Info on "cutting the base circle" (CAMS)
03-06-2008, 04:29 PM
#16
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Speaking of California cam grinders, does anyone know Bob Walters of Logicam? We spoke 18 years ago about making some cams for a 32v engine, since I'm finally getting around to doing just that it would be interesting to talk to the guy again.
Brendan, are you sure you want to do this so late in the game? Even if you find a cam grinder who will grind it right away, it will have to be nitrited afterwards. The shop will want to wait until a bunch of cams are ready because there's a big lot charge for nitriding and it makes sense to do many cams at the same time.
Brendan, are you sure you want to do this so late in the game? Even if you find a cam grinder who will grind it right away, it will have to be nitrited afterwards. The shop will want to wait until a bunch of cams are ready because there's a big lot charge for nitriding and it makes sense to do many cams at the same time.
Last edited by BC; 03-07-2008 at 01:10 AM.
03-06-2008, 04:30 PM
#17
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I could run the engine with the S4 set if I wanted to get stuff started, and leave the S3 cams until such time they were finally done. I guess.
03-06-2008, 04:33 PM
#18
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03-06-2008, 04:58 PM
#19
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Brendan:
Your theory on working to alter the lobe centers may work, but it is likely an extreme setup for 928 4 valve event timings. As Errka points outs there are simply too too few teeth for this to be a viable means of making an OEM cam behave like something different... my $0.02.
From what we have modelled on the 928 4V here at my shop, the cam tooth change will alter the cam by 18+ cam degrees, or 36+ crank degrees. The adjustment on the front sprocket TB sprocket is something like 7 cam degrees, or 14 crank degrees. So, if you have perfect cams with regards to their key slot / chain wheel angles to lobe center angles, you could narrow the lobe center angle on the intake by 22 crank degrees. Remember, this is the smallest shift assuming the 7 degrees of motion on the timing belt wheel.
Assuming my data on the S3 cams is correct with 120 degree lobe center angle, your setup would shift your lobe center angle to 98 degrees. At 98 degrees, the new set of valave events may cause other problems within your engine such as effective compression changes outside of your fuel choice as well as too much overlap for a boosted engine.
I would suggest reviewing your specific needs for valve event timings, such as max lift, intake valve closure and overlap angles int. vs. ex. as these are very relavent to your enigne's design and how well you will be able to tune it, once assembled.
Also, as it was mentioned in your earier post... Sorry it took 5 months for you to get your cam mod from Dema (Elgins). For anyone interested, there were some very real cicumstances as to why the delay took place. As the issues are very personal information, I will keep my friend's personal life private...
This said, I would also add in for the defense of any shop choosing to help us with our 928 engine builds, please keep in mind that these engine are not well know, the data on them is sparse and for most of us, we do not represent much value to any business to keep making a profit while breaking away from the more common work to handle our one-off requests. Looking at this critically, it really shows off the value in vendors like Mark Anderson, Carl Faucett, Dave Roberts and any other 928 vendors I have neglected to mention, for how their products help us as a very small market segment of "hot rodders".
(NOTE: Thanks to Dennis K., I have editted the math in this post based on my guessing from memory the spreadsheet Dennis and I did on the various 928 cams... sorry folks...)
Enjoy the rest of your build.
Regards
Your theory on working to alter the lobe centers may work, but it is likely an extreme setup for 928 4 valve event timings. As Errka points outs there are simply too too few teeth for this to be a viable means of making an OEM cam behave like something different... my $0.02.
From what we have modelled on the 928 4V here at my shop, the cam tooth change will alter the cam by 18+ cam degrees, or 36+ crank degrees. The adjustment on the front sprocket TB sprocket is something like 7 cam degrees, or 14 crank degrees. So, if you have perfect cams with regards to their key slot / chain wheel angles to lobe center angles, you could narrow the lobe center angle on the intake by 22 crank degrees. Remember, this is the smallest shift assuming the 7 degrees of motion on the timing belt wheel.
