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st185 pressures and temperatures
http://www.gt4dc.co.uk/forum/viewtopic.php?f=13&t=6861		 Page 1 of 1
Author:  Jon9985 [ Sun Dec 08, 2013 11:30 am ]
Post subject:  st185 pressures and temperatures
does anyone know or have experiance with what the maximum boost pressure the rev 2 internals can take and what egt would be the limit?
Author:  Nibbles [ Sun Dec 08, 2013 12:09 pm ]
Post subject:  Re: st185 pressures and temperatures
Same as the rev3 basically, although it will be a little more knock limited as the CR is a touch higher.

EGT will vary massively according to where the sensor is, i.e. port outlet end of the manifold will be the hottest (ideal but only reads 1 cylinder unless you have 4) , then just before turbo (a common place but only reads 2 cylinders). Some people read after the turbo to read all 4 cylinders but this will be much colder.
Author:  Jon9985 [ Sun Dec 08, 2013 12:31 pm ]
Post subject:  Re: st185 pressures and temperatures
so what is the max psi roughly that wont blow head off or throw rod?

my egt sensor is before turbo on one length of my log manifold where all port meet one.
Author:  Nibbles [ Sun Dec 08, 2013 1:05 pm ]
Post subject:  Re: st185 pressures and temperatures
The boost limit of 1.2 bar is what is generally accepted as the limit of what standard pistons can take before ringland failure. Like all 'commonly accepted' figures, it's probably a crock of *bleep* as running chargecooler or FMIC, extra oil cooling etc. etc. doesn't seem to come into it.

(1.2 bar is approx 17psi)

Chuck a set of forged pistons in and you can wind it up a bit further. With your PFC / rev3 setup you can get to 1.5 bar without swapping sensors although your injectors may run out of puff at higher RPM.
Author:  Jon9985 [ Sun Dec 08, 2013 8:01 pm ]
Post subject:  Re: st185 pressures and temperatures
ive got 540cc injectors in mine, think they from 205.

The figure of 1.2 is based on any more and your rings are toast, so if i can lower egts, technicly i should be able to run more boost.....??

arp bolts hold head down so its only my 1mm mhg that could leak or rods bend??
Author:  Nibbles [ Sun Dec 08, 2013 8:32 pm ]
Post subject:  Re: st185 pressures and temperatures
EGT isn't a direct proportion of cylinder combustion temperature as it's also affected by valve timing and ignition timing so it's not quite that easy.

i would think adding things such as WI which bring down combustion temps will help you get away with higher boost levels. Dropping compression ratio should also help - have a look at the following thread for info on a Russian guy running over 500BHP on 'standard' pistons.

viewtopic.php?f=1&t=4195

sklopendra wrote:
stock pistons supports 500+hp for sure but with increased combustion chamber for lower CR (15cc). Also pistons was tested at 2.4 bars of boost. Now engine covered ~8500km.

after milling.

Image

final polishing

Image


You will want to add monitors / safeties should either mixture go weak or WI pack up if you're pushing the limits.

You could either fit forged pistons (& possibly rods) straight away, probably won't cost much more than a WI kit, or you could go for what you can get and hope you catch ringland failure in time to save the bores.
Author:  Jon9985 [ Mon Dec 09, 2013 12:47 pm ]
Post subject:  Re: st185 pressures and temperatures
ok thanks for info chris. Am wanting to forge at somepoint but would like to see how much i can get out of standard first.
I will be writing report on td04 soon as have now redone dyno with interesting results. Am in process of stage 2 and just finalising and tinkering trying to perfect the hybrid.
Author:  two_OH_five [ Tue Dec 10, 2013 12:38 am ]
Post subject:  Re: st185 pressures and temperatures
I think 1.2 bar comes from the stock Ecu limit. Plenty of us have pushed it further with appropriate management. The ultimate stock limit will be injectors somewhere around 340hp or posterior cramp brought about by clenching while waiting for the big baboom
Its quite possible that the 185 pistons will take more abuse as bore clearances are greater and the pistons should be less fragile
Its been mooted that some 205 ringland failures are down to pickup on the bores rather than det. Probably not verifiable without labs and r&d budgets
Author:  Nibbles [ Tue Dec 10, 2013 12:43 am ]
Post subject:  Re: st185 pressures and temperatures
My `experience so far indicates that ringland failure seems to happen more with larger bore clearances (wear). My theory being that larger clearances and more blowby gasses carries more heat (and more shock waves) down by the piston to the top ring. No absolute proof on either count, just an observation and a theory to support it.
Author:  two_OH_five [ Tue Dec 10, 2013 1:45 pm ]
Post subject:  Re: st185 pressures and temperatures
I would sort of expect that though with out of spec wear. More blowby means more oil being burnt which will create more det. I wasn't trying to say the 185 pistons are detproof - should have said that really. But in high heat/load conditions more piston->bore clearance might be beneficial provided the rings can cope

It would be rreally interesting to know. I think it might have been DJ who saw cracked but not detached ringlands with bore scuffing that pointed to pickup and got the topic rolling
Author:  Nibbles [ Tue Dec 10, 2013 3:11 pm ]
Post subject:  Re: st185 pressures and temperatures
two_OH_five wrote:

I think it might have been DJ who saw cracked but not detached ringlands with bore scuffing that pointed to pickup and got the topic rolling


On Ezzy, one of the pistons had a cracked but not detached ringland. The bores are fairly loose - about .05mm oversize.
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