forged pistons

[gtcwildbill]

I'm building a 347 stroker. trying to decide on forged pistons or not. i think the warm up time for a forged piston may deter me from using them.advantages/disadvantages?

 

[bmc69]

Hypereutectic pistons are all you want to use unless you are going to spray nos or supercharge it. I don't even use forged pistons in some pretty high performance builds any more.

The bore clearance for a hyper piston is as small as gets.

 

[Broncobowsher]

Hyper is generally the best choice. Unless you are building something really wild at which point you should be talking to an engine builder and not us for advise.

Forged can generally withstand abuse a little better. A friend who has done a lot of wild stuff. Built engines that ran the indy 500, flat track motorcycle engines, worked with Gurney back in the 60s. He has forgot more than most engine builders will ever know. We had a discussion on pistons that he was going to use for a salt flat speed record bike. He likes forged for being a little more forgiving, they flex. But with the exact same engine a cast piston will make slightly more power because it transfers cylinder pressure to the crank instead of flexing the piston. Not that means anything on a street engine. But good to know that he things that a good cast piston is generally a good choice.

 

[blubuckaroo]

The only advantage I can see for Forged pistons is that the wrist pins don't need to be pressed in.
The disadvantage is the rattle.

 

[73azbronco]

Hyper as mentioned above, be very careful on proper ring gap and advance on ignition. I think my KB are limited to 32 degrees advance which is more than enough.

 

[matts460]

Never had the forged pistons in my 390 fe rattle ever. But the hyper pistons I had first time I built engine failed. Had one burn hole in top of piston. Ruined cylinder wall too. Hypers are picky about ring clearance and piston to cylinder wall clearance. Got Forged trw pistons aka speedpro, never had problems after that. 18 years motor still good no rattles when cold

 

[Broncobowsher]

The only advantage I can see for Forged pistons is that the wrist pins don't need to be pressed in.
The disadvantage is the rattle.

The last couple engines I built had cast hyper pistons and full floating wrist pins. Stock '88 5.0 HO mustangs had forged TRWs and pressed pins.

Press fit pins has more to do with the rods than the pistons. Although if you do floating pins the pistons better have the retainer grooves

 

[bax]

I run forged pistons.

 

[Broncobowsher]

Bax, you could break an anvil with a rubber mallet. You need all the help you can get.

 

[gtcwildbill]

Thanks for all the feedback. I am using an engine builder and forged is his recommendation. My stroker will be under 400 hp as I plan on keeping my c4.
It seems a little excessive to me. Another friend and also an engine builder suggests that I will always need to let the engine totally warm up before driving.

 

[pcf_mark]

I have forged in my 5.0 in my Bronco I drive regularly and in very cold weather. The pistons are a bit noisy on start up but I can fire it up and drive away when it is 10 degrees out. I drive nice until the engine warms up just like you would any engine you cared about. The piston rattle drops away after 2-3 minutes.

Forged pistons are more forgiving. If you run a good solid tune (ignition and carb settings) any piston will do. Forged are for fault tolerance when things are not so great. If you think you may get in a situation where you get a bad tank of gas or a really hot day and you have decent ignition advance you can get the engine to knock/ping forged give you margin for error. A hypereutectic can crack or pop a ring land.

Most new very high performance engine like Corvette, Viper, CTS-V, ZL1 Camaro and I think GT500 run hypereutectic. BUT they run EFI which can adjust if the gas is poor or the air is hot and you are in the gas or climbing a hill.

It is really a question of fault tolerance. I used forged because they were not much more money and I was considering supercharging. But when I get a sketchy tank of gas in July and hear a little ping when it downshifts I do not fret. If cast I would be adjusting my tune for a rare scenario just to be safe.

 

[broncnaz]

Thanks for all the feedback. I am using an engine builder and forged is his recommendation. My stroker will be under 400 hp as I plan on keeping my c4.
It seems a little excessive to me. Another friend and also an engine builder suggests that I will always need to let the engine totally warm up before driving.

Your friend is correct your engine will last longer if you allow it to warm up some before just taking off. That applies to pretty much any piston that is used although as they said forged kinda requires it. Most people in todays world just jump in and take off that's not real good for a engine.
Doesn't need to be fully warmed up in most cases but at least let it warm up enough so the choke kicks off or it comes off of high idle with EFI.

 

[73azbronco]

Never had the forged pistons in my 390 fe rattle ever. But the hyper pistons I had first time I built engine failed. Had one burn hole in top of piston. Ruined cylinder wall too. Hypers are picky about ring clearance and piston to cylinder wall clearance. Got Forged trw pistons aka speedpro, never had problems after that. 18 years motor still good no rattles when cold

Hole in piston is most likely an ignition advance issue. Hyper does not do pre ignition or over advancing.

Think about this, hyper or eutectic pistons expand at the same rate as the cylinder so the fit can be closer tolerance. Building a stroker, I wanted a consistent tolerance throughout the band of operation. And thats for the increased stroke as well. I'm not going to be advancing the motor above 30 degrees. The only other reason to have forged then, is to use it when pre ignition or detonation is or could happen, and or for use at high rpm above 6000. I'm not doing either, so hyper made the most sense. Bad fuel? well, thats a whole nother issue as I'm not going places known for bad fuel either.

 

[matts460]

After my machine shop guy looked it over it was most likely cylinder wall clearance worn ring land and top of piston over to the side was blown through I dunno was 18 year ago I don't care at this point! Also forged pistons usually weight close to the same so makes for easy balancing my trw's only had one piston need just little taken off when balanced. Balancing engine goes along way to longevity as well.