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Hey all,

Isn't it true that our 6MT is used on the 8000 RPM JDM EJ20 STi? If we shifted our EJ25 at 8000 RPM, we could do 0-60 in 1st and 2nd. My question is, what would need to be upgraded to support the increase in redline to 8000 RPM? I know at least an underdrive crank pulley.

Thank you.
 

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Bump for even better answer than the one I am about to give.

Basically, even if the transmission can handle it, I suspect the motor is what you should be concerned about. My understanding is that it is not as strong as other motors built by Subaru.
 

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There are a couple of Subies running around with STi 2.5 blocks with JDM version 7 heads, and they seem to be doing just fine. One of these runs a 20G turbo.

I am not sure if you can swap in the cams from a JDM STi or not, but to keep the stock heads you would need cams, and an ECU with an 8000rpm redline. An underdrive pulley is not necessary, that would simply reduce the rotating mass.
 

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The JDM heads bolt right up. The compression ratio with a standard head gasket will be about 8.66:1. To run a version 7 or 8 ECU, you will need to make some wiring changes. I wouldn't recommend trying to run JDM heads with the US ECU until there is a reflash available. Even then there may be complications.

The ECU cannot currently be reprogrammed on a US Sti, I hear that will be available this Spring or Summer. Even if you could increase the redline on the US ECU, the cams would not be optimized for 8000 rpm. You will likely have slower times by revving the engine to 8000rpm. Without proper valve springs and cams, you will get valve float. Perhaps a cam swap and an ECU reflash will work, but we will have to wait and see.

Also remember that you will need more fuel, and a larger turbo to create power at 8000rpm. The VF39 falls off before 7000 with 2.5L of displacement.

If I had the cash to do any major upgrades right now I would get a Version 7 RA head and ECU, the twin scroll exhaust from the Version 8 JDM STi, the PE1825F twin scroll turbo, some large fuel injectors (use top feeds with the version 7 heads/ecu), and a custom ECUTek reflash (available for version 7 STis) and a few other supporting mods like a FMIC, fuel pump, etc.
 

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One of the biggest factors for increasing RPMs is engine balancing.... though this might not be too big of a factor if you're only looking for about 1000 rpm over stock....

Small engine vibrations can become very big vibrations at higher RPM, and production engines aren't balanced individually, like you need for a high rpm application. 8000 isn't that high, particularly since the engine already redlines at almost 7k, but it would be foolish to try it without the proper tuning.

F1 engines, and even the spoon sports civic in GT3 (which im sure is an accurate representation or reality) redline at over 13,000 rpms....



And of course you'll be giving up your warranty.....
 

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From what i have found out is that the stock balancing with the same power is good for 8k rev, but you need to remember that it is easier to rev a car with 14psi and 300hp to 8k than it is one running 20psi and pushing 450whp.
Anyways what you will need if you want to rev that high and make it benifical to your 1/4 are such parts as
1-bigger turbo(cause it tappers even going to 7k)
2-bigger injectors (cause stock injectors are almost maxed as is)
3-valve springs
4-some dyno tunning
And you will also probably want new valves and retainers maybe a little port and polish while they are in there just to smooth things out and allow alot of top end flow and maybe a fuel pump depending on how much boost you want to push.
 

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why would you want to increase the RPM limit of your STi? one major drawback to doing that is you would most definately lose more in the low-end than you'd be gaining up top. so for everyday driving you're just setting yourself up for daily driving headaches. as for mechanical changes? there would be alot to look at besides the things mentioned above. Cylinder heads comes to mind. i have no idea what the flow numbers are on the stock STi heads are but are they enough to allow for a 8000rpm redline? camshafts would be a big factor. anyhow increasing performance has less to do with the redline of your motor and more with a good selection of aftermarket parts and a good gameplan and final goal. just having an 8000rpm might make you sound like a hero but it might just make you and your STi a dog.
 

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The Yamaha R6 use an advanced valve spring material which was not used (or needed) in the STi. Any OEM sets the redline based on the dynamic response of components above some rpm. After what I've seen with respect to component stresses vs. rpm, there's no way I would run over the mfg. set redline. Even their redline is set assuming that there will be very little total time near redline (assuming most race through the rpm's and shift down). My shift light is set at 6k, which is optimal for both acceleration and engine life (staying away from 7k can only help). No, I would not seek to up the max rpm. There are MANY other mods to go after for performance...
 
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