GTS Cam Broke What Would You Do?
02-08-2012, 10:55 PM
#46
Three Wheelin'
Greg,
I was referring to what would be the point for DLC coating for a completely stock GTS, with stock cams. I misunderstood the last post.
If you're going to go with bigger cams, you have to look at everything involved like you have said, then yes DLC coating is something to take into consideration.
Do it right, do it once.
I was referring to what would be the point for DLC coating for a completely stock GTS, with stock cams. I misunderstood the last post.
If you're going to go with bigger cams, you have to look at everything involved like you have said, then yes DLC coating is something to take into consideration.
Do it right, do it once.
02-08-2012, 11:50 PM
#47
Drifting
Greg, What an awesome read your post are. Thank you very much for sharing so much of your research and development with us. I for one am truly truly grateful.
Thank you
BTW the DLC google info is very interesting
http://www.richterprecision.com/dlc-coatings.html
Thank you
BTW the DLC google info is very interesting
http://www.richterprecision.com/dlc-coatings.html
02-09-2012, 12:08 AM
#48
Archive Gatekeeper
Rennlist Member
Rennlist Member
Link to header dyno results on William Anast's stock GTS, post #15:
https://rennlist.com/forums/928-foru...sentation.html
Here are some DLC lifter shots, alone and in situ. I still recall the 'facepalm' day when Greg had sent something like 40 lifters to be coated, and he got back 31- the rest weren't good enough. He was like, WTF am I going to do with 31 lifters? Took another few weeks to complete the set....
DLC'ed Lifters (I also have one that wasn't good enough, fished it out of the trash at Gregs- will try to find it and post a pic. For the life of me I have no idea why it wasn't good enough.....)
Cam lobes:
Lifters in situ, after a whopping 2500 miles:
https://rennlist.com/forums/928-foru...sentation.html
Here are some DLC lifter shots, alone and in situ. I still recall the 'facepalm' day when Greg had sent something like 40 lifters to be coated, and he got back 31- the rest weren't good enough. He was like, WTF am I going to do with 31 lifters? Took another few weeks to complete the set....
DLC'ed Lifters (I also have one that wasn't good enough, fished it out of the trash at Gregs- will try to find it and post a pic. For the life of me I have no idea why it wasn't good enough.....)
Cam lobes:
Lifters in situ, after a whopping 2500 miles:
02-09-2012, 02:23 PM
#51
Former Sponsor
Those are factory GT cams that were reground running on DLC lifters. Notice how the cam lobes appear to be polished. Notice the "lack" of the "928 streaks" that you always see on the lifters and cams. Really nice results.
02-09-2012, 02:55 PM
#52
Archive Gatekeeper
Rennlist Member
Rennlist Member
Just for reference (sorry, Richard, getting a little OT here), here are same '91GT cams, pre-regrind, unknown mileage, on the same cylinders during teardown, to illustrate the 'streaks' Greg mentioned.
There was some pitting on a few lobes, but nothing too bad.
There was some pitting on a few lobes, but nothing too bad.
02-09-2012, 07:19 PM
#54
Rennlist Member
Thread Starter
Okay so here goes...
I've learned from performance upgrading a 944 Turbo that Porsche component design is very exact. Everything is designed to do it's job within it's operating parameters and no more. What that means is if you improve the performance of one part in the system, you need to address the increased performance in almost every part of the system. That and because Porsche is already pushing the performance envelope is why performance upgrades get expensive quick.
From what I am reading on this thread, the above is true for upgrading cams on the 928. A change in the lift on the cams even going from the stock GTS to the stock GT cams at the very least requires the valve springs to be upgraded for mechanical reliability. This also means at some point there is a performance gain limit where exhaust, intake, valves, ignition and fuel delivery will also need to be addressed.
Where does that leave my GTS?
Well, currently Sean says he can pull just the drivers side head in a lot less time than pulling the engine for access to both heads. And while both cams can be changed without pulling both heads, changing the valve springs can't. For me to be comfortable upgrading cams I would have to put in the valve springs for that cam.
