid head lift. Once the engine has passed around 5500 rpm (based on the specific engine), you can ramp up the timing to a pretty extreme level. If you have RPM based boost, you could also raise that as well.
http://www.modularfords.com/threads/...boost-pressure
I definitely see a trend in documented builds that run higher CR (greater than 9:1) of head gasket issues. Many of them have focused on cooling (steam vents ect.) but I suspect that many of these failures were caused by head flex related to peak cylinder pressure. I believe the math shows I can make equivalent power by reducing CR and increasing boost pressure and the end result is less peak cylinder pressure. I would love to run a bit higher CR (especially for bottom end) but I am not convinced it will not result in head issues. I am counting on my extra stroke for bottom end.
Last edited by refresh951; 02-02-2013 at 01:34 PM.
02-02-2013, 01:49 PM
#192
Rocket Scientist
Rennlist Member
Rennlist Member
Very cool article. Thanks for that one.
That's interesting. And I appreciate the math behind it. Basically that article's math proves me wrong in one instance, but right in another. CR alone will not dictate the head lift. However, he's saying that boost is thermally more efficient at creating power and therefore is the better choice. Although, CR is, power wise (cylinder pressure), more efficient. Unfortunately, for us, we're limited to a specific peak cylinder pressure which means, according to his math and I assume what you're getting at as well, that boost will be more thermally efficient and, given the same peak cylinder pressure CR vs. boost, boost will make more power. That's obviously due to the thermally efficiency of boost (or use of an intercooler). However, that is in a perfect world of mathematics and theory. Don't get me wrong, I'm an engineer I live for the math. Unfortunately, though, if your intercooler, turbo, etc. is sized at all incorrectly, that's not going to be the case.
I have one other concern as well. He's comparing 8.5 to 9.5 CR. And in comparison, he is stating the 8.5 is more advantageous. The question is, how low can you go before you reach diminishing returns? To be extreme, we're obviously not going to run 2:1 CR and 150 psi of boost.
....or can we? 
Either way, this is an important topic for all 944 turbo owners that plan on pushing their engines. Whether we like it or not, we will all eventually hit our peak cylinder pressure limit.
That's interesting. And I appreciate the math behind it. Basically that article's math proves me wrong in one instance, but right in another. CR alone will not dictate the head lift. However, he's saying that boost is thermally more efficient at creating power and therefore is the better choice. Although, CR is, power wise (cylinder pressure), more efficient. Unfortunately, for us, we're limited to a specific peak cylinder pressure which means, according to his math and I assume what you're getting at as well, that boost will be more thermally efficient and, given the same peak cylinder pressure CR vs. boost, boost will make more power. That's obviously due to the thermally efficiency of boost (or use of an intercooler). However, that is in a perfect world of mathematics and theory. Don't get me wrong, I'm an engineer I live for the math. Unfortunately, though, if your intercooler, turbo, etc. is sized at all incorrectly, that's not going to be the case.
I have one other concern as well. He's comparing 8.5 to 9.5 CR. And in comparison, he is stating the 8.5 is more advantageous. The question is, how low can you go before you reach diminishing returns? To be extreme, we're obviously not going to run 2:1 CR and 150 psi of boost.
....or can we? Either way, this is an important topic for all 944 turbo owners that plan on pushing their engines. Whether we like it or not, we will all eventually hit our peak cylinder pressure limit.
02-02-2013, 02:03 PM
#193
Rennlist Member
Thread Starter
Very cool article. Thanks for that one.
That's interesting. And I appreciate the math behind it. Basically that article's math proves me wrong in one instance, but right in another. CR alone will not dictate the head lift. However, he's saying that boost is thermally more efficient at creating power and therefore is the better choice. Although, CR is, power wise (cylinder pressure), more efficient. Unfortunately, for us, we're limited to a specific peak cylinder pressure which means, according to his math and I assume what you're getting at as well, that boost will be more thermally efficient and, given the same peak cylinder pressure CR vs. boost, boost will make more power. That's obviously due to the thermally efficiency of boost (or use of an intercooler). However, that is in a perfect world of mathematics and theory. Don't get me wrong, I'm an engineer I live for the math. Unfortunately, though, if your intercooler, turbo, etc. is sized at all incorrectly, that's not going to be the case.
I have one other concern as well. He's comparing 8.5 to 9.5 CR. And in comparison, he is stating the 8.5 is more advantageous. The question is, how low can you go before you reach diminishing returns? To be extreme, we're obviously not going to run 2:1 CR and 150 psi of boost. ....or can we?
Either way, this is an important topic for all 944 turbo owners that plan on pushing their engines. Whether we like it or not, we will all eventually hit our peak cylinder pressure limit.
That's interesting. And I appreciate the math behind it. Basically that article's math proves me wrong in one instance, but right in another. CR alone will not dictate the head lift. However, he's saying that boost is thermally more efficient at creating power and therefore is the better choice. Although, CR is, power wise (cylinder pressure), more efficient. Unfortunately, for us, we're limited to a specific peak cylinder pressure which means, according to his math and I assume what you're getting at as well, that boost will be more thermally efficient and, given the same peak cylinder pressure CR vs. boost, boost will make more power. That's obviously due to the thermally efficiency of boost (or use of an intercooler). However, that is in a perfect world of mathematics and theory. Don't get me wrong, I'm an engineer I live for the math. Unfortunately, though, if your intercooler, turbo, etc. is sized at all incorrectly, that's not going to be the case.
I have one other concern as well. He's comparing 8.5 to 9.5 CR. And in comparison, he is stating the 8.5 is more advantageous. The question is, how low can you go before you reach diminishing returns? To be extreme, we're obviously not going to run 2:1 CR and 150 psi of boost.
....or can we? Either way, this is an important topic for all 944 turbo owners that plan on pushing their engines. Whether we like it or not, we will all eventually hit our peak cylinder pressure limit.
. Funny that so many engineers are attracted to our cars. I would think that the low boundry on CR is dictated by how much your willing to give up on the bottom end and what your turbo can deliver and in our case the high boundry on CR is dictated by head lift.
02-02-2013, 02:07 PM
#194
Rocket Scientist
Rennlist Member
Rennlist Member
ME here as well.
And agreed on that. Even with the lower compression, some response can be made up with a lot of low end timing and/or cam gear adjustment.
When I have more time I'll read that article more in depth. That's a good one.
And agreed on that. Even with the lower compression, some response can be made up with a lot of low end timing and/or cam gear adjustment.
When I have more time I'll read that article more in depth. That's a good one.
02-02-2013, 02:38 PM
#195
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I am also an engineer (ME). Funny that so many engineers are attracted to our cars.
I would think that the low boundry on CR is dictated by how much your willing to give up on the bottom end and what your turbo can deliver and in our case the high boundry on CR is dictated by head lift.
. Funny that so many engineers are attracted to our cars. I would think that the low boundry on CR is dictated by how much your willing to give up on the bottom end and what your turbo can deliver and in our case the high boundry on CR is dictated by head lift.