Is it just me, or are these pistons whacky?
10-29-2002, 07:38 AM
#1
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Is it just me, or are these pistons whacky?
Now I don't know how many of you followed Rob Langley's bizarre 951 <a href="http://www.986.org/sites/944faqs/RobHomePage/Archive/Car.htm" target="_blank">Turbo Chronicles</a> adventure. He was continually having blown headgaskets and sealing issues. Replacement parts went back & forth and Garrity even flew out to check out the engine. In the end, Rob gave up. But I'm wondering if there's something obvious that was overlooked here.
These are some stock 951 pistons. Stock 2.5L with 8.0:1 compression:
Now here's a 951 piston for 2.8L 106mm bored-out-to-the-max @ 9.0:1 compression:
Considering the larger capacity with the deeper bowl, it still gave more compression than stock.
Now here's Rob's pistons for his 2.8L stroker engine:
Wouldn't this appear to be way too much compression??? Not to mention that the sharp edges on the valve-relief cut-outs are a prime source for hot-spots and detonation. Also are the piston clearances kinda LARGE???
These are some stock 951 pistons. Stock 2.5L with 8.0:1 compression:
Now here's a 951 piston for 2.8L 106mm bored-out-to-the-max @ 9.0:1 compression:
Considering the larger capacity with the deeper bowl, it still gave more compression than stock.
Now here's Rob's pistons for his 2.8L stroker engine:
Wouldn't this appear to be way too much compression??? Not to mention that the sharp edges on the valve-relief cut-outs are a prime source for hot-spots and detonation. Also are the piston clearances kinda LARGE???
10-29-2002, 08:22 AM
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If I recall, one of the issues with that engine, which was a sleeved 3.0 liter ( he demanded a 2.8 non-sleeved engine due to the problems with the 3.0) was very high leakdown from the start. Garrity claimed he built the engine "loose" due to the different expansion rates between the iron sleeves and the aluminum pistons. I questioned that approach and also questioned the profile of the piston crown as well.With the amount of blow-by those piston tolerances must have allowed, it was probably pressurizing the crankcase and even physically lifting the head when he tried to run any amount of boost. Al tried better studs, higher torque values, all to no avail. Garrity blamed it on insufficient fuel, too much boost.
In any case a renlinster in KS bought the car with the 2.8 and must be happy with the new engine. Too bad Rob poured so much money into the car and grew sour on the whole expeirence and went Mazda Miata spec racing as result!
Who knows, only the shadow knows!
Hey Danno, how about that dissertation on cycling valve mods vs banjo bolt, vs check valve boost maximizer. Did you forget me? You forgot me, I am hurt!
James
In any case a renlinster in KS bought the car with the 2.8 and must be happy with the new engine. Too bad Rob poured so much money into the car and grew sour on the whole expeirence and went Mazda Miata spec racing as result!
Who knows, only the shadow knows!
Hey Danno, how about that dissertation on cycling valve mods vs banjo bolt, vs check valve boost maximizer. Did you forget me? You forgot me, I am hurt!
James
10-29-2002, 08:49 AM
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Yes Danno, we had this discussion on the 2-Rob's board a long time ago. When Rob posted that block picture, I guestimated his compression ratio at 9.5-10:1. That took him by suprise because Garrity claimed it was like 8.5:1. he wondered why he was having problems running 14-15 psi and I said his effective ratio was closer to 20psi.
Regardless, I think there was plenty of blame to go around. I like Rob, I've talked to him and bought a few of his used parts. I've also talked to Garrity and and bought my P&P head from him, he seems very sharp. But that motor had to be running high compression and I think Rob was nuts trying to run that motor with the ARC2 modifing Weltmeister chips, I think that was a recipe for disaster...
Anyway, I guess they are still friends and it's water under a bridge.
Regardless, I think there was plenty of blame to go around. I like Rob, I've talked to him and bought a few of his used parts. I've also talked to Garrity and and bought my P&P head from him, he seems very sharp. But that motor had to be running high compression and I think Rob was nuts trying to run that motor with the ARC2 modifing Weltmeister chips, I think that was a recipe for disaster...
Anyway, I guess they are still friends and it's water under a bridge.
