what would be a dream piston for the 'average' build?

[earlbrown]

I'm working with a high end piston manufacturer to make some pistons for our engines.

If the availability was like a SBC, what would be the specs you're looking for?

Forged and modern ring sets, of course.

Having the come to the deck surface would all for setting quench with head gasket thickness. (even though quench isn't as important in a turbo application). Having it way in the hole like the F-M slugs take that off the table. Being able to set the compression height also allows using different length rods.

Higher static compression than 8:1 adds VE, gives more bottom end, better gas mileage, helps cover up oversized cams, and just sounds meaner Needless to say I like static to be at least 9:1.


I'm thinking around forged, 9:1-ish with an ave 8445 head, close to 0 deck depending on favorite head gaskets, both press or floating options, and modern thinner rings.


Thoughts?


If I can figure out what to make I believe I can get a pretty good group purchase going on from a 3.805" all the way to 5.500" bore.

 

[turbodave231]

• Valve reliefs to handle larger lifts (.600) and larger valves (like MA heads GN1 or TA SE)
• Pin oiling
• Accumulator groove

 

[blackgn1]

If we are dreaming of a good piston does that also mean we can dream about the price? I know......cheap and performance don't belong in the same sentence. It would be nice to have some new choices. Different rod lenghts would be cool.

 

[earlbrown]

Dave, it's hard to say how much life a valve relief can take as far as lift. The lift amount will vary depending on the starting point with head-to-piston clearance at TDC and timing.

Price will be cheaper that others just not sure exactly how much yet. Instantly adjustable pin heights help with long rod (giggidy) selection. Plus, with thinner rings there's more room to move the pin up. That part is nailed down. Any CH that can physically fit, and any bore size from 3.500" to 5.500". The main thing I'm working on right now is the crown shape.

Accumulator groove is in the works all ready. I forgot to mention that.

 

[dsapper]

high end wish list?

asymmetrical piston skirts
2618 forging
option to have them coated...

All the toy's the exotic guys get

 

[turbobitt]

Options for lateral gas ports and different style wrist pin retention


Posted from the TurboBuick.Com mobile app

 

[novaderrik]

a reverse dome that mirrors the combustion chamber as closely as possible allows more static compression for a given fuel and amount of boost while also making more torque when not on the boost.

 

[earlbrown]

I thought about gas ports but I don't really think they're worth the extra trouble/expense. Once they fill up with carbon it's like having a normal piston. For a racer that does frequent teardowns or maybe an E98 user, it might be worth it to use them. I'll see what it would add to each slugs price.

Right not I'm looking at 4032. Mainly for price and piston to cyl wall clearance. I hate to use 'lesser' materials but it blows FM hypers out of the water already. I'll check and see if 2618 can be substituted without having to change the print and/or speed and feeds.

The pin retention will be either floating or press.

I've been thinking about a complex inverse dome shape that compliments the combustion chamber but once I started looking close it seems less fruitful. The chamber is so close to the bore of a 3.8 you really don't have any quench area to work with. Even moving up to a 4.055 doesn't leave much meat to trace. Plus having a dish that large would make the piston thin from the crown to the inside of the top ring land without moving the ring pack way down.

The inverse dish shape and size is where I'm spending the most time right now. I'd love to come up with a design (that works) that would use the same dish on all bore sizes and still maintain decent static compression. That's the trick having the same crown that will work on a stock stroke 3.800" all the way to a stroked 4.055". It's looking like somewhere in the low 20's cc's seems to be the ticket.

I hope to talk about making a dish that gives 9:1 (with an average 8445) and the dish diameter chases the bore as it gets bigger. If that's doable I'll start working on the optimum depth for the inverse dome and able of the ''walls'' going up to the quench area. I kinda like that idea better if it's economically feasible. (that and I need to beat it into my head that having quench isn't as important as I keep pretending it is with a turbo)

 

[turbobitt]

The floating pin can be retained a few ways, spiral locks, double spiral locks, and round wire ring. The spiral locks require a nice square edge to interface with on piston and pin. Round wire ring requires tapper on piston pins and the appropriate round groove in the piston.
AG


Posted from the TurboBuick.Com mobile app

 

[turbobitt]

Don't forget about pin oilers and/or double pin oilers.
AG


Posted from the TurboBuick.Com mobile app

 

[earlbrown]

The floating pin can be retained a few ways, spiral locks, double spiral locks, and round wire ring. The spiral locks require a nice square edge to interface with on piston and pin. Round wire ring requires tapper on piston pins and the appropriate round groove in the piston.
AG
Posted from the TurboBuick.Com mobile app

Correct. And if you have a piston set up for floating and you want to run press, all you do is toss the locks in a drawer and heat up the rod's little end.

