GTS Cam Broke What Would You Do?
02-08-2012, 04:32 PM
#31
02-08-2012, 04:39 PM
#32
Burning Brakes
Richard , I dynoed the car 91GT totaly stock 288 rwh on a dynojet , then with the triflow cams, no change . We determined that the cats were not letting the motor make power . every run as the cats tried to clean out the car picked up hp. I am now installing headers / X/ 2 1/2 system . Colins car last I heard was putting down 340+ hp with cams and a X only .So I am expecting 350+ and I did start with GT cams stock .
02-08-2012, 04:40 PM
#33
Nordschleife Master
If I got away with it, I'd just put the "free" GTS cam in and move along...don't take the engine out and don't do anything else. As I recall your car is making GREAT HP already! Save you a TON of money!
Sean, what is the charge for a set of Colin's cams and to put them in to a running ready to rock GTS? Just thinking about the '92 or the '95 someday... Love to get a GTS closer to Roger and Jim's power!
Sean, what is the charge for a set of Colin's cams and to put them in to a running ready to rock GTS? Just thinking about the '92 or the '95 someday... Love to get a GTS closer to Roger and Jim's power!
02-08-2012, 04:43 PM
#34
I did this way back when my belt sheared and I lost two valves on #4. Pulled the passenger side head....did just those two valves, new head gasket... and I think I was only out like $400 or so..not including my time of course. Did it in less than a week after work...since it was ...at the time, my daily...
I'd say just get it running...and then save your pennies to do up a second engine in your spare time...
I'd say just get it running...and then save your pennies to do up a second engine in your spare time...
Sean tells me he can pull just the one head without pulling the motor. Andy has offered to give me his GTS cams.
Now taking paypal donations rkd@zipbang.com to do it right i.e. pull the motor, inspect bottom end, porting, valves, guides, springs and GT or better cams.
Now taking paypal donations rkd@zipbang.com to do it right i.e. pull the motor, inspect bottom end, porting, valves, guides, springs and GT or better cams.
02-08-2012, 06:00 PM
#36
Nordschleife Master
I think I would keep it stock. As soon as you swap cams etc, then those changes are what get the credit for going fast. Keep it stock and losers have no excuses.
02-08-2012, 06:46 PM
#37
Supercharged
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Personally, I think you need to be prepared to pull the motor. Without knowing the exact history of the car, you have no idea if the correct coolant was used or if it was allowed to go acrid - in which case you may need to have the heads welded and decked. Wen Sean pulls the head, if it's all pitted and crappy looking, I'd pull the motor and do the other side too. Then pull have the "opportunity" to consider alternative cams and other parts.
Along the lines of hope for the best plan for the worst, hope for the cheap, plan for the expensive.
Along the lines of hope for the best plan for the worst, hope for the cheap, plan for the expensive.
02-08-2012, 06:50 PM
#38
928 Collector
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Personally, I think you need to be prepared to pull the motor. Without knowing the exact history of the car, you have no idea if the correct coolant was used or if it was allowed to go acrid - in which case you may need to have the heads welded and decked. Wen Sean pulls the head, if it's all pitted and crappy looking, I'd pull the motor and do the other side too. Then pull have the "opportunity" to consider alternative cams and other parts.
Along the lines of hope for the best plan for the worst, hope for the cheap, plan for the expensive.
Along the lines of hope for the best plan for the worst, hope for the cheap, plan for the expensive.
02-08-2012, 07:10 PM
#39
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If doing one side, I'd definitely do the other one at the same time too.
A set of modified '85-'86 cams might be cheaper and easier to find than GT cams.
Things like porting, polishing, and blueprinting can drive the cost up quite a bit pretty quickly, and not really provide than much of a power gain for the amount of money spent. Is a little more power really going to help a significant amount in the autocrossing that's done? Would that money be better spent on things like better tires, suspension, or brakes if the autocross performance is a major concern?
Your's is a pretty unique car. Value wise it would probably be worth more in the future if it were stock.
A set of modified '85-'86 cams might be cheaper and easier to find than GT cams.
Things like porting, polishing, and blueprinting can drive the cost up quite a bit pretty quickly, and not really provide than much of a power gain for the amount of money spent. Is a little more power really going to help a significant amount in the autocrossing that's done? Would that money be better spent on things like better tires, suspension, or brakes if the autocross performance is a major concern?
Your's is a pretty unique car. Value wise it would probably be worth more in the future if it were stock.
02-08-2012, 07:15 PM
#40
Former Sponsor
Hmmm. Interesting bunch of ideas. I can't say that I would agree with any of them, completely.
Normally, when one removes the valve covers from a GTS engine, it is quickly discovered that the engine actually "needs" more than one camshaft. The idea of running the oil cooler "under" the radiator may have worked great in Germany, but absolutely sucked, in US traffic. Note that almost any camshaft that gets installed will also suffer from this problem. Get a radiator with the oil cooler inside and run the oil through both coolers! I make the necessary lines.
