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06-02-2015, 02:06 PM #1
Off The Shelf (OTS) Custom ModMotor Pistons
OK guys, for those of you who are looking for pistons or have looked for pistons, you will be familiar with the problem of finding a manufacturer and then getting the specs correctly communicated and finally getting the piston you wanted. Usually things do not go the way you anticipated at first or the process is painfully long with something always just a little bit different than what you hoped for when you finally get the pistons.
I may have a fix for everyone in the next week or thereabouts.
If things work out as currently anticipated (always a challenge) I'll have a piston manufacturer that will be willing to build the piston, the way we all have wanted them built, and all you have to do is specify bore size and compression ratio. The rest will be already done for you, i.e. heavy wall H-13 pins, supercharged ring land placement, proper radial clearance for the rings, a TotalSeal AP Steel ring package, two country miles of PTV clearance, 0.200" skirts and any bore size your heart desires. All you will have to do is identify the piston by name for example XXXX, bore size and compression ratio — that's it!
The pistons will be individually replaceable if you do have a whoops (lets hope not) and the replacement will not require you to rebalance your crank — it will come within +/- a gram of what the original was. If this comes together the way I am hoping, ordering custom pistons will be sort of like ordering lunch in the old days when you could walk in and just say, "I'll have a cheeseburger, fries and a Coke", and you end up with the exact meal you wanted, the way you wanted it.
In a week or so I hope to have a 3D Acrobat image of the piston I can post up on the site here that will allow you to rotate, turn around and see the piston from every perspective. Stay tuned ...
Last edited by eschaider; 06-02-2015 at 02:13 PM. Reason: Spelling & Grammar
06-02-2015, 02:59 PM #2
Looking forward to seeing their work! Will we be calling this the "Special Ed" piston;)
06-02-2015, 04:08 PM #3
Regarding the pins.
Is there any point in specifying "super finished" on the pins? I have seen that term used by several manufacturers but none of them specified any performance differences.
06-02-2015, 07:59 PM #4
- Join Date
- Feb 2010
Awesome to hear! Look forward to seeing them and comparing them to mine to make sure I did ok!
06-02-2015, 08:44 PM #5
I would like to buy the strongest flat top pistons ( tool steel pins, thick skirts, etc) with super charger specific ring lands for my 4.6 that maintains the OEM pin offset ( no noise!). In other words, I want diesel like durability.
Something like this would be nice as long it does not make any noise:
06-02-2015, 09:33 PM #6
- Join Date
- Feb 2010
I got mine with zero offset, I'd prefer some slap to maintain reliability.
06-02-2015, 09:49 PM #7
And this is a close up of #1 counterweight on the same crank;
This surface finish is less than 1 Ra which is essentially the equivalent of a mirror as you can see from the reflected image of the snout.
The wrist pins that will come with these pistons are like the finish on that crank although they are one notch down strength-wise from the absolute best money can buy. The reason for that is because when you see the price of the best money can buy it would bring tears to your eyes and no measurable improvement for our application.
BTW I am a very big Winberg fan. After I committed to a custom billet, Randy Winberg was the only guy that would make a custom 4.6 crank for me and do it in Timken 4330V steel which is the same super steel the Top Fuel cranks from Bryant and Winberg are made from now.
There are a lot of details that would be nonsensical and boring for most about this piston however there is one other aspect of it that is unavailable anywhere else other then OEM. That is the special pin boss treatment for offset pins. In aftermarket pistons the pin boss is always on center and if you offset the pin you make the pillars that comprise the pin boss thinner in the thrust direction of the piston because of the offset. When OEM's use offset pins on hi performance engines and sometimes just grocery getters they will offset the pin bosses to match the pin offset.
These pistons will come with the pin bosses offset in the piston to exactly match the pin offset so both sides of the pin boss are identical. The upshot of all this geometric calisthenics is a pin boss that is equally strong on both sides. There are a number of other reliability considerations designed into the piston that are pure boring.
Usually (not always) only the special line or hand built engines in Detroit get this sort of treatment. For a hi-performance engine like our own the benefits can be very real. The thin side of the pin boss usually doesn't, but can fail and when it does you have a forged 4340 connecting rod swinging around on a rod journal like a weed whacker in your back yard. The damage it will do inside your engine is impressive in the extreme. It will surpass even your wildest imagination.
