More base circle questions
01-29-2009, 06:22 PM
#33
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Duh... GUess I was using that "new math", 1mm of base circle reduction would only change base radius .5mm so you get half the reduction added to lift.
So if you reduce the base circle 1.5mm you'd effectevly add 0.75mm of lift or .503" lift.
I know the 944 specs may be slightly different than the 16v valves, but JME starts using longer valves or lash caps at .526 with just better springs required from .503" They don't show any grinds in between .503 and .526 so it's not noted where the lashcap would be needed first. Carl is at .506 so I would assume you're safe to that point at least.
2mm reduction would net .513 and require the lifters to handle an additional 1mm.
Seems like base circle reduction would be much cheaper though the cam profile would not be as ideal as a true weld and grind. However you wouldn't have to worry about lobe clearance getting in the cam covers.
So if you reduce the base circle 1.5mm you'd effectevly add 0.75mm of lift or .503" lift.
I know the 944 specs may be slightly different than the 16v valves, but JME starts using longer valves or lash caps at .526 with just better springs required from .503" They don't show any grinds in between .503 and .526 so it's not noted where the lashcap would be needed first. Carl is at .506 so I would assume you're safe to that point at least.
2mm reduction would net .513 and require the lifters to handle an additional 1mm.
Seems like base circle reduction would be much cheaper though the cam profile would not be as ideal as a true weld and grind. However you wouldn't have to worry about lobe clearance getting in the cam covers.
01-29-2009, 08:37 PM
#34
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I thin hammer explained it once, but I don't know why we have such pointy cams and honda and Chevy and others all have very obtuse cams:
01-29-2009, 08:56 PM
#35
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when you reduced the base circle by.5 mm as Dennis did, isnt that reducing that one side by .5mm, in otherwords, the radius? This would mean that you get an increase in lift by that exact same amount as long as the lifter can pump up .5mm more and keep contact with the cam, which dennis has proved does work.
mk
mk
01-29-2009, 08:58 PM
#36
Administrator - "Tyson"
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01-29-2009, 09:13 PM
#37
Three Wheelin'
The radius of the cam lobe depends on the diameter of the lifter. A larger diameter lifter will need a more pointy cam lobe. A small diameter lifter, the most extreme being a roller, will have a rounded lobe.
01-29-2009, 09:31 PM
#38
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Ah, thanks.
01-29-2009, 11:42 PM
#39
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as I understand this issue:
removing base areas from the cam allows the lifter to pump up (fully). this increases lift not formerly available by moving the lifter further from the valve in the lifter bore.
as it is unclear from these discussions (here and on PP) how much or how little the lifter can be manipulated,---perhaps some one could offer the research and advise.
removing material from the ramps, as in Mike's pictures, does not increase lift or duration, but does speed up opening and closing removing duration, all other dimensions being equal.
as we all know, the limitation on the 16V is the cam bearing opening (camtower) diameter. if you take the radius of that opening, minus the radius of the stick, this will give you the maximum lift attainable. (I do not have those measurements on hand.)
as to cam bearings--yes, the cam bearing areas could be welded up and reground to a larger diameter, and a corresponding increase in camtower bearing bore could be done as well. this would allow larger cam lobes for more lift and duration. I have not measured how much can be done with this, but common sense tells me that if you can weld up the lobes, you can weld up the bearing areas as well. the limitation on this would be the camtower end plates, seals, gaskets and such (on the drive end of the cam tower). perhaps there is much room to work with in these areas (?) the cam non-drive end of the cam/camtower would be unchanged, as that end would be unaffected by increased cam lobe sizes.
another way to approach this is the Jesel system, which uses needle bearings in place of cam bearings. as we do not use a bearing per se, I believe it may be possible to use the needle bearing to facilitate a larger cam tower bearing opening for installing larger cam lobes. something to investigate with Jesel. this would be dependent upon what size needle bearing is available.
Frankly, I would not advise much more than the Euro cam grind due to the 928's vacuum needs. Carls' race cams are probably close to the max for a hot street engine. anything more than 240 degrees duration (@ .050 lift) nears the point of not building enough vacuum to operate brakes and other components, in addition to making high stall speed converters (3500 rpms and up) in auto boxes, headers, intake mods, and head porting, a must.
--Russ
removing base areas from the cam allows the lifter to pump up (fully). this increases lift not formerly available by moving the lifter further from the valve in the lifter bore.
as it is unclear from these discussions (here and on PP) how much or how little the lifter can be manipulated,---perhaps some one could offer the research and advise.
removing material from the ramps, as in Mike's pictures, does not increase lift or duration, but does speed up opening and closing removing duration, all other dimensions being equal.
as we all know, the limitation on the 16V is the cam bearing opening (camtower) diameter. if you take the radius of that opening, minus the radius of the stick, this will give you the maximum lift attainable. (I do not have those measurements on hand.)
as to cam bearings--yes, the cam bearing areas could be welded up and reground to a larger diameter, and a corresponding increase in camtower bearing bore could be done as well. this would allow larger cam lobes for more lift and duration. I have not measured how much can be done with this, but common sense tells me that if you can weld up the lobes, you can weld up the bearing areas as well. the limitation on this would be the camtower end plates, seals, gaskets and such (on the drive end of the cam tower). perhaps there is much room to work with in these areas (?) the cam non-drive end of the cam/camtower would be unchanged, as that end would be unaffected by increased cam lobe sizes.
another way to approach this is the Jesel system, which uses needle bearings in place of cam bearings. as we do not use a bearing per se, I believe it may be possible to use the needle bearing to facilitate a larger cam tower bearing opening for installing larger cam lobes. something to investigate with Jesel. this would be dependent upon what size needle bearing is available.
Frankly, I would not advise much more than the Euro cam grind due to the 928's vacuum needs. Carls' race cams are probably close to the max for a hot street engine. anything more than 240 degrees duration (@ .050 lift) nears the point of not building enough vacuum to operate brakes and other components, in addition to making high stall speed converters (3500 rpms and up) in auto boxes, headers, intake mods, and head porting, a must.
--Russ
01-30-2009, 01:34 AM
#40
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If you grind the base circle more than the lifter can accomadate, why couldn't you place a small .5mm thick shim washer between the spring top and bucket, assuming the bucket would still cover enough of the spring sides to remain stable. Seems like an easy way to snug things up since the lifter has some variance it can take up on it's own.
So grind the base circle 2mm on a Euro S and add a 1mm shim and you're back to stock with a larger lift?
So grind the base circle 2mm on a Euro S and add a 1mm shim and you're back to stock with a larger lift?
01-30-2009, 03:17 AM
#41
Three Wheelin'
If you grind the base circle more than the lifter can accomadate, why couldn't you place a small .5mm thick shim washer between the spring top and bucket, assuming the bucket would still cover enough of the spring sides to remain stable. Seems like an easy way to snug things up since the lifter has some variance it can take up on it's own.
So grind the base circle 2mm on a Euro S and add a 1mm shim and you're back to stock with a larger lift?
So grind the base circle 2mm on a Euro S and add a 1mm shim and you're back to stock with a larger lift?
01-30-2009, 01:54 PM
#42
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I had forgotten about lash caps. But they are usually pretty thick, relatively.
01-30-2009, 02:06 PM
#43
Also, extra lift could be gained by going to solid lifters. They can be made to order with varying size lash caps for adjustment. It would require two installs, one to get the base lash clearances and another to install the correct size lash caps.
Dennis
Dennis
01-30-2009, 02:19 PM
#44
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What kind of ongoing adjustment (if any) is needed with modern solid lifters?