Save your money on "port" work. Probably also "save" the horsepower by leaving them alone. Almost every modified cylinder head that I've fflowed on my flow bench flows less air than the stock port and valves. I've yet to test a single head with 968 valves that flows more air than the stock head does (except for the ones I've done, of course.) I "ground" a boat load of ports/heads into junk, trying to figure this head out, before I got to the point of actually "improving" the flow. It's a very sensitive port! I've got a set of heads here, done by one of my "competitors", equipped with bigger Titanium valves, which flow 15% less than a stock head....talk about a huge waste of money!
Colin and I do not completely agree on "cam profiles". That's all I think I should say, here. Note that I have respect for Colin and I consider him to be a friend....so this is not a "competative" thing....just a difference in ideas. We are working together to create a cam profile that suits my ideas about cam profiles.
Stock valve springs are marginal for stock GT use, above 6,400. Lindsey springs are just too stiff. There's a 944 valve spring that works adequately, until the lifts get above .425". For lifts higher than .425", I've been using a spring that I get from Porsche racing that works perfectly. Great seat pressure, great open pressure, and because they come from Porsche, they are virtually bullet proof. Also, because they come from Porsche, they are expensive. There's another spring that comes from Porsche racing that is even better, but at about $150.00 each, not many 928 people think they "need" this spring.
VW lifters have issues....there's no doubt about that. I take them apart, blueprint them, send them off to be micro polished, send them off to be DLC coated, inspect them carefully after coating, and re-assemble them. This process "eliminates" a full 20-25% of these lifters, which I simply throw away. "Real" DLC is expensive, so by the time this process is completed, along with all the "hand" work, these lifters are expensive. That being said, this might be the best money that I spend, when I build an engine. The reduction of friction is so extensive that we have had to "work" on getting the oil temperatures "up" in the engines with these lifters installed. Turns out that the huge majority of friction in a 928 engine comes from the cams "pushing" on the lifters (who would have guessed, with all those cams and lifters?) The "correct" valve spring (not too stiff) and a DLC lifter makes a huge difference. The DLC lifters also seem to virtually eliminate cam wear (which is one of the things that they are supposed to do), but I do not have enough long term testing to confirm that. Short term testing shows cam lobes that appear to be virtually polished. Rob Edwards probably has pictures.
I wouldn't even consider a S-4 cam. The lobe centers are not ideal....
The "best" power gains we have been able to obtain, from the GTS engine, have been from simply adding a set of my headers and exhaust and then Sharktuning. Amazing difference. Rob Edwards has dyno results.
Probably the absolute best thing that anyone could do for their GTS, while it is apart is to completely redo the crankcase and cylinder head ventilation system, while eliminating any of the oil that can get back to the intake system. Why Porsche "gave up" on ventilating the crankcase in these engines is beyond me....but "undoing" their engineering is of paramount importance. I have a brand new "street" ventiation system that I developed after we figured out the heads we filling with oil, which works great! The "racing" head oil removal system also works great, but perhaps a bit of overkill (and fairly expensive) for a street car.
If the car has ever been on a track...or a fast parking lot....Check the rod bearings. Check the rod bearings. Check the rod bearings. Not just 2/6.
Other than the above, I have no opinions of how to proceed....
Normally, when one removes the valve covers from a GTS engine, it is quickly discovered that the engine actually "needs" more than one camshaft. The idea of running the oil cooler "under" the radiator may have worked great in Germany, but absolutely sucked, in US traffic. Note that almost any camshaft that gets installed will also suffer from this problem. Get a radiator with the oil cooler inside and run the oil through both coolers! I make the necessary lines.
Save your money on "port" work. Probably also "save" the horsepower by leaving them alone. Almost every modified cylinder head that I've fflowed on my flow bench flows less air than the stock port and valves. I've yet to test a single head with 968 valves that flows more air than the stock head does (except for the ones I've done, of course.) I "ground" a boat load of ports/heads into junk, trying to figure this head out, before I got to the point of actually "improving" the flow. It's a very sensitive port! I've got a set of heads here, done by one of my "competitors", equipped with bigger Titanium valves, which flow 15% less than a stock head....talk about a huge waste of money!
Colin and I do not completely agree on "cam profiles". That's all I think I should say, here. Note that I have respect for Colin and I consider him to be a friend....so this is not a "competative" thing....just a difference in ideas. We are working together to create a cam profile that suits my ideas about cam profiles.
Stock valve springs are marginal for stock GT use, above 6,400. Lindsey springs are just too stiff. There's a 944 valve spring that works adequately, until the lifts get above .425". For lifts higher than .425", I've been using a spring that I get from Porsche racing that works perfectly. Great seat pressure, great open pressure, and because they come from Porsche, they are virtually bullet proof. Also, because they come from Porsche, they are expensive. There's another spring that comes from Porsche racing that is even better, but at about $150.00 each, not many 928 people think they "need" this spring.
