968 Oil Squirters Part Number?
07-07-2018, 12:45 PM
#16
Race Car
Personally, I wouldn’t tax this oil system any more than it already is, regardless of what the factory's intent on these were.
To the contrary, I look for ways to orifice existing feeds to meet just the demands necessary and if I had a block equipped with these from the factory, I'd be looking to delete them.
T
To the contrary, I look for ways to orifice existing feeds to meet just the demands necessary and if I had a block equipped with these from the factory, I'd be looking to delete them.
T
07-07-2018, 01:02 PM
#17
Nordschleife Master
Personally, I wouldn’t tax this oil system any more than it already is, regardless of what the factory's intent on these were.
To the contrary, I look for ways to orifice existing feeds to meet just the demands necessary and if I had a block equipped with these from the factory, I'd be looking to delete them. T
To the contrary, I look for ways to orifice existing feeds to meet just the demands necessary and if I had a block equipped with these from the factory, I'd be looking to delete them. T
I don’t see many other solutions here than piston oil cooling jets. Do you?
I agree that at stock piston weight, stock ring width, stock stroke, and stock redline rpm, the squirters may hurt more than help. But this is with higher rpms, longer stroke, thinner rings, lighter pistons, and more power
07-07-2018, 02:04 PM
#18
Race Car
My logic here is the following. Suppose you want a 968/928/944 to run at higher rpms and with longer-than-stock stroke. This by my logic requires thinner top ring than the early 1.5mm 928/944 top ring and especially the late 968/928/944 1.75mm top ring. Otherwise, it’s just going to flutter and cause all kinds of problems. Say 1.2mm with stock stroke and high rpms and 1.0mm with longer stroke and high rpms. Longer stroke and/or higher rpms will also require lighter pistons. The lighter pistons have to run cooler than heavier pistons, so cooling needs to be improved. At the same time, the thinner rings will reduce cooling and make the piston run hotter. Finally, the power levels are up a lot (otherwise, what’s the point?), so the heat flow needs are generally up.
I don’t see many other solutions here than piston oil cooling jets. Do you?
I agree that at stock piston weight, stock ring width, stock stroke, and stock redline rpm, the squirters may hurt more than help. But this is with higher rpms, longer stroke, thinner rings, lighter pistons, and more power
A combustion gas accumulator groove on the land between the 1st and 2nd ring controls flutter.
Likewise, gas porting, either lateral, or vertical if you aren't concerned that carbon could clog .040" holes, work to use compression to seal the ring to the cylinder wall which helps with flutter as well.
Another feature is to have multiple narrow grooves on outer piston diameter from top deck to the first ring groove.
This minimizes piston contact above the 1st ring in half when expanded due to heat.
They also have the secondary effect of disrupting detonation waves that would otherwise affect the top ring.
If you can creatively use waste oil that is already leaking out past bearing clearances re. the rod notch, then there is no net loss.
Using extra oil ring groove holes that are added in build spec or drilled by end user that put already scraped oil to work lubing the piston pin would take some heat out of the piston as well.
What about water or alcohol injection..?
T
07-07-2018, 02:19 PM
#19
Rainman
Rennlist Member
Rennlist Member
this is not an argumentative post, just observations and opinions.
can't really expect a 944 to live very long at 7000rpm with the stock oiling system so ring flutter is the least of your problems.
revs just wear stuff out faster - can't get enough stroke into a 944/928 block to make piston speed an issue, just get good rods.
flip side of the thermal problem, wouldnt a stock-type, thick and heavy piston be more resilient to heat issues than a lightweight thin-crown one?
and the alusil cylinders make for great "heat suckers" out of the chamber, maybe see about dropping the min. water temp with a lower-temp thermostat (or some kind of electronic water temp controller based on engine load?)
my favorite engine-design quote (taken from eng-tips forum, tons of great info over there) is a good way of saying, "don't overthink it".
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can't really expect a 944 to live very long at 7000rpm with the stock oiling system so ring flutter is the least of your problems.
revs just wear stuff out faster - can't get enough stroke into a 944/928 block to make piston speed an issue, just get good rods.
flip side of the thermal problem, wouldnt a stock-type, thick and heavy piston be more resilient to heat issues than a lightweight thin-crown one?
and the alusil cylinders make for great "heat suckers" out of the chamber, maybe see about dropping the min. water temp with a lower-temp thermostat (or some kind of electronic water temp controller based on engine load?)
my favorite engine-design quote (taken from eng-tips forum, tons of great info over there) is a good way of saying, "don't overthink it".
