zraffz

Hey I am building a 355 (actually an LT1 motor but I don't see what it matters). It's time to order pistons and I don't know what is best to use.
Motor is a 355 with Trick Flow 185cc (21 degree) heads, 234/238 .612"/.612" 111 lsa custom ground cam, 5.7"/3.48" stroke with Callies Compstar h-beam rods. Motor should be capable of around 450-475 crank horses.

On top of this set up I want to run the NX express direct port 250 or 300 shot of nitrous. (I would like to keep the compression in an area that I can still run pump fuel when I am not spraying the motor). Which pistons are best for my application?

305sbc

iTrader: (3)

Call SRP. They make a great forged piston with the top ring land moved down away from the crown to keep the heat away for heavy nitrous use.
They might also offer thermal coating on top.
If you're not into coatings, then you could perform a polishing to the crown area to get rid of any sharp edges and reduce the surface area.
Ask for two valve-reliefs only, and floating pins of course.
Don't go for the thin rings on a heavy nitrous engine.

I believe Ross and Mahle also make excellent forged pistons, but I don't have experience with those, so I can't really say.

vetteoz

iTrader: (13)

So you want a quality ( 2618 ) forged piston
http://www.strokerkits.com/index.php...info&Itemid=80
http://forums.nasioc.com/forums/showthread.php?t=907570

Need to use a CR calculator to work out F/T or dish size required to get your desired CR

zraffz

I contacted Diamond to see what they say. I gave them every detail on the build.

I'll contact SRP as well.

Mahle is out of the question because I am not reading anything good about them under heavy nitrous applications.

zraffz

Just because the piston is 2618 metal doesn't necessarily mean it will withstand 800-900 horsepower though? I originally looked at Manley Platinums which are 2618 but I didn't know how they would do at 6,800ish RPM with a big shot of nitrous. Am I being over concerned about this?

They seem a bit cheap to be good. Not to mention they are meant for a 23* head (although on a 21* head they would be increasing piston to valve clearance?).
http://www.summitracing.com/parts/MAN-590530-8/

Orr89RocZ

iTrader: (20)

I've used the SRP forged flat tops on my 383 to 7K rpm with 150 shots but nothing like you are thinking about. Huge difference in a 150 shot vs 250-300.

JE has good pistons too but some don't like them. Have them in my turbo motor. Or go with whatever diamond recommends. They both make a strong nitrous piston but they are dome versions. Diamond catalog has some for 3.48" strokes while JE does not. Domes give 12.5-13.0 to 1 comp Alittle high for a street/strip car. LT1's can get away with 12 to 1 compression with a big cam but more than that, i'm not sure how well that will do on 93 oct on the street.

Could go custom flat top with the top ring lands down abit farther than their shelf flat top pistons. Especially with 21 deg heads... Now thats not too far off 23 deg so it should still clear just fine if the valve pocket is large enough. May need to look into that.

Probe pistons makes a nice flat top with the top ring land down .240". That leaves a good bit of piston thickness to take the nitrous abuse.

Ross pistons has a heavy duty flat top that says up to 250hp nitrous shots.

I'm not really sure what else is available off the top of my head but I'd call an experienced engine builder who's done nitrous motors. I've only played with small shots and my friends play with sub 200 shots.

zraffz

How would something like the Manley Platinum series pistons hold up behind a 250-300 shot?
(Made of 2618 material, .185" deck, 1/16, 1/16, 3/16 rings)
http://www.summitracing.com/parts/MAN-590530-8/

Or the Probe SRS pistons (Made of 2618 material, .240" deck, 1/16, 1/16, 3/16 rings)
http://www.summitracing.com/parts/PBP-12334-030/

Or should I stick with a custom piston? Suggestions on pistons are more than welcome. Looking to keep compression between 11.7-12.2:1.

305sbc

iTrader: (3)

I would go with the thicker deck/crown myself.
Big N2O shots create intense heat for relatively short periods of time.
The more forged aluminum there, the better, so don't go light-weight on the pistons.
Forged does very well handling the heat as long as you don't detonate severely or have a sparkplug failure with the electrode falling onto the piston top.

The plugs are VERY important with large N2O shots. The plugs are the root cause of most piston failures with N2O. The plug tip is the hottest thing in the chamber and most preignition originates there.

The thicker the piston deck/crown, the more survival time this buys you when things go wrong.

Also FYI, a large N2O shot will almost always lower your optimum shift RPM by at least 500 RPM. You can still rev just as high or higher on the N2O, but you will run quicker by short shifting.

zraffz

Alright thanks.
I'm trying to keep it a street/strip (more like come out to cruise once in a blue moon and mainly keep the car for Friday night at the track). Thanks for the advice. Would love to hear some more.

Orr89RocZ

iTrader: (20)

Probe with .240" deck sounds like the best alternative now. It will handle those shots as long as the tune is good. Got to get heat out of the chamber like said. To quote the great head guru Darin Morgan

SO control the heat and the pistons have a chance at living.

305sbc

iTrader: (3)

http://s702.photobucket.com/albums/w...Spark%20Plugs/

That's a link to my photobucket albums concerning spark plugs.
It's everything you never knew you always wanted to know about plugs, and it is very relevant to using large N2O shots.
You should find some useful info reading the album and photo descriptions.
It's not really everything, but it's a good start.
The album of heat testing info should give you a good visual for what happens in the chamber with heavy N2O use.