What do you think of the strength of the liners/block compared with the strength of the rods and pistons? Subaru are using hypereutectic pistons in their latest WRC I believe and were criticised for doing so before the season and now the criticism has gone quiet. Apparently they claim they are far stronger than their old forged pistons. Is there an argument for not bothering to change the rods and pistons in this engine because you will only reach the limits of the liners and medium pressure block casting by doing so? I just don't like the look of those thin cylinder walls and delicate semi-CDB ribs for 500+ BHP. At what BHP do you think I will blow up my EJ257? ;) Discuss.

http://www.i-speed.us/images/sti_eng...prib_small.jpg

Good question John, I need to know the answers to this because i am considering the 2.5litre now my engine has expired :( Will the pistons and rods be ok for about 450bhp??

Scott

Didn't know your engine expired :( What happened?

Don't know if the internals will be safe, caution has been advised over 350 BHP.

I put the gruppe-s headers on and they pushed the engine above 400bhp and it did'nt like it :( Car felt fast for the first time in its life but piston 4 decided to not play. Sill! managed to get 346bhp on PE rollers yesterday on 3 and a bit cylinders ;)

So you would suggest changing the pistons,rods etc on the 2.5. I will be running the TD05/06 with APS FMIC etc.... so i should imagine it will get to about 450bhp!

My USDM STi 2.5 conversion now running.

I have to do maps. Difficult to do maps on the rolling road with high loads before running in procedure, and difficult to running in without correct maps :-)

So I believe that subaru knows well his work. Dont believe that new engines are worst.

Have seen dismantled STi 7 engines. Inside are not forged pistons but "only" cast. Also I havent reported blown STi 7-8 engines due to poor piston strenght.

scott,

I was just wondering if you noticed any knocklink activity after fitting the headers, also did you get the small bore gruppe-s stuff or large?

since fitting the small bore set , I am getting gear-change big red on the knocklink when really going for it. the big bore set did not suffer this. we have mapped around it but it leaves a flat spot at 5000rpm. a few have said not to worry about it but through det cans it is proper det:eek:. doing the breathers next then fitting an SX FPR.

was any changes made to the the map or fuel pressure, after fitting your headers?

Evo's pistons are apparently T6 hypereutectic - ie also not forged, and it doesn't seem to stop them :) We don't know if the STi's are T6 or not.

T-uk

I was mapping till 1 o'clock with Pat on saturday morning and everything was perfect :) not getting any activity on the Knock link what so ever ( 1 green light, sometimes 2) fueling was nice and rich too! The headers allowed so much more timing and the performance felt great. I just think it was a case of 400bhp being to much for the internals rather than getting any problems

Interestingly i got a check engine light on the way to Power engineering, thought it might be the usual crank shaft sensor as everything felt fine, so i did'nt bother about it :rolleyes: got on the rollers and my breathers were brething heavy (vented to atmo) and when i see 200bhp at the wheels i new something was'nt right :( Chris put the select monitor on it and the fault code was misfire on cylinder 4, Chris reset the ecu and i did slightly better with 346 at the flywheel. now whether the CEL was the start of the problem or the CEL sent the ECU to send funny signals to cause the failure we will never know!

headers are 39mm internal diameter!

Scott

I don't think so Scott, there are quite a few UK's and WRX's now happily running over 400bhp on std internals. What boost were you running after fitting the headers ?

Andy

Do they drive it like me though :D 1.45bar boost!

anyway lets not hi-jack John's thread and get back to the subject :)

[Edited by RB5SCOTT - 11/16/2003 1:20:08 PM]

lol we are on the subject - blown motors ;)

Boost sounds about right :-) The reason I ask is that you don't need much boost when running the headers and it's easy to go OTT and cause damage.

Andy

Nope, did'nt go mad with it, just progressed with the map and let it run with what it was happy with :)

Scott

keep discussing ;)

i will be intrested in one of these when mine goes pop (touches wood)

i would be happy with anything over 350bhp tbh

scott sorry to hear that..

I dont think pistons are really the issue.. I think its more down to rod strength and bearing quality.. (unless you crank a ring land)

Andy, are you using OEM bearings?

I dont see why the EJ257 wont do 400/400 with the right turbo..

I think its a case of choosing something that is efficient and doesnt blow hot air.. but not using something thats too big..

Ideally just getting a small turbo and no lag would be nice..

I think revs may kill it.. Carlos recommended not running over 6.5k red line.. which I think sounds sensible..

We are waiting for you to blow yours up john :D then we know how far to push..


