my 3.0 16v turbo is toast - comments pls
01-01-2008 | 10:01 PM
#33
Nordschleife Master
Joined: Feb 2003
Posts: 5,801
Likes: 3
From: Lebanon, OH
Laust interesting point on why only the gravity side is galled, on richness its been running data logging whilst tuning, its never got below 10 AFR and quicklly tuned up to low 11's.
Is it possible that the car was carboned up prior to turbocharging, the extra heat/pressure broke down the carbon, maybe mixed with fuel/oil and gone down that side - the pistons were very very clean for 100k mls.
968turbos2, its using stock 951 oiling system for the turbo also running a 60 thou restrictor, oil pressure are 4 bar plus about 3 on idle, oil is changed every 5k's but every 3ks since turboed, mainly castrol 10-60
synthetic. I use an EMS so the fact ECU doesnt control knock anymore - only me and I am pretty sure there has been none, I've been very careful with that.
Ski - thanks I will be taking advice on the new clearances to use dont want to go through this again, just need to assess the bore damage then I will know what piston size I will go for, but I guess I will have to take the block out and to a machinist to tell that - unless there is another trick to use? The bores dont look anywhere near as bad as the pistons.
BTW, the oil control rings are not spotless, but dont seem to show foreign objects in there either.
AFAIK that other turboed 3.0 with stock internals on higher boost have used 968 engines, they have the forged stock pistons and I guess larger clearances? For example 9M supercharged versions they went up to 11psi and tracked them on stock comp.
I measured one of the comp rings at the top of the bore 26 thou gap.
rgds
mike
Is it possible that the car was carboned up prior to turbocharging, the extra heat/pressure broke down the carbon, maybe mixed with fuel/oil and gone down that side - the pistons were very very clean for 100k mls.
968turbos2, its using stock 951 oiling system for the turbo also running a 60 thou restrictor, oil pressure are 4 bar plus about 3 on idle, oil is changed every 5k's but every 3ks since turboed, mainly castrol 10-60
synthetic. I use an EMS so the fact ECU doesnt control knock anymore - only me and I am pretty sure there has been none, I've been very careful with that.
Ski - thanks I will be taking advice on the new clearances to use dont want to go through this again, just need to assess the bore damage then I will know what piston size I will go for, but I guess I will have to take the block out and to a machinist to tell that - unless there is another trick to use? The bores dont look anywhere near as bad as the pistons.
BTW, the oil control rings are not spotless, but dont seem to show foreign objects in there either.
AFAIK that other turboed 3.0 with stock internals on higher boost have used 968 engines, they have the forged stock pistons and I guess larger clearances? For example 9M supercharged versions they went up to 11psi and tracked them on stock comp.
I measured one of the comp rings at the top of the bore 26 thou gap.
rgds
mike
01-01-2008 | 11:02 PM
#34
Thread Starter
Racer
Joined: Jul 2005
Posts: 364
Likes: 4
From: Sydney Australia
you may be right on tolerances, some other guys have made similar comments.
Before this happened I was developing an feeling that the customised manifold was not flowing evenly based on plug colours. My thinking was 4 was getting a lot of air, 1 was the least, 2 & 3 in between, if you look at the wear patterns they correspond exactly.
Piston 4 is the worst condition = more air, leaner mix, hotter burn - so supporting the theory that it was caused by increased heat, maybe tight Porsche tolerances and the pistons expanded onto the bores.
So this could be suggesting to anyone boosting the high compression S2 motor in future to stay at 6 or 7psi or go straight to a thicker HG if they want the 'stock' approach.
Before this happened I was developing an feeling that the customised manifold was not flowing evenly based on plug colours. My thinking was 4 was getting a lot of air, 1 was the least, 2 & 3 in between, if you look at the wear patterns they correspond exactly.
Piston 4 is the worst condition = more air, leaner mix, hotter burn - so supporting the theory that it was caused by increased heat, maybe tight Porsche tolerances and the pistons expanded onto the bores.
So this could be suggesting to anyone boosting the high compression S2 motor in future to stay at 6 or 7psi or go straight to a thicker HG if they want the 'stock' approach.
