Don Terrill’s Speed-Talk

I'm one of the street guys running 2618 just because I could and we (CP) used this motor to try out several ideas we wanted to incorporate into the CP Bullet line. My combo uses the Pro Stock boxed forging and a 1.220 compression distance with tight piston to bore clearances on the skirt and the ring lands and the ring grooves. An interesting thing showed up when I got my rings and they varied .0006 within the set thereby negating my plans for very tight ring grooves so we settle for.001 to .0012 after some hand lapping of the rings. I put in 6 lateral gas ports for grins. This is a 4.600 bore with .927 pins, 10.5:1 cr and it's doing very well right now at .004 ptw utilizing a new cam and barrel configuration. No piston slap when cold which should help the longevity. Looking back, I'm sure that this combo would be a major failure without the CNC equipment that's available today. Most of the features that the X or Box style forging that I used can be had with the older round style forgings with great success due to these CNC machines.

I was somewhat of a piston guy once upon a time too. Not directly involved like the "big kids" here, but something of a hanger on doing the catalog, marketing, sales and distribution stuff for what was once a good sized outfit. We made and sold plain old cast, cast hyper, and forged pistons. And we had considerable OE business that gave me access to some rather smart folks that tried their level best to teach me things. Assume that about 30% of it actually stuck, and recognize that the below is thus about 30% correct - and out of date at that.

As I was led to understand, the variances between 4032 and 2618 were rather small within the realm of actual performance in an engine. Something akin to one of those Venn diagrams we all learned (and promptly forgot about) as kids. The two alloys probably have a 90%+ overlap in any measured parameter that really counts. Its the fringes that determined which was best for a given application, and altering design or adding coatings could drive that overlap toward 100%.

The OE guys liked the 4032 stuff for long term durability - the silicon content helped on ring groove, skirt, and pin boss wear. Their definition of durability was in the 150,000 mile context, as measured by emission and fuel economy mandates that do not allow any degradation over a long timeframe. Those measurements are in no way comparable our hot rods - where we think that if it runs good, makes good power, and don't smoke its a great package. Its not that either one of us is wrong - it is just that different between OE and aftermarket. Many of the OE parts had already adopted skirt coatings, and were moving in the direction of exotic ring and pin coatings that would reduce or eliminate the 4032 advantage there.

While I was peddling parts we were "married" to 4032 for another reason - cost. Not material cost or machining cost - but forging costs. We were using WWII vintage mechanical presses that really did not like to run 2618 (we tried - and failed). The big old presses were pretty fast, and were paid for decades ago, making the forge blanks very inexpensive. When we were making them in Missouri, the machining costs were never really much of a discussion point. They were making +/-20,000 pistons per day - many of them hypereutectic. The impression I got was that compared to cutting hyper at >16% silicon, the 4032 was easy-peasy.

Since I was the marketing guy, I did my level best to highlight the advantages of the material we were using, and the limitations of the materials used by my competition. Since the argument still continues a decade after my departure I will take credit for a "job well done"...

My ex-employer fixed that whole piston business thing by moving the manufacturing to India about 6 months after my exit. Nobody ever said so - but I would wager that their overall piston volume is 30% of what it once was. But they lowered their costs and margin went up. Some VP probably got a bonus for that move.

zeek wrote:"2618" AKA "Mahle Metal".

Most pistons made of 2618 forgings in the USA are not designed the same a as Mahle and Cosworth and need more room temperature skirt clearance. Controlled as versus free expansion is key here

zeek

How exactly do they accomplish the controlled expansion.

Just the material's expansion rate.

Got my Piston's back from Line2Line awhile ago, didn't want to bump the post but somebody already did it for me





I was very pleased with the quality

If you can get your hands on a forged OE Honda F20C piston then I would recommend it, you'll learn lots with a straight edge and simple measuring tools and that's a design that is now 17yrs out of date. Top ringland is barrel shaped and looking on top of the crown you'll notice it's oval too. Bore clearance is less than leading manufacturers were using with cast pistons many years ago, and not by a little bit either, spec on P182 here: http://www.wedophones.com/Manuals/Honda ... Manual.pdf

The top ringland is not only oval in circumference and barrel shaped from the side, but it's also been treated in some way as it's dark grey, I'm assuming anodised, to stop it wearing, but unsure why they only did that part.
A lot of aftermarket piston manufacturers are still pretty dumb and so are your pistons, that's why they still say use .040 clearance on a 3.385 piston, they haven't done any R&D, so as long as it slops up and down ok without nipping it does the job - to a fashion. I wouldn't be at all surprised if aftermarket slugs for that engine are nowhere near as cleverly designed as the Honda ones were.
The problems are finding an intelligent piston manufacturer who has the equipment to do the job and also someone who can design one, but if you take some pointers yourself from something like the F20C you'll get a lot closer than most to designing a good piston, then you've got to do your own R&D and find out how close you can get it before it hits the bore, because your block and bore is unlikely to be made in the same way as that one was......

Mahle powerpak 4.125/1.125 pistons here. According to Mahle they could be either allloy. Got some slap noise when cold after I finished break in. Hot no noise. How's that for a p/w debate.