You are proposing to add cost and complexity to address a problem you have only conjectured to exist.
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My logic here is the following. Suppose you want a 968/928/944 to run at higher rpms and with longer-than-stock stroke. This by my logic requires thinner top ring than the early 1.5mm 928/944 top ring and especially the late 968/928/944 1.75mm top ring. Otherwise, it’s just going to flutter and cause all kinds of problems. Say 1.2mm with stock stroke and high rpms and 1.0mm with longer stroke and high rpms. Longer stroke and/or higher rpms will also require lighter pistons. The lighter pistons have to run cooler than heavier pistons, so cooling needs to be improved. At the same time, the thinner rings will reduce cooling and make the piston run hotter. Finally, the power levels are up a lot (otherwise, what’s the point?), so the heat flow needs are generally up.
I don’t see many other solutions here than piston oil cooling jets. Do you?
I agree that at stock piston weight, stock ring width, stock stroke, and stock redline rpm, the squirters may hurt more than help. But this is with higher rpms, longer stroke, thinner rings, lighter pistons, and more power
I don’t see many other solutions here than piston oil cooling jets. Do you?
I agree that at stock piston weight, stock ring width, stock stroke, and stock redline rpm, the squirters may hurt more than help. But this is with higher rpms, longer stroke, thinner rings, lighter pistons, and more power
07-07-2018, 02:23 PM
#20
Race Car
Accumulator Groove V-shaped groove machined in the 2nd ring land that adds to the volume between the top and second ring. This groove accumulates residual gasses from combustion which alleviates top ring flutter and premature second ring wear, improving ring seal.
Anti Detonation Grooves (Contact Reduction Grooves) Also know as contact reduction grooves, which limit the piston/cylinder contact during high temperature and high RPM. These grooves also protect the top ring by disrupting detonation waves.
Won't help you in what you are looking for but you can view both of these features on a real life piston in the pics of 16v piston I need to get rid of that I posted on Valve reliefs on 951 pistons for 16v head (photos)
T
07-07-2018, 02:40 PM
#21
Race Car
Disagree...
Contrary to popular belief, I believe period interval (shifting through rev range) 7000+ rpms is not a problem, we do it all the time.
6000-6500rpms at +30/sec per lap in a 90 minute race.
Engine I am doing now will live 99% of life in anger at 4500-7200+ rpms.
Wet sump.
Undecided that after heat soak whether a more dense or lighter piston is better or worse.
If I had concerns of @ptuomov, I'd be looking at piston top coatings, making sure my exhaust flanges at the head or self aligning with the port so exhaust moves out with minimal restriction and having an exhaust design that maximizes extrication to fill cylinder with as much a percentage of fresh charge (as close to 0 remnants of previous combustion) as possible.
If his model is lowering reciprocating weight, I'd use Ti pins instead of a drastically lighter piston but my mind is still out on whether lighter weight or a heavier piston is really better after heat has already soaked either.
Cooling fuel before injection is also another option.
T
Contrary to popular belief, I believe period interval (shifting through rev range) 7000+ rpms is not a problem, we do it all the time.
6000-6500rpms at +30/sec per lap in a 90 minute race.
Engine I am doing now will live 99% of life in anger at 4500-7200+ rpms.
Wet sump.
Undecided that after heat soak whether a more dense or lighter piston is better or worse.
If I had concerns of @ptuomov, I'd be looking at piston top coatings, making sure my exhaust flanges at the head or self aligning with the port so exhaust moves out with minimal restriction and having an exhaust design that maximizes extrication to fill cylinder with as much a percentage of fresh charge (as close to 0 remnants of previous combustion) as possible.
If his model is lowering reciprocating weight, I'd use Ti pins instead of a drastically lighter piston but my mind is still out on whether lighter weight or a heavier piston is really better after heat has already soaked either.
Cooling fuel before injection is also another option.
T
07-07-2018, 03:46 PM
#22
Nordschleife Master
I've seen some and read about many 928 S4s having big blowby problems and oil being ejected from the breathers at high rpms. It is my personal conclusion that this happens because the 1.5mm top ring starts to flutter. I have a blowby meter, so I've got some data on this, including the engine currently in my car being tight as a glove up to 6700 rpm. Are you seeing similar issues with 944S 2.5L engines that have the 1.5mm top ring? The blowby and oil ejection issues are much worse in 928 GTS models that have 85.9mm stroke and the wider 1.75mm top ring. Are you seeing similar issues with breather and oiling system in the 3.0L S2's and 968's that also have the 1.75mm rings and even longer stroke?
