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Hello my fellow car enthusiasts,

here is the dilemma I just built my motor it made 403WHP current set up RB25DET Tomei MX8265 Turbo, tomei elbow, trust downpipe, test pipe 3” all the way back. 
740cc injectors, R8 coil packs, 3”FMIC, Z32 MAF, HKS filter, greddy electronic boost controller, nitto crank collar, ACl main and Con rod bearings, all gaskets replaced. Stock bore running a Haltech, walbro 255 FP. 
 

anyways I had the car for about 4 days after the tune then it starts misfiring I never even had the chance to have it WOT to feel the power. 
The car starts misfiring swap the plugs out gap em @.8 it’s fine. Eventually the next day I start her up she’s running like shit again. I do a compression test and it was bad. I believe it has bore wash/glazed. #3 cylinder 
Does anybody here on the forum know the exact ring gaps for OEM rings? Do you go a little bit bigger for more boost? And if so can someone who is knowledgeable shed some light? 
 Do OEM rings and stock pistons need bigger ring gaps for more boost? Or is that only for aftermarket pistons?? Currently pulling her apart again:( 

thank you 

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Don't pull it apart yet!

Its pretty easy to end up with fuel wash in the bores of a brand newly built motor, and it's unlikely to be ring gaps. Drop the oil and determine if it is fuelly first.

In a brand new engine the rings need to bed to the bore. You didn't say, but hopefully the machine shop did hone the bores to put a good cross hatch finish on it to help the new rings bed.  Either way, it takes some hard load running (not babying it for 5,000klm like your grandfather used to) to bed the rings in properly.

Until the rings are bedded properly you will get some fuel in the oil. If the car is misfiring at this time the likelihood of fuel wash is about x1 million because there is more unburned fuel in the cylinder for longer.

So....put good plugs in then run it hard for say 1,000klm. Spirited hills driving is great because you load it up at different rpm. If you only have freeways etc then at least run it in different gears and whatever different revs you can that are safe, and load it up hills (eg flat in 5th). Of course keep you ear out for pinging incase the tuner set those unusual load points properly.  If there is a misfire you need to find and fix the cause first.

Alternatively, take it back to the dyno and run it in there. Assuming the car is running OK they can do the run in much faster because the dyno lets them set the different load points and how long they want to stay there.

Not much point doing a (dry) compression test until the rings are bedded. You could do the test again with a few ml of oil in each cylinder and see if that gives a different result; that would make it more likely rings are the issue.

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As for ring gaps [we are talking compression rings]...generally err on the large side, a slightly larger gap has almost no effect on performance or the motor.  Clocking your rings helps . Too small and you risk scoring the bore due to rings expanding as they heat up then the ends butting together, finding no room, still expanding, so bulging out into the cylinder wall. 

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