I have a friend who is building a 383 LT1 in my garage. We got done last night fitting all the rings. Since my buddy insists he'll never use nitrous they were set @ .026 gap as recommended by the tech sheet with the pistons.

There were other gap settings for nitrous, blown, turbo, yada yada...

My question is if we open the gap up a bit to say the nitrous setting; .032 how much would this really effect sealing compression or whatever? Personally I'd be inclined to error on the side of a bit too big.

I just have this sneaky feeling he's gonna want more after this buildup.

What do you guys with 383's run for a gap?

 

What kind of rings are you using. 26 sounds pretty wide for an N/A setup. If i remember, speed pro recommended .016-.018 top for street on their plasma moly rings. I went with their street/strip gap of .018-.020 for the tops and that's with a 4.155 bore

 

I agree with ralf that seems like a big gap, I set mine at .018 for my plasma moly's.

 

That gap sounds like what is called for for hypereutectic pistons. Fine and dandy but if so, he definitely should stay away from nitrous. I'd stay with spec but yes I would always err on the side of a slightly wider gap rather than too close.

 

I run 0.024" on my turbocharged motor. A bigger gap will just give a larger leakdown #. were talking a percent or two. It also won't last as long due to the gap progressively getting larger with miles. No biggie for most performance minded people.

 

Click this link below, these are the pistons. They are Hypers. Then click the special clearance requirements box.

http://www.kb-silvolite.com/performa...etails&P_id=94

I think he ran out of money for forged. However everything else from the piston down IS forged.

 

Like the Kid said, if they're Hypers......be real careful with the nitrous. I've seen too many of them break even N/A, and for the small cost difference i woulda gone with the forged.

 

I'd go a step farther and say Do Not Use Nitrous on HyperUs at all.

Of course, there will probably be those who will say blah, blah, blah; just don't say you haven't been fore-warned.

Jake

 

Here is what the KB page says about top ring gap. Some interesting reading.

Special Notice on Top Ring End Gap.

The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.

Example: 4" bore "Street Normally Aspirated" = 4" bore x .0065 = .026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as .060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.

 

I have read about a lot, AND I MEAN A LOT, of KB piston failures when their gap recommendations are not followed.

Some want to blame it on the quality of the piston but, in reality, it's because the builder didn't follow the specifc KB directions and specifications for gapping the rings.

Jake

 

This is true of any hyper piston. My machinist who is a respected craftsman in this area among many racers and others, even admitted to me that he had such failures at first with these because he just set them up like any other piston. He then conferred with KB at a trade show and found out what he was doing wrong and has had no problems since. Lots of low buck and econo class racers use them. They are perfectly fine within their design limits.

 

allt4, also let your friend know he'll be experiencing alot of noise from piston-slap with thos KB's......most noticeable upon cold start-up until the engine is warmed up. some folks DO NOT appreciate this particular litlle feature at all, its normal with the KB's.

 

I've never heard a peep out of them. What kind of piston clearance was the engine set up with that you experienced this in?

 

I haven't measured the clearances for the piston to wall. However I can believe the slap mentioned above. The side without the skirts do seem sloppy, not like a normal pinston when you install it, it's tight all around.

There isn't any problem with the block or parts, everything was blueprinted, balanced. When I first slid a piston in the bores I was worried untill I read the specs and how they're supposed to expand more yada yada...

This is my first experience with KB pistons, so it's definately a learning experience.

 

This is exactly the reason I posted originally.

 

The recommended cylinder clearances of the KBs are tight. They CAN successfully be run loose, but if they are set up as recommended, they should VERY quiet.

RACE ON!!!

 

Yes, I don't remember the exact street spec but it was pretty snug.

 

Here it's on that chart...

 

Yes. Look at ALLT4's chart 1 1/2 to 2 thousandths, for a street 350. The reason is, they don't expand much like a forged piston. That is the reason for the noise complaints, above. If they are set up loose, they stay loose.

RACE ON!!!

 

In case anyone is curious as to "how loose is too lose" regarding noise. It is .002 or greater. KB claims .0025 or greater will make noise. This is not true. .002 will make noise.