How strong is the Standard EJ25 crank?
05 October 2011, 03:24 PM
#1
How strong is the Standard EJ25 crank?
I'm having my engine re-built next week and am trying to work out if I need a nitrided crank...
I want the engine to take 450bhp and similar torque safely.
Spec is now:
STI crank (35 miles old, no obvious wear)
ACL bearings
ARP 11mm studs
Cosworth gripper HG's
Mahle forged pistons
Manley H section rods
I want the engine to take 450bhp and similar torque safely.
Spec is now:
STI crank (35 miles old, no obvious wear)
ACL bearings
ARP 11mm studs
Cosworth gripper HG's
Mahle forged pistons
Manley H section rods
05 October 2011, 03:42 PM
#2
Without wishing to sound critical, why has your chosen engine builder not gone through all the build options and power variations with you ? 
Looks to me like you're in danger of spending money quite blindly atm without any real idea of the outcome/cost or capabilities of your build.
Just an observation, no offence intended
Looks to me like you're in danger of spending money quite blindly atm without any real idea of the outcome/cost or capabilities of your build. Just an observation, no offence intended
05 October 2011, 03:50 PM
#3
Scooby Projects have been very helpful and have offered plenty of advice.
However, I'd like to gather as much information from different sources as possible so I can make an informed deicison (there is quite some money involved after all!)
However, I'd like to gather as much information from different sources as possible so I can make an informed deicison (there is quite some money involved after all!)
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05 October 2011, 04:17 PM
#9
Yeah about 10 minutes ago after advice in another thread Hence my post Just an observation but the engine builder should have a spec list for your power aspirations. Adding bits due to good fortune of asking the right questions on here is a dangerous way to spec an engine build IMHO. Like I said just an observation 
Hence my post Just an observation but the engine builder should have a spec list for your power aspirations. Adding bits due to good fortune of asking the right questions on here is a dangerous way to spec an engine build IMHO. Like I said just an observation
05 October 2011, 04:22 PM
#10
I take your point mate, as I said, the engine builder has explained the options to me, but I figured there's nothing wrong with a little extra research.
Learning from other people's experiences and sharing knowledge is what the forum is for after all.
So after all, that - do you have any advice /experience on the crank?
Learning from other people's experiences and sharing knowledge is what the forum is for after all.
So after all, that - do you have any advice /experience on the crank?
05 October 2011, 04:27 PM
#11
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The subaru cranks are normally pretty good so you shouldnt need worry there, just note that nitriding is just a hardening of the outer surface of the crank, but every little helps
Tony
Tony
05 October 2011, 04:40 PM
#12
Yeah about 10 minutes ago after advice in another thread Hence my post Just an observation but the engine builder should have a spec list for your power aspirations. Adding bits due to good fortune of asking the right questions on here is a dangerous way to spec an engine build IMHO. Like I said just an observation
Hence my post Just an observation but the engine builder should have a spec list for your power aspirations. Adding bits due to good fortune of asking the right questions on here is a dangerous way to spec an engine build IMHO. Like I said just an observation As you are said,best is contact engine builder,which recommend parts for this.
I take your point mate, as I said, the engine builder has explained the options to me, but I figured there's nothing wrong with a little extra research.
Learning from other people's experiences and sharing knowledge is what the forum is for after all.
So after all, that - do you have any advice /experience on the crank?
Learning from other people's experiences and sharing knowledge is what the forum is for after all.
So after all, that - do you have any advice /experience on the crank?
If you are not put nitrided crank,your weakest link will be crank,not the pistons,rods but crank
Jura
05 October 2011, 06:34 PM
#13
meh. Harder does not mean stronger. Glass is harder than metal, but its brittle.
The nitrided OEM crank isn't stronger than the standard OEM crank, it only adds surface hardness, not strength. Another internet faux pas.
The #1 reason for the nitrided crank, is that the new scoobs have lead free bearings, so the crank has to be nitrided to "avoid" scoring.
If your OEM crank is still fine, I wouldn't spend any cash on the Nitrided one.
The nitrided OEM crank isn't stronger than the standard OEM crank, it only adds surface hardness, not strength. Another internet faux pas.
The #1 reason for the nitrided crank, is that the new scoobs have lead free bearings, so the crank has to be nitrided to "avoid" scoring.
We've nitriding our cranks for several years now. We found that one of the major problems with spun rod bearings, other than the obvious oiling issues, was that the rod journals would gall with the slightest metal to bearing contact, which would subsequently spin the bearing in the rod housing. This situation was exacerbated when using race bearings, which were stronger but seemed to have an inferior embeddable layer versus OEM. We have had oil starvation issues with nitrided cranks and found that although the bearing shell were almost worn to the steel backing, the rod journals were still absolutely pristine!
We have employed both ion nitriding and liquid QPQ (quench, polish, quench) on crankshafts, rods and camshaft/lifters. The ion nitriding generally has a dark gray appearance, where as the liquid nitriding has the black finish. Ion nitride treatment will have a greater case depth versus Liquid nitriding. It also is performed at lower temperature and will therefore minimize distortion.
We post-polish the journals on our liquid nitrided cranks, but not through the black layer as this layer has a very low coefficient of friction. The surface hardness after this process is fantastic! Stock cranks that we have had tested averaged around 25 HRC (Rockwell hardness C scale). The version 8 JDM sti cranks, which are Tufftrided ( a shallow nitride process) from the factory were above 30 HRC.
