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Old 07-14-2008, 09:21 PM   #1
tmeultraman
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Default valve springs = higher rpm?

a tuning shop told me that by changing the valve springs you can attain higher rpm? granted this is on a motor with forged pistons and rods (2.0l) but is it really that simple as adding on valve springs and a tune to hit 8000rpm?
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Old 07-14-2008, 10:17 PM   #2
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True to a point. They mean you will be capable of revving to a higher point. A stock motor has no problem hitting the limiter, so you'd have to go about changing that too.

On carb'd cars back in the day.....new or fresh valve springs would allow the car to rev a little higher before the valves would start to float. At that point, the rpms kinda hover and it sounds nasty......

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Old 07-14-2008, 10:26 PM   #3
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Better valve springs do allow you to rev higher, but without some form of moving the rev limiter up, it's really doesnt benefit you much.

Plus you should be sure that you are going to be able to make power at the higher rev's, otherwise the only good thing it would really do is allow you to drop into peak power on an upshift.


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Old 07-15-2008, 06:58 AM   #4
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All other factors remaining the same and just changing the valve springs can result in a slightly stronger top end. This is because as the standard springs may allow you to hit the rev limiter the motor may be producing low power output due to valve float and valve bounce.
The stronger springs will better control the valves at higher rpms and make them follow the cam profile more closely which results in better high rpm power.

I think this is what the tuning shop was probably getting at.

However without changing the cams to really produce power in those higher rpms you will find that by changing gear at 7k you will actually be faster than trying to shift at 8k.
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Old 07-15-2008, 07:12 AM   #5
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^^^ Yup....I agree.

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Old 07-15-2008, 09:36 AM   #6
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This is all true, but it doesn't even touch on the whole oiling issue at higher RPM. Even if you changed the cams to make the power, the stock 2.0 crank doesn't like to spin 8,000 rpm and the rod bearings get all pissed off.
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Old 07-15-2008, 10:24 AM   #7
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Quote:
Originally Posted by bluescoobywagon View Post
This is all true, but it doesn't even touch on the whole oiling issue at higher RPM. Even if you changed the cams to make the power, the stock 2.0 crank doesn't like to spin 8,000 rpm and the rod bearings get all pissed off.
be careful what you say, as there is more than one stock EJ205 crank design

You are correct though that the entire engine has to be prepared to make high rpm power...not as simple as cams and valve springs. Far from.

Last edited by Homemade WRX; 07-15-2008 at 11:20 AM.
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Old 07-15-2008, 10:47 AM   #8
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Quote:
Originally Posted by bluescoobywagon View Post
This is all true, but it doesn't even touch on the whole oiling issue at higher RPM. Even if you changed the cams to make the power, the stock 2.0 crank doesn't like to spin 8,000 rpm and the rod bearings get all pissed off.

Thank you sir. Nice to see someone else who realizes how demamnding high rpm is on your engine
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Old 07-15-2008, 03:05 PM   #9
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cool. actually the motor has oversized mahle pistons and a sti 2.5l crank along with acl race and rod bearings, i forgot to mention that, while it started out as a 2.0 its an open block 2.2, though i havent actually verified the actual end displacement yet as the motor is still being broken in, my builder tuner told me to expect it to run like a 2.0 with faster spool and better torque... so if im understanding what everyone is saying then my motor can run to 8,000 rpm but without more agressive cams then the power really wont be realized?
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Old 07-15-2008, 04:01 PM   #10
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if its just a piston rod 2.2L with stock ports...cams, valves and springs will help the top end...8000 and a .82AR 35R wouldn't be too bad of a combo and I imagine it would hold power decently. I would highly recommend opening up the throat of the valve seat if/when doing your oversized valves.