Usually, the car factories seem to design engines such that the peak power rpm is 90-95% of the ring flutter critical rpm, like the 928 S4/GT were sized. This doesn't mean that the car won't live above the ring flutter critical rpm, it just means that reliability is impaired and a lot of other oiling and breather system problems appear that need to be endlessly band-aided. That's my understanding anyway, caveat lector applies of course.
From the piston temperature perspective, I believe that a heavier and thicker-crown piston with a high compression height and tall top land are always better. That's how they do diesel pistons that need to just deal with very high temperatures and gas pressures, but not high rpms. However, if you start turning high rpms and increasing the stroke, the piston weight must go down. Otherwise, rod bearings and/or rods and/or piston wrist pins and/ot piston wrist pin bosses will give up. Right? So from temperature perspective, one should always use the widest top ring and heaviest pistons that the rpm and stroke allow. Unfortunately, as rpms and stroke go up, the maximum ring width and maximum piston weight come down.
Gas porting, accumulator grooves, etc. may have minor effects on the ring flutter, but they are minor compared to the basic F=m*a issues with longer strokes and higher rpms. That's about tinkering on the margins, not meaningfully changing the realistic rpm range for the bottom end.
Splash lubing or oil from the bore walls does not produce a piston cooling effect of the same magnitude as piston oil cooling jets. Mahle piston book sizes the flow rates of those at 3-5 kg of oil per kWh of engine output, which can pull something like 30% of the total heat our of the piston with about 30C degree (safe) increase in the oil temperature that hits the piston. Once you think about it in terms of kg of oil per kWh of engine output, it's obvious that oil from bore walls is not going to move the needle compared to piston oil squirters.
Usually, the car factories seem to design engines such that the peak power rpm is 90-95% of the ring flutter critical rpm, like the 928 S4/GT were sized. This doesn't mean that the car won't live above the ring flutter critical rpm, it just means that reliability is impaired and a lot of other oiling and breather system problems appear that need to be endlessly band-aided. That's my understanding anyway, caveat lector applies of course.
From the piston temperature perspective, I believe that a heavier and thicker-crown piston with a high compression height and tall top land are always better. That's how they do diesel pistons that need to just deal with very high temperatures and gas pressures, but not high rpms. However, if you start turning high rpms and increasing the stroke, the piston weight must go down. Otherwise, rod bearings and/or rods and/or piston wrist pins and/ot piston wrist pin bosses will give up. Right? So from temperature perspective, one should always use the widest top ring and heaviest pistons that the rpm and stroke allow. Unfortunately, as rpms and stroke go up, the maximum ring width and maximum piston weight come down.
Gas porting, accumulator grooves, etc. may have minor effects on the ring flutter, but they are minor compared to the basic F=m*a issues with longer strokes and higher rpms. That's about tinkering on the margins, not meaningfully changing the realistic rpm range for the bottom end.
Splash lubing or oil from the bore walls does not produce a piston cooling effect of the same magnitude as piston oil cooling jets. Mahle piston book sizes the flow rates of those at 3-5 kg of oil per kWh of engine output, which can pull something like 30% of the total heat our of the piston with about 30C degree (safe) increase in the oil temperature that hits the piston. Once you think about it in terms of kg of oil per kWh of engine output, it's obvious that oil from bore walls is not going to move the needle compared to piston oil squirters.
07-07-2018, 04:20 PM
#23
Race Car
I've seen some and read about many 928 S4s having big blowby problems and oil being ejected from the breathers at high rpms. It is my personal conclusion that this happens because the 1.5mm top ring starts to flutter. I have a blowby meter, so I've got some data on this, including the engine currently in my car being tight as a glove up to 6700 rpm. Are you seeing similar issues with 944S 2.5L engines that have the 1.5mm top ring? The blowby and oil ejection issues are much worse in 928 GTS models that have 85.9mm stroke and the wider 1.75mm top ring. Are you seeing similar issues with breather and oiling system in the 3.0L S2's and 968's that also have the 1.75mm rings and even longer stroke?
Usually, the car factories seem to design engines such that the peak power rpm is 90-95% of the ring flutter critical rpm, like the 928 S4/GT were sized. This doesn't mean that the car won't live above the ring flutter critical rpm, it just means that reliability is impaired and a lot of other oiling and breather system problems appear that need to be endlessly band-aided. That's my understanding anyway, caveat lector applies of course.