4vpc wrote:A lot of aftermarket piston manufacturers are still pretty dumb and so are your pistons, that's why they still say use .040 clearance on a 3.385 piston, they haven't done any R&D, so as long as it slops up and down ok without nipping it does the job - to a fashion. I wouldn't be at all surprised if aftermarket slugs for that engine are nowhere near as cleverly designed as the Honda ones were.

Or maybe they just have different design criteria/constraints

like some shmuck putting 30 psi boost or bunch of nitrous.....................you pick, but usually not warranty at 100,000mi or emissions....

Sheesh.

BigBro74 wrote:

4vpc wrote:A lot of aftermarket piston manufacturers are still pretty dumb and so are your pistons, that's why they still say use .040 clearance on a 3.385 piston, they haven't done any R&D, so as long as it slops up and down ok without nipping it does the job - to a fashion. I wouldn't be at all surprised if aftermarket slugs for that engine are nowhere near as cleverly designed as the Honda ones were.

Or maybe they just have different design criteria/constraints

like some shmuck putting 30 psi boost or bunch of nitrous.....................you pick, but usually not warranty at 100,000mi or emissions....

Sheesh.

They're just nowhere near as intelligent and/or haven't put the required R&D in, not all obviously, but some surprisingly big names.
You can put a lot of boost and make a lot of power through a stock F20C piston.

4vpc wrote:They're just nowhere near as intelligent

it must be my day-

Are you freakin' kidding me right now?

What exactly are the criteria for piston manufacturer "intelligence"

I absolutely must know-so that I never make a mistake buying pistons from these people...

Also, Please inform us as to who is "near as intelligent"

BigBro74 wrote:

4vpc wrote:They're just nowhere near as intelligent

it must be my day-

Are you freakin' kidding me right now?

What exactly are the criteria for piston manufacturer "intelligence"

I absolutely must know-so that I never make a mistake buying pistons from these people...

Also, Please inform us as to who is "near as intelligent"

Do you understand this feature of a piston, I posted it up earlier: " looking on top of the crown you'll notice it's oval too"` and "The top ringland is not only oval in circumference, but"
?

Using the upper land or the second land along with anodizing is not some magical oriental top secret. Both Mahle (referenced in the thread) and Goertze (division of my former employer) used that strategy from time to time.

It's done to stabilise the piston when the skirt is short or other issues need to be addressed such as in efforts to reduce crevice volume and cold start emissions.

Putting a run contact and scuff potential above a working ring land is not a sign of superior design. It's a sign of tuning desperation as they try to meet stupid environmental rules.

Environmental rules aren't stupid, people who think they are, well...
To create a standard production engine that puts out 120bhp per litre, revs to 8800+, covers huge amounts of mileage without needing rebuilding or breaking and meets all emission rules didn't come from someone low on intelligence.

4vpc wrote:

BigBro74 wrote:

4vpc wrote:A lot of aftermarket piston manufacturers are still pretty dumb and so are your pistons, that's why they still say use .040 clearance on a 3.385 piston, they haven't done any R&D, so as long as it slops up and down ok without nipping it does the job - to a fashion. I wouldn't be at all surprised if aftermarket slugs for that engine are nowhere near as cleverly designed as the Honda ones were.

Or maybe they just have different design criteria/constraints

like some shmuck putting 30 psi boost or bunch of nitrous.....................you pick, but usually not warranty at 100,000mi or emissions....

Sheesh.

They're just nowhere near as intelligent and/or haven't put the required R&D in, not all obviously, but some surprisingly big names.
You can put a lot of boost and make a lot of power through a stock F20C piston.

i agree on the R&D when you are going to sell thousands and thousands of sets the cost of R&D can be readily absorbed. when you order a one of set off custom pistons they wouldn't do any testing specific to your application, its all best guess, generic, err on side of caution otherwise its too expensive.

4vpc wrote:If you can get your hands on a forged OE Honda F20C piston then I would recommend it, you'll learn lots with a straight edge and simple measuring tools and that's a design that is now 17yrs out of date. Top ringland is barrel shaped and looking on top of the crown you'll notice it's oval too. Bore clearance is less than leading manufacturers were using with cast pistons many years ago, and not by a little bit either, spec on P182 here: http://www.wedophones.com/Manuals/Honda ... Manual.pdf

The top ringland is not only oval in circumference and barrel shaped from the side, but it's also been treated in some way as it's dark grey, I'm assuming anodised, to stop it wearing, but unsure why they only did that part.
A lot of aftermarket piston manufacturers are still pretty dumb and so are your pistons, that's why they still say use .040 clearance on a 3.385 piston, they haven't done any R&D, so as long as it slops up and down ok without nipping it does the job - to a fashion. I wouldn't be at all surprised if aftermarket slugs for that engine are nowhere near as cleverly designed as the Honda ones were.
The problems are finding an intelligent piston manufacturer who has the equipment to do the job and also someone who can design one, but if you take some pointers yourself from something like the F20C you'll get a lot closer than most to designing a good piston, then you've got to do your own R&D and find out how close you can get it before it hits the bore, because your block and bore is unlikely to be made in the same way as that one was......

How do you get the rings to seal at .040 clearance?