I was thinking about doing the STI gauges on my GC8 impreza, but I don't want the 7900 redline just for show, so what do I have to do to my engine to get that (without causing damage of course)?

Just have the ECU reprogramed.

But there would be too much valve float past 7000rpms anyway... You would AT LEAST have to upgrade the valve springs, but something like the Cobb Racing cams which move the power range up 1000rpms would definatly help as well since your power would suck past the stock power peak anyway.

Alot. Cams, valve springs, probably a new forged crank.

Cams shouldnt be the real concern at 7900 RPM... the Connecting rods should be. Since valve float isnt near as bad as loosing a rod at 7900 RPM.

You will more than likely throw a rod very fast if you run at 7900 RPM due to the extreme unloaded forces on the rod. Rods are made for a specific stress level, so getting rods made to handle the extreme stresses of that high of an RPM on a big bore 2.5L engine like this is very important.

You are probably looking at a complete rebuild of the engine, New crank, new rods, new pistons, new valve springs, new valves, and at that point why not just get a nice Cobb semi closed deck block, and new heads. You will probably be looking at spending 10,000$ in the end to build a bullet proof 7900RPM engine.

If you want to just do an ecu hack, go ahead, but you will blow your engine in the first run more than likely for many reasons.

You could do the ECU hack, or programmbale engine management and get to 6750 pretty safely, but anything above that is up to you.

how high would a new valve train would let you rev safely, without considering what kind of cams would be needed to make power up there yet..? How about for a low(5-8 psi) boosted engine?


=vic

what are the fuel and timing maps up there above fuel cut??? do they exist? also wold the EJ22t block be able to handle 7000 for get the heads.. as i plan to get STI heads...

I am going to say it again... you are missing the fragile part of the system. its NOT the valve train. Its the Rods!!!

I mean what good does a valvetrain thats tuned do, if a piston disconnects from a rod and implants itself in the head...

There are a few good books out there I would read about how engines work in high end forced induction setups. One of the best is Corky Bell's "Max. Boost" and his "Super Charged!" book. Both address that when you increase the Rev limit you need to focus on the core internals of the engine, and stresses that the stresses on the rods at higher RPM's are the main killer of high rev engines.

The Valve train may have some float to it, but thats rather minor compared to the damages that will be caused when you loose a crank or a rod.

Going to near 7000 - 8000 RPM will take engine internals made for that. A crank, Rods, Pistons, and Valvetrain made to handle those speeds. You cant get by with just doing one part unless you are building a few run grenade engine.

If you want to do it, spend the money and do it right.

You people have no faith in subaru engines. You DO NOT NEED a new crank. Your crank will spin 8,000 rpms at 500hp all day long. The rods in your engine are the same material/design as the ones in a wrx which has a factory redline past 7000. And I think they are the same as the ones in JDM engines which rev even higher. I never had a JDM engine apart so I cant prove that. The only point to mention is the 2.5l does have a larger bore and stroke. With stock cams and no boost you can rev it up to about 7800 before you notice any valve float.(on DOHC heads). I have a Haltech so i can enter in any rev limiter i want.

The rods in your engine are the same material/design as the ones in a wrx which has a factory redline past 7000

hehehehe you just go on believe'n they are the same.

just cause the WRX can do something does not at all mean the 2.5RS can. the EJ20 is a 2.0L engine... the EJ25 is a 2.5L engine. There is MUCH more mass in the pistons on those con rods, thats why there is a lower red line. When you start throwing around more mass/weight you need rods designed for that at a pre determined rev limit.

You just keep on thinking the stock rods can handle 500 Hp all day long and when you finnaly get a grip on reality, do a search in this forum for how many 2.2, 2.5 and 2.0L engines have bent rods. The Crank is also a weak point... I know I have read about 3 or 4 cracked cranks in here so far.


I love when people think just cause the WRX engine internals can do something it means the RS's can do the same... and even more precious... the JDM can do something so the RS can do the same hehehe thats like saying "my Lancer OZ rally edition can rev and run the same as an Evo" get real...

Read a book about dynamic stresses on engine components. Its sort of sobering to read about the forces that the rods/crank deals with.

But eh, if you feel like its safe to run at 7000 RPM on a stock internals EJ25, be my guest, and have fun!

I'm not fully disagreeing, but I am definitely not agreeing either.

