My understanding was that wossner are low expansion material more suited to road use and lacked the out and toughness of the more conventional forgies.

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If at first you don't suck seed, try drier grain.

Forged pistons are not all equal. You should select an appropriate piston for the design requirements of the engine.

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GT4DC Events Co-ordinator
1996 ST205 UK

if you look at the wossner clearance specs they are only running 0.0027" where a CP is 0.0035" which is nothing. This is quoting off the shelf material specs.

The new generation of materials does give such a broader range of usage compared to the older style thoughts on forged piston designs. Prime example people who were running over 500bhp would use large clearance pistons to allow for the added heat expansion, for instance Ross used to be a common piston to use for high bhp with its 0.0060" clearances and its associated piston slap.

I've designed CP pistons in the past for a street application when i was doing testing with a high silica content running 0.0012" piston clearances, yet also then used the 86.25mm pistons i designed but still keeping the same material found in CP pistons and there 0.0035" clearance ranges in engines running 950bhp and 2.7bar of boost pressure without issues.

i ran 3 sets of the high silicone alloy pistons, 1 upto 450bhp without issues. after strip down i found there to be minimal longevity or effects on running the high silica allow compared to the more stable and stronger low silica allow with the 0.0035" expansion compared to the 0.00.12" so i stopped testing on these. This was all done to try and resolve the old fable of a forged engine won't last as long as a factory item, purely because of the forged piston design. After research i came to the conclusion it wasn't the piston design which leads to this but the nature of its power and usage.

If you really look at what's available these days, there clearance and material specs are all extremely similar and negligible. It all comes down to there designs to how they last. Like i said i found wossner to have weak skirts from past experience.

Just my experience.

Tim
TB Developments

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Can I ask after how many miles you decided there was minimal longevity differences?

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GT4DC Events Co-ordinator
1996 ST205 UK

Bearing in mind I know of one standard GT4 engine that's gone past 250K miles now and still going strong, not been gentle driving either.

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If at first you don't suck seed, try drier grain.

jesus and I thought mine had done well at ticking over 141,000 miles.... still on the same turbo and block and hammered on trackdays, gotta love Toyotas!

His turbo did pack up a few months back, and he changed the shells last year but the head hasn't been lifted as far as I know, certainly still on original pistons & bores.

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If at first you don't suck seed, try drier grain.

superb, sounds pretty much like mine, runs sweet as a nut, no noises, doesnt burn oil or anything so happy days so far.

When we had the bore scope in it was in superb condition inside also so happy days!

My original engine covered about 147k miles. It hadn't failed either but did have a 'tired' feel about it. Still very good going in my view. I'm looking forward to getting it apart to look at the bores.

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GT4DC Events Co-ordinator
1996 ST205 UK

good stuff, my test to see how tired my engine and turbo are is very technical.

It usually involves a back road and a thrash through to the top end of second to see how quick it hits the red line, and its around an identical time to what it was after I first did the fmic way back in 2008 so as un technical as it can be. haha

It was tests against the 2 different pistons did the 0.0012" clearance and the normal 0.0035" clearance. Engines did approx 60k miles and were from one of the first engines I build many years ago.

it was just to see the stigma that forged engines don't last as long as a factory built engine. like someone have said here 200k without problems. Its mainly put down to the expansion rate of the forged pistons, causing slap premature wear etc etc. So by the same logic a forged piston with a small 0.0012" clearance should show alot less wear than a forged piston of 0.0035" where from my testing there was negligible difference

I think again most of this goes back to the old style pistons that were 0.0060" and 0.0075" was common place for an uprated piston.

To put this into perspective the stock OEM pistons are 0.0028"-0.0035" on the st185 engines.

Tim
TB Developments

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That's a reasonable amount of miles although not massive so not really possible to draw any great conclusions although its interesting.

Something from your previous post did catch my eye as well:



Really?

Most CP's are made from 2618 Alloy but pistons made from 4032 Alloy are also widely available from manufacturers (including CP). These materials are massively different. The aluminium is alloyed with different elements, so to say they are extremely similar??

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GT4DC Events Co-ordinator
1996 ST205 UK

That mine Chris ?

Its just under 100 miles shy of 290,000 now . Only replaced bottom end shells at err about 240k and turbo at 253k. No head lift yet, will wait until 300k. No boost cut, and has run up to 23 psi, have nice boost creep often giving about 17psi on the stock known as paper head gasket.

--
Darryl

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--

Darryl

Stop driving like a granny Darryl

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

yes but if you look at the expansion rates between the 2 units and what's is suggested by the manufacturer then they are very similar the high silica alloys being recommended in the 0.0027" and the low silica stronger units in the 0.0035" which are actually still within Toyota specs for a OEM piston.

Now the test i did was between a high and low silica piston, the low silica was the normal 2618 alloy, and then the high silica was a tweaked 4032 setup that gave a 0.0012" clearance. nearly 2.5 times smaller than the off the shelf 4032 alloy. I know 60k isn't a huge amount of miles but its more than enough to see how the pistons are wearing in the bores, skirt witness marks etc. and between the 2 extremes they was negligible differences.

now remember there isn't even a piston off the shelf that uses that material i tried so really between the 2 extremes of modern day piston setup of 2618 vs 4032 your talking 0.0008" difference in expansion rates. But the high silica are more prone to cracking by definition alone.

This is why I said with modern day forged piston materials its more important to go via design over advertised material specs. Long gone of the days where high silica was 0.0027" and stronger high silica was 0.0075" (where you compromised longevity for strength) As I said earlier I've used the 0.0035" CP piston in engines running 950bhp at 9500rpm and 2.7bar of boost pressure without issues.

There also isn't a huge difference in design between all the brands on the market place, none are comparing full length to cut back skirts or ultra lightweight etc.

So there isn't a night and day differences, I just found wiseco a little noisy, and wossner has a weaker skirt in some of the applications i was using. where with CP i've never had an issue from any piston, plus they work along side me with some development work i've had done where the others weren't very interested so i've just stuck with those pistons for the engines i build as i feel i can trust the product. But i woudln't flat out refuse to use the other brands if people asked me to.

Tim
TB Developments

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