10-29-2002, 09:44 AM
#7
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"he demanded a 2.8 non-sleeved engine due to the problems with the 3.0"
That last photo of Rob's engine was from his Chapter-4, which would be the first engine he got? Also the block is obviously a 2.5L block from the fully wet cylinders. Another photo from that chapter showed Rob filing this block by hand to make clearance room for the rods.... a foreboding warning of things to come...
"Garrity claimed he built the engine "loose" due to the different expansion rates between the iron sleeves and the aluminum pistons."
That's the part I don't understand. From reading his diary, it appears that Rob sourced the pistons himself.
"I guestimated his compression ratio at 9.5-10:1. That took him by suprise because Garrity claimed it was like 8.5:1."
Yeah, I asked him for his compression numbers several times. He always seemed to skirt around giving me a straight answer. Like simply answering my question, "Have you done a compression-check?" To which he wouldn't even give me a YES/NO answer, strange.... Perhaps he was in denial about the numbers that he got back?
"was the rod length the same?"
I would hope that they didn't reduce compression by having the piston not be flush with the deck at TDC. The lost of squish on the edges would be a major detriment to power. I don't think Garrity would take that kind of route. Short rods would only be needed if you're trying to re-use the stock pistons at a lower-compression; definitely a compromise. Also from the photo of the middle-piston, the reflection of light at 3 o'clock appear to be continous going across the piston to the cylinder tops, so it appears that the piston is flush with the top. Again indicating way too much compression.
"how about that dissertation on cycling valve mods vs banjo bolt, vs check valve boost maximizer. Did you forget me? "
Nope, just trying to dig up research material. It's been about a decade since drilling the cycling-valve was in fashion. A similar approach would be to insert a bleeder valve somewhere before the CV to bleed off a constant % of air. I'll finish this yet!
That last photo of Rob's engine was from his Chapter-4, which would be the first engine he got? Also the block is obviously a 2.5L block from the fully wet cylinders. Another photo from that chapter showed Rob filing this block by hand to make clearance room for the rods.... a foreboding warning of things to come...
"Garrity claimed he built the engine "loose" due to the different expansion rates between the iron sleeves and the aluminum pistons."
That's the part I don't understand. From reading his diary, it appears that Rob sourced the pistons himself.
"I guestimated his compression ratio at 9.5-10:1. That took him by suprise because Garrity claimed it was like 8.5:1."
Yeah, I asked him for his compression numbers several times. He always seemed to skirt around giving me a straight answer. Like simply answering my question, "Have you done a compression-check?" To which he wouldn't even give me a YES/NO answer, strange.... Perhaps he was in denial about the numbers that he got back?
"was the rod length the same?"
I would hope that they didn't reduce compression by having the piston not be flush with the deck at TDC. The lost of squish on the edges would be a major detriment to power. I don't think Garrity would take that kind of route. Short rods would only be needed if you're trying to re-use the stock pistons at a lower-compression; definitely a compromise. Also from the photo of the middle-piston, the reflection of light at 3 o'clock appear to be continous going across the piston to the cylinder tops, so it appears that the piston is flush with the top. Again indicating way too much compression.
"how about that dissertation on cycling valve mods vs banjo bolt, vs check valve boost maximizer. Did you forget me? "
Nope, just trying to dig up research material. It's been about a decade since drilling the cycling-valve was in fashion. A similar approach would be to insert a bleeder valve somewhere before the CV to bleed off a constant % of air. I'll finish this yet!
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10-30-2002, 12:28 AM
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IT seams the basics of engine building were thrown out the window with this one . First when building and engine of any type you must come up with a formula.What are you looking to get a high rpm engine running low boost a low rpm motor running high boost etc. etc.Then you sorce out the parts needed to build the desired engine knowing what compression ratio you want the flow rates the cam lift and deration etc. etc. It sounds like maybe two many chiefs and not enough indians on this project.The big question is how do we get him out of that Miata and back to a real car. <img src="confused.gif" border="0">
10-31-2002, 09:41 AM
#11
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Posted on behalf of Rob L.
Hi max,
I seem to have lost my Rennlist registration. Would you please post this response for me.
Rob
Hi everyone. Good to hear from the 944 Turbo world again. I do miss my 944 T (aka the Yellow Beast). I do have a 996 aero kit now as a occasional track car but primarily a daily driver. I did buy a Miata (girlie car) for spec Miata racing.
