Go Back  Rennlist - Porsche Discussion Forums > Water Cooled Technical Discussion Areas > 928 Forum
Reload this Page >

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

Notices
928 Forum
Sponsored by:
Sponsored by: 928 Specialists

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

 
Old 09-14-2005, 12:23 PM
  #31  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

You guys are right. they are coming out tonight.

By the way, i did measure them and compare them to a set of s4 cams i have. they are the same lift as 85 cams, which are the same lift as GT cams. what the profile is? that will have to be determined. considering the cams have numbers similar to 85 cams, i would suspect they are close to them. plus, from what was said, the 85 cams would have less peak torque and broader hp up top and thats what it looks like on the dyno compared to an equally prepared GT of Ron's. same hp exactly and pretty close to the same peak torque. just a slightly differnt shaped curve up top. (less peaky)

mk

Originally Posted by IcemanG17
Mark
You gotta pull those cams and get them measured...inquiring minds want to know...I think its safe to say they are not run of the mill GT cams...probably closer to the Devek B1 cams! Either way the differences will be very telling to the Holberts cars secrets!
Brian
mark kibort is offline  
Old 09-14-2005, 01:26 PM
  #32  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

just found a way to measure the fine tuning cam timing. I finally figured out what the manual was talking about. got #6 cylinder at TDC 0 at the compression stroke of #1 and found a surface which allowed for perpendicular measurement of the decent of the #6 lifter. moved the crank 20 degrees advance and the movement was 2mm almost exactly. so, its unlikely the grind is GT and certainly not S4, but it sure looks like 85-86!!! i think the spec is 1.8mm for passenger side and 2.0mm driver side. (driver side for both 85 and 87 cams are 2.0 , while passenger side is 1.6 for '85 and 1.8mm for S4)

thoughts?
(glad i can do some of this stuff before it was all mangled!)

MK
mark kibort is offline  
Old 09-14-2005, 01:52 PM
  #33  
Jim bailey - 928 International
Addict
Rennlist Member

Rennlist
Site Sponsor

 
Join Date: Jul 2001
Location: Anaheim California
Posts: 11,542
Likes: 0
Received 0 Likes on 0 Posts
Default

Mark it is critical that you determine the installed height of the valves.. the 85/86 spec is 41 mm intake 40 mm exhaust the 87> is 42.6 intake 41.6 exhaust and the length of valves is DIFFERENT note that 85-86 valves are 112.20 mm intake 111.20 exhaust while 87 > is intake 114.7 exhaust 113.7 . Simply bolting on a stock set of cams has another set of risks... Also Your exhaust ports have 2 or three studs ?? Mixing and matching different but similar parts is never easy.
Jim bailey - 928 International is offline  
Old 09-14-2005, 02:21 PM
  #34  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

GREAT!! now you tell me!!

so, the heads have the 3 bolt studs on the headers. sounds like it could be an S4 cam set with 85-86 grind . in that case, your saying that the 85-86 cam may not work due to the valve hights and lengths???

sounds like the 85 cam wont be a bolt on affair, unless they are exactly the same as the ones on the car. i still dont understand how it can matter though. if the cam lobe is identical (as far as lift) why wouldnt it work? i measured the comparison of the S4 cams and 85-86 and they are the same except the 85 has 1mm more lift. so, why wont they just bolt in?

thanks,

MK
now it sounds like i may need to investigate someone to fix the cams. buy new cam chains and put it together!


Originally Posted by Jim bailey - 928 International
Mark it is critical that you determine the installed height of the valves.. the 85/86 spec is 41 mm intake 40 mm exhaust the 87> is 42.6 intake 41.6 exhaust and the length of valves is DIFFERENT note that 85-86 valves are 112.20 mm intake 111.20 exhaust while 87 > is intake 114.7 exhaust 113.7 . Simply bolting on a stock set of cams has another set of risks... Also Your exhaust ports have 2 or three studs ?? Mixing and matching different but similar parts is never easy.
mark kibort is offline  
Old 09-14-2005, 02:32 PM
  #35  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

Jim, so, do the differences in lifters or castings in the head, make up the difference? it seems to me that it woudnt matter as long as the cam nominal circle (???) is the same and the lift is the same?

so the valves peak out of the heads 1.6mm farther with an 87. PLus, the length of the valves are 2.5mm longer. does this matter because the heads will mount the cams at a hight to have the proper lift , right? where is that valve installed hight measured from?

anyway, is it really adding more risk. please let me know what can go wong if i put in the 85 cams. as i said, by measureing all the lengths and cam profiles ive found the other 3 cams to be the same. (obviously , i couldnt measure duration ) but the lobes of both cams are the same , except the 85 has the 1mm more lift.
whatcha thinking??

MK
mark kibort is offline  
Old 09-14-2005, 05:06 PM
  #36  
John Veninger
Addict
Lifetime Rennlist
Member
 
John Veninger's Avatar
 
Join Date: May 2001
Location: New Jersey
Posts: 3,839
Likes: 0
Received 0 Likes on 0 Posts
Default

Mark,

I have a set of S4 cams you can borrow to get you to the race.
John Veninger is offline  
Old 09-14-2005, 05:13 PM
  #37  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

thanks John!! very nice of you.

so, then what would i use in the race??

kidding!