01-02-2008 | 12:09 AM
#35
Nordschleife Master
Joined: Feb 2003
Posts: 5,801
Likes: 3
From: Lebanon, OH
you may be right on tolerances, some other guys have made similar comments.
Before this happened I was developing an feeling that the customised manifold was not flowing evenly based on plug colours. My thinking was 4 was getting a lot of air, 1 was the least, 2 & 3 in between, if you look at the wear patterns they correspond exactly.
Piston 4 is the worst condition = more air, leaner mix, hotter burn - so supporting the theory that it was caused by increased heat, maybe tight Porsche tolerances and the pistons expanded onto the bores.
So this could be suggesting to anyone boosting the high compression S2 motor in future to stay at 6 or 7psi or go straight to a thicker HG if they want the 'stock' approach.
Before this happened I was developing an feeling that the customised manifold was not flowing evenly based on plug colours. My thinking was 4 was getting a lot of air, 1 was the least, 2 & 3 in between, if you look at the wear patterns they correspond exactly.
Piston 4 is the worst condition = more air, leaner mix, hotter burn - so supporting the theory that it was caused by increased heat, maybe tight Porsche tolerances and the pistons expanded onto the bores.
So this could be suggesting to anyone boosting the high compression S2 motor in future to stay at 6 or 7psi or go straight to a thicker HG if they want the 'stock' approach.
Reason being that the cylinder walls expand at a rate in our cars that is higher then that of the piston. Cast pistons do not expand as much as forged pistons. So what happens is your tolerances get larger and with the short piston skirts this allows for piston slap under boost. They simply are not made to deal with tolerances much higher then stock.
01-02-2008 | 01:19 AM
#36
Thread Starter
Racer
Joined: Jul 2005
Posts: 364
Likes: 4
From: Sydney Australia
you may be right Fishey, its beyond my experience level, but when I think about slap wouldnt it be greater on the thrust side?
Either way it seems that I reached the limit of an S2 engine on stock compression and 10psi....live and learn hey!
rgds
mike
Either way it seems that I reached the limit of an S2 engine on stock compression and 10psi....live and learn hey!
rgds
mike
01-02-2008 | 04:13 AM
#37
Racer
Joined: Apr 2005
Posts: 421
Likes: 0
From: Estonia
I think that its a problme with EGT and expansion rates. My 951 block looked exactly the same with stock bottom end. and My egt was many times near to 1000-1100 celcius.
Now with my 968 engine being turboed, i never have run ove 850c with celsius.
So it could be many things
NA engines usually run around 600-700c EGT right?
High egt and ritch mixture what could be cause for this.. And I have seen S2 pistons witch are forged (no sign of casting) and I know that the limitation for those is around 400 crank hp but could be more.
Markus
Now with my 968 engine being turboed, i never have run ove 850c with celsius.
So it could be many things
NA engines usually run around 600-700c EGT right?
High egt and ritch mixture what could be cause for this.. And I have seen S2 pistons witch are forged (no sign of casting) and I know that the limitation for those is around 400 crank hp but could be more.
Markus
The factory forged units are much better for boosting because of there expansion rates however even they are not ideal because of the piston skirt design. Since the forged units expand more under boost they will keep a tighter tolerance to the cylinder wall. The issue you are having is a common one when you boost a N/A motor with cast pistons that where not made with high cylinder pressures along with high heat expansion rates in mind.
05-27-2008 | 08:42 PM
#38
Instructor
Joined: Feb 2008
Posts: 149
Likes: 1
From: Hawaii
Sorry I read this post late.
Since being in the aftermarket turbo business since 1976, I would say that too much boost was put upon the engine. also I dont think the ignition map was correct. Stock old rings can still handle 4-6 psi of boost. The stock hi-compression has to be factored in to how much boost you are running. also the type of gas is a big factor. I have boosted many motors with over 150k miles on them with excellent results.
Here are some baseline figures for turboing stock engines.
Example:
Base compression: 10.5:1
Expected boost 15 PSI
Estimated Compression from boost: add 4:0
Total Estimate Boost: 14.5:1
So in other words trying to tune 14.5 to 1 compression with pump gas will end you up in big trouble! This is only an example. try and put you info in and post it up.
about EGT....It is best not to run 1400F before the turbo Exh. inlet. Some of the BB Turbos can handle 1600F for short bursts but it is not recommended. If you are measuring after the Exhaust housing subtract 200F.
