Forge pistons & stock rods (what's the point).

I've noticed there's a lot of people in the US that are building engines with forge pistons and still using stock rods.

Can someone enlighten me on "what's the point in it"

All I can think is to cut costs, but why not just leave the pistons alone too.

Cheers

John

Forged pistons are lighter, and stock rods are very good at their job?

Dish design is better at delaying det?

As above, the stock rods are silly strong. Whilst the stock pistons are pretty good forged ones are always going to be tougher and able to take more punishment from det etc.

When building up a supra engine, to a certain level anyway, the actual compression strength of the components is fine for the most part (bar the obvious weak points that everyone knows). It's only really when going into serious realms of power that the rods need changed along with the main caps etc etc etc.

So can you buy pistons to fit a stock bore or are they all oversized .020 and .040 thou.

So can you buy pistons to fit a stock bore or are they all oversized .020 and .040 thou.

I've seen stock sized ones before. Not sure that all brands do them though, I'm pretty sure some are oversize only.

Hum. Detonation is like an arc welder in your combustion chamber. No piston material is going to withstand that. Maybe light knocking will pit them less, but is that really a reason to perform such an expensive change? I thought that any change in piston from stock is driven by a need to reduce their mass, so you can up the rev limit. Any other function and the stock piston deals with perfectly well.

I also suspect the dish design on the stock pistons has very good anti-detonation properties already, as Toyota a) made them for a turbo engine that has to deal with crap servicing, crap fuel, and high induction temps, and b) they have massive R&D departments with decades of research history. Aftermarket tuning parts suppliers are going to be hard pushed to better that - maybe Cosworth

I've only ever heard of bent rods due to rampant detonation or hydraulic lock, has anyone ever broken one simply due to running massive power? And snapping a bolt due to high revs doesn't count, that's a bolt issue, not a rod issue

Hum. Detonation is like an arc welder in your combustion chamber. No piston material is going to withstand that. Maybe light knocking will pit them less, but is that really a reason to perform such an expensive change? I thought that any change in piston from stock is driven by a need to reduce their mass, so you can up the rev limit. Any other function and the stock piston deals with perfectly well.

 

I also suspect the dish design on the stock pistons has very good anti-detonation properties already, as Toyota a) made them for a turbo engine that has to deal with crap servicing, crap fuel, and high induction temps, and b) they have massive R&D departments with decades of research history. Aftermarket tuning parts suppliers are going to be hard pushed to better that - maybe Cosworth

 

I've only ever heard of bent rods due to rampant detonation or hydraulic lock, has anyone ever broken one simply due to running massive power? And snapping a bolt due to high revs doesn't count, that's a bolt issue, not a rod issue

I've never fully understood the piston thing, I'm only regurgitating what I've read/heard before... mostly from the MR2 forum.

The 3S-GTE would fail above 350hp, as it had done on many occasions. It was drummed into all of us that it was the pistons failing and that forged ones would be required to take any power above those levels.

I think rotating mass is a big seller. Plus piston design is from late 80's early 90's with the 2JZ. So the current ranges are more modern. Materials are better, forging process is better. Etc.

Also, engines with high stress and high miles might well fail at any time. A new built engine gives some reassurances, not much, just some.

Also, of late, the better ECU's like Syvecs have pushed the game on with features like Active-Knock, Fine resolution fuelling, etc, which save an engine, not toast it.

There's has to be companies out there that do forge pistons taylored for a stock bore.

There's has to be companies out there that do forge pistons taylored for a stock bore.

There are, said so in post 6

There are, said so in post 6

I'll refraise that then Scotty, does anyone know which make of pistons do stock sized forge pistons.

Am I right in saying stock is 86mm? If so I think CP do them. There are definitely other brands too.

I reckon its silly to change the pistons only and use the original rods, based on the strength of the OEM I would at least replace them with new items.

Toda do a 86mm and 87mm piston..

http://www.todaracing.com/en/product/piston/2jz-gte.html

so if i understand maybe only for the lighter side of aftermarket rods no really need to change them . or it's somehow like changing the Getrag for a Holinger gearbox

I'll refraise that then Scotty, does anyone know which make of pistons do stock sized forge pistons.

As Scott M said, there are stock bore pistons and 8.5:1 from CP (I believe other brands too):

http://www.horsepowerfreaks.com/partdetails/CP/Engine/Pistons//18096

Pistons from Wiseco:

http://www.spracingforum.com/forums/showthread.php?412-Black-Friday-Teaser-Wiseco-Custom-10-1-CR-2JZ-Pistons-amp-more-from-Sound-Performance

There are also these, but 8.0:1 from Wossner:

http://www.horsepowerfreaks.com/partdetails/Wossner/Engine/Pistons//18341

Stock pistons have cooling voids cast into the crowns, that shake a constantly changing oil volume around internally, that enters through one underside hole from the block oil squirters that only the TT and my modded N/A blocks have, and exits through another, dramatically cooling the piston crown and ring pack. I have never seen a forged 2JZ piston with this feature, although Tomei do some for the RB engine (I have them in my RB). So you gain on lightness and strength with a forged piston, and more controlled expansion characteristics, but lose out on crown cooling. This is offset by the alloy used having a much better thermal stability than cast-able alloys.

Stock rods may be quite strong, and will stand quite high compressive forces without breaking or crippling, but they are not so good at expansive forces when the engine RPM limit is raised substantially. This is where a billet or forged after market rod should come into its own, assuming you know what it's made of and it has proper heat treatment and stress relief. that PROBABLY excludes stuff from China, or China via the USA. We have some of the VERY best rod and piston makers in the world in the UK, but people like to be clever and buy cheap.