The parts total for GT cams and Springs comes up to around $3,500. The only thing I would be saving by upgrading the cams and valve springs now versus pulling the motor to specifically upgrade the cams would be the cost of pulling just the drivers side head.
The parts total for Colin' Stage 2 cams, valve springs, valves, and lifters and it's $7,000. The only thing I would save by doing Stage2 now would be the cost of pulling the motor and of the bent valves being replaced.
So, with the relatively low miles on my car I'm thinking the wise thing to do for now is to just pull the one head, repair the valves, go back stock, rebuild all the timing belt stuff, and have Sean address any other issues he finds. With the consideration that if we find a deteriorated head gasket or bad lifters it will time to yank the motor and open er up all the way.
I've learned from performance upgrading a 944 Turbo that Porsche component design is very exact. Everything is designed to do it's job within it's operating parameters and no more. What that means is if you improve the performance of one part in the system, you need to address the increased performance in almost every part of the system. That and because Porsche is already pushing the performance envelope is why performance upgrades get expensive quick.
From what I am reading on this thread, the above is true for upgrading cams on the 928. A change in the lift on the cams even going from the stock GTS to the stock GT cams at the very least requires the valve springs to be upgraded for mechanical reliability. This also means at some point there is a performance gain limit where exhaust, intake, valves, ignition and fuel delivery will also need to be addressed.
Where does that leave my GTS?
Well, currently Sean says he can pull just the drivers side head in a lot less time than pulling the engine for access to both heads. And while both cams can be changed without pulling both heads, changing the valve springs can't. For me to be comfortable upgrading cams I would have to put in the valve springs for that cam.
The parts total for GT cams and Springs comes up to around $3,500. The only thing I would be saving by upgrading the cams and valve springs now versus pulling the motor to specifically upgrade the cams would be the cost of pulling just the drivers side head.
The parts total for Colin' Stage 2 cams, valve springs, valves, and lifters and it's $7,000. The only thing I would save by doing Stage2 now would be the cost of pulling the motor and of the bent valves being replaced.
So, with the relatively low miles on my car I'm thinking the wise thing to do for now is to just pull the one head, repair the valves, go back stock, rebuild all the timing belt stuff, and have Sean address any other issues he finds. With the consideration that if we find a deteriorated head gasket or bad lifters it will time to yank the motor and open er up all the way.
02-09-2012, 08:15 PM
#57
Archive Gatekeeper
Rennlist Member
Rennlist Member
Hard to beat a properly refreshed stock- numbers-matching low miles 5-speed GTS in the second greatest color ever applied to a 928's shell. 
02-09-2012, 08:19 PM
#58
Former Sponsor
Okay so here goes...
I've learned from performance upgrading a 944 Turbo that Porsche component design is very exact. Everything is designed to do it's job within it's operating parameters and no more. What that means is if you improve the performance of one part in the system, you need to address the increased performance in almost every part of the system. That and because Porsche is already pushing the performance envelope is why performance upgrades get expensive quick.
From what I am reading on this thread, the above is true for upgrading cams on the 928. A change in the lift on the cams even going from the stock GTS to the stock GT cams at the very least requires the valve springs to be upgraded for mechanical reliability. This also means at some point there is a performance gain limit where exhaust, intake, valves, ignition and fuel delivery will also need to be addressed.
Where does that leave my GTS?
Well, currently Sean says he can pull just the drivers side head in a lot less time than pulling the engine for access to both heads. And while both cams can be changed without pulling both heads, changing the valve springs can't. For me to be comfortable upgrading cams I would have to put in the valve springs for that cam.
The parts total for GT cams and Springs comes up to around $3,500. The only thing I would be saving by upgrading the cams and valve springs now versus pulling the motor to specifically upgrade the cams would be the cost of pulling just the drivers side head.
The parts total for Colin' Stage 2 cams, valve springs, valves, and lifters and it's $7,000. The only thing I would save by doing Stage2 now would be the cost of pulling the motor and of the bent valves being replaced.
