As i'm about to start my engine rebuild, i was looking at the repair manual and i saw different specs for the piston ring gap size.

You can take a look here


Page 9-15 (Engine specification) and page 9-128 (Piston and Con rod)

I'm a bit confused

Found on the forum that a lot have been running more like 0.021 top ring gap and 0.024 second ring.
Should i follow the repair manual or not? right now, without any gapping on my brand new NPR ring, i have 0.012 top and 0.023 bottom.

Thx!

How much boost do you plan on running? The more boost you run the more ring gap you want. More boost= more heat which will cause the ring to expand. If there is not enough clearance the ring closes the gap as it heats up and continues to expand which will score the cylinder bore and possibly chip out a piece of the piston.

Also always run at least a couple more thousandths clearance on the 2nd ring than the 1st ring. Failing to do so can cause an issue called ring flutter where pressure builds between the rings and unseats the top ring

High boost (over 30 psi) or Big NOS shot, bore size x .008" = suggested ring gap from Manley.
I am gapping mine right now. I run .024" top and .028" 2nd with .015" to .019" oil rings. I do run high boost though. No blow by, seals great on my other motors.

Bock said:

Found on the forum that a lot have been running more like 0.021 top ring gap and 0.024 second ring.
Should i follow the repair manual or not? right now, without any gapping on my brand new NPR ring, i have 0.012 top and 0.023 bottom.

Thx!

Click to expand...

I'd run that top ring at .018" and leave the bottom ring alone. Make sure to file any burrs off the edge of the ring after file fitting.

I'll be running stock boost now but i do have link and a 20G sitting on the shelf staring at me

Just finished to gap my ring, went with 0.020 top and leaved the bottom at 0.023. It should be fine!

I think you were smart!

Should work just fine. .021 and .024 here. Car sees 30psi+ on a 62mm and logs well north of 60lb/min. No smoke or excessive catch can filling. This is also with a loose .0045 PTW.