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Old 08-13-2003, 11:13 PM   #1
STiLess
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Default STi has a shorter stroke than the Evo?

Hi i am new here and if I act like a newb, please dont flame me too bad.

Well anyway I was reading the june issue of road and track, and I saw that the STi has a stroke of 79mm compared to the Evo's 88mm. If this information is correct, then could someone please inform me why it would be so difficult for the STi to hold 8000 rpms? I have read a couple of threads that discussed the weakened crank strength of the STi due to the longer stroke of the 2.5L compared to the 2.0L, but at the same time I have herd of ecu reflashes for the Evo to hold 8000 rpms. So why would the STi not be able to do the same as the Evo which has a longer stroke? I am not trying to be arrogant; I just found this new issue to be perplexing.

Of course this information could be wrong, and if it is, could someone please inform me of the correct bore x stroke of the Evo and STi?
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Old 08-13-2003, 11:26 PM   #2
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I'll let the STi experts tell you the real reason the 2.5 turbo can't do 8k rpm. Actually it probably can, just not for any extended period of time.

Suffice to say, a lot of variables are involved. It's not enough just being "strong" enough to handle 8K rpm. It also has to be light enough to do the high RPMs without causing severe vibration or damaging recprocating forces. That includes the bottom end AND the valvetrain. So if for example the STi crank, pistons, con rods, could already handle 8K rpm or better, doesn't mean neccessarily that the valvetrain can, or vice versa.

I'm just picking on the valvetrain because very often it is the first thing to let go in an over-rev situation.
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Old 08-13-2003, 11:35 PM   #3
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I'd like to think that I've been paying attention to stuff like this, and I haven't seen anybody try it yet. We don't even have an ecu upgrade yet. I would think it should be able to take it though. Keep in mind the stock turbo would be hopelessly out of breath.

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Old 08-13-2003, 11:52 PM   #4
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The EJ257 shortblock should be able to take 8K till the cows come home. The EJ257 shortblock might even be able to take 9K for long periods of time depending on the bearings, oiling system and rods.

The heads are a different matter. The however should take 8K all day long if they got the normal STi springs instead of some softer ones with our lower rpm limit.

As for why the STi has a 7K limit stock?? Well isn't 1K of puke and die enough for you?????
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Old 08-14-2003, 12:15 AM   #5
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I specificaly remember that one of the reasons that people are doubting the 257 is that the stroke is longer than the 205 and therefore, more prone to stress. At the same time, it seems illogical to say that the 4g63 will have less crank issues than the 257 because the 4g63 has a longer stroke. I remember there was a very long thread about this issue. Am I just missing a bigger picture?
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Old 08-14-2003, 12:17 AM   #6
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Quote:
Originally posted by XT6Wagon
As for why the STi has a 7K limit stock?? Well isn't 1K of puke and die enough for you?????


Yep, we need another 1000 rpm of tapering power where the stock turbo is totally maxed out!

It will do just fine with bigger turbo, the heads+cams are good enough. When Clark ran that AVO450 on the sti at 16 psi, it made peak power at redline. Thus, you would think it would continue making usable power beyond that. It remains to be seen what will happen with more boost though.

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Old 08-14-2003, 08:57 AM   #7
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Did you happen to look at the bore dimensions on the STi and EVO? I think the STi has a much larger bore, which means the pistons are bigger (more mass). Higher piston mass will translate into more force on the crank bearings. I don't know if this is the reason there is only a 7K rpm redline, but it may be part of it. At this point, nobody really knows how much the engine can take and what the weak link is.
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Old 08-14-2003, 11:42 AM   #8
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Default Boxer Engine

Also remember that you are comparing the Lancer Evo's in-line 4 to the Impreza's boxer 4.
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Old 08-14-2003, 11:53 AM   #9
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Quote:
Originally posted by Mr. Grinch

I'm just picking on the valvetrain because very often it is the first thing to let go in an over-rev situation.
Absolutely right. Not sure about the stock STi engine's limits, but in general it is pretty common to replace camshafts and valve springs when trying to make an engine run high RPMs.
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Old 08-14-2003, 12:35 PM   #10
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Default Re: Boxer Engine

Quote:
Originally posted by dbarnblatt
Also remember that you are comparing the Lancer Evo's in-line 4 to the Impreza's boxer 4.
I am just curious, why is an inline better (not saying that it is) than a boxer in terms of the ability to rev? I know everyone has herd of skylines making 1000hp with 12k of rpms.

Also the Sti has a signifigantly larger bore than the Evo. 99.5mm compared to 85.0mm. I know ths will also have an effect on the stresses in the Evo and STi, but how much?

