Piston Design
Turbo Mini Forums

Ok so I'm really interested in what makes a piston good for turbo applications...

Thick ring lands, dish/no dish, floating/press fit pin... Are there any particular design requirements?

Why I'm interested is because I can't find any good turbo smallbore pistons... and I'm good with CAD... and I need good pistons for my project...

I want to have a crack at designing a good strong piston with hopefully some help from you all! :)

It has to be able to deal with the heat above all so start thinking ceramic like the germans do.

Own the day

What is wrong with a decent omega forged piston and a decent amount of undercrown oil cooling unless you are going to use huge boost but then something else will probably be the limiting factor.
You can go to the extent of bridging the pin bosses to the skirt and optimised crown thickness etc etc but why bother?

But you live in the land where the best small bore pistons are made, and they're cheap too.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Yeah I know, but most pistons for smallbore's are for NA applications... How many dedicated Turbo pistons have you seen for a smallbore? On the other hand, there's tons for big bores!

I'm sure people said "why bother turboing a 998, get a 1275!" ... but we all know how fun that can be..

I'm sure there are good pistons out there.. I'm just curious as to what would make the perfect piston.

Someones gotta experiment! 8)

There are many issues with designing a piston as you may know if you are contenplating designing one.
The main issue will be bending under the gas pressure loading but I would very much doubt an omega piston will have any problems unless you use massive boost. They are quite thick anyway.
If you cool the piston then the crown temp will be much lower /less prone to det and therefore the properties will be even better.

There are many issues with designing a piston as you may know if you are contenplating designing one.
The main issue will be bending under the gas pressure loading but I would very much doubt an omega piston will have any problems unless you use massive boost. They are quite thick anyway.
If you cool the piston then the crown temp will be much lower /less prone to det and therefore the properties will be even better.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

If you really must design your own , a version of this one would probably have the best specific performance (strength/weight ratio) when fully optimised
(if there is no pic attached then do a google image search for 'Mahle box piston)

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I've got a set of Hypatecs sitting beside me!

Good point I guess, If it ain't broke don't fix it...

EDIT: That's like what I was thinking... when do you see a piston like that for a smallbore!?

Edited by spraycanmansam on 13th Feb, 2008.

Why not just get a set custom made ?

The custom made JE pistons I got for my LS1 cost about £285 for four. Not a horrendous price by any means. Cant rem if it was including, or +vat.
I ordered via a UK dealer, but obviously they came from the US.

SHort skirtless pistons like that are good for high revving, short stroke motors.

The longer the stroke, the bigger the skirt IMO, to stop the piston rocking about in the bore.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will

TBH I found my copy of AutoCAD again and wanted something to do

I'm also a bit skeptical about my Hypatecs... Dont get me wrong, they're reputation speaks for itself.. 'benjamin''s putting out 140hp with them, they just don't 'look' like they were meant for turbo... I'm thinking of getting some 998 versions and milling a bit off the top and a dish. They have thicker ring lands and look sturdier...

stevieturbo that's a good price for custom made... do they design it and you just give them a few details?

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Haha, I may just do that...

Have you ever just looked at something and thought "Is it really going to be up to it?"

They're for a 1098, hence the milling... got a 295 too

It's probably not worth it in terms of creating something groundbreaking, but It's not something you do everyday

You must also remember that pistons are not round pieces of alloy all the way down their length - how will you determine what the skirt/ crown expansion with temp will be for "your" design - hence allow for this in the initial design to machine parts from?

I can see you ending up with one of two things

- a seized motor
- a smoky motor

If you want something specific like the other guys have said ask an experienced company to design them for you

just a thought

If Carling made Mini engines
it would probably be like this one!

Hasn't anyone watched "The Indian?" All I have to do is make a mould and pour the melted metal in and I'll have a landspeed record breaker!!

Ok so maybe it's not a great practical idea... I might just have to tinker on the computer

I know what you mean about the clearances too.. a mate runs a car in speedway ( do you have that over there? ) and they're building a development motor...

They set what they thought was the right clearances but they were running methanol and its cooled the block but the piston's expanded from the heat and seized at BDC, letting the rod punch through and shatter the piston :(

At least they learnt to slacken the clearances a bit Was going like a beauty until that :)

"the worlds fastest indian" melt some old ones down and jobs a good un'

I just went through the same trouble trying to find pistons that I liked for my 1098. I finally gave up and decided to have some made to my specifications…we will see how they work once I get the car back the road.

Some of the big differences from the original….got rid of the 4th ring, took that real estate to make much larger ring lands, got rid of the oil groove below the oil ring and added additional holes in the oil ring groove, added anti-detonation groove to reduce friction, replaced the cir-clips with double spiral locks (therefore they should never pop out on me), they are now forged, and some other slight mods.

I found it a worthwhile excercise cading a piston, I did it to see how much the pin could be moved up the piston and still keep a decent dish and ring positions.

Its suprising how "top heavy" a mini piston is, the pin is way over half way down the piston.

yes this is the reason why mini pistons are hopelessly heavy too. too much metal above the pin. Longer rods or a block skimmed 7 mm would help, together with custom pistons.

or a longer stroke.

yes, but that will make the engine less rev happy. Light pistons are more important on a revver.

On 13th Feb, 2008 spraycanmansam said:
TBH I found my copy of AutoCAD again and wanted something to do

I'm also a bit skeptical about my Hypatecs... Dont get me wrong, they're reputation speaks for itself.. 'benjamin''s putting out 140hp with them, they just don't 'look' like they were meant for turbo... I'm thinking of getting some 998 versions and milling a bit off the top and a dish. They have thicker ring lands and look sturdier...

stevieturbo that's a good price for custom made... do they design it and you just give them a few details?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will