I am in the process of rebuilding a 350, and I am ready to drop the pistons in. I was checking the ring gaps and I was getting .013 to .012 on the top rings. (seemed tight to me) I checked a couple of books that I had and they said the recommended specs fall between .010-.020 for the top ring and .018-.026 for the second.

I was just wondering what you guys recommend running? Do you think this is too tight? It will be daily driven n/a no boost, just the mods below.

Also, do you want the second ring gap to be smaller or bigger than the first?



Here are the specs

1994 5.7 350 bored .030 over
stock rods, crank, and heads
Speed Pro Hypereutectic teflon coated flat top pistons
Sealed Power Chromemoly Piston Rings(SLP-E-251K030)
Edelbrock Performer TBI intake manifold (3704)
Headman shorty headers
Crane 2030 powermax cam
* Advertised duration: 264 intake/274 exhaust
* Duration at .050 in.: 204 intake/214 exhaust
* Gross Valve Lift: .423 in. intake/.446 in. exhaust
* Lobe separation: 110 degrees

 

what kind of pistons is the big question, gaps change with piston types. what you read in your manual is for factory type pistons in a factory type application. you migth want to check with your ring and piston maker if you're running anything other than a stock set up. some if not all hypers require an increased end gap on the top ring

 

I am using Speed Pro Hypereutectic teflon coated flat top pistons

Quote from Speed-Pro

"Speed-Pro’s cast hypereutectic material is a relative newcomer to the performance market, and has several attractive features. Our hypereutectic pistons operate perfectly with standard ring end gaps , and have conventional ring land locations. When compared to traditional cast pistons, which are not designed for performance use, the hypereutectics are significantly stronger, particularly in the highly loaded ring land, skirt and pin bore areas."

do you think I should open up the gap a little with my mods?
Will it be ok as is?

 

.012" is a little tight for a motor that will see full throttle use.

You can open it up a little to around .018" to .026" for
a street performance car.
Being a little too big (within reason) is better than too small.
The ring gap closes up with the heat of a full throttle blast.
Any full throttle pinging you may encounter will really close up the ring gaps. OUCH!

Look up the recommended ring gaps for a performace oriented motor like a old GM 350Lt-1 from the late 60's early 70's.
The ring gap called for is a little bigger than on a low compression
low power motor.

Wether the sec ring gap should be bigger or smaller than the top gap depends on the piston design used. When in doubt follow the manufactures recomendation. different ring land heights and pressure grooves make a difference.
I believe Federal mogul now recomends a larger second ring gap on their hypereutectic pistons.

I'd check the piston to bore clearance too. could also be too tight. may need more cylinder honing.
Are you sure that the ring is square in the bore?