87 Burb

Getting ready to redo a bottom end. Might see some boost down the road. Looking at forged pistons and wondering if they are difficult to live with.

From what I gather, forged are loose in the bores when cold and expand to fit properly after they've warmed up. Apparently they rattle and you get piston slap when cold.

With forged pistons, do you need to let the engine warm up before you pop it in Drive? How long?

Do the loose pistons at cold startup wear out the bores faster? Is this significant? Are there other longevity issues with forged vs. hyper?

Can you still run a .040 quench or do you need to open this up due to piston rock at cold startup?

What has been your experience with forged pistons?

KrisW

iTrader: (5)

I have never had any of those problems that you described with forged pistons. Never. Not once...

I ran the piston to bore clearance that TRW and Speed Pro told me to. I don't remember back then if that was different than stock specs or not. I just did what they said, and it was fine.

I have had a grenade failure with the hyperutectic pistons. Apparently they don't like to run lean. My partner was in the burnout box and then -BAM- one more 355 on the scrap heap. I'll never run those again, the forged don't cost that much more.

If it's a money issue and you just need a little more for forged, take a pizza job for a month and then buy the forged. Otherwise, new cast flat tops are good.

psy4s

If you are going to run any boost at all, You should use forged. I always use forged, and I have not worn out a bore from it. You make your engine sound like a piece of glass. It is not. A good engine builder will have your engine fine with the piston clearance. If you are running fuel injection, Start it up and drive it off, just like you would any other engine.
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• The engine is a mild 383 (6.27 liter)
• (5.7 liter-350 cu in block, with 4.030 bore and 3.750 in stroke)
• Using a new stand alone TPI harness, without the EGR, or VATS.
• It uses VSS, and 3 wire O2 sensors.
• The Engine has 10-1 compression
• MAHLE forged pistons flat tops SBC-425030F05.
• Eagle 5.7 H-Beam Connecting Rods
• Forged Summit One Piece Rear 383 Crank
• AFR 195 Eliminator cylinder heads part #1038
• 1 5/8 in headers.
• Comp Cams 08-467-8 cam, 280XFI HR13
• Intake Duration 280,
• Exhaust Duration 288
• Intake @ .050 230
• Exhaust @ .050 236
• Valve lift intake .576
• Valve lift exhaust .570
• Lobe Angle 113°
• Hydraulic Roller Lifters
• The intake is a Modified LT1, Front matched to the Twin 58mm for increased flow, and Entrance and Runners Polished.
• Fuel is delivered through 36# Holley injectors
• The throttle body is a BBK twin 58mm

87 Burb

KrisW: Which forged pistons were you using?

Here's why I ask:

Talking to a local engine builder about the SRP 5.7 rod 31cc inverted domes for a Vortec 383 which would put me at 8.5 to 1. He said that even though they have high silicon content and are more dimensionally stable than most forged pieces, you won't be doing any ambulance runs with these. You need to let the engine warm up.

Talking to a tech person at JE about their 6 inch rod 28cc forged inverted domes (8.8 to 1), he says with the SRP or the JE, they are going to make noise when cold.

How big of a problem is this?

GofasterFirebird

iTrader: (3)

I've got SRP forged. I do feel it is always good to let your engine get to operating temp before going WOT buuuut I have never had an issue with noise. You'll be fine. Go forged.

customblackbird

iTrader: (15)

im in the same boat as far as going forged or not. i think forged is a better choice but i also heard that hyp pistons are better for a daily driver.... once u throw boost at it you change that... go forged as i will be doing the same for my 383 that i might boost later in life.

hey psy4s!
wat are u getting with your combo... mine and yours are very close, and im in the process of putting mine together. i have all the parts except the rotating assembly.
im goin wit 383 1piece seal roller block
HSR... ported and portmatched to felpro1206
patriot 195cc heads, ported, port matched to felpro1206, roller cam dual spring upgrade good for .671 lift, polished stainless valves, vitton seals, 5 angle valve job, partly CNC bowl blend.
XFI280 cam
1.6 extruded full roller aluminum rockers
58mm TB
30#SVO ford injectors
grannelli MAF
new true roller timing Cloyes chain, new hydraulic lifters, comp cams extreme energy .100 longer pushrods
Kirbane billet adjustable fuel regulator, walbro255 high pressure pump.

im looking for 480hp mabye 500 if i do alil more to the heads or something. what you pushing out or running in the 1/4???