From the piston temperature perspective, I believe that a heavier and thicker-crown piston with a high compression height and tall top land are always better. That's how they do diesel pistons that need to just deal with very high temperatures and gas pressures, but not high rpms. However, if you start turning high rpms and increasing the stroke, the piston weight must go down. Otherwise, rod bearings and/or rods and/or piston wrist pins and/ot piston wrist pin bosses will give up. Right? So from temperature perspective, one should always use the widest top ring and heaviest pistons that the rpm and stroke allow. Unfortunately, as rpms and stroke go up, the maximum ring width and maximum piston weight come down.
Gas porting, accumulator grooves, etc. may have minor effects on the ring flutter, but they are minor compared to the basic F=m*a issues with longer strokes and higher rpms. That's about tinkering on the margins, not meaningfully changing the realistic rpm range for the bottom end.
Splash lubing or oil from the bore walls does not produce a piston cooling effect of the same magnitude as piston oil cooling jets. Mahle piston book sizes the flow rates of those at 3-5 kg of oil per kWh of engine output, which can pull something like 30% of the total heat our of the piston with about 30C degree (safe) increase in the oil temperature that hits the piston. Once you think about it in terms of kg of oil per kWh of engine output, it's obvious that oil from bore walls is not going to move the needle compared to piston oil squirters.
Usually, the car factories seem to design engines such that the peak power rpm is 90-95% of the ring flutter critical rpm, like the 928 S4/GT were sized. This doesn't mean that the car won't live above the ring flutter critical rpm, it just means that reliability is impaired and a lot of other oiling and breather system problems appear that need to be endlessly band-aided. That's my understanding anyway, caveat lector applies of course.
From the piston temperature perspective, I believe that a heavier and thicker-crown piston with a high compression height and tall top land are always better. That's how they do diesel pistons that need to just deal with very high temperatures and gas pressures, but not high rpms. However, if you start turning high rpms and increasing the stroke, the piston weight must go down. Otherwise, rod bearings and/or rods and/or piston wrist pins and/ot piston wrist pin bosses will give up. Right? So from temperature perspective, one should always use the widest top ring and heaviest pistons that the rpm and stroke allow. Unfortunately, as rpms and stroke go up, the maximum ring width and maximum piston weight come down.
Gas porting, accumulator grooves, etc. may have minor effects on the ring flutter, but they are minor compared to the basic F=m*a issues with longer strokes and higher rpms. That's about tinkering on the margins, not meaningfully changing the realistic rpm range for the bottom end.
Splash lubing or oil from the bore walls does not produce a piston cooling effect of the same magnitude as piston oil cooling jets. Mahle piston book sizes the flow rates of those at 3-5 kg of oil per kWh of engine output, which can pull something like 30% of the total heat our of the piston with about 30C degree (safe) increase in the oil temperature that hits the piston. Once you think about it in terms of kg of oil per kWh of engine output, it's obvious that oil from bore walls is not going to move the needle compared to piston oil squirters.
By your own admission, you are "tinkering on the margin" as you said your engine is tight up to 6700rpms, 10% margin on improvements listed is all you need to go 7400.
That said, splashing lube seems to work fine on 944T before squirters were introduced with hotter CC/piston temps.
Do you know anyone with your configuration that has tried a belt driven crankcase vacuum pump...?
T
07-07-2018, 04:33 PM
#24
Nordschleife Master
You misread - oil from cylinder walls to lube pin = less heat transferred to piston, marginal admittedly but any bit helps.
By your own admission, you are "tinkering on the margin" as you said your engine is tight up to 6700rpms, 10% margin on improvements listed is all you need to go 7400.
That said, splashing lube seems to work fine on 944T before squirters were introduced with hotter CC/piston temps.
Do you know anyone with your configuration that has tried a belt driven crankcase vacuum pump...? T
By your own admission, you are "tinkering on the margin" as you said your engine is tight up to 6700rpms, 10% margin on improvements listed is all you need to go 7400.
That said, splashing lube seems to work fine on 944T before squirters were introduced with hotter CC/piston temps.