 

[turbofabricator]

Better ring package. Modern rings are much better than stock ring package. The stock piston works really well for most folks, though. We do not run much over 6500 with 95% of the builds. Crown thickness is critical. Pin clearance and oiling is also very important. Valve reliefs close to the edge of the piston can crack it. Piston alloy is critical too. Gas ports are not used in any street car that will se significant mileage. The weak rings needed for gas ports will die in a street car very fast. (Except with alcohol) good luck with your project.

 

[earlbrown]

The strength of a stock 3.8 piston is great. They're just heavy and too far in the hole! The reason I started this was after my first 4.1 build. In order to get 9:1 static, I had to knock .035" off the deck (''tall deck block''), shave the heads, put oversized valves sticking into the combustion chamber, and buy expensive ass Cometic .027" gaskets. ... and at the end of the day I still have FM hypers (that I cracked two of in less than a second from a 3/4sec lean blast).
If these pistons already existed, I could have left that meat on the deck, ran cheaper off-the-shelf gaskets, and got my compression and quench with a CH change and not had to take the full .030" overbore.

I've got another phone meeting tomorrow with them. For money reasons I'm looking at 4032 instead of 2618 (along with noise). The ring pack is defiantly going to be an upgrade. 1.5mm, 1.5mm, 3mm with a gas distribution groove should free up a lot of parasitic loss and put that power to the wheels.
The standard pin oiling is broached but I think I'm going to make forced pin oiling standard even though there's a slight price increase. The crown thickness will be with supercharging and long term street use in mind.
I do have the option to install horizontal gas ports for a small price bump. I talked to a tech and he said I can leave them out of the final print and they can be added easily and fairly cheaply on a case by case deal. I'm not the least bit worried about vertical gas ports. Other than winning a bench race, they're useless in a street engine.

The main thing I like about this project is infinite bore O.D. and infinite compression height with no change in price. It opens the doors for 6" aftermarket rods, budget BBC rods, etc... If you've got a stock block that will clean up at .002" over, that's not a problem. The other cool thing is that square decking a block can be stopped as soon as it's clean. Then make the pistons to match after removing as little as metal as needed.

Over the years I've seen many people that just flat out won't bore their block and build an engine with shitty ring seal before it's even fired the first time. With these, a block can be honed back round with no taper (saves on the machine shop costs too not having to automatically pay for a bore job)

 

[we4Mateo]

This thread is totally blowing my mind right now. Keep it coming.

 

[earlbrown]

^mine too

This all started because I wanted a set of BBC small dome pistons for my boat with a different OD and CH... Then I thought to my self "Self, how hard would it be to have them make a reverse dome piston for a GN?"..... Turns out there's more to it than just "give me a slug with a dent in it" LOL

 

[turbotroy]

Cool thread, subscribed

 

[TurboBuRick]

Centered full float wrist pins in a stock like dish pistons cc'd for 9 to 1 compression would be nice.

Rick

 

[earlbrown]

Full float will be standard and 9:1 is what I'm shooting for.

It's not an exact science because I've been working on a reverse dome shape that will still give good static compression with a stock stroke 3.805 bore all the way up to a 4.1 bore size with and without a stroker crank. That one's been a real pain, but I've just about got that finalized.

Next is mocking up a block with a set of 8445's with O/S valves and see how far from center the edges of the valves are. I doubt it'll change my current inverse dome design, but if there's any extra's there, I'll be taking advantage of it.

 

[dr_frankenstein]

This is super awesome that your chasing such a well designed piece for the price... Im sure many of us would be plenty happy with a plain dish or D-cup at these prices... I would be and im very open to the idea for some super street forged budget pieces.

There are other ways of pulling the compression up if you need it...

 

[ek02]

Attached is a photo of a JE custom forged "spherical dish" piston for a 4.1 with a 3.967 bore and 3.625 stroke. Your idea exactly for a standard bore that can be honed .002 over. This piston is 9.5-1 CR with .030 surfaced iron heads and .030 Cometics. It would be close to 9-1 with stock heads and .040 gaskets. This was for an N/A nitrous engine. The same piston with the same pin height, but for a 3.965 bore has .5 more compression. The block was zero decked with that piston and .040 gaskets for 10.5-1. The problem with this design was piston to valve clearance. The valve eyebrows are cut as deep as they could be without weakening the piston. With .526 lift I had .080 on the intake and .100 on the exhaust with .030 off the heads, stock 4.1 deck, and the .030 Cometics. That clearance would probably work as long as there was no valve float. GN1 heads solved the clearance problems because the valves are moved closer to the center of the cylinder, and there is more clearance in the dish. I don't even need any valve reliefs with GN1's. If you can come up with an "adjustable" design for all bore sizes and strokes at a reasonable price (less than the $950.00 including pins and rings and coating that JE gets!) it would be a big help.