Forged Piston Size question

[turbo84voyager]

Is there a reason why it appears most people who go with forged pistons tend to bore the cylinders out? Reason I am asking is all but one of the engines I have built over the years never needed to be bored out just a hone and were in spec according to my machinist. Yet when I bought my set of forged pistons a few years ago I was told by the supplier they almost never sell std size pistons. Am I missing something here? I am going to need to buy a set of forged pistons for my SRT4 engine soon and I am guessing ( didnt go to the machine shop yet) it will not have to be bored out and just need a hone to clean up the cylinders.


Thanks,

Justin

[turbovanman²]

The reason we go oversized is 9 times out of 10, the bore isn't perfect or its damaged. If your bores spec out and you have the proper clearance with the forged, then get a STD size.

[135sohc]

I think alot of the sizing discrepancy between different brands of forged pistons has to do with chrysler having 5-6 different 'standard' bore sizes. How do you define anything if there is no consistency from the beginning ?

Somewhere I read it on here that one of the piston companies who makes slugs for our engines sizes their 'standard' size at the larger end of chryslers A-E ? scale. Like a letter F or G if they existed. so not quite a true .020 over but not 'standard' either.

[turbovanman²]

I think alot of the sizing discrepancy between different brands of forged pistons has to do with chrysler having 5-6 different 'standard' bore sizes. How do you define anything if there is no consistency from the beginning ?
.

That is also a good point, and this happens with alot of OE's, but maybe not so much anymore.

[trannybuster]

Is there a reason why it appears most people who go with forged pistons tend to bore the cylinders out? Reason I am asking is all but one of the engines I have built over the years never needed to be bored out just a hone and were in spec according to my machinist. Yet when I bought my set of forged pistons a few years ago I was told by the supplier they almost never sell std size pistons. Am I missing something here? I am going to need to buy a set of forged pistons for my SRT4 engine soon and I am guessing ( didnt go to the machine shop yet) it will not have to be bored out and just need a hone to clean up the cylinders.


Thanks,

Justin

I sure wouldnt spend that kind of cash on pistons and NOT have it bored or honed...IMO

[22mopar]

I have never seen perfect cylinderwalls on any used engine. Even my race motors show wear near the top after just one season.

your machinist needes to measure bore size ¼" below the deck surface. You'll pretty much always find that's the point of the most wear.

[bfarroo]

Forged pistons also tend to require a bit more clearance than cast since they expand more, this could allow cleaning up of the cylinders without needing a true overbore.

[Directconnection]

I have never seen perfect cylinderwalls on any used engine. Even my race motors show wear near the top after just one season.

your machinist needes to measure bore size ¼" below the deck surface. You'll pretty much always find that's the point of the most wear.

Correct, and same thing I see at our shop. Using the CK-10 (rigid hone setup) you'll see the voids from what the rings cause at TDC. Typically, just a few tenths of a thousandths, but it makes a shadow.

Reason why people go oversized is mostly from what Simon said, and also.... most pistons have the bore/clearance size built into the piston. For example: a +.020 cast piston might measure 3.4635" and a forged Venolia could measure 3.4610" to get you that 3.4650" bore. I wish a std. bore forged would be 3.4450 or a couple thousandths more.... then that would work (except for the ring gaps of a std ring)

[22mopar]

Forged pistons also tend to require a bit more clearance than cast since they expand more, this could allow cleaning up of the cylinders without needing a true overbore.

This isn't a true statement. forged pistons come smaller than cast pistons to fit the 'standard' bore size (or over bore size).

[trannybuster]

^^Whats not true about it? A forge piston DOES expand more than a cast piston. I have never seen std forged pistons that would fit straight into a std bore, that makes NO SENSE. Now you could have (4) pistons custom made for each hole, but then you might just as well bore/hone it...??

[Directconnection]

^^Whats not true about it? A forge piston DOES expand more than a cast piston. I have never seen std forged pistons that would fit straight into a std bore, that makes NO SENSE. Now you could have (4) pistons custom made for each hole, but then you might just as well bore/hone it...??

Read my post I made before his....

But I'll re-itterate: Pistons aren't made to a size... but to a *BORE* size. 3.4450 is std bore, so a cast piston will measure 3.4440 while a forged piston will measure 3.4420. As they say at my shop: "the clearance is built into the piston"

[Vigo]

My opinion is that the reason most forged pistons sold are oversize is that most of the people buying them dont know jack ----. Seriously, ALL OVER THE INTERNET there are people telling you cant make power on stock pistons and you need a 'built' motor, they cant explain what fails and why, and they want you to replace things that never break in the first place. So all the people wanting to make power think 'ahh a thousand people on the forum cant be wrong' and start talking to a machine shop that doesnt want to build an engine without boring it because why say no to easy money if the guy thinks he has to bore it anyway?