You are mostly correct about my first 3 liter engine that Garrity built. Here are the facts...
Garrity bored (104 mm), sleeved, and assembled the engine. The pistons were obtained from Albert Broadfoot. Albert used these pistons on his 3 liter 944 T racecar. The reason we went with the pistons was Garrity's inability to source them from anywhere else in a timely fashion. Garrity initially ordered a custom set from JE pistons but after waiting 6 months they sent them and they were not correct. So, to avoid another 6 month delay I got a set from Albert who had them on the shelf. They were also JE pistons custom designed with a 4 mm offset wristpin location to reduce the compression and allow stock rods. As far as the actual compression ratio...Garrity told me they were 8.5 : 1. I did run a compression test when I got the engine and the numbers were between 155 and 160 on all cylinders. The leakdown was a big concern for me. They all had 20% when cold and still had over 15% when the cylinders were warm.
I spent over a year replacing headgaskets (solid copper), studs (raceware), adding fuel monitoring and improvement devices (gauges, huge injectors, custom chips etc...) and still could not keep a headgasket in the car. I finally asked Garrity to replace the engine. Garrity kept his word and replaced it with one of my specifications.
The car in it's final form had a stock bore that had been honed to 1 size over as the cylinder walls had to be cleaned up. Stock Mahle (Porsche OEM) 1 size over pistons, custom rods, 968 crank for a total of 2.8 liters. This engine ran well but unfortunately I had run out of patience and resolve. I sold the car to a very nice guy who I just heard from a few weeks ago. The car is running well and the only problem he has had is a lower balance shaft seal oil leak. I agreed to split the cost of the seal replacement and all is well. He has had the car since June (nearly 5 months now) and is making some mods of his own at this point.
So, If you want to know my take on big bored engines versus staying close to stock.....I lean toward closer to stock. Personally I would not recommend boring cylinders and installing sleeves. If you are considering it please read my experiences.
<a href="http://www.986.org/sites/944faqs/RobHomePage/Archive/Car.htm" target="_blank">http://www.986.org/sites/944faqs/RobHomePage/Archive/Car.htm</a>
Also, look around for people that have done it.....believe me they are few and far between. I would be surprised if you find anyone who is happy with it or has had reliability beyond a few months.
Just my 2 cents.
Take care
I hope to hear from you on my webboard.
<a href="http://www.funcarsonline.com/frames/944board/944board.htm" target="_blank">http://www.funcarsonline.com/frames/944board/944board.htm</a>
Rob
Hi max,
I seem to have lost my Rennlist registration. Would you please post this response for me.
Rob
Hi everyone. Good to hear from the 944 Turbo world again. I do miss my 944 T (aka the Yellow Beast). I do have a 996 aero kit now as a occasional track car but primarily a daily driver. I did buy a Miata (girlie car) for spec Miata racing.
You are mostly correct about my first 3 liter engine that Garrity built. Here are the facts...
Garrity bored (104 mm), sleeved, and assembled the engine. The pistons were obtained from Albert Broadfoot. Albert used these pistons on his 3 liter 944 T racecar. The reason we went with the pistons was Garrity's inability to source them from anywhere else in a timely fashion. Garrity initially ordered a custom set from JE pistons but after waiting 6 months they sent them and they were not correct. So, to avoid another 6 month delay I got a set from Albert who had them on the shelf. They were also JE pistons custom designed with a 4 mm offset wristpin location to reduce the compression and allow stock rods. As far as the actual compression ratio...Garrity told me they were 8.5 : 1. I did run a compression test when I got the engine and the numbers were between 155 and 160 on all cylinders. The leakdown was a big concern for me. They all had 20% when cold and still had over 15% when the cylinders were warm.
I spent over a year replacing headgaskets (solid copper), studs (raceware), adding fuel monitoring and improvement devices (gauges, huge injectors, custom chips etc...) and still could not keep a headgasket in the car. I finally asked Garrity to replace the engine. Garrity kept his word and replaced it with one of my specifications.