Hang tight guys this thing is winding up pretty quick now. I think you will really like these 'off the shelf custom pistons'.
BTW Cobraracer, these pistons will easily meet the requirements you specified in your opening sentence.
06-02-2015, 10:12 PM #8
Looking forward to seeing these things. I have an old beat up engine on the stand right now in dire need of a rebuild and I don't feel like waiting for a set of custom Manley pistons to come in (last set took almost 2 months).
06-03-2015, 02:56 AM #9
06-03-2015, 04:11 AM #10
06-03-2015, 04:27 AM #11
Ed, the finish on your custom crankshaft is just incredible!
Was that done to promote oil shedding? Or just so it makes it obvious that there are absolutely no machining flaws?
Was that finish included 9n the price you mentioned a while ago?
But if I ever got a crank like that made I bet it would get me in a lot of trouble. It might go something like this.......
DREW! You love than crankshaft more than you love me. I bet you would rather have it in bed than me!
"I'm thinking, I'm thinking."
06-03-2015, 09:00 AM #12
My name suggestions from back in April in the "custom pistons thread" when I suggested this very thing!Can we just get one of the piston manufacturers to make these heretofore custom pistons a standard catalog part for boosted 4.6 engines? Just call it the "Ed". How about the "Mini Pro Mod"? I believe that's what one of the pistons companies said they thought it sounded like when Ed spec'ed it out to them.
06-03-2015, 10:07 AM #13
That particular 4.6 crank in the pics is not mine. For a race only application I would have done it. For a primarily street application I elected not to. The cost was not that expensive ~$300 or $400 if I recall. The issue is the maintenance of the crank when it is not in an engine. The unprotected but highly polished surface is very susceptible to rusting from moisture in the air. That first rust dot is a stress riser that did not exist before. The finish is a race use preparation that belongs on a race crank not necessarily a street crank — but it sure does look pretty.
06-03-2015, 11:44 AM #14
"forgings with a quiet-running 0.050-inch pin offset are John's choice. The pin offset reduces "flop over" at top dead center, allowing a better ring seal with modern, narrow rings. John specifies a little more barrel to piston skirts going into forced-induction engines such as this one for the same reason. The pin is 22mm in diameter with 0.155-inch-thick H13 material-hard stuff. Because of the nitrous, the piston dome is also thicker at 0.250-inch."
06-03-2015, 01:37 PM #15
Blown engines and in particular blown gas have higher combustion temperatures and pressures. If you have a good handle on your fuel system you can safely run 1.2mm and 1mm tops. If you don't, you'll just kill the rings and the pistons. A "safe" top ring thickness for someone who is a first timer or is primarily using it on the street is 1.5mm. The 1.5 mm ring has lots of forgiveness for everything from a less than optimal tune to the occasionally bad tank of gas that comes out of the pump. It will not however save you from a bad tune — nothing can.
For a street driven vehicle that does not have to optimize the power output per unit of displacement there is no reason to run the 1 mm type rings. Those types of cars should be running 1.5 x 1.5 x 3.0mm ring sets. For a race car my litmus test is how tightly the competitors cars bunch up in qualifying. If you can qualify 16 cars within one tenth of a second (0.1 secs) then you need to worry about this kind of stuff. If the 16 cars need more than a tenth of a second to go from the bottom to the top of the qualifying ladder then you have other more pressing matters to worry about and spend money on.
John's comments about the silence of the offset pin design is again spot on. In addition to silence the pin offset subtly moves the torque around in the engine's operating rpm band. Some people think this is a distinction that makes the difference between winning and loosing. I tend to dismiss that claim although it will ever so slightly modify the appearance of the torque curve. More importantly, the offset pin will be more gentle with the pistons and liners producing slightly better looking parts when you pull the engine apart to freshen it.
The piston slap you hear while audibly offensive is also a contributor to collapsed piston skirts. With only 0.0035" PTW imagine just how hard that piston skirt has to slap the cylinder bore to produce the sound you hear. Now consider how long it will take hitting the wall that hard to collapse one of those thin skirt n/a pistons. This is one of the reasons knowledgeable engine builders build blown motors with such robust skirts.
The piston in your post #14 looks like a piston I would spec out. My bet is, if you didn't spec it yourself then, John is the designer. Either way it is a very fine blown gas piston. Most guys, who are in the know, would give their eye teeth for pistons like that,
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