Assuming my data on the S3 cams is correct with 120 degree lobe center angle, your setup would shift your lobe center angle to 98 degrees. At 98 degrees, the new set of valave events may cause other problems within your engine such as effective compression changes outside of your fuel choice as well as too much overlap for a boosted engine.
I would suggest reviewing your specific needs for valve event timings, such as max lift, intake valve closure and overlap angles int. vs. ex. as these are very relavent to your enigne's design and how well you will be able to tune it, once assembled.
Also, as it was mentioned in your earier post... Sorry it took 5 months for you to get your cam mod from Dema (Elgins). For anyone interested, there were some very real cicumstances as to why the delay took place. As the issues are very personal information, I will keep my friend's personal life private...
This said, I would also add in for the defense of any shop choosing to help us with our 928 engine builds, please keep in mind that these engine are not well know, the data on them is sparse and for most of us, we do not represent much value to any business to keep making a profit while breaking away from the more common work to handle our one-off requests. Looking at this critically, it really shows off the value in vendors like Mark Anderson, Carl Faucett, Dave Roberts and any other 928 vendors I have neglected to mention, for how their products help us as a very small market segment of "hot rodders".
(NOTE: Thanks to Dennis K., I have editted the math in this post based on my guessing from memory the spreadsheet Dennis and I did on the various 928 cams... sorry folks...)
Enjoy the rest of your build.
Regards
Last edited by Jim Morton; 03-07-2008 at 02:35 AM.
03-06-2008, 05:14 PM
#20
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You could move the cam gear by one tooth, and advance/retard from there with a 32V'r. That wouldn't ease the separation anxiety, though.
03-06-2008, 07:49 PM
#21
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Thread Starter
Brendan:
Your theory on working to alter the lobe centers may work, but it is likely an extreme setup for 928 4 valve event timings. As Errka points outs there are simply too too few teeth for this to be a viable means of making an OEM cam behave like something different... my $0.02.
Assuming my data on the S3 cams is correct with 114 degree lobe centers, your setup would shift your lobe centers to 92 degrees. At 92 degrees separation, the new set of valave events may cause other problems within your engine such as effective compression changes outside of your fuel choice as well as too much overlap for a boosted engine.
I would suggest reviewing your specific needs for valve event timings, such as max lift, intake valve closure and overlap angles int. vs. ex. as these are very relavent to your enigne's design and how well you will be able to tune it, once assembled.
Your theory on working to alter the lobe centers may work, but it is likely an extreme setup for 928 4 valve event timings. As Errka points outs there are simply too too few teeth for this to be a viable means of making an OEM cam behave like something different... my $0.02.
Assuming my data on the S3 cams is correct with 114 degree lobe centers, your setup would shift your lobe centers to 92 degrees. At 92 degrees separation, the new set of valave events may cause other problems within your engine such as effective compression changes outside of your fuel choice as well as too much overlap for a boosted engine.
I would suggest reviewing your specific needs for valve event timings, such as max lift, intake valve closure and overlap angles int. vs. ex. as these are very relavent to your enigne's design and how well you will be able to tune it, once assembled.
While I have not changed my compression from stock S4, the fuel choice I have planned the entire car around is one of my keys for keeping this car together at high boost pressures. By that I mean the fuel is my main tool in removing the chance of detonation and pre-ignition that would usually be present in an engine of nearly 10:1 compression (though I am closer to 9.4:1.) with the amount of air I will be pushing in. Its Ethanol, or more specifically, E85.
So I will be relying on the fuel (and proper tuning) to make sure the engine is only subjected to the controlled and linear rise in pressure that arises out of a controlled and proper combustion process.
Since I have that as a platform, I want to make sure that I put the heads on there with enough cam so as to not be a serious restriction. The small additional lift of the S3 was what interested me, but with its published additional overlap (seems to me that its good for NA, not so good for Supercharging) - maybe I should sell them and just use the S4 set I have, with some additional lift from a base circle cut. Any advice on this Jim?