I have spun my RS to ~7300rpm and haven't had a single problem (numerous bad downshifts to 4th from ~115) other then I had no fueling to keep going (damn limiter!).

Subaru may make all the rods, however it is likely that the 2.5 rods are made more cheaply then any of the turbo motors. I have seen exactly one bent rod on a 2.5, and one shredded rod in a 2.0T (MY02WRX) - though it wasn't the fault of the rod, rather the bearing.

While tolerances in manufacturing processes vary, I don't think Subaru would vary much between the two types of motors, so bearing are not very likely to go before components.

The mass of the 2.5 pistons versus the 2.0T pistons isn't much different, the real issue is the stroke difference increasing load on the crank bearings as with the longer the stroke, the faster the pistons move at the same RPM's. Destroking a 2.5L motor would yeild excellent results in acheiving a high-revving motor.

In the end... do I believe that the 2.5 RS motor can spin to 7900 without self-destructing? Touchy, but I would give it a bit of use (a week with my driving habits) before it comes apart. Do I believe that the 2.5 RS motor's design is capable, with upgraded components, to spin to 7900? Yes, without a doubt. What would I replace to do so? Pistons, rods, valve springs/retainers, and all bearings. Possibly valves if the stockers can't handle the extra seat pressure.

At the same time as upgrading the entire motor, you might as well go much lower compression (say 8.5:1) and throw 20psi into the motor through a big turbo. You'll be revving high already, and will need to make high-end power to back up the fact that you can actually rev that high.

I actually had a conversation with a local engine buider who was building a forced induction handa engine as I spoke to him and he told me that another problem at high RPMs would be the N/A's stock oil squirters. As at high rpms they are putting a lot a weight in oil up into the underside of the piston, which on the down stroke, has to be pulled back down. This is like an additional 40 to sixty grams(a lot when tollerances are close)

Just food for thought, as you should probably look at all of the aspects and changes you will be causing within the engine, when you change how it performs. And please remember that "reliable" at the high performance end of the engine scale(ie.. 1100hp RB-24's, 420hp SR-20det's, 440hp 2.2 Litre JUN EJ-20 convertions) is only 16 to 20K miles. If you are willing to replace/rebuild that often, have at it. I like the benefits that it induces, it's like heroin. But beware, the pocket book bolemia.

I'm thinking the OEM ECU doesn't have fuel maps for that far past the rev limiter. The Haltech can be programmed up to 16k RPM if you want to build yourself a Formula 1 Subaru engine :devil:

I have my redline set at 6700 rpm right now since the adjusted timing and stuff should be OK at that level. Beyond that I haven't a clue. My injectors went static at 6700 when I hit it last weekend, so I'm thinking I'll need to increase those just a little to compensate as well.

~Garrett

STi rods are different than standard issue wrx rods........

Kevin

the RS doesn't rev high because it's a SOHC engine with a midrange dominate power band. There's nothing above 6.5k, so it's not worth revving the engine up there.

You can always just go STI conversion( 276 PS and reliable all day long power), 7950 rpms.

Hmm... Reading all this makes me want my 1.8 to have a 7000 redline even more :p

I dont give a damn if I blow my 1.8 cause I can just swap in a 2.2 or 2.5 for cheap as nails :D

But the only lead I have on bumping the redline via ECU is reprograming the ECU for $500, and thats just too much for so little :(

The rods in our engine are not the weak point. I have heard many people spin the engines way past 7,000rpm's without hurting a rod.

Besides, if anything, the Rod Bolts are the weak point of a rod assymbly, not the rods themselves. that's rediculous.

Eric

PS: I have never heard of a Rod that has a lower tensil strength than it's rod bolt from the factory so explain how the rod can be the weak link please? :rolleyes:

Eric

Easiest way to a 7900 rpm redline?

STi conversion.

Fuel cut on my RA is at 8450 :)

Originally posted by Cacophony
Easiest way to a 7900 rpm redline?

STi conversion.

Fuel cut on my RA is at 8450 :)


i hate you :p


-vic

yea...but like S2000's, they're still slow :devil:

Seems to me you are going at this backasswerd. Build the engine to handle high RPMs than worry about a guage.

Its like buying a big wing to stick on the back of a Toyota Tercel. Than asking what needs to be done to make it functional.

JMHO.

well his name is decepticon.....


sorry just had to... :lol: