Forged or cast pistons?

[Dennis The Menace]

I'm kicking around going to 103 build, and was wondering which is best; forged or cast pistons?  Looking for longevity, problem free motor for all around riding and touring, not for racing.

What is pro and con?

TIA

menace

[HD/Wrench]

  This should get intresting.

SE cast pistons are not set up for over sized valves from stock
SE forged & other forged pistons are
KB piston has larger valve pocket as well.

All will work, when the chips are down a forged piston will take more abuse. Cost of a forged that requires no extra work are about 50 more dollars.

Built too many engines to count with cast and forged. Budget may dicate which one you buy. Cost for us to machine larger valve pockets is 40 bucks. We use mainly CP pistons.

[ederdelyi]

>>This should get intresting.<<

Nah. Really pretty cut and dry. Cast is fine for moderate compression and reasonable operating RPMs. If you are going racing, running high compression and hitting redline all the time forged is likely a more reasonable choice.

Either one can do the job if set up properly, cast or hyper pistons are the predominant choice in most OEM applications including some very high performance models. A good cast piston is better than a marginal forged and vice versa.

[Sc00ter]

I have had great success using CP coated forged pistons....

http://www.cppistons.com/products/harley/

[Gulfstream]

>>This should get intresting.<<

Nah. Really pretty cut and dry. Cast is fine for moderate compression and reasonable operating RPMs. If you are going racing, running high compression and hitting redline all the time forged is likely a more reasonable choice.

Either one can do the job if set up properly, cast or hyper pistons are the predominant choice in most OEM applications including some very high performance models. A good cast piston is better than a marginal forged and vice versa.

Got to totally agree here...if you're not going to be running more than 10.5:1 compression or spinning the motor past 6200 RPM's a good cast or hyper slug is fine!

[Big Dan]

I run forged J-E pistons. In a former life, long ago, I worked in a premier automotive race engine shop. I know that cast pistons are plenty adequate for most uses, but I just can't bring myself to use 'em. For the relatively few extra dollars, I like the peace of mind I get from running good forged pistons.

[taz95dog]

big dan i agree , why not?  it's always better to be on the safe side...imho... ...taz...

[jsachs1]

Then you have the compression height "thing" with the later flywheel assy.
John

[ederdelyi]

John,

Correct me if I'm wrong, but isn't that more of a rod length/cylinder length issue? Is the CH of the pistons out of spec as well? Just curious, I haven't messed with the later stuff much ... sorta lost interest.

[Hillside Motorcycle]

We use forged here.
They are a lot stronger.

[JAFHR]

Can you get tighter spec's with the forged piston as opposed to the cast or is that vis versa? Or is it that you need tighter specs with the forged pistons. I ran forged in my Road King, no problems there. What about piston slap? 

[lasmittys1]

I'm kicking around going to 103 build, and was wondering which is best; forged or cast pistons?  Looking for longevity, problem free motor for all around riding and touring, not for racing.

What is pro and con?

TIA

menace

I can't tell if your using a largemouth bass or Northern pike bait here.

[ejk_dyna]

<<Correct me if I'm wrong, but isn't that more of a rod length/cylinder length issue? Is the CH of the pistons out of spec as well? Just curious, I haven't messed with the later stuff much ... sorta lost interest.>.

Axtell and Mike Roland separately said that their pistons had the same CH for the 96's and were coming up with zero deck height (+-)just like before...which seemed to suggest QC issues on pistons CH. Don't recall anyone measuring a set that was way down the hole though.

[ederdelyi]

Interesting. That's not typical of the vendor that HD was using for either OEM or SE stuff ... I know they don't use Arias for some of the SE stuff anymore, have they gone to a new vendor for the OEM cast? Boo-boos and QC issues are not uncommon when switching vendors, especially if it involves offshore manufacturing.

[jsachs1]

John,

Correct me if I'm wrong, but isn't that more of a rod length/cylinder length issue? Is the CH of the pistons out of spec as well? Just curious, I haven't messed with the later stuff much ... sorta lost interest.

Ed,
It's a rod issue that cropped up on the later flywheels(dickhead rods).Mike Roland sells,through Kury,pistons with slightly longer skirts,(stability)and .015" more compression height.
John

[sean fxd]

John,

I remember what ejk dyna said.  Mike Roland said his pistons for the 96" motors (4.375) had the same CH as his 103 pistons for the old 88.  And he said the new pistons were right on as far as deck height was concerned.  That seems to imply the down the hole issue was not rod related.  Or maybe the bikes he was doing did not have this issue to begin with...bad batch of rods intermixed in the production run?

The .015 additional CH is the same on both the new and old pistons right?  I remember Mike saying he did that to allow oem head gasket and still get right squish.

Sean

[GoFast.....]

I think 0 deck is a issue with any engine including Automotive.

[11.7to1]

Can you get tighter spec's with the forged piston as opposed to the cast or is that vis versa? Or is it that you need tighter specs with the forged pistons. I ran forged in my Road King, no problems there. What about piston slap?  


The post above was/is the highest point of consideration that was overlooked in this thread, although there were other considerations that were presented as well.

A cast or hypereutectic alloy has less propensity for thermal expansion than does a forged piston, therefore piston to bore tolerances can be held much tighter than a forged piston, extended engine life is a result.

[JAFHR]

Thank you 11.7 to 1  I felt a little jilted. I thought it was a good question, but threads have a life of they're own.

[nc-renegade]

A cast or hypereutectic alloy has less propensity for thermal expansion than does a forged piston, therefore piston to bore tolerances can be held much tighter than a forged piston, extended engine life is a result.

That is correct, though a good engine builder will fit the forge piston to cylinder taking the expansion into consideration.  For long term reliablity with forged pistons, it is critical to give the engine adequate time to heat up and stabilize before taking off.

What I like about a good forge piston, such as Wiseco are the valve pockets are sized for large valves, skirts are coated and the weight and measurements are very well matched between sets.

[11.7to1]

We recently had a 5.4L Trition engine returned to us that had accumulated one million documented miles since 1997. We replaced it with a new one for the customer just so we could tear it down and analyze. Cast pistons.

Forged pistons can be assembled in an engine but their long term reliability under normal operating conditions is a far cry from the reliability of a cast piston under the same conditions. It is agreed a good engine builder will fit the forged pistons accordingly, but lets not confuse that, with them then being equal to a cast piston with respect to longevity.

The original poster stated this was his main concern, longevity.

With the latest metallurgical advancements and casting technologies, I would find it hard pressed to justify a forged piston for a street driven, normally aspirated engine. The new supercharged Cobra R is making 540 horsepower and using a cast-hyper piston.

But old traditions die hard.

[Hillside Motorcycle]

Thing is also, that OEM castings do not allow for oversize valves, larger TDC lifts, as do most all outfits that offer forged units.
Scott

[Dennis The Menace]

Thanks for the responses, gentlemen.  I have learned a lot here.  I am planning to go with a 103, either bore my existing cyls or buy new, not sure yet.  But, looks like I will buy cast pistons.  Forged may be overkill for just daily riding.  Also, I am using stock heads, but will probably get a little polishing and porting done.  And, probably a Tw6-6 cam.

I dont have anything else planned.  I believe with the cam and 103 BB that I can use the stock gaskets, pushrods and valve springs.  It should help to have a little better CR than stock too.

Dennis

[taz95dog]

dennis, if you're going bigger and changing cams,i would do the heads.i was told that if you can't get the air in and out(heads) you won't get near as much power.the squish area, also is very important.i don't really understand all this,but it's what i was told...bill...