Monotherm pistons

MINK · Feb 28, 2012

Hotrodtractor said:
Piston design. By designing a piston with weight only where it needs to be can come out to the same weight or lighter than an off the shelf production piston. The trick is to put material where it is needed and not where it is not needed. Compare the pictures earlier in this thread with each other and you'll see what I mean.

And even then chances are you will use a lighter rod to compensate the weight. I would still rather be as light of an assembly as possible.

strokin'_tatsch · Feb 28, 2012

Aren't the pistons Swamps is coming up with still a little heavier than an aluminum piston? Pretty sure I remember them being about 1 lb heavier than aluminum. I'll have to check their website, pretty sure that's where I saw that.

juniort444e · Feb 28, 2012

From what i understand they use a heavy more durable material, but shave weight in areas that are not detrimental to the strength of the piston. If you notice the monotherms are missing most of the skirt where as the regular mahles have a huge skirt. Either way, i would rather have a tiny bit more weight that will handle heat better and have the metal expand at the same rate as the block helping make a better seal. And i would also think losing some weight in a connecting rod and wrist pins and other areas would help out as well.

Hotrodtractor · Feb 28, 2012

MINK said:
And even then chances are you will use a lighter rod to compensate the weight. I would still rather be as light of an assembly as possible.

Its not all about weight - I can make the piston out of a solid slug of aluminum - but if it can't hold up as well as a marginally heavier steel piston - then it doesn't matter.

FWIW - I know of a common rail engine running monotherms - there are nice little divots that match the spray pattern in the injector tip..... do you think that an aluminum piston would put up to that level of torture?

MINK · Feb 28, 2012

Hotrodtractor said:
Its not all about weight - I can make the piston out of a solid slug of aluminum - but if it can't hold up as well as a marginally heavier steel piston - then it doesn't matter.

FWIW - I know of a common rail engine running monotherms - there are nice little divots that match the spray pattern in the injector tip..... do you think that an aluminum piston would put up to that level of torture?

Not at all - guess I'm wondering if it's really that important on the 7.3s, where are 7.3 piston failures you've seen?

Hotrodtractor · Feb 28, 2012

MINK said:
Not at all - guess I'm wondering if it's really that important on the 7.3s, where are 7.3 piston failures you've seen?

They crack in the bowl - and can ultimately torch through the crack and blow into the crankcase - sometimes they break up before that happens. Fuel bowl tweaks and design variations can all but eliminate that issue - but there are limits on what can be done with that design. By making a new piston - we can increase strength, improve its ability to stand up to high pressure injection, give it ability to hold up to higher cylinder pressures (within reason - other limits exist).

Plus best of all - if you have to ask - maybe you don't need em.

MINK · Feb 28, 2012

Hotrodtractor said:
They crack in the bowl - and can ultimately torch through the crack and blow into the crankcase - sometimes they break up before that happens. Fuel bowl tweaks and design variations can all but eliminate that issue - but there are limits on what can be done with that design. By making a new piston - we can increase strength, improve its ability to stand up to high pressure injection, give it ability to hold up to higher cylinder pressures (within reason - other limits exist).

Plus best of all - if you have to ask - maybe you don't need em.

Lol you know I don't need them - I was more curious on more info, I can see the importance of bowl design changes period but wasn't sure if a monotherm was really needed in the 7.3 application material wise. I have always thought they were the way to go in the cr world however.

PowerstrokeJunkie · Feb 28, 2012

I was under the impression they were using a aluminum skirt for the billet pistons, like the two piece pistons in the OTR trucks?

blackbetty13 · Feb 28, 2012

Big Bore said:
Does it? Are you sure? Because we really want you to be perfectly at ease with the design from one of the foremost innovators and experts on 7.3 Powerstroke parts, and you really seemed to seriously question their design.

I was just asking a question, because I didn't know. I was not expecting a 12 year old reply in return. Sorry for asking a question on a forum. I figured that was allowed in a place like this, guess not. I honesty thought everything was centered to spec. Saw the pic and asked.

Chvyrkr · Feb 29, 2012

12V pistons are the same way.

Big Bore · Feb 29, 2012

blackbetty13 said:
I honesty thought everything was centered to spec.

What spec?

Powerstroked162 · Feb 29, 2012

Big Bore said:
What spec?

You've made your point LOL

Let him breathe a little

09stroker · Feb 29, 2012

juniort444e · Feb 29, 2012

He's gots small hands.

Jason, send me a pm with some of those companies you were talking about. Im trying to get a list so when the time and money are right in line, i can get these rolling for my build.

NyCowboy87 · Feb 29, 2012

MINK said:
Not at all - guess I'm wondering if it's really that important on the 7.3s, where are 7.3 piston failures you've seen?

This is what happens to 7.3 pistons.

fbilly420 · Mar 1, 2012

I have 2 trophies just like those hanging in my garage. Engine only had 110K on it

SINNER · Mar 1, 2012

Bean said:
Mahle is now working on Dmax Mono's and once those are done they will probably go to the 6.7's. I doubt they ever do 7.3's and be a long time before they get to the 6.0/6.4 piston. Mahle is a very high OEM production place and these hi-po pistons are very small short runs so getting them done takes allot of time just waiting to fit the short runs in between the huge oem runs.

Mono's are heavier then a cast or forged aluminum piston but not by much once you add in the wrist pin weights.

If you really had to have a set they might do some from billet but expect to pay probably 4k+ for a set.

The Cummins mono's are 230 grams heavier per piston weighed out with the wrist pins. So on a V8 engine that is approx. 1800 grams of weight added to the rotating mass.

Anyone attempting to add that much weight to the reciprocating mass on a V8 with questionable block integrity better pay careful attention to the internal balancing of that engine. Or stand way back when it is spun hard.

powerstrokenstang · Mar 1, 2012

But if you go with carrillos in your 7.3 they are around 200g lighter than a stock forged.

MINK · Mar 1, 2012

powerstrokenstang said:
But if you go with carrillos in your 7.3 they are around 200g lighter than a stock forged.

Which is the same case with the cummins; carrillo vs. 12v rod

If your comfortable with factory weight assembly then yes there is no issue with that setup.

Charles · Mar 1, 2012

These aren't gassers...

How many 7.3's have you seen rod the block because they pulled the pin out of the piston, or stretched rod bolts and similar?

The problems are power load (bending rods into horseshoes) and thermal load (cracking pistons and making cool designs on the tops), not inertial loads.

At 7000rpm, I'd worry about piston weights a little. When you look at the stroke of the cummins crank, rod weight and piston weight, the whole thing comes into much better perspective. A 7.3 could add gobs of weight before it started approaching similar piston acceleration forces to a stock 5.9 at the same rpm.