Piston Ring Gap for a 395

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Sep 11, 2004 | 04:35 AM

ROCNDAV

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Piston Ring Gap for a 395

I'm gonna start tackling my short block this weekend. As per Lunati's instructions that came with the 395:

Minimum gap clearance is .004" per inch of cylinder diameter for top rings. Example: 4" bore x .004" = .016" minimum top ring gap clearance. Minimum gap clearance for second ring is .003" per inch of cylinder diameter (.012" for 4.00" bore). (NORMALLY ASPIRATED ENGINES ONLY).

This is to be a daily driver, NA, T56, 3.42 gears. I know the use of power adders requires me to open up the gap a bit (.021" or so), but how much is too much for NA? Do I go .016 (top) and .012 (2nd ring), which is the bare minimum for my 3.903 pistons, or is there some reason I should be opening the gap a few more thousands.

I've searched the site and found various threads on gap but nothing for my stroke and/or use

Thanks,
David

Last edited by ROCNDAV; Sep 11, 2004 at 02:45 PM.

Sep 11, 2004 | 02:54 PM

ROCNDAV

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Anybody?

Sep 11, 2004 | 04:02 PM

Jason99T/A

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On the naturally aspirated 3.905" motors I build, the end gaps get set at .018" top/.023" second.

Sep 11, 2004 | 09:05 PM

Camaroholic

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This article might help.

It talks about setting ring gaps, and why you should set the 2nd ring gap larger than the first one.

http://www.rosspistons.com/pdf/ross_...stallation.pdf

Sep 11, 2004 | 10:15 PM

Taspeed

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i prefer the 18-20 on the top ring and 22-24 on the 2nd ring. Depends on how high i am running the compression and how radical i get with the cam. Generally 18 and 22 will work for most things, even a small dose of nitrous. you should generally gap the second ring .004 larger than the top one.

Sep 12, 2004 | 02:14 AM

ROCNDAV

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I know (well, actullay found out by searching) the second ring gap is usually bigger by a few thousands on N20 cars, but I thought or understood that NA cars go smaller on the second ring. I was just quoting the box and papers that came with the lunati pistons, but then again that may be a standard printing for most pistons.

That Ross installation sheet had some good info on there. They also recommend .004 x diameter for top ring, which would be .015612 (3.903 x .004) or .016". According to the ross sheet, they recommend .019515 (3.903 x .005) or .020" versus the Lunati .012" 2nd ring gap. So why go 18-20 on the top instead of 16? I'm not trying to say I dont need to go 18-20, rather, I'm trying to understand why?

Will the gap affect ring life by increasing the gap .002~.004" ? As stated before, this will be a daily driver car, with no track time (well, maybe one time).

The cam that I chose (Lunati 55009LUN http://www.holley.com/HiOctn/ProdLin...CC/Chevy6.html) has the following specs:

RPM Range 3500~6500

Duration:

Adv Intake/Exhaust: 300/300
@ .050" In/Ex: 242/242

Lift:

@ valve .595"
@ lobe .350"

LSA: 112

As for the compression, my pistons are 10.6:1 CR 3.903 -11cc Reverse Dome Lunati. I'm not sure what final compression will be just yet as I will still have to choose the correct head gasket and still need to know how much to mill off of my 317 heads (after they get ported).

I guess the general consensus is to go 18 on top and 23 for the 2nd?

Thanks,

David

Sep 12, 2004 | 11:56 PM

Taspeed

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I have built a few 12.5:1 + compression ls1's and I preferr a couple .000's larger. It relieves a little stress on the top ring land of the piston...especially with the stock replacements as they tend to break the top land. With a fairly stock compression build you can use the .016 and .020 gaps. I always use a larger 2nd ring gap. It has been proven and tested over and over again by several of the major players and racers that it frees up hp at higher rpm's and relieves stress that tends to build up between the top 2 rings on the compression stroke. Basically it means less chance of building pressure and breaking a ring.