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Old 10-16-2001, 01:35 AM   #1
WRXwannbe
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Default Valve spring and what do they mean to you.

Are higher rate valve springs worth it to acheive higher revs?

I want to rev my 1st gen EJ20 up to at 8k. When lookingfor maxium RPM what mechanics should I examine in the headwork?
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Old 10-16-2001, 01:41 AM   #2
Eric SS
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in short: yes. to go 8k and/or run substantial boost at lower rpm's you must buy springs.

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Old 10-16-2001, 01:41 AM   #3
iodine23
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At some point you're going to be floating the valves if you don't have stronger springs. Your cams will be moving so fast they'll actually be slapping the valves open and dropping out from underneath them. So the timing of the valves actually becomes irregular and unpredictable. This really screws up any tuning assumptions you may have made.

If you really want to rev high, get stronger valve springs. It may be worth investigating the RPM at which valve float starts on your EJ20. I think they say the EJ25 is somewhere around 7200rpm, which is definitely below your 8k goal.
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Old 10-16-2001, 02:07 AM   #4
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your both right,

that was my assumptions. It's just soo damn expensive, buyt they could be the single most improtant link to achieving higher revs.
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Old 10-16-2001, 02:14 AM   #5
Eric SS
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Also, to elaboratre on my high boost comment, if you run high boost, the pressure behind the valves can actually cause them to float at an rpm that if there was no boost, they wouldn;t float.

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Old 10-16-2001, 07:39 AM   #6
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I hear this often, but I wonder how many people have actually ever seen it happen. It doesn't seem like there is enough surface area on the back of the valve to be able to push it open that way. I mean, there can't be more than about 2 square inches of area right? Assuming that (correct me if I'm wrong; I actually think it's less for most engines but 2 is an easy number to multiply by), then even at 10psi there is only 20 pounds of force on the back of the valve. That can't be enough to push it open. I guess at huge boost pressures (say, 30psi, where obviously with our hypothetical 2sq in. it would be 60lbs of force) then maybe it makes sense to me. But not on any mortal engines.

Someone correct me if I way off here, and definitely explain it. I'm just trying to understand the mechanics of it.

edit:

After rereading your post, Imprezinator, I think I'm understanding. You're saying that due to the pressure on the back of the valve preventing it from closing as quickly as it would at atmospheric pressure, it'll float at lower rpms. So in effect, this will give you a "lower spring rate" on the valve? Right? Wrong?
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Old 10-16-2001, 11:32 AM   #7
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Cobb's site says the stock 2.5RS valve springs have a seat pressure of 45lbs. Now if we assume you're running 15psi of boost, then your valves would need 3 square inches of surface area to be lifted off their seats by the boost. This turns out to be just under 2 inches in diameter. That seems a little large to me... does anyone know the stock valve size on the 2.5RS?
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Old 10-16-2001, 07:15 PM   #8
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From Cobb:

Intake Valve Diameter 1.420"
Exhaust Valve Diameter 1.240"

(This is for the EJ25)


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Old 10-16-2001, 07:19 PM   #9
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Why is everyone ignoring atmospheric pressure in the calculations above? If you are running 15psi of boost, there is almost 30psi of pressure pushing on the back of the valve. Assuming a valve with 2 square inches of surace area, that seems to me to be 60 pounds of pressure fighting a 50 pound valve spring.


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Old 10-16-2001, 08:07 PM   #10
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bsquare: good point, but I still don't think that's quite right. After thinking about what you said, I realized I forgot all about the pressure inside the cylinder in my post above. And you're assuming vaccuum inside the cylinder, which probably isn't right either.

After intake, the air/fuel mixture is at manifold pressure. It's then compressed, so the cylinder is at higher pressure. Combustion causes more pressure still. On exhaust the cylinder pressure has to be higher than that of the exhaust system downstream (i.e. atmospheric plus backpressure) in order for the exhaust to want to flow out of the cylinder rather than back in. Back to intake, we don't care about cylinder vs. manifold pressure since the valve is open, not seated.

So I guess that at the very least the cylinder should be somewhere around atmospheric pressure, except maybe during intake when the manifold may be at vaccuum, not boost.
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Old 10-16-2001, 09:43 PM   #11
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I dunno, I just asked if it's a good idea since I'm trying to go higher in the revs.

Less irratic valve movement when the camshaft slaps the valve lasher.
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Old 10-17-2001, 03:46 AM   #12
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I would defintily get stiff valve springs. The valve train is the ONLY thing holding back any of the subie motors from turning ALOT of RPM. I'd also look into Ti retainers, which are a nice item to add to the package. Hollow valve stems and other methods of getting the valve train lighter is also a good idea. Maybe soidium filled hollow valves on the exaust side if you are going to be racing alot, as they take the heat alot better than any other kind.
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Old 10-17-2001, 04:13 AM   #13
Eric SS
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I must agree with XT6Wagon. Like stated in previous threads, the only really legitimate thing holding our cars back is the valve springs.

Unlike inline-4 engines, our Boxer-4 engines are iherently balanced, meaning they don;t really need counterweights. This being said, there is very little stress on the Main bearings. Get some good valvesprings and a different set of cams (That will rev high enough) and any Subaru motor (esp. the EJ22T ) is good to about 8,000rpm's!

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Old 10-19-2001, 05:32 AM   #14
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Also the short stroke makes for a nice stress free rev. Lets put it this way, even the "crappy" EJ-25 has a shorter stroke, and about as good R/S ratio as the Integra Type-R's B18C5. So the EJ motor with the WORST R/S and longest stroke experiences LESS stress at high rpm than Honda's screamer. I haven't done the calculations, but the old EA-82T with a decent bottom end should be capible of 12K rpm. The heads suck far to much for that to work unless also boosted, but just think 12K!!!!! RPM as easy (
bottom end wise) as 9K on the B18.

If I get the car I am looking at tomarrow, I am thinking about building a 10K rpm daily driver.
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