So, with the relatively low miles on my car I'm thinking the wise thing to do for now is to just pull the one head, repair the valves, go back stock, rebuild all the timing belt stuff, and have Sean address any other issues he finds. With the consideration that if we find a deteriorated head gasket or bad lifters it will time to yank the motor and open er up all the way.
I've learned from performance upgrading a 944 Turbo that Porsche component design is very exact. Everything is designed to do it's job within it's operating parameters and no more. What that means is if you improve the performance of one part in the system, you need to address the increased performance in almost every part of the system. That and because Porsche is already pushing the performance envelope is why performance upgrades get expensive quick.
From what I am reading on this thread, the above is true for upgrading cams on the 928. A change in the lift on the cams even going from the stock GTS to the stock GT cams at the very least requires the valve springs to be upgraded for mechanical reliability. This also means at some point there is a performance gain limit where exhaust, intake, valves, ignition and fuel delivery will also need to be addressed.
Where does that leave my GTS?
Well, currently Sean says he can pull just the drivers side head in a lot less time than pulling the engine for access to both heads. And while both cams can be changed without pulling both heads, changing the valve springs can't. For me to be comfortable upgrading cams I would have to put in the valve springs for that cam.
The parts total for GT cams and Springs comes up to around $3,500. The only thing I would be saving by upgrading the cams and valve springs now versus pulling the motor to specifically upgrade the cams would be the cost of pulling just the drivers side head.
The parts total for Colin' Stage 2 cams, valve springs, valves, and lifters and it's $7,000. The only thing I would save by doing Stage2 now would be the cost of pulling the motor and of the bent valves being replaced.
So, with the relatively low miles on my car I'm thinking the wise thing to do for now is to just pull the one head, repair the valves, go back stock, rebuild all the timing belt stuff, and have Sean address any other issues he finds. With the consideration that if we find a deteriorated head gasket or bad lifters it will time to yank the motor and open er up all the way.
I'd pull both vavle covers, first, and look at all the camshafts. The GTS cams tend to get pretty "beat" up from the "oil" temperature issue. If all the cams look good, proceed from there.
I'll take one head off, with the engine in the car, but not two.
I have changed valve springs with the heads installed, but that seems like it would be silly, with the intake system off, the front of the engine apart, and the cams out. Hell, there's only 10 bolts left to having the head off.....
02-09-2012, 09:30 PM
#59
Rennlist Member
Thread Starter
From what I remember though still kinda in a daze that fateful Saturday, Sean did pull the cam cover on the driver's side and the cam lobes on that side looked pretty clean and smooth. That bit off the end of the exhaust camdid attract most of my attention.
02-09-2012, 09:53 PM
#60
Sorry about missing your calls Richard, been busy today, call me in the morning.
Question, why would you have to change the springs if putting in GT cams? The factory didn't specify a different one did they? I can see it if the car spent it's life up in the higher RPM ranges, hell, the S4 would need better springs if it did also. The GTS cams are toned down but the rest of the valve train is the same as the S4/GT correct? I've had the covers off of Rogers GTS with S3 cams in for two years and everything looks the same as when I put them in there and the same goes with Jim M's GTS with GT cams. What am I missing here?
As to the condition of the cams, drivers side look great, compared to other 928 cams I've seen. Not as pretty as the DLC coated stuff.
And yes, I can pull the one head, and see what everything else looks like, if the gaskets look crappy, the engines coming out. I don't have any desire to work on two heads and all of that with fenders in the way.
Question, why would you have to change the springs if putting in GT cams? The factory didn't specify a different one did they? I can see it if the car spent it's life up in the higher RPM ranges, hell, the S4 would need better springs if it did also. The GTS cams are toned down but the rest of the valve train is the same as the S4/GT correct? I've had the covers off of Rogers GTS with S3 cams in for two years and everything looks the same as when I put them in there and the same goes with Jim M's GTS with GT cams. What am I missing here?
As to the condition of the cams, drivers side look great, compared to other 928 cams I've seen. Not as pretty as the DLC coated stuff.
And yes, I can pull the one head, and see what everything else looks like, if the gaskets look crappy, the engines coming out. I don't have any desire to work on two heads and all of that with fenders in the way.