[d.b. cooper]

1) If i were to switch from basic cast pistons(non-hypereutectic) to forged, would i need to do anything to the cylinder walls (assuming the walls are ok)? Can i just "pop" them in there, so to speak?

2) i want to eventually return the engine to the street (it's track-only for now), so is there a forged piston that will "act" like a cast piston?

a) OR would a hypereutectic piston work and be a good compromise if i want to run no more than 7-8lbs of boost.
b) Would the stock cast pistons work at 7-8 lbs, IF i'm very careful with the tune? i'm even willing to run E85 as it's track only for now.

Engine is:
---262 cid 90 degree chevy v-6, 2-bolt main, stock block
--- 9.3 to 1 compression (although, i assume with a piston change, compression could change as well)
---- cast aluminum pistons
---- target is 300hp/350tq hopefully at lower rpm vs. higher rpm as we can't spin it faster than 5600 with the stock bottom end.
---- Don't want to run anymore than 8lbs of boost, unless with forged pistons and even then no more than 12-ish because i don't want to push it with the stock bottom end. Car is light enough to run 11's with 300hp.

 

[d.b. cooper]

P.S.
The idea is to keep the engine as "stock" as possible as the car is only about 1940 lbs. with engine and trans (TH-350) installed.

 

['48 Austin]

There will be all kinds of opinions on this question. I would call your piston manufacturer and get their advice. Piston thermal expansion will be different for different piston designs and materials. Plus you're talking boosted. Make some phone calls.

 

[Moosecountry]

piston to wall needs to be around 6-7 thou for a race engine. Ring gap needs to be opened for boost. Need to rebalance engine so while you are in there, recheck all your bearing clearances. May as well refresh the engine,,,

 

[johnsongrass1]

Sorta......the best way is to bore/hone and replace the rings. Your already all the way in there so it makes the most sense.

Try to find a piston with the same weights as the original ones.
Another consideration is if the pistons are floated or pressed pin.

Answers below

Do you know what your looking at now? Do you have a piston PN for either?

1) If i were to switch from basic cast pistons(non-hypereutectic) to forged, would i need to do anything to the cylinder walls (assuming the walls are ok)? Can i just "pop" them in there, so to speak?
There's no difference in bores except for the hone for the rings may be different depending on the ring you want to use.


2) i want to eventually return the engine to the street (it's track-only for now), so is there a forged piston that will "act" like a cast piston?
Not really. Forged will grow more with heat.

a) OR would a hypereutectic piston work and be a good compromise if i want to run no more than 7-8lbs of boost.
b) Would the stock cast pistons work at 7-8 lbs, IF i'm very careful with the tune? i'm even willing to run E85 as it's track only for now.
Hypers at 8psi willl be fine if your very conservitive with the boost tunes. IE, don't put too much heat in them. Hypers are likely to break apart and let go of the small rod end rather than just melt a hole in the crown.


Engine is:
---262 cid 90 degree chevy v-6, 2-bolt main, stock block
--- 9.3 to 1 compression (although, i assume with a piston change, compression could change as well)
---- cast aluminum pistons
---- target is 300hp/350tq hopefully at lower rpm vs. higher rpm as we can't spin it faster than 5600 with the stock bottom end.
---- Don't want to run anymore than 8lbs of boost, unless with forged pistons and even then no more than 12-ish because i don't want to push it with the stock bottom end. Car is light enough to run 11's with 300hp.

 

[Chad & Karen]

Forged pistons "grow" more than cast pistons. So the piston to wall clearance needs to be correct for them.
You are running cast now, chances are good, you will be able to have the bores honed to the size needed to get the larger piston to wall clearance. This is assuming the bores are in good shape and have no wear.
Ring gap, for a boosted engine is different than a n/a.
you didn't say, but I will assume it has stock rods in it. You should at least, install arp rod bolts, and have the big end resized. Budget is always something that has to be part of things like this.
I don't think you are going to get away with just buying forged pistons and off you go.
A hone to size to new pistons, new rod bolts ,and balance. at least. As it will be hard to get forged pistons that are the same weight as the cast you are running now.

A light car, and if you play it safe with the tune, cast can live. PROBLEM is with boost it is too easy to turn up the wick, and get greedy . and then

 

[BogiesAnnex1]

Forged pistons from high silicon 4032 alloy will have thermal expansion properties similar to your hyper castings. 2618 alloy will be more dimensionally reactive to temperature change and as a result require more clearance be honed into the walls to prevent scoring from the greater expansion of this alloy.

Way out on the top end it is generally conceded that 2618 is stronger than 4032 but 4032 is far stronger than your cast hypereutectic pistons which in supercharged and NOx situations have a bad habit of just disintegrating which usually puts the pin through the cylinder wall.

For ring breakin I think even with 4032 pistons it would be good to just freshen the cross hatch a little bit.

Bogie

 

[curtis73]

I agree with Bogie on the 4032, (although I had forgotten the alloy numbers) but also I think a good hypereutectic would be fine at your boost levels as long as you make sure detonation isn't happening.

Think if it as a sliding scale of malleability versus rigidity. Cast pistons are very rigid, but their hardness mean that they break like glass when they reach their limits. Forged pistons will be more compliant because they will deform/change at the limit. Still bad if you take it too far, but at least not catastrophic. (as in a nice window in the side of your block).

Hyp pistons kinda bridged the gap. 4032 kinda slides in between hyp and 2618.

I'll be running stock hyp pistons in an LS and initially it will be making about 550 hp. I won't even think about problems. Once I get more access to E85 round these parts, it will get a different cam and a modest turbo with about 6-8 psi shooting for 750hp. I won't lose an ounce of sleep over it... but I will be monitoring the knock sensors.

 

[Chad & Karen]

Problem with hypers, like Bogie stated, they shatter and when they do, they make a mess. A costly mess.

 

[64nailhead]

You can use cast pistons if your tuning skills are good. But one mistake or snafu and you’ll turn a piston into dust and most likely your motor into a boat anchor.

Assuming your tuning ability is good, then a snafu is something like a plugged fuel filter, an overlooked exhaust or intake leak, a weak cooling system component.

I strongly recommend a 4032 piston for street use and a 2618 for something over 14psi. The 2618 requires a lot more piston to wall, which sucks if you intend to drive this in the winter. Ask why lol.