Stock rebuild, piston ring gap for F/I?

[JasinC19]

Hey all

I just wanted a second opinion from experienced engine builders.

I am having a 306 short block build at the machine shop. I told him they may be a small chance of a mild boost supercharger in the future. He recommended we gap the piston rings further apart.

He said that the few extra thousandths of an inch would not affect N/A performance. He also said it would not increase oil consumption. (Maybe a tiny bit)

What would you guys think about all of this? It doesn't sound like gapping them as he is suggesting would have any negative side effects, but it also just sounds odd to me that this is the case.

Experienced information is very appreciated,
Jason

 

[txstang84]

With my last 306 build, I went 0.018" first ring, 0.016" second ring-to my knowledge, it never had issues, and I ran a Vortech V1 pushing 10-12lbs for about 3 years...I think the general rule is 0.004" per 1" of bore, so 0.016" would be the minimum, but if you're planning on boosting it throw in a few thousandths. And if you're running KB pistons, they recommend closer to 0.022" for top ring if memory serves.

Oil consumption should not be affected...

 

[NIKwoaC]

The added heat from forced induction will cause the rings to expand more and therefore, the actual operating gap is less. Putting a larger gap on the top compression ring for an engine that is expected to see boost is pretty much standard procedure.

And no, you will notice no effect N/A. The ring gap is such a small fraction of the total combustion area of the piston that it is almost negligible.

 

[Rick 91GT]

Actually one of the newer methods is to gap the second ring larger to help prevent ring flutter and increase seal...

What is the ring material your using? Do you know the PT#? Then I can recommend a ring gap... Do you know the piston to wall clearance on the motor? Forged or Hyper piston?

 

[JasinC19]

Thanks for the replies.

He is using Scat forged rods and Probe SRS forged pistons. The rings I believe are plasma-moly construction.

I can get the exact part numbers later today.

 

[Rick 91GT]

If it is a plasma moly ring, Id go .020"-.021" top, .024"-.025" second.....if boost is on the future.

Sometimes it is best to let your builder decide, nothing like having an outside source tell you what clearances and gaps you need when they are not building the motor. I know I wouldnt like someone tell me what gaps to do....

 

[txstang84]

Actually one of the newer methods is to gap the second ring larger to help prevent ring flutter and increase seal...

I stand corrected-never heard this one before...

 

[NIKwoaC]

Actually one of the newer methods is to gap the second ring larger to help prevent ring flutter and increase seal...

Iiiiiinteresting.... That is not something I've heard before.

 

[Rick 91GT]

I started seeing in about 3 years ago, Mahle has actually changed their paperwork that comes with the rings to reflect it So far it has worked out well... be surprised what we do with cylinder finishes as well Ive been doing the ring gap that way for about 4-4.5 years.

 

[txstang84]

I'll keep this in mind when I assemble my 4.6...any thoughts there for ring gap, or do you have this addressed somewhere on another thread? I'm not using Mahle slugs, but I def don't wanna toast any rings or lands.

 

[Rick 91GT]

You want me give all my secrets away huh? Just shoot me a message when your ready, I take into consideration the application, piston brand, boost, etc...yadda, yadda Every motor is alittle different.

 

[NIKwoaC]

I know you engine builders have some serious voodoo with your rings and cylinder finishes, and I have seen some seriously mind-F results from combos that you would not think to make a lot of power. There is a lot of power to be had in the bottom end and I know my junk with the ball hone cylinders is a JOKE!

 

[JasinC19]

I'll just be happy when my rebuild is finally fired up and back on the street. It's been a long 3 months... I can't wait to get my short block back.

 

[txstang84]

You want me give all my secrets away huh? Just shoot me a message when your ready, I take into consideration the application, piston brand, boost, etc...yadda, yadda Every motor is alittle different.

I tried to send you a message already...it was kinda long-winded, I was just looking for some assistance, but I guess I didn't write/send it correctly since I never received a reply.

 

[Rick 91GT]

I tried to send you a message already...it was kinda long-winded, I was just looking for some assistance, but I guess I didn't write/send it correctly since I never received a reply.

I got it this morning...

 

[txstang84]