[72projectbird]

How many miles on it? If you stick a bore scope in the cylinder, do you see any scoring or signs of ring contact having been made?

If you're not running boost or nitrous on it, I wouldn't worry about the gap. Make sure the tuneup is good, timing set up right with no detonation on pump gas, and run the hell out of it.

[nalvarez]

Originally Posted by 72projectbird

How many miles on it? If you stick a bore scope in the cylinder, do you see any scoring or signs of ring contact having been made?

If you're not running boost or nitrous on it, I wouldn't worry about the gap. Make sure the tuneup is good, timing set up right with no detonation on pump gas, and run the hell out of it.

It has roughly around 1000 miles. No boost or nitrous planned for it. Recently did a compression test and everything looked good there, haven't stuck a camera in the cylinder yet though.

[nalvarez]

Originally Posted by 72projectbird

How many miles on it? If you stick a bore scope in the cylinder, do you see any scoring or signs of ring contact having been made?

If you're not running boost or nitrous on it, I wouldn't worry about the gap. Make sure the tuneup is good, timing set up right with no detonation on pump gas, and run the hell out of it.

It has roughly 1,000 miles on it. Probably a little less. I just performed a compression test and everything looked good there. I haven't stuck a camera in the cylinder. I do not have any plans to run boost or nitrous.

[chiphead]

At the risk of being alarmist, here's my take:

At 11 compression and a head/cam combination that is going to be very good at cylinder filling, there is a cylinder pressure risk. If the tuneup gets off, or get a bad batch of fuel, the risk is some detonation. A forged piston motor is able to shake some of that off, worst case you get accelerated rod bearing wear, maybe lift a headgasket fire ring. A KB hyper piston is much more likely to pinch a ring land, even with good rings.

You can drive it moderately, but I would not run the hell out of it. Enjoy the car, take it easy and save up for the piston/ring swap.

[mgarblik]

Well, you have a pretty complicated situation there, I am sorry to say. You have a bunch of parts that are not
optimum for long engine life IMO. First, KB Hyperutectic pistons are bottom shelf parts. I don't use them in any builds, unless the customer, (student) insists on using them or it's the only thing we can get for the application. I would just use Badger, Silvolite, Ohio Piston, Egge, or some other cheap replacement piston instead. Then a good set of rings and cross your fingers. The comment some engine builder made about hyperutectic pistons being stronger than forged can only make sense if he has some weird definition of what "strong " means. They are strong in the sense of being extremely brittle, like glass. Glass is strong until it breaks. These pistons keep their shape, are extremely quiet, wear resistant, and can ruin very tight in the bores. Due to being very hard and brittle, what they can't take is ANY detonation or pre-ignition. Very unforgiving. That's were softer, forged pistons really shine. They can take considerable detonation without cracking.
Next we get to your plain iron rings. They should break-in very quickly even in a tapered or out of round cylinder which is good. But as Steve mentioned, they are not even OE grade rings. Plain iron rings are often called "rebuilder" rings. They generally have a 35,000-50,000 mile life span and will begin using some oil around 35,000 miles generally. For most hobbyist's, this is 15 years of use. On the plus side, your ring gap issue will go away pretty quickly. Those plain iron rings are so soft, the gap will probably wear into specs. in a couple thousand miles. Personally, I would just run it, carefully. Make sure it NEVER overheats, and never detonates, which will be a bit of a chore. Keep a very close ear on the engine for any pinging or detonation especially under light load. With the parts combination in that engine, I would have a hard time justifying a tear down if it's running fine. Hope it all works out OK for you.

A little side note for the engine builder crowing about the virtues of hyperutectic pistons: There is a reason EVERY engine manufacturer, domestic and import, when designing a high performance version of an engine use forged pistons. This is the first upgrade they build into their design, especially if supercharging or turbocharging. Been that way for 70+ years. Why would the engineers put "weak" forged pistons in all those high performance applications if cheaper, stronger, hyperutectic pistons are better?

[nalvarez]

Thank you for the response. After everyone's thoughts here, I'm just going to baby it for now and save up/plan for a teardown a bit further down the road. I don't plan on going to the track or anything and just want to cruise around town for now. Im also going to put a afr gauge on it and make sure the fueling is dialed in.

[mgarblik]

That sounds like a good approach. If you put an AF gauge in, if you keep it running around 14:1-14.2:1, that should be plenty safe at cruise. Low to mid 13's under heavy throttle. No reason to be afraid of it IMO. It may give you many years of fun service depending on how you use it. I have a student from 2 years ago that insisted on installing those awful 8 valve relief cast pistons with OE iron heads 68 GTO 400. It made about 360 hp on the dyno and he loves it. So I wouldn't be too concerned

[lust4speed]

If the engine is going to be run hard (which includes summer heat with stop and go driving) the KB chart recommends .0080 gap times the bore (for towing but using this one for safety). Say we have a 4.15" bore at .030" over so 4.15x.008=.0332 gap rounded up would be a .034" recommended gap.

I've only set up two engines with these pistons and I called and talked to the KB tech several years ago. First interesting thing he said was they were on their sixth formulation with the pistons and they are getting close. This was awhile ago so maybe several more changes and maybe they got the piston formulation down. The tech said that he wouldn't run anything less than .036" gap on a .030" over 455 at 4.18 bore and he would be more comfortable at .038" on the top ring.

From the looks of the chart it does look like they have put in print what the tech said on the phone. I've seen two engines where a seized top ring took the top land of the piston off. Better to be safe than sorry and end up with a disaster on a hot summer day. .022" sure is on the road to having the ends butt and seize in the bore.

Also while the gap seems excessive the ring is growing much more than a ring in a normal forged piston so at hot operating temperature both rings have close to the same gap.