03-06-2008, 07:51 PM
#22
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Thread Starter
Also, as it was mentioned in your earier post... Sorry it took 5 months for you to get your cam mod from Dema (Elgins). For anyone interested, there were some very real cicumstances as to why the delay took place. As the issues are very personal information, I will keep my friend's personal life private...
03-06-2008, 08:33 PM
#23
Rennlist Member
Hey Brendan,
May not be a bad idea to look at the specs for the cams available for the S/C'd DOHC Mustangs. That would probably get you in the ball park as to an ideal grind. You may find that the S4 cams are far enough out of wack that isn't worth messing with. Or you may find that the S3 cams are spot on, but could use a little more lift. At least this way you have some kind of baseline to compare with. JMHO.
May not be a bad idea to look at the specs for the cams available for the S/C'd DOHC Mustangs. That would probably get you in the ball park as to an ideal grind. You may find that the S4 cams are far enough out of wack that isn't worth messing with. Or you may find that the S3 cams are spot on, but could use a little more lift. At least this way you have some kind of baseline to compare with. JMHO.
03-06-2008, 09:01 PM
#24
Rennlist Member
Brendan,
This is all my opinion & you could always snicker & blow it off. If I was doing what you are doing my main concerns in a camshaft profile would be lobe seperation angle (LSA), & overlap. Which is affected to some degree by the LSA. 928 Porsche cams, all of them, are mild grinds intended to long outlive the vehicle warranty. Designed for sophisticated 'suits' that long to feel like they drive a performance car. Not '***** to the wall' performance. I would use the S4 cams for the simple reason that you are doing (due to your fuel of choice which has its benefits as you know) something that hasn't been done. When this motor starts for the first time you will have many other things that you need to iron out. You don't need the added confusion of sorting out a more radical cam profile. You should have plenty of power initially to keep yourself happy. You can always install hotter cams once you see what effect your engine build has in total. It's very hard to sort out more than one engine change at a time. You never know which innovation is in your way. Once you know what the engine is doing with a baseline cam profile then you can start spicing it up. The camshaft has always been known as an engine's 'brain'. No sense in confusing it before it has a chance to live. Just my opinion, 'like a belly button.........', you know the rest.
Hammer
This is all my opinion & you could always snicker & blow it off. If I was doing what you are doing my main concerns in a camshaft profile would be lobe seperation angle (LSA), & overlap. Which is affected to some degree by the LSA. 928 Porsche cams, all of them, are mild grinds intended to long outlive the vehicle warranty. Designed for sophisticated 'suits' that long to feel like they drive a performance car. Not '***** to the wall' performance. I would use the S4 cams for the simple reason that you are doing (due to your fuel of choice which has its benefits as you know) something that hasn't been done. When this motor starts for the first time you will have many other things that you need to iron out. You don't need the added confusion of sorting out a more radical cam profile. You should have plenty of power initially to keep yourself happy. You can always install hotter cams once you see what effect your engine build has in total. It's very hard to sort out more than one engine change at a time. You never know which innovation is in your way. Once you know what the engine is doing with a baseline cam profile then you can start spicing it up. The camshaft has always been known as an engine's 'brain'. No sense in confusing it before it has a chance to live. Just my opinion, 'like a belly button.........', you know the rest.
Hammer
03-06-2008, 09:55 PM
#25
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Thread Starter
Thanks for your thoughts guys.
Hey Brendan,
May not be a bad idea to look at the specs for the cams available for the S/C'd DOHC Mustangs. That would probably get you in the ball park as to an ideal grind. You may find that the S4 cams are far enough out of wack that isn't worth messing with. Or you may find that the S3 cams are spot on, but could use a little more lift. At least this way you have some kind of baseline to compare with. JMHO.
May not be a bad idea to look at the specs for the cams available for the S/C'd DOHC Mustangs. That would probably get you in the ball park as to an ideal grind. You may find that the S4 cams are far enough out of wack that isn't worth messing with. Or you may find that the S3 cams are spot on, but could use a little more lift. At least this way you have some kind of baseline to compare with. JMHO.
