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Hi, I have a new set of Wossner pistons and rings for my stock 100mm bores. What ring gap are you guys using? I've been reading lots of posts and there doesn't seem to be consistent numbers. I called Mike at Lindsey Racing and he advised me to gap the top two rings to .017" - .018" and .025" on my bottom ring. Wossner's site recommends .006" x bore for the top two rings and .015" min on the bottom
And the Porsche 951 manual specs the gaps different as well?
Last edited by mahoney944; 02-13-2017 at 12:21 AM.
LR's recommendation of 0.018 lines up with an "NA race" engine per Wossner...
0.0045*3.937 = 0.0177"
I'd go with what the piston/ring manufacturer says.
While it'd probably be fine running the "NA race" gap per LR, the phrase "loose runs, tight don't" comes to mind considering the potential for extra piston expansion due to higher heat in the turbo chamber.
Porsche's specs were for Porsche's original pistons and rings, and Wossner's stuff is likely not identical in composition.
Agreed, I would think the Wossner chart would be what to go by but I don't know what gaps experienced 944 turbo builders go by with Wossner pistons and rings. Our blocks after all are a little more of a unique material than a typical engine and the properties of thermal expansion certainly effect it in a respective way.
wossner recommends .0236" gap on the top two rings and .015 minimum on the lower ring....
So where did all of you with wossner pistons and rings gap each ring to and would you gap it there again after you've put some miles on the engine and monitored oil consumption?
It is about the temp built up in the combustion chamber. The turbos build higher temps, ergo there is more ring growth due to temp. So .024" as I do not know of any feeler gauge that goes to 10,000th of an inch.
It is about the temp built up in the combustion chamber. The turbos build higher temps, ergo there is more ring growth due to temp. So .024" as I do not know of any feeler gauge that goes to 10,000th of an inch.
So set the first two rings to .023 - .024 and what about the 3rd? Says minimum of .015 but I've read people have gapped them between .025 and .03
Seems odd to have a smaller gap on the oil scrapers than the combustion rings? what gap is most ideal for the 3rd ring (oil scrapers)
The top 2 rings are cut large so they can be cut for the proper tolerance for your application. The third or oil scraper is normally cut to the proper size, it has some give so it can collapse on itself if needed.
When I do my rings it is per the cylinder the ring goes in. I measure, cut and place it on the piston, then move to the next. The 951s pistons are considered square top so you can use a piston to push the inch or so into the cylinder so you can get your measurement. If you don't have an extra piston I have an extra 104 mm.
So set the first two rings to .023 - .024 and what about the 3rd? Says minimum of .015 but I've read people have gapped them between .025 and .03
Seems odd to have a smaller gap on the oil scrapers than the combustion rings? what gap is most ideal for the 3rd ring (oil scrapers)
Hi, I'm glad you put those numbers up. I have the same pistons for a 951. You have to convert 100mm to inches. I did the math and got .2287 for the top rings, so .23 is right. I wanted to make sure I did it right. Thank you for your post
Hi, I'm glad you put those numbers up. I have the same pistons for a 951. You have to convert 100mm to inches. I did the math and got .2287 for the top rings, so .23 is right. I wanted to make sure I did it right. Thank you for your post
Mahoney's math is correct.
You must have missed a zero somewhere in your calculations.
Hi, I'm glad you put those numbers up. I have the same pistons for a 951. You have to convert 100mm to inches. I did the math and got .2287 for the top rings, so .23 is right. I wanted to make sure I did it right. Thank you for your post
mm to inches divide by 25.4
Inches to mm multiply by 25.4
Well I've gapped my rings but I've come across a interesting topic. What is the proper temperature to gap rings at? My engine is in a cold garage (anywhere from 20 - 40 F) so I've had a small space heater next to the block during this winter. I gapped the rings just after removing the space heater from the block, so the block wasn't frozen or all that hot either. I gapped the top ring so my .022" feeler gauge was loose and the .024" started half way or so but was tight. I left the space heater off of the block over night and checked the top gap again this morning. The .02" feeler feels loose and the .022 I can get to go but its tight, so I estimate the gap to be about .021" which means the temperature of the block shrunk the gap .002" or so. This made me start to think, if the ring expands when the engine gets hot and the bore expands when it gets hot as well. Will my gap stay relatively the same under thermal expansion give or take a few .001"s ? What temperature should I gap at or does it really matter all that much?
Hi, I'm glad you put those numbers up. I have the same pistons for a 951. You have to convert 100mm to inches. I did the math and got .2287 for the top rings, so .23 is right. I wanted to make sure I did it right. Thank you for your post
Originally Posted by rlm328
Mahoney's math is correct.
You must have missed a zero somewhere in your calculations.
Well I've gapped my rings but I've come across a interesting topic. What is the proper temperature to gap rings at? My engine is in a cold garage (anywhere from 20 - 40 F) so I've had a small space heater next to the block during this winter. I gapped the rings just after removing the space heater from the block, so the block wasn't frozen or all that hot either. I gapped the top ring so my .022" feeler gauge was loose and the .024" started half way or so but was tight. I left the space heater off of the block over night and checked the top gap again this morning. The .02" feeler feels loose and the .022 I can get to go but its tight, so I estimate the gap to be about .021" which means the temperature of the block shrunk the gap .002" or so. This made me start to think, if the ring expands when the engine gets hot and the bore expands when it gets hot as well. Will my gap stay relatively the same under thermal expansion give or take a few .001"s ? What temperature should I gap at or does it really matter all that much?
I believe you are over thinking it, you are talking .001". The engine block will have a max temp of 240 F. I have gapped in a cold garage (50 F) and summer temps (upper 90s) in Houston and have not had any problems.
Of course you can be like a lot of members on this site and move your motor into the living room so you can work on it and watch YV at the same time.
01-31-2017, 06:06 PM
944 Turbo Wossner Ring Gap