EvilCartman

iTrader: (1)

I've been running forged pistons from Wiseco for 4 years, 2 of those years the car was my daily driver. Never had an issue of jumping in the car and driving down the road. I don't ever recall hearing piston slap when cold. When I had the heads off the engine last year to bump the compression up, the cylinder walls looked great.

AlkyIROC

My engine has forged pistons but isn't driven on the street. I don't notice any piston slap when I fire it up. During a race day, I fire it up in the morning to build heat in the engine then shut it off and let the heat soak through the entire engine. I don't have the benefit of running the engine for long periods to build a lot of heat.

JE and SRP are both good forged pistons. I use JE because they're lighter than SRP. More for a race application than street use.

KrisW

iTrader: (5)

I'm embarrassed to say that I used the cheapest forgings I could get at the time. 1 set was TRW (back in 93-ish? maybe?) and the last set was speed pro. Both sets had no problems ever. Just do what the piston manufacturer says, not the spec sheet for a stock engine. This may be where your machinist's problems are coming from...

87 Burb

Lots of votes for forged pistons. Sounds reassuring. Other than price, are there no downsides to using forged pistons?

kerplunk318

iTrader: (3)

im running srp forged, they are a little loud when cold but i dont mind, barely noticable with the hood closed, get em

89305formula

iTrader: (5)

i used to get piston slap when it was real cold out with my speed pro forged pistons but since i went from cast heads to aluminum heads i no longer have the noise

Viprklr

iTrader: (5)

I've HEARD that forged will wear the bores out faster. Heard. Hasn't happened to me yet. I've also actually heard piston slap with forged slugs in my buddies 79 Ford somethingorother. I haven't heard any slap in mine though. But it's kinda hard to hear much of anything over my exhaust.

Sonix

iTrader: (1)

Forged might be heavier, depends on the piston, but something to look at.
Typically the downside is the price. If you don't need 'em, don't waste the cash on them. I dare say 80% of the people who buy forged pistons don't really need them. I'm talking about the guys with a 350-400HP SBC NA, running forged pistons because a buddy told them to. Cast would be fine there, or hyper.
To me, forged is only needed for LARGE amounts of nitrous, and/or a big blower or maybe a high revving turbo motor.
TRW/Speedpro ones are cheap enough that if you're confident you'll have boost in the (near?) future, give'r.

psy4s

This should be exactly what you are building. It even has the heads you are using. I am sending you this because it is what I used as the pattern for mine. Mine should flow a little better since I am using AFR heads, but I do not know that for sure. To pick my cam, I actually called Comp Cams and gave them all the information for my car. The cam I am using, and injectop size was per their instructions. I wont have access to a Dyno or the race track till spring. Then I will post my actual numbers.
Use the link at the bottom, It will take you to the web site. It is a pretty good site.



http://www.golenengineservice.com/html/fi_facts.html

customblackbird

iTrader: (15)

thanks psy4s, i guess i should be expecting around that except my comp ratio will be lower so i'll prob loose alil hp. but i should make more tq bc of the HSR over the miniram and LT1.

thats exeactly what i heard about forged pistons and why they are not better than hyper bc they where the bores out faster and seem to heat and cool (expand and shrink) slower than hypers. which is not a good thing for daily drivers. still since many havent had problems i guess they would be ok. if u set them correctly with the rings etc.

Travis&camaro

HI, I have a set of forged wisco pistions in my snowmobile and I burned the top right off in to the exhaust manifold b/c it was running lean... SO I baught a set of good HYper ones for my 350 I figure I saved around $300 witch is a bit of money but will find out if I should of went better when I start running it hard.