The car in it's final form had a stock bore that had been honed to 1 size over as the cylinder walls had to be cleaned up. Stock Mahle (Porsche OEM) 1 size over pistons, custom rods, 968 crank for a total of 2.8 liters. This engine ran well but unfortunately I had run out of patience and resolve. I sold the car to a very nice guy who I just heard from a few weeks ago. The car is running well and the only problem he has had is a lower balance shaft seal oil leak. I agreed to split the cost of the seal replacement and all is well. He has had the car since June (nearly 5 months now) and is making some mods of his own at this point.
So, If you want to know my take on big bored engines versus staying close to stock.....I lean toward closer to stock. Personally I would not recommend boring cylinders and installing sleeves. If you are considering it please read my experiences.
<a href="http://www.986.org/sites/944faqs/RobHomePage/Archive/Car.htm" target="_blank">http://www.986.org/sites/944faqs/RobHomePage/Archive/Car.htm</a>
Also, look around for people that have done it.....believe me they are few and far between. I would be surprised if you find anyone who is happy with it or has had reliability beyond a few months.
Just my 2 cents.
Take care
I hope to hear from you on my webboard.
<a href="http://www.funcarsonline.com/frames/944board/944board.htm" target="_blank">http://www.funcarsonline.com/frames/944board/944board.htm</a>
Rob
10-31-2002, 06:47 PM
#13
Rob,
The 2.8 stroker motor pistons look exactly like the type in my 928. I have a 104mm bore with the J&E pistons. We used a coating that didn't last the first go round so now we are trying a new piston coating. We also used Total Seal rings that chewed-up the cylinder bore. The Alusil bore does not like the total seal rings. We switched back to the Porsche rings.
I hope my new engine and all the new modifications hold-up to the rigors of some spirited driving. Honestly, I would never try to modify the Alusil Porsche engine bore again. The whole process has been a big pain. I would have put cylinder liners if I had to do it all over again or leave it stock and add some serious boost! Any piston manufacturer can make a piston that is compatible with a steel bore but try and get the tolerances down on an aluminum bore with an aluminum piston and a coating that will last.......it's hard as hell to make that piston compatible with the Alusil bore!
Jim
The 2.8 stroker motor pistons look exactly like the type in my 928. I have a 104mm bore with the J&E pistons. We used a coating that didn't last the first go round so now we are trying a new piston coating. We also used Total Seal rings that chewed-up the cylinder bore. The Alusil bore does not like the total seal rings. We switched back to the Porsche rings.
I hope my new engine and all the new modifications hold-up to the rigors of some spirited driving. Honestly, I would never try to modify the Alusil Porsche engine bore again. The whole process has been a big pain. I would have put cylinder liners if I had to do it all over again or leave it stock and add some serious boost! Any piston manufacturer can make a piston that is compatible with a steel bore but try and get the tolerances down on an aluminum bore with an aluminum piston and a coating that will last.......it's hard as hell to make that piston compatible with the Alusil bore!
Jim
10-31-2002, 10:05 PM
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Actually, the pistons with a 4mm offset only countered the increased 8mm stroke of the 3L crank. That puts the top of the flat piston at the same location as the dished factory one making a very small combustion chamber. I'm almost certain he didn't use shorter rods to lower the compression either...
10-31-2002, 10:14 PM
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Any piston manufacturer can make a piston that is compatible with a steel bore but try and get the tolerances down on an aluminum bore with an aluminum piston and a coating that will last.......it's hard as hell to make that piston compatible with the Alusil bore!
~~~~~~~~~~~~~snip
Yeah, the guys at Reynolds metals did a wonderful job didn't they! They are actually local here, I know a few engineers that claimed to have worked on the project.
A few years back, when I was rebuilding the engine on a 944 of mine, one of the engineers I know at Reynolds told me that he had just melted down a 944 block they had at the shop!! They were not allowed to sell,or give away, any of them that they had as engineering samples due to their strict contract with Porsche!
~~~~~~~~~~~~~snip
Yeah, the guys at Reynolds metals did a wonderful job didn't they! They are actually local here, I know a few engineers that claimed to have worked on the project.
A few years back, when I was rebuilding the engine on a 944 of mine, one of the engineers I know at Reynolds told me that he had just melted down a 944 block they had at the shop!! They were not allowed to sell,or give away, any of them that they had as engineering samples due to their strict contract with Porsche!