pending bore, you'll be a 2.35-2.4L
if 97.5mm you're 2359cc

Last edited by Homemade WRX; 07-15-2008 at 04:08 PM.
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Old 07-16-2008, 12:01 PM   #11
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I don't think a open deck 2.2 will like much boost for very long.
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Old 07-16-2008, 12:48 PM   #12
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well, what are his power goals?
2.5RS engines and EJ205's have taken plenty of abuse and IIRC the EJ22 had thicker cylinder walls than a 2.5RS...The RS engine also shorter rod ratio (guess that won't matter if he's doing the same stroke and rod) and a higher bore/wall thickness ratio too than the EJ22.
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Old 07-16-2008, 01:57 PM   #13
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ive heard that open deck blocks wont take as much boost but then again im going no larger than a 20g and pump gas anyways (leaning towards 18g) as this is a dd and will be a street car, not drag so boost wont be super high anyways, so that being said i ve seen many stock block ej205's handle these mods so the fact that the pistons, rods, bearings, etc.. have been replaced i think the open deck will be just fine, i was just hoping to be able to slide further right in the powerband.... thanks for all the replies
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Old 07-16-2008, 02:18 PM   #14
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well the semi closed decks hold no real value over a semi-closed deck when talking cylinder pressure. The benefits of it having the small tabs that "locate" the cylinder is to keep the clyinder from "walking"...
walking becomes more of an issue with the higher the bore/cylinder wall thickness and with the shorter the rod ratio. The ratio makes it less stable and the shorter rod exerts more force on it.
Stroking the engine will move your curve to the left, not the right
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Old 07-16-2008, 10:31 PM   #15
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Quote:
Originally Posted by Homemade WRX View Post
well the semi closed decks hold no real value over a semi-closed deck when talking cylinder pressure. The benefits of it having the small tabs that "locate" the cylinder is to keep the clyinder from "walking"...
walking becomes more of an issue with the higher the bore/cylinder wall thickness and with the shorter the rod ratio. The ratio makes it less stable and the shorter rod exerts more force on it.
Stroking the engine will move your curve to the left, not the right
you sir, are correct about it going left... but 8000rpm sounds sooo nice..
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Old 07-17-2008, 10:59 AM   #16
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8000 rpms sounds nice until you get a bearing or rod failure. then it sounds AWFUL lol. the more power you can make at lower RPMs the better.
remember, piston speed and oiling are major isssues as you rev higher and higher.
with a 20 or 18g i am not sure 8000 will make efficient power.
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Old 07-17-2008, 11:09 AM   #17
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Quote:
Originally Posted by Homemade WRX View Post
be careful what you say, as there is more than one stock EJ205 crank design

You are correct though that the entire engine has to be prepared to make high rpm power...not as simple as cams and valve springs. Far from.
I know... the Spec C with the 8k redline has the super nifty, super special crank, but the block is modified as well.

Quote:
Originally Posted by tmeultraman View Post
cool. actually the motor has oversized mahle pistons and a sti 2.5l crank along with acl race and rod bearings, i forgot to mention that, while it started out as a 2.0 its an open block 2.2, though i havent actually verified the actual end displacement yet as the motor is still being broken in, my builder tuner told me to expect it to run like a 2.0 with faster spool and better torque... so if im understanding what everyone is saying then my motor can run to 8,000 rpm but without more agressive cams then the power really wont be realized?
Remember that the factory redline for the 2.5 is 6500 rpm, but with the smaller pistons, you could probably go to 7,500 without worries if you added a shim or two to the oil pump and monitored pressure. Without oiling mods, it won't be reliable above that. I'm building a 2.5 that I'll spin to 8,000 rpm, but I've got a lot of oiling mods including a ported/shimmed pump, ported passages in the block, modded crank, oil accumulator (for reliability, not revs), and of course oil temp and pressure gauges.

