i know it isn't much but how much can hyperutectic pistons handle when it comes to nos in a sbc 355

I can tell you that we had a 1989 IROC that we sprayed 150 shot on for about 3 1/2 years of racing, ( approx. 80 bottles) with no damage to the pistons. We never tryed any more than that, so I really can't entirely answer your question. I do know that when a hyperutectic piston reaches its failure point it disentigrates into very small pieces all at once unlike a cast or forged piston that will crack or break into chunks.

You might try the below link some of the tech articles might be helpful...

http://www.kb-silvolite.com/index2.php

Greg

thanks for the help guys so you say you had hyperutectic pistons for three years and never had a problem somebody told me all i had to do was increase the top ring gap to .033 does this sound about right to you guys like i said i know my way around a small block i just never used nos before

The 89 car ran a nos wet plate kit and we used a second fuel pump that came in when the nitrous was activated. The short block was stock, (never even had it out of the car). As long as you run them a little fat on the fuel tune and keep your timing conservative the hyperutectics will live

do any of you think that a 150nitrous sys. that basicly is just for looks ( meaning used only once in a while) in a 355cid , 4340 fordged crank /recond.stock rods, S.P. Hyper.pistons Clevit -H bearings is worth the cost and since most here are O.K. with Nitrous and hyper pistons.
Engine is built ,looking hard at NOS?

thanks y'all

You do want a slightly larger ring gap withforced air inductionand or nitrous. It will create more blowby, but when everything is superheated, it will expand and seal better.

ORIGINAL: hotrodguy1986

thanks for the help guys so you say you had hyperutectic pistons for three years and never had a problem somebody told me all i had to do was increase the top ring gap to .033 does this sound about right to you guys like i said i know my way around a small block i just never used nos before

bigger ring gap? OK if the ring gap the std. .30 over you get with a new set of pistons??
and we only use the lower setting, on the nitous kit 75,125 ,150, 200 hp
my real goal is to build this Camaro for wife, daughter,granddaughter
I know this sounds a little silly, but thats the deal. want a good running Camaro that
can be pumped up when they want show off a little.other then that going over the whole car ground up am not looking huge horsepower out of the 355 -fordged crank,recond. steel rods , S.P. Hyperu. pistons ClevitH bearings,steel roller rockers 1.52.1,Crane 4340 push
rods, 268h Comp.Cam -hi-po lifters,, gear drive time, two timing cover,Milling Z28 oilpump, oil panis a kick out baffels and trap door 71/2"Qt.,GM windage tray,block is aline honed deckedand race prepped. using chevy 487x 2.02 heads with guides, screw in studs& polylocks . Air gap intake & Holly S/A 670 carb. brass freeze plugs and pipe tap oil gallery plugs NOW with all thatcan I use the nitrous 125 HP set up
thanks ,reallyoldguy

If the pistons are 30 over you need rings that are also 30 over. The ring gap should always be checked before assembly as the last thing you need is for the rings to expand enough to bind and damage the pistons and cylider wall. The nitrous will generate a lot more heat and pressure inside the cylinder, and all the extra heat and pressure hits the top ring. As Norman mentioned, the top ring gap should be set around 0.030" bigger than normal to allow for the extra expansion. The blowby will not be that bad if the rings are installed and the gaps staggered properly.

z28pete, the sealed power pistons came as a set pistoms are the coated ones and the ring set thatcame in thebox, these pistons are .30 over as are the rings -do we now pull the pistons and file the rings to a larger gap ?- guys understand i'm new to nitrous. I worked as a GM mach. in dealerships for years. and raced back in the 60s-70's but out of cars for many years.
I do know my way around a wrench on them old cars. and this78 Camaro has been in the barn since 1983. Idid most ofengine building onour race team . but sure as monkeys live
trees. engine building has gone right by doing 90mph.
so can understand what you guys are saying -just a little slow in the old brain pan???
need all the HELP I can get
Thanks, reallyoldguy

You should always check the ring gap even if the rings were supplied with the pistons. The gap should be checked with the rings in the cylinder that they are going in. If you plan to use heavy doses or nitrous or heavy boost, the top ring gap needs to be larger because they will expand more due to the extra heat.

z28 pete, did that, rings cked. outed . what is the best guess on the finile gap. all cyls. run + or - .02 .
would .35 ring gap do it
ROG

I disagree with the theory of the top gap being bigger!!! I set my rings at .028 top an .030 bottom. You are right about the top getting heat an expanding more but the second ring needs to be larger so that any cylinder pressure tht gets past the top won't get trapped between them, it will lift the top ring land an ruin the piston an possibly hit the head, been there an done that.Evan if ya just jet it too rich, unburned fuel can get past the top ring an build pressure between them, ya don't want that, let it go past the 2nd an into the crankcase. Ya gotta run a good "crankcase evacuation system " or a vacume pump. I run a simple Moroso Evac kit from my headers to my valve covers an they work great on my small block an my BBC, 50.00 bucks is all they cost an they pull lots of vacume. Now for the kicker, My motors are for heavy nitrous use, you can get by with a slightlytighter ring gap on a street motor that will not see much nitrous, under 180hp.Just make sure the second ring is 1-2 thousands bigger than the top.

da z28 thanks all the info. I get is good. i'm sorting all this out. hoping to to find the right combo.
I idea is for a go fast road machine. back in the day 60's70's we were building iron just for the strip or light to light. now it's more about Big Horse Power road killers. And I kind of like that .

I know what ya mean, I started inthe early 70s street racing too. Things have changed alot but if your willing to learn you'll still pull some wins against these youngins. I forgot to mention that hyperutectic pistons are stronger than cast but much more prone to shattering or breaking apart under detonation.Retard timing about 1.5-2 degrees for every 50hp of nitrous ya spray.Watch your timing an tune up-read plugs for detonation, lots of guys spray em hard an they seem to last but a forged is better for nitrous.

da Z28--I looked into the hyper. pistons only after I started thinking about all the exter work involved in fordged pistons as i see read it the these hyper. piston do expand nearly as much as fordged. so that was one reason for my picking the hyper.s as for ring gapping back in the day We all had sore fingers fileing rings -on ring gapping machines for sale back then?. the more info . I got on the hypers , I like what I saw .since I'l not building an all out streetracer Iway of thinking is thehypers. were the best bet??? it's only now after looking into nitrous that any questins started to pop up in my brain pan??? keep the info. coming been a long time since I was a hard core night rided:D

I think your absolutly right, detonation should be watched for real close with hyperutectics, it should with any piston. As long as your careful with timing an a safe octane fuel they should work fine. A friend of mine sprayed 250 to his lots of times, an I had a 350 targetmaster(260hp) with stock cast pistons an hit it with a375hp shot.all summer long. I still have the shortblock on a engine stand, it is in fine shape an only needs re-ringed an bearings from a summer of racing, never hurt it. If ya just spray it now an then it'll last a long time.