Brendan,
This is all my opinion & you could always snicker & blow it off. If I was doing what you are doing my main concerns in a camshaft profile would be lobe seperation angle (LSA), & overlap. Which is affected to some degree by the LSA. 928 Porsche cams, all of them, are mild grinds intended to long outlive the vehicle warranty. Designed for sophisticated 'suits' that long to feel like they drive a performance car. Not '***** to the wall' performance. I would use the S4 cams for the simple reason that you are doing (due to your fuel of choice which has its benefits as you know) something that hasn't been done. When this motor starts for the first time you will have many other things that you need to iron out. You don't need the added confusion of sorting out a more radical cam profile. You should have plenty of power initially to keep yourself happy. You can always install hotter cams once you see what effect your engine build has in total. It's very hard to sort out more than one engine change at a time. You never know which innovation is in your way. Once you know what the engine is doing with a baseline cam profile then you can start spicing it up. The camshaft has always been known as an engine's 'brain'. No sense in confusing it before it has a chance to live. Just my opinion, 'like a belly button.........', you know the rest.
Hammer
This is all my opinion & you could always snicker & blow it off. If I was doing what you are doing my main concerns in a camshaft profile would be lobe seperation angle (LSA), & overlap. Which is affected to some degree by the LSA. 928 Porsche cams, all of them, are mild grinds intended to long outlive the vehicle warranty. Designed for sophisticated 'suits' that long to feel like they drive a performance car. Not '***** to the wall' performance. I would use the S4 cams for the simple reason that you are doing (due to your fuel of choice which has its benefits as you know) something that hasn't been done. When this motor starts for the first time you will have many other things that you need to iron out. You don't need the added confusion of sorting out a more radical cam profile. You should have plenty of power initially to keep yourself happy. You can always install hotter cams once you see what effect your engine build has in total. It's very hard to sort out more than one engine change at a time. You never know which innovation is in your way. Once you know what the engine is doing with a baseline cam profile then you can start spicing it up. The camshaft has always been known as an engine's 'brain'. No sense in confusing it before it has a chance to live. Just my opinion, 'like a belly button.........', you know the rest.
Hammer
03-06-2008, 10:18 PM
#26
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Since I have that as a platform, I want to make sure that I put the heads on there with enough cam so as to not be a serious restriction. The small additional lift of the S3 was what interested me, but with its published additional overlap (seems to me that its good for NA, not so good for Supercharging) - maybe I should sell them and just use the S4 set I have, with some additional lift from a base circle cut. Any advice on this Jim?
03-06-2008, 10:34 PM
#27
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Thread Starter
http://store.summitracing.com/partde...6&autoview=sku
EDIT:
That was a great comment Adam - look here:
http://www.steeda.com/products/comp_...obra_03-04.php
You can see that they jack up the duration QUITE a bit for the supercharged cams, as well as the INTAKE lift.
The lobe separation is 114 degrees, until the wicked one on the bottom with 116.
03-06-2008, 10:44 PM
#28
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Thread Starter
Oh Jeez - does that chart make using the S3 intake and the S4 exhaust a good idea for putting more air in the chamber?
Early open and later close on the S3 cam, and a LATER opening of the exhaust valve of the S4?
03-06-2008, 10:56 PM
#29
Brendan,
Hammer nailed it exactly, & if thats not enough think about this. The S3 cams you have are the same
ones Todd has in his mtr & he is making 818 crank hp on 91 octane. If those cams can support that
level than you should be covered. Quit dicking around with **** that don't fixing and just get that bitch
on the road
Hammer nailed it exactly, & if thats not enough think about this. The S3 cams you have are the same
ones Todd has in his mtr & he is making 818 crank hp on 91 octane. If those cams can support that
level than you should be covered. Quit dicking around with **** that don't fixing and just get that bitch
on the road
03-06-2008, 10:57 PM
#30
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Thread Starter
I am talking to Todd right now. He agrees with you guys