Forged internals/blocks

[Gress]

Hey, I keep seeing loads of people buy a second hand car on the cheap (Old Subarus, Civics etc) and putting in a huge amount of money on internals, far more than the car is worth. Forged pistons, camshaft, crank etc. What's the point in that?
I can understand wanting a much stronger conn rod to allow for higher RPM as well as wrist pins,bearings and valves but getting a stronger piston and crankshaft seems pretty useless. The weight saving of only about 15% by switching from iron to aluminum for pistons is understandable but still a bit silly considering the price in comparison to the power gain you could get from just swapping engines or increasing boost pressure.
If your timing belt slips, run the motor without enough fuel/oil or anything that would generally blow a motor, it isn't going to matter what your piston's made out of, it's dead either way.

Can someone explain the reasoning behind forged parts please, I'm looking to buy a 2000-2004 Subaru soon and seeing people drop £4500 on forged internals when the car can be bought for £2200 is really confusing me. I must be missing something right?

[Master Bean]

MOAR power.

[DickP]

Stronger internal parts mean you can increase the power by fuelling / boost etc. without blowing the engine apart.

[Boosted LS1]

Stock pistons and con rod bolts are items likely to get destroyed so it's worth upgrading those. That said, factory fit mahle etc are pretty bullet proof. Stock cranks even cast ones are usually strong and not an issue. As for most stock rods, they're nearly all forged these days.

[Hol]

Some pistons and rods are the limiting factor in realising the full tuning potential of a car.

It’s not the case on every car, or every manufacturer year for the same car (Impreza years differ) and in some cases the limitation Is the turbo or gearbox instead.

A lot of cars running forged engines were also bought cheaply with blown engines where the previous owner was (let’s be kind) overly ambitious, on the tuning limits of the engine.

The difference in Rebuilding an engine with standard or forged parts is the parts cost. The labour is basically the same.

If it’s a keeper, or you want a safer power margins forge it. If it’s a daily and the standard pistons aren’t made of chocolate, then don’t.



(Some people do like the pub bragging rights though).

[thebraketester]

I am guessing the likes of aftermarket forged pistons are much lighter (and of course stronger) than stock items.

More lighter... more better.

It’s fairly easy to get 550+bhp out of a VAG TFSI. 2.0T. It’s easy to see the apeal.

Edited by thebraketester on Thursday 14th June 18:40

[GreenV8S]

Gress said:

putting in a huge amount of money on internals, far more than the car is worth. Forged pistons, camshaft, crank etc. What's the point in that?

To support a massive power increase. If you don't want that, you don't need to do anything to the engine internals.

[Coatesy351]

Forged pistons can withstand more heat, higher rpm's, higher boost because of how the alloy grains as the piston is created. Cast piston tend to shatter or melt when pushed beyond their capabilities.

[Boosted LS1]

Coatesy351 said:

Forged pistons can withstand more heat, higher rpm's, higher boost because of how the alloy grains as the piston is created. Cast piston tend to shatter or melt when pushed beyond their capabilities.

This can be true for crap engines but some manufacturers make super strong pistons that have been scuff tested to oblivion. No matter what you throw at them they'll never break or seize unless you're crazy.

I'm a big believer that some manufacturers over engineered the product. Other's, especially modern stuff just built to a 'minimum cost' situation. Those will certainly break.

[stevieturbo]

Gress said:

Hey, I keep seeing loads of people buy a second hand car on the cheap (Old Subarus, Civics etc) and putting in a huge amount of money on internals, far more than the car is worth. Forged pistons, camshaft, crank etc. What's the point in that?
I can understand wanting a much stronger conn rod to allow for higher RPM as well as wrist pins,bearings and valves but getting a stronger piston and crankshaft seems pretty useless. The weight saving of only about 15% by switching from iron to aluminum for pistons is understandable but still a bit silly considering the price in comparison to the power gain you could get from just swapping engines or increasing boost pressure.
If your timing belt slips, run the motor without enough fuel/oil or anything that would generally blow a motor, it isn't going to matter what your piston's made out of, it's dead either way.

Can someone explain the reasoning behind forged parts please, I'm looking to buy a 2000-2004 Subaru soon and seeing people drop £4500 on forged internals when the car can be bought for £2200 is really confusing me. I must be missing something right?

The explanation is idiots not knowing what they're talking about...garages filling them full of crap, and just general lack of knowledge everywhere.