We have employed both ion nitriding and liquid QPQ (quench, polish, quench) on crankshafts, rods and camshaft/lifters. The ion nitriding generally has a dark gray appearance, where as the liquid nitriding has the black finish. Ion nitride treatment will have a greater case depth versus Liquid nitriding. It also is performed at lower temperature and will therefore minimize distortion.
We post-polish the journals on our liquid nitrided cranks, but not through the black layer as this layer has a very low coefficient of friction. The surface hardness after this process is fantastic! Stock cranks that we have had tested averaged around 25 HRC (Rockwell hardness C scale). The version 8 JDM sti cranks, which are Tufftrided ( a shallow nitride process) from the factory were above 30 HRC.
05 October 2011, 06:39 PM
#14
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meh. Harder does not mean stronger. Glass is harder than metal, but its brittle.
The nitrided OEM crank isn't stronger than the standard OEM crank, it only adds surface hardness, not strength. Another internet faux pas.
The #1 reason for the nitrided crank, is that the new scoobs have lead free bearings, so the crank has to be nitrided to "avoid" scoring.
If your OEM crank is still fine, I wouldn't spend any cash on the Nitrided one.
The nitrided OEM crank isn't stronger than the standard OEM crank, it only adds surface hardness, not strength. Another internet faux pas.
The #1 reason for the nitrided crank, is that the new scoobs have lead free bearings, so the crank has to be nitrided to "avoid" scoring.
If your OEM crank is still fine, I wouldn't spend any cash on the Nitrided one.
Tony
05 October 2011, 07:08 PM
#15
Thanks for the feedback folks.
Anyone else have experience of big power on the standard crank?
What sort of cranks do people use for more than 400 bhp?
Out of interestt, what do Scooby Clinic use in their SC450 performance package?
Anyone else have experience of big power on the standard crank?
What sort of cranks do people use for more than 400 bhp?
Out of interestt, what do Scooby Clinic use in their SC450 performance package?
05 October 2011, 07:13 PM
#16
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well roger clarke motorsport have advised me a standard subaru crank, even my version 4 crank is strong enought for nearly 500hp the main problems with our bottom ends is lack of oil and **** mapping which causes detination and rams that piston and rod down on the bearings into our cranks : >
05 October 2011, 07:23 PM
#17
You have'nt said what your engine is, is it a 2.5 or 2.0 using a 79mm crank making it 2.1,
if its a 2.5 using a semi closed deck block , your limit is going to be head gaskets, a OE 2.5 crank will see well over 500hp without issue, plenty of 2.35's out there on std 79mm cranks seeing high 700's without complaining.
if its a 2.5 using a semi closed deck block , your limit is going to be head gaskets, a OE 2.5 crank will see well over 500hp without issue, plenty of 2.35's out there on std 79mm cranks seeing high 700's without complaining.
05 October 2011, 07:23 PM
#18
2.5l using standard 2.5 crank...30,000 miles on it, 20,000 of those running 485bhp and similar torque
Headgaskets went 5000 miles ago so all was stripped down. Crank was like new, one bearing had very slight marks, so replaced the lot as it was daft not to.
I would have no qualms using a stock 2.5 crank for 500 - or more - as long as everything else is up to scratch and correctly specified...and the engine is properly maintained of course.
Engine now running over 520, but not enough miles on it to comment on whether the crank's ok
Headgaskets went 5000 miles ago so all was stripped down. Crank was like new, one bearing had very slight marks, so replaced the lot as it was daft not to.
I would have no qualms using a stock 2.5 crank for 500 - or more - as long as everything else is up to scratch and correctly specified...and the engine is properly maintained of course.
Engine now running over 520, but not enough miles on it to comment on whether the crank's ok
05 October 2011, 07:28 PM
#19
Great feedback folks, sounds like a nitrided crank may be overkill for me then.
Don't mind saving that 500 quid to be honest!
Anyone heard of a standard crank "failing" (other than from oil starvation)
Don't mind saving that 500 quid to be honest!
Anyone heard of a standard crank "failing" (other than from oil starvation)
05 October 2011, 08:14 PM
#20
You have'nt said what your engine is, is it a 2.5 or 2.0 using a 79mm crank making it 2.1,
if its a 2.5 using a semi closed deck block , your limit is going to be head gaskets, a OE 2.5 crank will see well over 500hp without issue, plenty of 2.35's out there on std 79mm cranks seeing high 700's without complaining.
if its a 2.5 using a semi closed deck block , your limit is going to be head gaskets, a OE 2.5 crank will see well over 500hp without issue, plenty of 2.35's out there on std 79mm cranks seeing high 700's without complaining.
It's a 2006 Hawkeye STI (euro model), so it's the standard crank from a 2.5L STI.
05 October 2011, 08:25 PM
#21
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A perfect condition stock 2.5 crank is absolutely fine.
If we are buying a new crank, we go for the nitrided ones as there isn't much in the cost. If I had a top condition stock crank there already, I'd use it.
If we are buying a new crank, we go for the nitrided ones as there isn't much in the cost. If I had a top condition stock crank there already, I'd use it.
05 October 2011, 09:34 PM
#23
Engine Specialist
The question I would ask is if anyone has ever seen a standard crank fail due to the crank material or manufacturing defect alone. I think you won't find many if any at all!
Graham
Graham
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