Discussion in 'VW Mk3 Jetta, Passat TDI and other/older diesels' started by diesel guy, Jun 25, 2007.
Was reading about forged vs cast pistons, we have cast right?
The 1Z has the older piston style, found in the passat and most 1998 jettas.
The 1999+jettas until 2005 all have the same pistons, the sme pistons that were found in the european 110hp diesels. The difference was in the turbo and injection pump, and injectors. Bolt those on and you have a 110hp...of course, easier said than done!
I know the acura NSX and the s2000 both have forged pistons. Rare for a production auto engine. I think some BMWs do, but don't quote me on that. The s2000 pistons actually have a higher piston speed at redline than their honda f1 engines....yeah...so they need to be strong.
Something I read on another forum :
Simply put...forged is like the elastic in your underwear...it will stretch and bounce back more than cotton (cast) will...cotton stretches, deforms and tears...the elastic will stretch and bounce back to a degree but when an atomic wedgie (massive load/detonation) is applied it will still break...
horrible analogy but who said I was a wordsmith
Nooooow ... under the same mechanical stress, a forged alloy deforms less than a cast one. (higher modulus of elasticity) It is just capable of deforming more before it actually breaks. (higher elastic limit at elongation)
As an additional note, the Pumpe Duse cylinders in the 2005.5+ cars are "trapezoidal shaped" but I am pretty sure that they are cast. That is the exact wording in the factory service manual. I don't have the measurements for the pistons, but this is common for many forged pistons. They are trapezoidal shaped in profile and oval from the top. This is because the pin vs skirt area expand size are different.
that is why the pumpe duse pistons are trapezoidal shaped...because the tops expand more than the bottom. Now how much more trapezoidal shaped than a normal piston I don't know.
yes, cheesy I know, but the analogy works, doesn't it?
I wouldn't worry about having cast pistons, they do the job fine. However, with your car, the mk3 late jetta and mk4 pistons (until the pumpe duse) are just better. See the faq, the 1000 answered questions for more details. The short answer is that the pistons are stronger and were the same pistons as in the 110 hp euro diesel engine.
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