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Holbert Car cam update. Two MORE teeth found after 4 race weeknds after oil change

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Holbert Car cam update. Two MORE teeth found after 4 race weeknds after oil change

 
Old 09-16-2005, 06:36 PM
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what about valve spring bind, etc. he says we need to evaluate that first and i may need to replace the springs. however, he is looking for a set.

I dont have much time!!

GT cams anyone????

mk

Originally Posted by Louie928
Why not get some B1 cams from Marc T.? They work really well.
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Old 09-16-2005, 07:32 PM
  #62  
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Originally Posted by mark kibort
what about valve spring bind, etc. he says we need to evaluate that first and i may need to replace the springs. however, he is looking for a set.

I dont have much time!!

GT cams anyone????

mk
Yes. You'd need different springs. Actually, the stock springs aren't strong enough for GT intake cams because many GT cams that have been used for a while show pits just after the top of the intake lobe. The lifters bounce off of the lobe and give it a whack. With the different springs, you'll need to measure the spring height, use shims as required, etc. Anyway, it is a time consuming task, but worth it. With all you need to do, maybe swap in some S4 cams and run it until you get all the ducks lined up. Adam Birnbaum got better than S4 performance by using GTS intake and S4 exhaust cams. Anybody with some GTS cams laying in the dust bin?
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Old 09-16-2005, 07:46 PM
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but, i have cams (had, but toothless) that have the GT lift and duration. from a micrometer, the cams are identical to GT cams (holbert cams and 85-86cams) so, does this mean that the 85-86 had better springs stock than an S4?
anyway, dont know what springs the holbert car has now, but they look pretty new as most all of the internals. No pitting on the cams after 4 seasons of racing and 30,000miles of pretty tough driving. (20,000 of that are unknown toughness miles!) 4 race seasons later, the cams are out.

MK

Originally Posted by Louie928
Yes. You'd need different springs. Actually, the stock springs aren't strong enough for GT intake cams because many GT cams that have been used for a while show pits just after the top of the intake lobe. The lifters bounce off of the lobe and give it a whack. With the different springs, you'll need to measure the spring height, use shims as required, etc. Anyway, it is a time consuming task, but worth it. With all you need to do, maybe swap in some S4 cams and run it until you get all the ducks lined up. Adam Birnbaum got better than S4 performance by using GTS intake and S4 exhaust cams. Anybody with some GTS cams laying in the dust bin?
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Old 09-16-2005, 07:58 PM
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Originally Posted by mark kibort
but, i have cams (had, but toothless) that have the GT lift and duration. from a micrometer, the cams are identical to GT cams (holbert cams and 85-86cams) so, does this mean that the 85-86 had better springs stock than an S4?
anyway, dont know what springs the holbert car has now, but they look pretty new as most all of the internals. No pitting on the cams after 4 seasons of racing and 30,000miles of pretty tough driving. (20,000 of that are unknown toughness miles!) 4 race seasons later, the cams are out.

MK
I think '85/'86 do have different springs than an S4, but I don't know unless I check the shop manual, or PET. I know the spring height is different. Evidently, whatever springs you have are compatible with GT (like) cams with 10mm lift.
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Old 09-16-2005, 08:04 PM
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on the 85 that maybe true due to the different valve hight and head config.


so, since i have springs that seem to be compatible with the GTcam, is that enough for the B1 cam??

MK

Originally Posted by Louie928
I think '85/'86 do have different springs than an S4, but I don't know unless I check the shop manual, or PET. I know the spring height is different. Evidently, whatever springs you have are compatible with GT (like) cams with 10mm lift.
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Old 09-16-2005, 08:35 PM
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what about using the 85s on the intake and the s4s on the exhuast? that seems like could be quick fix with out too much power loss?
(or GTS on the exhaust)

Mk
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Old 09-16-2005, 11:37 PM
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Originally Posted by mark kibort
on the 85 that maybe true due to the different valve hight and head config.


so, since i have springs that seem to be compatible with the GTcam, is that enough for the B1 cam??

