Looking to get some opinions on the ring gaps on a forged 347 motor. I have diamond pistions and looking to spray 250 max. Car is mostly race hardly ever street driven. My bore is 3.905

I was told by diamond

Mutiply bore by .004 for the top ring

Mutiply bore by .006 for the second ring

Oil scraper between .015-.030

So that would put me at .015 for the top and .023 for the second.

Dunno about that sounds pretty tight for a motor that will see almost 800 horses at the flywheel.

 

Anyone?

 

Double check what Diamond told you, and then do it. Listen to the ring manufacturer!!

 

I know Diamond probably wouldn't recommend that for a 250 NOS shot though. Probably more like .006 per inch of bore (or maybe even more depending on the rings and the ring lands). A little too much will not hurt you but too little with NOS can take out the piston.

 

Well i called again this morning and talked to another tech he said that I should

Mutiply bore by .006 for the top ring

Mutiply bore by .008 for the second ring

So that would put me at .023 for the top and .031 for the second. Now I'm really confused???

 

just for a comparison. When I spray an ls1 or chevy motor I use .018-.20 for the top ring and add .004 for the second ring. I normally wont go much above .028 for the second ring just for around town driveablitly and blow by reasons. High compression motors I use .018 and .022.

 

with spray, you dont want to go to tight, i would say a hair loose is better. id call some ls1 engine builders and ask for specks, i think we did mine 19 top, and about 22 bottom. i forget tho, i did it different when i did my FI motor.

 

I went .022 and .030 on mine and so far oil consumption hasn't been an issue. If your main concern is nitrous I would lean a little on the wide side, but not too much if your not going above a 250 shot. Maybe try Diamond one more time and take the average of the three calls!

 

I agree with what Erik said above. Are the pistons nitrous sepecific? If not, the ring land is probably not super thick and much closer to the top of the piston (and closer to the heat of the cylinder). This would require you to open the gap up slightly more. It all boils down to HEAT. The ring material, cylinder temperature, ring location,etc. all play a huge roll in determing ring end gap. I would definitely err on the loose side with a setup like yours.

FWIW, the last 346ci forged motor I built for a customer spraying a 300 shot, I had the gaps at .026/.032. No issues after countless bottles through the car.

 

Just do a .022 top and a .026 bottom. Nos is going to creat a lot of heat. So the rings are going to open up a little. You dont want them to butt up. I did mine at a 20/24 for a turbo set. Not as much heat there.