So basically my theory is people are ignorant.

[trannybuster]

Read my post I made before his....

But I'll re-itterate: Pistons aren't made to a size... but to a *BORE* size. 3.4450 is std bore, so a cast piston will measure 3.4440 while a forged piston will measure 3.4420. As they say at my shop: "the clearance is built into the piston"

I dont disagree..the piston dictates the bore and clearence. My point is your going to be hard pressed to find a used engine you can throw a set of new pistons and expect spot on clearence and straight bores, it aint gonna happen, so therefore your not going to buy a set of forged piston that go right in and your going to bore it/hone(as you stated also). Ive found that 90% of the time, if you buy std size forged for our engines you can simply hone.
Vigo, I ran 18psi on hyper pistons for quite some time! But as well know preignition or detonation at high psi and your done! You aint kiddin, they drool once you they smell the green of your money and tell you whatever you want to hear. He must cringe when he see me, because I know when I need just a hone job, and I tell him what I want or dont want AND I always dbl check their work...

[22mopar]

Read my post I made before his....

But I'll re-itterate: Pistons aren't made to a size... but to a *BORE* size. 3.4450 is std bore, so a cast piston will measure 3.4440 while a forged piston will measure 3.4420. As they say at my shop: "the clearance is built into the piston"

Yep that's exactly as I stated too. but apparently everyone else knows more that us that build engines for a living.

---------- Post added at 10:08 PM ---------- Previous post was at 10:03 PM ----------

I dont disagree..the piston dictates the bore and clearence. My point is your going to be hard pressed to find a used engine you can throw a set of new pistons and expect spot on clearence and straight bores, it aint gonna happen, so therefore your not going to buy a set of forged piston that go right in and your going to bore it/hone(as you stated also). Ive found that 90% of the time, if you buy std size forged for our engines you can simply hone.
Vigo, I ran 18psi on hyper pistons for quite some time! But as well know preignition or detonation at high psi and your done! You aint kiddin, they drool once you they smell the green of your money and tell you whatever you want to hear. He must cringe when he see me, because I know when I need just a hone job, and I tell him what I want or dont want AND I always dbl check their work...

you are correct about not likely to find a used engine with perfect cylinders. (thats why one has the engine bored!!!!)

however yes, I've bought forged pistons and they go right in. You cannot just hone cylinders and put in forged pistons. I build race motors that are blueprinted and clearanced, not slap together junk. When I do a refresh on my race motors, if the cylinders have wear, I hone then knurl the pistons to maintain correct clearance. Usuall get 2-3 years before the block needs to be bored again and new pistons.

[trannybuster]

Its all good...

[22mopar]

I just built a 2.2 with Wiseco forged pistons. The bore is .030 over (3.475). the piston measures 3.467" I have a set of keith black hypereutectic which measure 3.473 both are for a 2.2 w/ .030 over bore.

[trannybuster]

Hate wrestling with pigs in the mud...your fast Im slow, your cool, Im not.......feel better now.

[22mopar]

nope, I just know the facts and don't have much tollerance for those that pretend to.

[turbovanman²]

My opinion is that the reason most forged pistons sold are oversize is that most of the people buying them dont know jack ----. Seriously, ALL OVER THE INTERNET there are people telling you cant make power on stock pistons and you need a 'built' motor, they cant explain what fails and why, and they want you to replace things that never break in the first place. So all the people wanting to make power think 'ahh a thousand people on the forum cant be wrong' and start talking to a machine shop that doesnt want to build an engine without boring it because why say no to easy money if the guy thinks he has to bore it anyway?

So basically my theory is people are ignorant.

I disagree, we recommend forged because if your going to the trouble of rebuilding your engine, why not spend a couple hundred dollars more and have piece of mind? One mistake with cast and you have ashtrays. Your friend with the 2nd Gen van is a prime example, he rebuilt with cast, made a mistake and blew it up, what, within 2 weeks? Most don't have that kind of time, energy and money to redo an engine over and over again plus you get pretty pissed off them sell the car off.

[Vigo]

I disagree, we recommend forged because if your going to the trouble of rebuilding your engine, why not spend a couple hundred dollars more and have piece of mind? One mistake with cast and you have ashtrays. Your friend with the 2nd Gen van is a prime example, he rebuilt with cast, made a mistake and blew it up, what, within 2 weeks? Most don't have that kind of time, energy and money to redo an engine over and over again plus you get pretty pissed off them sell the car off.

The thing about the point your making is him blowing it up had nothing to do with him still having standard bore pistons, so how is that related to the OP's question? For the record, the new motor has STD BORE forged pistons. Unless your motor is just heavily worn or has deformed/damaged cylinders in the first place, there is no point to overboring it when you can just order pistons to fit the bore you have after honing it.