I think i have a line on some GT cams, and if not, i may and try to modify the 85s. still lots of questions. JIM, owes me some answers as his point are very concerning

mk
Originally Posted by John Veninger
Mark,

I have a set of S4 cams you can borrow to get you to the race.
mark kibort is offline  
Old 09-14-2005, 06:02 PM
  #38  
[email protected]
Addict
Rennlist Member
 
Stan.Shaw@Excell.Net's Avatar
 
Join Date: May 2001
Location: Wilbraham, MA
Posts: 2,757
Likes: 0
Received 0 Likes on 0 Posts
Default

I could lend you a set of '86 cams to race with, so you could use JV's to get there and then mine to race. Once you are done, I would have my modified cams

Stan.Shaw@Excell.Net is offline  
Old 09-14-2005, 06:09 PM
  #39  
Jim bailey - 928 International
Addict
Rennlist Member

Rennlist
Site Sponsor

 
Join Date: Jul 2001
Location: Anaheim California
Posts: 11,542
Likes: 0
Received 0 Likes on 0 Posts
Default

Mark you appear to have 87> heads the three bolt exhaust flange that is a good thing. I just recall where S-4 larger valves were installed in an 86 head but to the 87 specifications and once the lifters pumped up the valves could not close which had nasty results. My main point is the 85-86 and the 87> heads and valves are much different. Also when regrinding camshafts some will cut down the base circle so the same lobe now measures as a higher lift. These are some of the questions only you can find the answers. You need to have a good cam grinder measure your cams.
Jim bailey - 928 International is offline  
Old 09-14-2005, 06:11 PM
  #40  
slate blue
Addict
Rennlist Member

 
slate blue's Avatar
 
Join Date: Jun 2002
Posts: 3,289
Likes: 0
Received 0 Likes on 0 Posts
Default

Jim is right in pointing out the differences, I don't believe they will effect what you are doing though. I have as you are probably aware modified a set of 85 cams, no problem. Why no problem, well they have the same base circle as the GT and S4 cams. The reason for the different installed valve heights has to do with the heads. They are what is different, check out the Porsche service bullitens. The combustion chambers and many other things are slightly different.

My verdict you will have no problem, the mods I had done were about $325 USD, I'm thinking about getting them reground and DLC coated. I got my lifters back from a Nascar guy who micropolishes them, they look like new now. I didn't want to run a new cam on old lobes or visa versa.

Cheers Greg
slate blue is offline  
Old 09-14-2005, 06:35 PM
  #41  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

thats kind of what i was thinking. I think , as Jim clarified, that as long as the heads are S4 , there shouldnt be any issues. i think the main issues are in the valve areas.

so, anyone know who could modify a set of 85 cams in a hurry??

thanks,

MK
mark kibort is offline  
Old 09-15-2005, 12:45 PM
  #42  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

all cams in hand!!!!!! took about 3 hours to pull them out. not a big deal.

now, need some cams!

by the way, did some more verification of what cams they are.. timing was set to 2.0mm on pass and 2.0mm on driver (spec is 1.8 and 2.0 respectively for S4 cams and 1.6 and 2.0 for 85-86 cams)
so, it certainly is not a GT cam as that particular spec is in the 3mm range for both.

so, based on how i was measuring, i certainly could be .2mm off. so, i think they are S4 cams with 85 lift. base circle seems to be the same, bearing widths are the same.

Now i need to find out how to modify the driver exhaust cam , as all others will bolt in after hacking off the uneeded ends.

any ideas.

GT cams will probably be the answer!

tick tock. 2 weeks for the race! well, i know i can put them together in a few hours, just need the cams!!!!!
HELP!!

MK

by the way, the lift is 10mm on the 85 cam (same as GT), vs the 9mm for the S4 cam. i have all three sets in front of me and was measuring and marking cams last night!

Last edited by mark kibort; 09-15-2005 at 01:43 PM.
mark kibort is offline  
Old 09-15-2005, 01:17 PM
  #43  
[email protected]
Addict
Rennlist Member
 
Stan.Shaw@Excell.Net's Avatar
 
Join Date: May 2001
Location: Wilbraham, MA
Posts: 2,757
Likes: 0
Received 0 Likes on 0 Posts
Default

I have a set of '86 cams just sitting here waiting for my project, but have another set (still in a motor). $400 plus shipping would get them there quickly.
Stan.Shaw@Excell.Net is offline  
Old 09-15-2005, 01:42 PM
  #44  
mark kibort
Addict
Rennlist Member
Thread Starter
 
mark kibort's Avatar
 
Join Date: Feb 2003
Location: saratoga, ca
Posts: 29,752
Likes: 0
Received 0 Likes on 0 Posts
Default

Id give you $ 1000 for them if that one was modified!

Thanks Stan!! but i already have a set of 85 cams, thats what ive been comparing them to.

do you have any information on how they can be modified? im thinking the grinding of the 85 thrust bearing on the driver exhaust cam is pretty straight forward. NOW, how do you add a thrust bearing surface? how about cut a hex on the cam, make a thrust bearing (round outside to match the needed thrust bearing surface , but with a hex center to match. cut in half, and then have two allen head bolts clamp it to the shaft though a couple of drilled holes!

hows that for an idea for making it work?

mk


Originally Posted by [email protected]
I have a set of '86 cams just sitting here waiting for my project, but have another set (still in a motor). $400 plus shipping would get them there quickly.
mark kibort is offline  
Old 09-15-2005, 01:55 PM
  #45  
[email protected]t
Addict
Rennlist Member
 
Stan.Shaw@Excell.Net's Avatar
 
Join Date: May 2001
Location: Wilbraham, MA
Posts: 2,757
Likes: 0
Received 0 Likes on 0 Posts
Default

Sorry, I leave those questions to the experts at the machine shop
Stan.Shaw@Excell.Net is offline  

Thread Tools
Search this Thread

Contact Us - About Us - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: