How Does The Stock Pistons Fail?

[brother_david]

Hope you guys can help me out here, has searched the forum without finding an answer!

Its said that the Rb25det pistons on the R33 gtst fails at about 450hp, and my question is if they cant stand the heat they're exposed to at that output, or if they fail mechanicly/cracks and go to pieces?

Cheers!

-David

[Dale FZ1]

Fatigue, mechanical loads, elevated piston speed, and in most cases I would say knock due to poor tuning. Broken ring lands is normally the evidence to look for.

I have heard of some picking up in the bores from heat, but that was of the out of coolant / engine overheating variety.

[Cjmartz2k]

+1 for poor tuning, and 450hp isn't some magical number that can't be breached. I've been doing well over 500hp at the motor for over a year now.

[Guilt-Toy]

its cold in japan though ?

[GeeTR]

+2 - det induced

Setups that aren't over revved, and aren't subjected to high temps, take a lot more 450.

I don't think its the heat that would kill a piston (hurt its metallurgical strength) Rather, I think the heat would cause det and that would kill it.

[nuclear_skyline]

The piston can fail in the ring-land region because it cannot stand the amount of explosive energy its being subjected to... Tuning can help tempretures and detonation, but the more boost you run, the more explosive force being generated, the higher the stress on the piston.

[djr81]

Oh dear.

A few fundamentals:

The compressed fuel/air mixture in your cylinders does not explode. It burns, quickly. There is an important difference. An "explosion" is referred to as detonation.

Detonation will, as has been pointed out, rapidly destroy your pistons (and bearings to boot).

A properly tuned motor will not detonate, hence it can be ruled out as a cause of failure AS FAR AS THIS QUESTION IS CONCERNED.

Which leaves up with what as a cause of failure? Well, amongst other things:

Too many rpm.

Too much combustion pressure for the rings either because of insufficient tension or simply old age.

Too much combustion pressure helping accelerate bearing failure.

Insufficient cylinder cooling. Note that the strength of metals (particularly aluminium) falls away markedly as temperature increases.

But don't forget that pistons etc wear/distort and generally suffer from mileage and hard work. So whilst your 450hp RB25 may last for a time it wont be forever and probably not for very long.

[GeeTR]

^^ thank Christ.. thanks djr

[nuclear_skyline]

Too much combustion pressure for the rings either because of insufficient tension or simply old age.

What I was trying to say in a much more proficient way

[brother_david]

Really helpful answers i've got!

Since i live here in Sweden and at extremly hot summers we've reached just about 30 degrees Celsius, or 85 degrees Fahrenheit i guess its about the same temps as in Japan? Anyways, right now its 0 degrees C or 32 degrees F outside. I f i consider outside temps a big part of wareage

What i was thinking of when posting this thread was if it was worth spending good time mapping it as good as possible, and through that push the rebuild of the bottom a while, atleast about 6-7 months. I was heading for the tracks this summer, but now i'm probably best of with rebuilding it before i push it to hard. Probably ill start with keeping the boost at about 1.2 BAR as a maximum and after the rebuild head for higher boost if needed.

Since i'm going TT (twin 2530's) with my RB25 i was wundering if you've can help me decide whether to go with twin Z32 AFM's or just a single Q45, joining the air-intakes on the turbos?

Cheers and thanks for your help!

-David

[a20089]

Since i live here in Sweden and at extremly hot summers we've reached just about 30 degrees Celsius, or 85 degrees Fahrenheit i guess its about the same temps as in Japan? Anyways, right now its 0 degrees C or 32 degrees F outside. I f i consider outside temps a big part of wareage

Wow considering most people in this thread are from Australia and extremely hot summers are low to mid 40's Celsius external temp is probably not a major consideration.

[GeeTR]

30 degrees Celsius

Lol'chops, yah we get many a low 40's in eastern Oz.

Its not so much the external air temp, its the combustion temperatures (500-1000^C) Those last few 100 degrees are more about AFR ratios, boost pressure and advanced ignition IMO.

[brother_david]

Hehe ok then temps aint that different

[Cjmartz2k]

I'm in Okinawa, Japan, so it's pretty warm here. It's a sub-tropical island. It gets into the 50's (sometimes the occasional 40 something) in the winter and will tickle 100F in the summer, but it's humid as a mutha.

[brother_david]

Can be really annoying if its too humid, had one of those big thunderstorms a while ago, could cut watercubes out of the air for days!

Just started to polish the 2530's yesterday, spent 2 hours on one of the compressors and it came up better then i thought, but im not done for days yet, its still very grainy so ill hit it with a wet&dry P150 and start over again But practice makes perfect! Then its off to TIG-weld a new manifold and new downpipes and fit em!

Heres a quickie

[GeeTR]

Good work dood, polishing is a farking khunt by hand... did a RB26 plenum.. never again.

PS: Humidity is g o o d for petro chemical combustion motors. Water vapor aids chamber mixture outer shell shedding. (burning)

Embrace the shirt sticking your back rofl.

[Adz]

Im running 500hp flat out on the track with a stock 25. So far so good. It all comes down to supporting mods. Ie good tune, good cooling, good turbo, cooler and exhaust.

They are renound to be fragile. They crack eaisly from knock from what i have been told.

[Cjmartz2k]

I 100% agree. Seems some on here think they will magicaly explode after 400hp, but i've been will above that figure for almost two years now, and have several friends that are the same, but beat there cars WAY more than me.