David

John, Subaru do claim the pistons are 3 times stronger than forged items, they also have less thermal expansion than forged items which is why Subaru closed up the piston to bore clearance. There are several reports of Sti7 and beyond nipping in the bores over 450HP. As for the rods, I don't believe they have changed anything with these items, breakpoint is around 450 HP but again that depends on what revs I suppose. Which is cheaper? Put a decent set of rods & pistons in with the bigger clearances and be safe or to replace the whole motor when it lets go?......Food for thought Eh? Maybe just better to buy the USDM block & crank and source your own pistons & rods :D

After speaking to a couple of people at PE yesterday i now know i am not the only thinking the above :P

It would be a real shame to split the new Block to change the bearings.... But if they need doing...

Rob

I'm still on the original bearings that the little japanese man put in there in 1995 :) I've yet to find someone that builds them better :)

Don't worry John, this is a good omen :D I've been in this situation for 18 months now....... they are still waiting........:D :D

Andy

The only issue with the Hypereutectic pistons will be heat damage, as they are not as tolerant as forged items. Which is why they are not used so often in turbo applications. At normal operating temps though, they are stiffer, wear less and expand less, so not bad.

I don't know anyone that has reported a Subaru main bearing go. And the big ends seem to be fine if you look after them, but not detting the bollox off the engine.

Go for it I say, just a shame the engine wasn't available 12 months ago, as I would have gone for one myself i think.

Paul

Andy..

The 'WE' isnt the usual we..

David

I have an EGT limit in mind of about 850C - lower if I can. A 2.5 running at 450 BHP should not I would imagine be hotter at the piston crown than a 2.0 running at 400 BHP, but there are many factors at work. I intend to either run methanol in the petrol tank, or water/methanol injection. I am not going to run it very lean at all, and hoping to only have to use 1.3 bar max.

The factory rev limit for these engines in the US is 7000-7200, so I intend to stick to that. I am a believer in tension/revs killing rods theory far more than a weeny bit of compression ;)

Detonation prevention will be bordering on paranoid as usual.

Part of my confidence is that I got my previous engine to over 90% of my power target without the benefit of headers, with weaker pistons and rods, lower compression and 463cc less. EGTs on that were about 910C. I did not run it for thousands of miles to see if it melted, but it was not pampered whilst it ran and was running fine when removed.

[Edited by john banks - 11/16/2003 10:16:51 PM]

John,

Re "I have an EGT limit in mind of about 850C - lower if I can. A 2.5 running at 450 BHP should not I would imagine be hotter at the piston crown than a 2.0 running at 400 BHP".

I don't understand your logic. To produce X horespower you will be burning a given amount of fuel. To make 450 hp you will be burning more fuel than when making 400 hp. Surely the more fuel you burn, the more heat you will need to sink to the piston crown, whatever capacity your engine is. I can only guess that you are assuming that the larger piston crown area of the 2.5 will spread the additional heatload across the crown and leave a similar average temperature... but it still means the piston is subject to a larger amount of heat energy to dissapate.

Moray

Not so.

The end resultant for power is pressure, not heat, which is a by product. The flame temperature is not in itself directly linked to power, so it's possible to make more power with the same flame temperature, although IIRC flame speed will have to increase, which can be acheived by higher pressure pre ignition cylinder pressure (ie more boost or efficiency).

Paul

Agreed. :) However, I just wonder if the longer stroke and modestly higher mechanical compression ratio of the 2.5 will increase thermal efficiency the extent that a 50bhp hike will not increase crown temps. Would be nice if it does.

when you talk about the bore, r u refering to the bore of the uppipe ?????

BTW personally I wouldn't rev the engine above 6500rpm, have not found any xtra HP by revving it more, at least not with the stock ported headers ;) .....

Carlos H.

I hope it does run cool Moray, as this will be my main limit of how far I tune it.

Carlos

Its the internal bore of the Gruppe-s headers i.e 39mm

the smaller bore gruppe-s set also have a smaller collector and possibly shorter pipe work but I will have to check with john banks car when it comes back. I am sure my newer set are closer the sump and oil filter . with jb's set I had to bend a radiator bracket out the way but my set are about 4" away.

edit to add that the car pulls well to the limiter. with the big bore set it was very easy to hit the limiter , with the smaller bore set it can be felt to just peak before the limiter which suits me more. not sure if jb has any DD graphs to back this up but he was driving the car today and started giggling like a wee lassie at one point while closing in on the red line:) , I think he will need to wear a nappy when he gets his motor back :rolleyes:.

[Edited by T-uk - 11/17/2003 9:47:06 PM]

Unfortunately to use any decent smoothing on the Road Dyno it doesn't read usefully after about 6200 RPM - it seems to smooth on both X and Y axes. The giggle is what counts :)