Since being in the aftermarket turbo business since 1976, I would say that too much boost was put upon the engine. also I dont think the ignition map was correct. Stock old rings can still handle 4-6 psi of boost. The stock hi-compression has to be factored in to how much boost you are running. also the type of gas is a big factor. I have boosted many motors with over 150k miles on them with excellent results.
Here are some baseline figures for turboing stock engines.
Example:
Base compression: 10.5:1
Expected boost 15 PSI
Estimated Compression from boost: add 4:0
Total Estimate Boost: 14.5:1
So in other words trying to tune 14.5 to 1 compression with pump gas will end you up in big trouble! This is only an example. try and put you info in and post it up.
about EGT....It is best not to run 1400F before the turbo Exh. inlet. Some of the BB Turbos can handle 1600F for short bursts but it is not recommended. If you are measuring after the Exhaust housing subtract 200F.
05-29-2008 | 05:31 AM
#39
Instructor
Joined: Jan 2005
Posts: 156
Likes: 0
From: San Diego, California
Yeah I've turboed NA motors before too without problems as long as you keep detonation in check (lower boost levels, conservative ignition timing). There's no reason a well tuned turbo on an NA motor will magically cause the pistons to score the cylinders.
Do the tops of the pistons or the chambers have any evidence of detonation? (tiny pits)
Do the tops of the pistons or the chambers have any evidence of detonation? (tiny pits)
05-29-2008 | 06:56 AM
#40
Thread Starter
Racer
Joined: Jul 2005
Posts: 364
Likes: 4
From: Sydney Australia
thanks for the recent posts guys, but its all done & dusted now. I have moved on, the new engine is almost finished with all new pistons, rods, bearings and a list of other goodies too long to type. I plan to post the rebuild & pics when finished.
regards
mike
regards
mike
07-06-2008 | 06:11 PM
#41
Addict
Rennlist Member
Rennlist Member
Joined: Aug 2002
Posts: 1,941
Likes: 1
From: Kalifornyuh
You know, if you are running stand alone, perhaps a switch to using E85 as fuel would be in your best interest. It would yield much lower piston and exhaust temps and is naturally resistant to detonation so you can run bigger boost.
You are somewhat asking for trouble using the stock rods as well but I'm sure someone has asserted this already.
You are somewhat asking for trouble using the stock rods as well but I'm sure someone has asserted this already.
07-06-2008 | 07:25 PM
#42
Drifting
Joined: Mar 2006
Posts: 2,931
Likes: 0
From: midwest
if the 3L factory pistons are cast I suspect the expansion rate with increased EGTs (From boost) is the culprit.
The low boost on high compression cast pistons is not different than supercharging on high compression cast pistons - a bad deal all the way as I see it
The low boost on high compression cast pistons is not different than supercharging on high compression cast pistons - a bad deal all the way as I see it
07-07-2008 | 04:23 AM
#43
Rennlist Member
Joined: Feb 2006
Posts: 18,926
Likes: 99
From: Australia
You know, if you are running stand alone, perhaps a switch to using E85 as fuel would be in your best interest. It would yield much lower piston and exhaust temps and is naturally resistant to detonation so you can run bigger boost.
You are somewhat asking for trouble using the stock rods as well but I'm sure someone has asserted this already.
You are somewhat asking for trouble using the stock rods as well but I'm sure someone has asserted this already.
I agree with the idea of the E85 as well, but we don't have much of that around yet. Things are changing slowly so perhaps something for us to look to in the future.
Hey Mike, what's your progress?
07-07-2008 | 09:57 PM
#44
Thread Starter
Racer
Joined: Jul 2005
Posts: 364
Likes: 4
From: Sydney Australia
very slow Patrick, I hope to pick up the engine next week and start assembly, its got the new Wossner forged pistons which are Swain PC9 coated and the gold ceramic TBC on top along with Wossner forged rods, ARP fasteners and a list of other goodies and new stuff.
Hopefully be back together in the month as long as business allows me to spend time on it.
rgds
mike
Hopefully be back together in the month as long as business allows me to spend time on it.
rgds
mike
