DumpdEJ6

Hey guys, let me get your advice on this...I'm building an LSVTEC and putting it together, here are some of the pertinent specs:

B18 LS block/crank/rods

Block bored 81.5mm and honed

NPR USDM ITR (P73AO) pistons, 81.5mm

NPR piston ring set 81.5mm

So everything matches up, I go to check the ring gap, and 1st ring is 0.019", which seems really big to me as my research has come up with a ring gap of around 0.014"-0.015" to be optimal for a N/A engine with compression around 12:1.

2nd rings are all right at 0.017", which seems about right, from what I can tell it should be around 0.017"-0.018".

Haven't done the oil control rings.

All measurements were taken after wiping the cylinder walls with WD-40 and pushing the rings down about 1 1/2" down from the top of the block with a piston, making sure it was square and flat in the cylinder.


TL;DR: Top ring gap 0.019", should be 0.014", correct?

blackeg

its become more common practice to gap the top ring smaller than the 2nd in case any gas gets between the rings it can exit quickly. .014 top is a bit tight imo i would not run that. you can go by the itr specs in the helms. what cams is thing going to have.

you "can" run .019 top if you do open up the 2nd ring to like .021 but id want tighter some around like .016 top -.019 2nd.

on the last 3 81-82mm builds ive done all the rings that came with the pistons and even the hastings ring all come with gaps too big for all motor right out of the box. i bought a set of je proseal rings i run in the turbo car. they were like .010 out of the box leaving plenty of room to get the desired gaps. good luck man seems like you know whats going on and with the right rings with will turn out perfect

DumpdEJ6

Thank you for replying, it's been a while and I was losing hope that someone knowledgeable would answer lol. Yeah it kinda sucks, they are the rings that came with my 81.5mm NPR pistons so I figured they would either be good or a little tight. Looks like I'll have to buy new ones. I've heard Hastings rings are good, should I buy 81.5mm Hastings rings or err on the safe side and get 82mm and grind them down? Sucks because I had bought a set of 81.5mm Hastings rings and sold them because everyone said to run the rings that come with the pistons. This is my first engine build so I'm second- third- and fourth-guessing everything I do lol.

TheRealTegger

According to my September/05 copy of Car Craft magazine, the top ring gap is smaller than the lower gaps to make sure the upper ring is always loaded and never allowed to become unloaded.

Apparently excess pressure under the top ring can unload it, which can cause considerable damage.