Forum » General Engine Building Discussion » EVO 8 4G63 PISTON RING CLEARANCE


General Engine Building Discussion

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Hello, what is the recommendation on the piston rings and deck clearance for a 800-1000whp e85 EVO 8?

It's a little tricky to advise you here because you do need to take into account the recommendations from the ring manufacturer first and foremost. I almost exclusively used JE pistons in our drag engines and for a 1000 whp E85 build I'd be looking at a top ring gap in the vicinity of 18-19 thou with the ring packs we used.

Yeah I'm Using Cp Pistons with NPR rings than came without a spec sheet, I normally use 0.019" on top and 0.022" on second ring and in most cases oil rings are above 0.018" so i didn't touched, but in this case the oil rail rings have 0.010" looks too tight to me, also i have never use this type of 3 pieces oil rings with a wire into the expander (Nifflex expander)

I know you have a lot experience with 4g63 built, do you guys have any course about 4g63 built included clearances and tricks?

In Engine Building Fundamentals and Practical Engine Building I don't see a practical measured examples as a pistons to valve, pistons to counterweight and oil rings (their is many oils rings type) clearance and properly installation, i have seen yes a theoretical instructions, Is there a place where I can find that?


For your help

We currently don't have a worked example planned for the 4G63. While they have their peculiarities like any motor, realistically there's nothing too unique with them. Our drag engines targeting 1000+ whp and 10,000 rpm used a clearance of 0.002" on the big ends and 0.0025" on the mains. Getting rid of the balance shafts is advisable but don't just cut off the balance shaft that comes out of the oil pump and blank it like many do. This is a common cause of oil pump failure. Instead it's advisable to have a machinist turn the counter weight off this shaft so that it is essentially an idler shaft. This gives full support to the oil pump gear. Beyond this, the 4G63 is really a pretty straight forward engine to build in the EVO 5-9 guise. The earlier ones had issues with their thrust bearing arrangement but this was rectified from 5 and above.

With the 4G63 you shouldn't realistically ever be in a position of having clearance issues between the crank and piston, and even piston to valve clearance is normally ample with most shelf stock pistons until you're stepping into the 290+ deg and 12+ mm lift region. Of course we never want to assume but that's been my experience. We had our own piston part design that JE made for us which I knew had ample clearance for any cam we could throw at it. If you want to see how to check the valve to piston clearance then this is covered in our 'How to Degree a Cam' course.

The only other issue you can strike is if you're running an alloy rod and/or stroker crank in which case the rod clearance to the bottom of the bore can be an issue. You can check this (and the crank counterweight clearance for that matter) with plasticine or play doh during dummy assembly. I also used a bore scope to visualise the clearance there as it can be hard to get in there to see. With the oil ring rails, just follow the ring manufacturers directions. These typically need a minimum of 0.015" clearance but aren't super critical beyond that.