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What turbo are you running scargo? That's sort of why I didn't say ring gap numbers before. For top rings stock says .008 - .010. CP is around .020. Cosworth is .012 - .018. They're so all over the place that my numbers don't mean much. Plus it depends on the ring material, and use of the car. For my personal car if it ever manages to get finished I'm going to run .015. That is likely to be on a pump gas 35r setup. I am almost finished with another engine I did .015 top gap on, it was with Manley pistons. Should be around 350 whp or so when it's done. If it butts rings then I have an expensive repair bill for someone and I'll post on here not to do it lol. But it shouldn't. I don't like running huge gaps because for one I can't see the rings getting so much hotter that they need to be double the factory clearance and for two I think it's why it seems like an accepted fact that built motors don't last like a stock one in terms of mileage.
I'm running a Polka Pickle with the (small), 8cm hot side. For those unfamiliar, that is a Blouch 2.5XTR, a stock location ball bearing turbo with internal wastegate. It has worked really well for me, in combo with my mild porting, Full Race pipes and my other mods. At EFI, on their Mustang dyno, the late Chris S. tuned me to a mild, road racing 395WHP/393FPT.

I am not sure why stock gap would be so small, but it could be the cast pistons playing a part. I don't want to run excessive gap either, but I don't want to go against CP specs either.
My younger brother was a turbo'd VW drag guy and he liked Total Seal gapless rings. I see they do not recommend their rings for turbo applications. Not sure why... A lot will depend on the boost you wish to run.:eek::D YMMV I am still learning...
 

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scargo: using plastigage measures only 1 (one) area of the crankpin , either mains or rods, i have always used a micrometer. i measure pins at left and right side then move the micrometer 90 degrees
and remeasure. the results will tell you pin diameter AND whether the pin is truly round. as for tighter clearances, absolutely not. on the race motors , BMW and Porsche that i have built in the last 30 years.
0.002" is fine. make sure to up oil pressure to 100 psi on a warm engine. please use a TOP quality
synthetic oil. wider ring gaps only allow more compression to blow by the rings, which reduces power and adds to contamination of the engine oil with combustion by-products. there is a company which sells gapless rings. the # 2 compression ring is actually 2 rings formed to fit together in the ring land.
less blow-by= more power production. please maintain factory ring land specs (width), rings do a lot of flexing (wobble) as they travel up and down in cyl bore.
 

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Thanks for answering me. As you may have noticed above, Total Seal did not recommend their gapless rings for my application. Not sure why.
I Plastigauge on multiple spots when I use it and I do mic everything. I just don't trust any one measurement method. I had my head shop go through my parts, balance the crank and assembly and re-check everything I did and everything I measured. Since this is my first build from scratch of a Subie EJ257 motor I am very cautious.
I don't know whether I mentioned it earlier, but I have a JDM 12mm oil pump for the new build. I have gone through it and smoothed up everything internally. It seems there is a lot of controversy about what pump is enough, but that is mired in ambiguity. Nobody (that I know of) states shims used, spring used, spring pressure or exactly what engine and how it was built. It ends up being anecdotal evidence, and worthless AFAIAC.
My logic is that I am building a DVACS race motor that is not completely new. Heads have only 4K on them and the block 17K. New cams. I hope the head guy checked the cams with the bores (but they look quite nice).
My current motor has a nine quart oil system with everything external. I run Royal Purple race oil. I was thinking of using the 12mm pump with a dry sump system, where the external pumps only scavenge, like with the Cosworth design.
Thanks.
Update: I am assembling a 450WHP built motor with this 12mm pump. I will block the pressure relief valve and am using a Peterson Fluid Systems 09-0160 10AN Remote Relief Valve.
 

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This thread is great stuff. Answered a lot of my questions that I had. I picked up a short block about a week ago and have to finish taking it apart. Guy said it has a spun rod bearing and about 30,000 on it. He got it from the dealer in late 2011 so it has the forged crank :). I'm going to see what shape the rod journal is in and if it can just be polished I'll use it. Having a hard time choosing rods and pistons. I was thinking either cp or Wiseco. The only thing with Wiseco is they're already coated so I won't be able to measure them accurately. I was thinking Manley turbo tuff rods. I'm not looking for stupid power probably 350-375whp when all is said and done. But I'm going to send the block to a shop to be cleaned and honed and see what they get for a bore size first. Hopefully I can use a 99.5mm but if not I'll go to 99.75. If anyone has any suggestions or other input on parts they used I'd appreciate it. Everyone seems to be going with king xpg bearings so I'll probably use those.
 

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Aren't piston to cylinder wall, ring end gap, and bearing clearances provided by the manufacturer of the parts being used?
 

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