VW lifters have issues....there's no doubt about that. I take them apart, blueprint them, send them off to be micro polished, send them off to be DLC coated, inspect them carefully after coating, and re-assemble them. This process "eliminates" a full 20-25% of these lifters, which I simply throw away. "Real" DLC is expensive, so by the time this process is completed, along with all the "hand" work, these lifters are expensive. That being said, this might be the best money that I spend, when I build an engine. The reduction of friction is so extensive that we have had to "work" on getting the oil temperatures "up" in the engines with these lifters installed. Turns out that the huge majority of friction in a 928 engine comes from the cams "pushing" on the lifters (who would have guessed, with all those cams and lifters?) The "correct" valve spring (not too stiff) and a DLC lifter makes a huge difference. The DLC lifters also seem to virtually eliminate cam wear (which is one of the things that they are supposed to do), but I do not have enough long term testing to confirm that. Short term testing shows cam lobes that appear to be virtually polished. Rob Edwards probably has pictures.
I wouldn't even consider a S-4 cam. The lobe centers are not ideal....
The "best" power gains we have been able to obtain, from the GTS engine, have been from simply adding a set of my headers and exhaust and then Sharktuning. Amazing difference. Rob Edwards has dyno results.
Probably the absolute best thing that anyone could do for their GTS, while it is apart is to completely redo the crankcase and cylinder head ventilation system, while eliminating any of the oil that can get back to the intake system. Why Porsche "gave up" on ventilating the crankcase in these engines is beyond me....but "undoing" their engineering is of paramount importance. I have a brand new "street" ventiation system that I developed after we figured out the heads we filling with oil, which works great! The "racing" head oil removal system also works great, but perhaps a bit of overkill (and fairly expensive) for a street car.
If the car has ever been on a track...or a fast parking lot....Check the rod bearings. Check the rod bearings. Check the rod bearings. Not just 2/6.
Other than the above, I have no opinions of how to proceed....
02-08-2012, 08:57 PM
#42
Three Wheelin'
RKD, I did email you and kinda recommended a repair with stock parts.
Greg's post does bring up something important that I would do myself if I were in your shoes.
Assuming a niceley running stock GTS is appealing, I would resist the urge to make performace mods and concentrate on reliability.
The one area I would splurge on is DLC lifters. That's a very expensive item but the benefits are great. I even like them on the billet cams I make and those are something that just don't wear like traditional castings. Wear isn't therefore a worry for me but the lower friction and reliabilty are huge.
What wears out a cam isn't high speeds but low. The slower the speed, the greater the friction over the nose of the cam. that's why F1 engines idle at 4000 rpms, to keep the cams from self destructing. It's also why I keep high idle speeds on my engines and avoid letting them idle long.
With hot oil Like Greg mentioned, wear is even worse and then there's modern oil additives changing all the time.
BTW, be careful with DLC coatings and unknown suppliers that are cheap. It's something that should be rather expensive and it's very appealing for a company to cash in on that by sending out parts that look blackish. Don't even think about shopping around for cheap DLC.
Greg's post does bring up something important that I would do myself if I were in your shoes.
Assuming a niceley running stock GTS is appealing, I would resist the urge to make performace mods and concentrate on reliability.
The one area I would splurge on is DLC lifters. That's a very expensive item but the benefits are great. I even like them on the billet cams I make and those are something that just don't wear like traditional castings. Wear isn't therefore a worry for me but the lower friction and reliabilty are huge.
What wears out a cam isn't high speeds but low. The slower the speed, the greater the friction over the nose of the cam. that's why F1 engines idle at 4000 rpms, to keep the cams from self destructing. It's also why I keep high idle speeds on my engines and avoid letting them idle long.
With hot oil Like Greg mentioned, wear is even worse and then there's modern oil additives changing all the time.
BTW, be careful with DLC coatings and unknown suppliers that are cheap. It's something that should be rather expensive and it's very appealing for a company to cash in on that by sending out parts that look blackish. Don't even think about shopping around for cheap DLC.
02-08-2012, 09:15 PM
#43
Supercharged
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RKD, I did email you and kinda recommended a repair with stock parts.
Greg's post does bring up something important that I would do myself if I were in your shoes.
Assuming a niceley running stock GTS is appealing, I would resist the urge to make performace mods and concentrate on reliability.
The one area I would splurge on is DLC lifters. That's a very expensive item but the benefits are great. I even like them on the billet cams I make and those are something that just don't wear like traditional castings. Wear isn't therefore a worry for me but the lower friction and reliabilty are huge.