Quote:
Originally Posted by tmeultraman View Post
ive heard that open deck blocks wont take as much boost but then again im going no larger than a 20g and pump gas anyways (leaning towards 18g) as this is a dd and will be a street car, not drag so boost wont be super high anyways, so that being said i ve seen many stock block ej205's handle these mods so the fact that the pistons, rods, bearings, etc.. have been replaced i think the open deck will be just fine, i was just hoping to be able to slide further right in the powerband.... thanks for all the replies
A 20G isn't going to be able to support 8,000 rpm very well and an 18G doesn't have a chance. At a guess, an 18G would pick up no more than 5 hp at high rpm with the addition of cams. This is because you're still limited by the turbo at that point. They would still boost the midrange power, though. However, an EWG would add some top end power to the mix...
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Old 07-17-2008, 01:54 PM   #18
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Quote:
Originally Posted by bluescoobywagon View Post
I know... the Spec C with the 8k redline has the super nifty, super special crank, but the block is modified as well.
um...you are very uninformed and the part number and pictures have been taken numerous times...the EJ205 (later part number) is the same physical crank as the EJ207 spec c...the spec c crank is however nitride treated (big woop). The block is also standard EJ207 part number IIRC.

Regardless of what he builds, oil will need to be addressed if trying to spin high rpm's. If high rpm's are his goal, he's already going about it the wrong way with the entire shortblock.

Just my $0.02,
Micah
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Old 07-17-2008, 03:39 PM   #19
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GM was campaigning a drag Cavalier that had an 800 hp Quad4 motor using all stock internals. They kept pushing the motor until something broke and then they replaced the broken part with another from the bin and tried again. Eventually they had the magical combination of stock parts that held together at 800hp so they could say that a stock motor could handle 800hp. Was it a motor that you could assemble yourself with the correct part numbers? No...

Do you have any links to one of these numerous threads so that I can become un-uninformed. The NASIOC search engine is crappy...
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Old 07-17-2008, 06:32 PM   #20
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Quote:
Originally Posted by bluescoobywagon View Post
I know... the Spec C with the 8k redline has the super nifty, super special crank, but the block is modified as well.
Please explain the block modification.........

oh, and search the "crossdrilling our crankshafts" thread.....
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Old 07-17-2008, 07:39 PM   #21
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[quote="Homemade WRX"] so, after ordering a new crank for a customers ej20 build I discovered that subaru's new replacement crank is cross drilled the same as the spec c crank. So I figured I would share.
new part number

new crank 1

new crank 2

new crank 3

old crank 1

old crank 2
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Old 07-17-2008, 10:41 PM   #22
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It would be interesting to compare the new crank to a Spec C crank as well. My 2.5 crank will be crossdrilled similar to the new crank. There are plenty of people in the crossdrilled crank thread that don't think it's a good idea, but Subaru seems to think so...
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Old 07-17-2008, 11:10 PM   #23
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sponaugle has posted the part numbers...that's why I say they are the same...

I tend to think there is a better way to deliver the oil through the mains where certain forces will be but fraction of what they are otherwise.
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Old 07-18-2008, 12:00 AM   #24
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as rpm increase so does the load on the bearings and other engine internals - even if you changed the valve springs you would add extra load to the bearings and they would prematurely fail at higher rpm then oem.

If you want to increase the rev limit safely, you need to upgrade all load bearing parts to ensure they are capable of safely handling the increased load associated with increased rpm.

At a minium, you'd have to also change the bearings (make the clearences a little looser too), the stock rods and most likely the valves - you "may" be ok with the crank and pistons.

You will also need to ensure oil supply and pressure is suitable for the increased rpm.


I have outlined the most basic steps - but there are more things you need to do if you want to dramatically increase the rev limit and not have your engine die. Most reputable engine builders know what you need to do - and they all charge for their assistance
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Old 07-18-2008, 01:11 AM   #25
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acl bearings were used along with the mahle pistons and forged connecting rods which accompanied the valve springs so if thats true then i have the minimum requirements... anyways at this point i believe it wont be truly used anyways as i dont think ill put a turbo big enough to use it to its true benefit.. thanks for all the responses, while ill probably tune for it being a dd it wont hit 8 to often,..
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