Jump to content
SAU Community

Recommended Posts

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

Link to comment
https://www.sau.com.au/forums/topic/209149-how-does-the-stock-pistons-fail/
Share on other sites

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.

+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.

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.

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.

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 :thumbsup:

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

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 :thumbsup:

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.

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 (500-1000C) Those last few 100 degrees are more about AFR ratios, boost pressure and advanced ignition IMO.

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.

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 :D

post-25855-1205053948_thumb.jpg

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.

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.

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.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • yeah first and reverse is where you will find clutch release issues (whether hydraulic or mechanical) because the difference in revs required is the highest there; particularly changing down from 2nd to 1st when still moving. To be clearer though, it is possible that the clutch release bearing is the wrong height. This is less likely than a hydraulic issue but it is not unheard of when you are mixing and matching
    • Quite right, if you make it to that pension you deserve every cent
    • Hi all, Restoring r33 series 1 rb25det. All the heater hoses were on their way out, have replaced them and put it all back together. After testing I noticed a small leak from behind the head on the actual metal water line to the turbo when cars warm. I tried running a longer hose over it but it kept leaking...   I am about to take the (stock) manifold off again😔 to change the water line does any one have any lines they recommend? I was looking at Aeroflow Turbo Oil & Water Line Set but not sure what everyone else recommends. Car is completely stock but want to upgrade turbo eventually. it looks like ill have to disconnect a lot just to replace these lines so if there's anything else recommended to do please let me know. Thank you in advance!
    • From memory, on the R33 GTSt at least, while everyone says "It's not adjustable", I found when I changed clutches in mine, it just needed a small adjustment on the rod length. But be very wary here, as you could end up trying to push the pushrod in the master too far, or blowing out the slave.   Most likely though, if the master/slave isn't bypassing internally or leaking out, then the throw out is the wrong height compared to the fingers on the clutch, so when it moves to disengage the clutch, it isn't 100% disengaged. You can check part of this out too by jacking the car up, having the engine running, put your foot on the clutch and try to engage 1st gear. If it goes in pretty easy (Compared to the ground) and/or the wheels start turning a fair bit and it takes a bit too much brake pedal to bring them back to a stop, this is likely the issue.  I'm not sure if you can adjust the height of the forks etc in these though, it's been that long since I've touched any RB gearbox.
    • That's all good, I thought I was missing some interesting feature! Maybe @PranK can double check if that is something that is meant to be operating or not.
×
×
  • Create New...