Do you know anyone with your configuration that has tried a belt driven crankcase vacuum pump...? T
Almost all the heat to the piston comes from the combustion chamber:
Moving the redline from 6700 to 7400 is not trivial or tinkering at the margins. That sort of change and unchanged reliability would require, in the ball park, -18% reduction in piston weight (more generally, reciprocating weight) while keeping piston strength and temperature the same. It would also require about -18% reduction in top ring width, which would reduce piston cooling, while the pistons now have lower mass and thus lower thermal inertia. If the top ring was moved higher to reduce piston weight, then there are even more additional cooling needs. To keep reliability the same, in my opinion, one has to find some additional way to cool the pistons. I can't come up with anything else than piston oil squirters.
07-07-2018, 05:07 PM
#25
Drifting
Smaller rod journals help with higher RPM’s. Ask Honda. And regular oil changes with quality oil and filters helps. The number one killer of oil is aeration, meaning oxygen molecular will oxidize the oil and even if it looks new it may not be. The quality of oil and of the filter matter quite a lot. As does the temperature of the oil. Now here’s a thought, if there was no oxygen in the crankcase would the oil last longer at normal operating temps due to not being oxidized?
07-07-2018, 05:20 PM
#26
Nordschleife Master
Smaller rod journals help with higher RPM’s. Ask Honda. And regular oil changes with quality oil and filters helps. The number one killer of oil is aeration, meaning oxygen molecular will oxidize the oil and even if it looks new it may not be. The quality of oil and of the filter matter quite a lot. As does the temperature of the oil. Now here’s a thought, if there was no oxygen in the crankcase would the oil last longer at normal operating temps due to not being oxidized?
I agree that excessive oil temperatures and oil aeration together are a big problem.
I think (but do not know) that piston oil squirters will increase aeration somewhat. Reducing the density of crankcase atmosphere would probably reduce air going into the oil and help separate air out of the oil, but I am not sure.
However, overall, once I get the heat out of the piston and into oil, I think I can deal with it. I can always add external heat exchanger volume and cooling air flow thru those heat exchangers to get the heat out of the oil.
07-07-2018, 05:22 PM
#27
Race Car
LOL, I'm with you 100% on it not being trivial.
Doing a max rev 7500 rpm 16v 2.5 liter right now.
More to it than even answering just the questions pertaining to your specific concerns, other aspects are always etc., etc., etc.
But I think you are stuck at combustion chamber peak or while under combustion temps where in reality the interval where the engine is flushed with cool fuel/air is nearly balanced in a cycle time vs time from combustion to exhaust push exit past the port.
Cooler air intake and a cooled fuel system will definitely have an impact.
What is the destined use of this car/engine...?
What we always do after a checkers, or cycle this method on a yellow, is select highest gear and go WOT on lap back to pits as gap allows, which opens the intake to atmosphere and the engine is moving as much fuel and air through for a low rpm as possible. This, in my experience starts the cool down cycle of the heat saturation to the point that by the time the car backs into it's slot, the cooling fans are rarely even running.
T
Doing a max rev 7500 rpm 16v 2.5 liter right now.
More to it than even answering just the questions pertaining to your specific concerns, other aspects are always etc., etc., etc.
But I think you are stuck at combustion chamber peak or while under combustion temps where in reality the interval where the engine is flushed with cool fuel/air is nearly balanced in a cycle time vs time from combustion to exhaust push exit past the port.
Cooler air intake and a cooled fuel system will definitely have an impact.
What is the destined use of this car/engine...?
What we always do after a checkers, or cycle this method on a yellow, is select highest gear and go WOT on lap back to pits as gap allows, which opens the intake to atmosphere and the engine is moving as much fuel and air through for a low rpm as possible. This, in my experience starts the cool down cycle of the heat saturation to the point that by the time the car backs into it's slot, the cooling fans are rarely even running.
T
07-07-2018, 05:30 PM
#28
Nordschleife Master
The question in the back of my mind is how much would have to be changed to move the redline up from 6700 rpm to about 7700 rpm, and whether it's worth the agony.
07-07-2018, 05:46 PM
#29
Drifting
There’s this company that makes crankscrapers for our cars if you haven’t seen them yet. I like their oil pick up tube support as well. Seems to help with higher RPM’s.
https://www.crank-scrapers.com/Porsche_944.html
https://www.crank-scrapers.com/Porsche_944.html
07-07-2018, 05:49 PM
#30
Nordschleife Master
There’s this company that makes crankscrapers for our cars if you haven’t seen them yet. I like their oil pick up tube support as well. Seems to help with higher RPM’s.
https://www.crank-scrapers.com/Porsche_944.html
https://www.crank-scrapers.com/Porsche_944.html