What wears out a cam isn't high speeds but low. The slower the speed, the greater the friction over the nose of the cam. that's why F1 engines idle at 4000 rpms, to keep the cams from self destructing. It's also why I keep high idle speeds on my engines and avoid letting them idle long.
With hot oil Like Greg mentioned, wear is even worse and then there's modern oil additives changing all the time.
BTW, be careful with DLC coatings and unknown suppliers that are cheap. It's something that should be rather expensive and it's very appealing for a company to cash in on that by sending out parts that look blackish. Don't even think about shopping around for cheap DLC.
Greg's post does bring up something important that I would do myself if I were in your shoes.
Assuming a niceley running stock GTS is appealing, I would resist the urge to make performace mods and concentrate on reliability.
The one area I would splurge on is DLC lifters. That's a very expensive item but the benefits are great. I even like them on the billet cams I make and those are something that just don't wear like traditional castings. Wear isn't therefore a worry for me but the lower friction and reliabilty are huge.
What wears out a cam isn't high speeds but low. The slower the speed, the greater the friction over the nose of the cam. that's why F1 engines idle at 4000 rpms, to keep the cams from self destructing. It's also why I keep high idle speeds on my engines and avoid letting them idle long.
With hot oil Like Greg mentioned, wear is even worse and then there's modern oil additives changing all the time.
BTW, be careful with DLC coatings and unknown suppliers that are cheap. It's something that should be rather expensive and it's very appealing for a company to cash in on that by sending out parts that look blackish. Don't even think about shopping around for cheap DLC.
. j/k
02-08-2012, 09:16 PM
#44
Three Wheelin'
Last time I asked a set of INA light weight DLC coated lifters were ~$2500. You can get a set of German made INA light weight lifters for $12 a piece.
Does the benefits really outweigh the cost that much? There are 32 valve 928s out there with over 300K miles on them, never opened, that still run fine. And with the head getting flooded with oil at high RPM the valve train should last a long time, with exception to the GT cam cars with stock springs....Its not like there are 928 valve trains failing left and right from wear and tear.
The internal oil cooler is a neat idea.
Does the benefits really outweigh the cost that much? There are 32 valve 928s out there with over 300K miles on them, never opened, that still run fine. And with the head getting flooded with oil at high RPM the valve train should last a long time, with exception to the GT cam cars with stock springs....Its not like there are 928 valve trains failing left and right from wear and tear.
The internal oil cooler is a neat idea.
02-08-2012, 10:27 PM
#45
Former Sponsor
Last time I asked a set of INA light weight DLC coated lifters were ~$2500. You can get a set of German made INA light weight lifters for $12 a piece.
Does the benefits really outweigh the cost that much? There are 32 valve 928s out there with over 300K miles on them, never opened, that still run fine. And with the head getting flooded with oil at high RPM the valve train should last a long time, with exception to the GT cam cars with stock springs....Its not like there are 928 valve trains failing left and right from wear and tear.
The internal oil cooler is a neat idea.
Does the benefits really outweigh the cost that much? There are 32 valve 928s out there with over 300K miles on them, never opened, that still run fine. And with the head getting flooded with oil at high RPM the valve train should last a long time, with exception to the GT cam cars with stock springs....Its not like there are 928 valve trains failing left and right from wear and tear.
The internal oil cooler is a neat idea.
I just took apart a Marc Thomas' stroker engine apart that had less than 5,000 miles on it. Brand new GT cams, when it was assembled, with stock valve springs. 2 of the cams are junk, one other I'm going to have to think about. You simply can't add weight to the valve train (968 valves) and "twist" these engines to 7,000+, with the stock pieces and expect it to live.
I'm sure those GT cams cost around $1200 each, even back in 2006. If a lightweight lifter with DLC on it would have saved those cams (and they would have), how much are those lifters worth?
Lightweight lifters might have been enough to save those cams, but I'd never suggest that anyone stick a set of the INA lightweight lifters in, without a really careful inspection....and that means getting the break-in coating off of the lifter to polish it and inspect it.
Now what do you do with that "naked" lifter? I send them to the French and let them DLC coat it.
As soon as the valve lift goes up, the stock spring simply will not do the job. It won't work with GT cams and heavy valves. It won't work with GT cams and 6,800 rpms. The lifters loose contact with the lobes and the nose of the cam gets beat to crap.
Like most things in life, selection of pieces, when you start cutting corners, is a matter of how many times you want to do the same job over. I find these engines expensive to do high performance work on, when they are done correctly the first time. I get engines that have been done/redone 2-3 times before I see them. While they don't cost any more to do, when I redo them the 4th time as if I'd done them the 1st time, the owners tend to add up all 4 rebuilds when they try to figure out how much the car is costing them. They never seem happy.
Buy the right stuff once.
Have someone who knows what the hell they are doing put it together.
Swallow hard once and enjoy it forever.