Shown as early as your second sentence.....as you can be sure none of those cars have had their owners fit a "forged camshaft"

And in the case of a Subaru...the OEM crank is forged anyway so anyone using that term as some sort of upgrade....again, either mislead or just silly. Or because it sounds good down the pub.

And no, a stronger conrod is not just to allow higher rpm's....partly because it takes other factors to allow higher rpm's although at some point rod strength may be a factor in surviving higher rpm's...not not actually getting there.
But in the case of Subarus, certainly classic cars had very weak rods and they could fail at 350-400hp.

01+ cars fair better, but they're still not superb.

And often people change cranks and rods in a Subaru, because they have a habit of stting big ends, which necessitates the replacement of some of those parts anyway. So some people would likely tell you they've a new forged bottom end...when in reality they probably just got their engine fixed. Again...in part it can be naivety of it all...or garage misleading etc etc etc

And Subarus are renowned for having weak pistons ( except some STI models ) so it's a no brainer that if you're in the engine it can make sense to upgrade.

As for your comment about iron to aluminium pistons.....TBH I've only just noticed it. If I'd seen it earlier I wouldnt even have bothered trying to explain the rest.

Iron pistons....WTF. Have a few more drinks.

[Boosted LS1]

^ Maybe he's got confused with pistons that have expansion struts? More or info about iron pistons from the OP might help.

Crikey, if you google 'iron pistons' one answer comes up 'forged iron pistons' for forged alloy pistons.. Worrying, no wonder people get confused, doh.

Look at this! Iron pistons. Maybe the OP's friends are using these.

http://archive.commercialmotor.com/article/11th-au...

Edited by Boosted LS1 on Friday 15th June 08:40

[stevieturbo]

And aside from that, 2000-2004 covers a hell of a wide range of Subaru models and any car at £2200 would be largely scrap and high risk.

[stevieturbo]

Boosted LS1 said:

^ Maybe he's got confused with pistons that have expansion struts? More or info about iron pistons from the OP might help.

Crikey, if you google 'iron pistons' one answer comes up 'forged iron pistons' for forged alloy pistons.. Worrying, no wonder people get confused, doh.

Look at this! Iron pistons. Maybe the OP's friends are using these.

http://archive.commercialmotor.com/article/11th-au...

Edited by Boosted LS1 on Friday 15th June 08:40

But all those aspects point to the same thing. Lack of knowledge/understanding, then making claims as to what parts may be in there either before or after any work. Most claims are false or misleading....at least as far as the person stating them is unaware.

[stevesingo]

Ferrari is reportedly trying to implement steel pistons in to their F1 engines.

[227bhp]

stevesingo said:

Ferrari is reportedly trying to implement steel pistons in to their F1 engines.

For discussions sake, pros, cons and why not or never been done before?

1. turnthreadintosomethinginteresting

[stevieturbo]

Steel slightly different than iron though.

I guess that with F1 now, the weak link in the engine is becoming the pistons ? In terms of withstanding temperatures and cylinder pressures with boost/fuel/engine size limitations etc

[chuntington101]

I'm sure I read somewhere that some WW2 ears aero engines ran steel pistons with ally tops attached to them. Could be wrong though.

Steel would be stronger than ally. Maybe they can make them as light with less material / material in the right location?

[227bhp]

Less thermal expansion so tighter clearances, can handle higher temps without melting. Mind you the alu head would melt instead. I wonder if you could run really high CR with them and perhaps some ceramic coating to the combustion chamber, maybe that is the direction they're going in.

[Boosted LS1]

stevieturbo said:

Boosted LS1 said:

^ Maybe he's got confused with pistons that have expansion struts? More or info about iron pistons from the OP might help.

Crikey, if you google 'iron pistons' one answer comes up 'forged iron pistons' for forged alloy pistons.. Worrying, no wonder people get confused, doh.

Look at this! Iron pistons. Maybe the OP's friends are using these.

http://archive.commercialmotor.com/article/11th-au...

Edited by Boosted LS1 on Friday 15th June 08:40

But all those aspects point to the same thing. Lack of knowledge/understanding, then making claims as to what parts may be in there either before or after any work. Most claims are false or misleading....at least as far as the person stating them is unaware.

I completely agree with you. Interestingly I have a Merc 119 engine here. The tech spec mentions iron coated alloy pistons. They look pretty normal to me but I'll look into it some more.