I'm building a 355 TPI motor and was wondering how much abuse the hyperutectic pistons can take. I know many people who put mild superchargers on stock motors. I heard it's OK to run boost as long as I keep the motor from detonating. I'm running a set of speedpro pistons with a 9.8:1 CR. I'll be using aluminum 'Vette heads. Just wanted a small nitrous shot (for 'insurance'...). I know hyperutectic is a hard material, but hard doesn't mean strong...

 

hard...in this case, means brittle. In all honesty, Hyp's are excellent for a N/A engine and are great as far as wear and tolerance goes. BUT, for blower and/or nitrous applications THEY ARE A WORSE CHOICE THAN CAST. You're actually safer going non-N/A w/ cast than you are w/ the Hyp's

 

They are basicaly tuff but indeed are more brittle & they don't take well to detonation at all. They also retain more heat than common cast or forged pistons.
if you never detonate you will be ok. If you do it will be finished pretty quick. If you do use them it is a good idea (especially on a forced induction or nitrous app) to get their tops ceramic coated to keep them cooler.
If you are going forced and sprayed you would be safer to go with forged.

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Tracy /AKA IROCKZ4me
'86 IROC-Z Camaro
"Cogito ergo zoom"

• 355 cid
• AFR heads
• Arizona Speed & Marine hydraulic roller cam w/ AFR hydra-rev kit
• modified SLP runners
• TRW forged pistons/ceramic coated
• fully balanced
• Edelbrock headers/ceramic coated
• SLP cat-back
• Paxton supercharger
• Nitrous Express nitrous oxide

My IROC-Z
EFI Performance Club on Yahoo
Club IROC-Z

 

I fully agree with both posts above.

 

I guess you're right, just confirming my suspicion...I heard today about the new Viper, and wanted to do something about it, but I guess I have to decide if I want to use a power adder. I should take my own advice...don't cut corners! I, too, agree with both posts. I guess I have some decision-making to do; ODB, I decided to use the #416 heads on a LTR 350 I'm using as a replacement, N/A (future)...The 355 I'm building now will be a new street motor for my existing Camaro. Eager to see how they work...

 

with 416's you have plenty of room to unshroud valves without killing the compression. Open the plug side of the chamber up to match the bore of your block. After .500 lift the flow tends to want to go that way.

I use cheapo TRW's for testing purposes because they are disposable and not so brittle. I've never had an application where I'd ever use hyper-you-cracked-it pistons. I'd even go for stock cast before those.
For durability talk to J.E., SRP, or Ross etc.. not cheap but you'll sleep better at night.

 

For the most part all factory pistons are hyperutectic. You can run 75-100 shot of NOS without trouble. Just make sure to have enough fuel volume/pressure when you spray it. Also watch how much timing you run when you intend to spray it. Gap the sparkplugs a little smaller, run a good ignition. You also may want to run an in car adjustable timing control. For extra insurance, buy the NOS octane additive.

[This message has been edited by Cobra R (edited March 12, 2001).]