MK
I don't think so. You'd have to check for coil binding for sure and I doubt that the seat pressure is enough. I believe 944 S2, or 968, springs are good with the B1 cam. Marc Thomas would know.
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Old 09-16-2005, 11:42 PM
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Originally Posted by mark kibort
what about using the 85s on the intake and the s4s on the exhuast? that seems like could be quick fix with out too much power loss?
(or GTS on the exhaust)

Mk
I think S4 exhaust would work ok. I have my doubts about the GTS exhaust cams. I believe Adam Birnbaum tried GTS cams in his S4 and wasn't too impressed. It seemed to fall off at the high rpm end more than with S4 cams. He replaced the GTS exhaust cams with S4 exhaust cams and got a noticable improvement (dyno) over either all GTS or all S4 cams.
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Old 09-17-2005, 12:20 AM
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thats interesting. maybe thats the hot combination? why would GTS exhaust cams be worse than S4 cams with less duration and lift? (1mm lift differnce and about 10degrees diff in duration)

if thats so, i wonder if the GT exhaust is even worse? or, following this logic, maybe the GT intake and the GTS exhaust is the hot ticket?? lots of possiblities there ! maybe the magic is in some precentage of lift or duration intake vs exhaust. (and of course, the overlap ,which i have no concept of)

by the way, what did adam get in HP with the GTS intake and S4 exhaust cams.
what was the gain over the pure GTS set up. Geeee, he is making me feel like a wimp thinking that job is a tough one. you mean he chose to take a perfectly running engine cam setup apart!!!!???

mk


Originally Posted by Louie928
I think S4 exhaust would work ok. I have my doubts about the GTS exhaust cams. I believe Adam Birnbaum tried GTS cams in his S4 and wasn't too impressed. It seemed to fall off at the high rpm end more than with S4 cams. He replaced the GTS exhaust cams with S4 exhaust cams and got a noticable improvement (dyno) over either all GTS or all S4 cams.
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Old 09-18-2005, 12:11 PM
  #70  
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Default First comparisons of the Holbert vs 85-86 cams

The first comparisons of the 85 vs Holbert cams, is that the 85 cams based on orientation of the spocket, seems to be advanced 5 degrees on the intake cam. the sprocket teeth align exactly on a intake lobe, while the 85 cam lobe is forward of the cam sprocket teeth by 5 degrees ( 1/4 tooth pitch, and there are 19 teeth). this my not be an indicator if the other exhaust cam is off by the same amount. I have to think about that one for a second and do some more checking. first of all, sprocket teeth relative to the keyway for a start.

mk
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Old 09-18-2005, 03:37 PM
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Mark,

I agree, you need to index from the keyway.
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Old 09-19-2005, 12:22 AM
  #72  
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sorry, just did some comprehensive measurements. I had the intake cams pointing backward. the 85 cams are retarded (not advanced) by 4 degrees. the keyways match up, and the exhaust cams are the same all the way around. i even traced the lobes and they are the same too. I guess the holbert cams are GT cams as i understand the 85 86 cams had a retarded intake cams, giving more top end HP and less midrange torque.

the s4 cams both intake and exhaust, are 4 degrees retarded vs the holbert cams.

all the base circles are the same and the only difference is the lift being 10/9mm intake and exhuast vs the s4 being 9/8mm .

Now, if i can get that cam mod'ded, im in buisness, maybe even better hp up top. otherwise, i may be installing S4 exhaust cams! (ahhhhh)

MK


Originally Posted by mark kibort
The first comparisons of the 85 vs Holbert cams, is that the 85 cams based on orientation of the spocket, seems to be advanced 5 degrees on the intake cam. the sprocket teeth align exactly on a intake lobe, while the 85 cam lobe is forward of the cam sprocket teeth by 5 degrees ( 1/4 tooth pitch, and there are 19 teeth). this my not be an indicator if the other exhaust cam is off by the same amount. I have to think about that one for a second and do some more checking. first of all, sprocket teeth relative to the keyway for a start.

mk
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Old 09-21-2005, 01:24 PM
  #73  
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Just talked to Elgin, cams should be ready by this friday. If not, Plan B is using 2 exhaust cams from a GTS,(they are only .5mm lift worse than GT or 85cams, and .5mm better than S4)
Plan C is B1 cams from Devek, and plan D maybe using a guy back east that actually has done this modification and can turn the cams around in 2 days. but then, it puts me with 2 days before race day to get it running. (fine, if i didnt have a day job!) Plan E would be put in S4 exhaust cams only.

Mk
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Old 09-21-2005, 01:27 PM
  #74  
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Adam, any details to add here . I think this is very interesting. wonder if its all about the "system" effects of such changes. the fact that the GTS/S4exhaust had the best dyno hp is curious.

MK

Originally Posted by Louie928
I think S4 exhaust would work ok. I have my doubts about the GTS exhaust cams. I believe Adam Birnbaum tried GTS cams in his S4 and wasn't too impressed. It seemed to fall off at the high rpm end more than with S4 cams. He replaced the GTS exhaust cams with S4 exhaust cams and got a noticable improvement (dyno) over either all GTS or all S4 cams.
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Old 09-21-2005, 01:56 PM
  #75  
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Mark,

Would you provide contact information for the "guy back east" that has done it? Did you get a price?
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