Last edited by STiLess; 08-14-2003 at 12:49 PM.
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Old 08-14-2003, 12:52 PM   #11
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Quote:
Originally posted by Red Rocket
When Clark ran that AVO450 on the sti at 16 psi, it made peak power at redline
I missed that - got a link?
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Old 08-14-2003, 01:00 PM   #12
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Quote:
Originally posted by Austin
I missed that - got a link?
I think he was intentionally vauge about it.......

http://forums.nasioc.com/forums/show...ghlight=avo450

http://forums.nasioc.com/forums/show...hreadid=398554
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Old 08-14-2003, 01:29 PM   #13
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Default Re: Re: Boxer Engine

Quote:
Originally posted by STiLess


I am just curious, why is an inline better (not saying that it is) than a boxer in terms of the ability to rev? I know everyone has herd of skylines making 1000hp with 12k of rpms.

Also the Sti has a signifigantly larger bore than the Evo. 99.5mm compared to 85.0mm. I know ths will also have an effect on the stresses in the Evo and STi, but how much?
A boxer balances out the piston movements by making them nearly opposite of each other. A 4 cyl inline usually requires a damper / balancer on the crank to reduce vibration, unless something is done to reduce weight of the moving parts (which reduces vibration).

Skylines and Supras are known for high rpm because they are inline 6s, not 4. An I6 has almost perfect balance between the reciprocating weight, there is always a cyl going down opposite the one going up, so there are very limited harmonic vibrations. A V12, which is two I6 in a V, is even better.
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Old 08-14-2003, 01:42 PM   #14
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I would just assume that the point of view from SOA is that there is nothing left from the turbo at after 7k so why make reliability suffer when there is no performance gain. But I am very interested to see what the rev limit is that still maintains reliability with an upgraded turbo.

(Please don't flame me for being a mechanical idiot if I say something way wrong.) Even if it were only 7500rpm, that could make a bit of difference in the 1/4. From what I have read one of the minor complaints of running the STi in the quarter is you really don't get the use of sixth gear. Well, it could be a bit of a juggling act to keep the boost high in the right range and not be caught going from 5th to 6th at the finish line if you keep uping the rev limit and the amount of boost both. But I would think that tuners wouldn't have any problems getting that down.

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Old 08-14-2003, 03:30 PM   #15
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Quote:
Originally posted by Red Rocket


I think he was intentionally vauge about it
Thanks
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Old 08-14-2003, 04:35 PM   #16
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Default Re: Re: Re: Boxer Engine

Quote:
Originally posted by Mr. Grinch


A boxer balances out the piston movements by making them nearly opposite of each other. A 4 cyl inline usually requires a damper / balancer on the crank to reduce vibration, unless something is done to reduce weight of the moving parts (which reduces vibration).

Skylines and Supras are known for high rpm because they are inline 6s, not 4. An I6 has almost perfect balance between the reciprocating weight, there is always a cyl going down opposite the one going up, so there are very limited harmonic vibrations. A V12, which is two I6 in a V, is even better.
Ah now that makes perfect sence. Thank you for enlightening me.
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Old 08-14-2003, 04:48 PM   #17
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I agree with what Red Rocket is saying. The first goal should be to make useable power up to redline. By that I mean, it's still giving more acceleration if you stay in gear to redline than if you were to shift to the next gear. If you've still got useable power beyond that, depending on your gearing, then you might start looking at extending the redline (and at some point upgrading things like the valvetrain depending how far you go).

If the power isn't useable up to redline (the way the car is stock with the exception of first gear) no sense in changing redline.

According to the info posted in another thread, the shift points for gears 2-5 are around 6500 rpm, for max acceleration.
shift points


From another thread here:

STi Top Speed

STi Top speed theoretical at 7k:
(1) 36
(2) 56
(3) 76
(4) 99
(5) 138
(6) 176

As far as shifting into 6th gear in the 1/4 mile, I don't see how that's even possible, on the stock STi. Even if you shift at 6500 I don't see you getting out of 5th gear on a stock STi, considering 5th gear does 138mph at 7k rpm. So that would be about 128mph in 5th gear at 6500 rpm.

Unless you know something I don't, I don't see stock STi doing 128 mph at the end of the 1/4 mile.

For reference, M3 does 138 in 4th gear, you don't even get into 5th in the 1/4 mile, 5th and 6 don't exist for practical purposes. STi does about 99 mph at 7k in 4th. So you'd need some serious mods to bring up the redline AND the useable power to have an STi tuned for 4th gear finishes, or some change to gearing / tire sizes.

But since STi isn't really intended for 1/4 mile why tune it for that? Neither STi or M3 is suited for drag racing. It's better to be out there to have fun, and if you're really into drag racing with a car that is not optimized for it, you'd be focusing instead on bracket racing, which amounts to getting the most consistent times over several races, not all-out speed. This focuses more on your driving and prep skills than on performance boosting mods. These skills will serve you well if even if and when you do move on to real drag cars.

Last edited by Mr. Grinch; 08-14-2003 at 05:00 PM.
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Old 08-14-2003, 06:57 PM   #18
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Quote:
Originally posted by Red Rocket




Yep, we need another 1000 rpm of tapering power where the stock turbo is totally maxed out!
Didnt you know another 1000RPM will put you in Bonus Honda VTEC mode?

What a noob....
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Old 08-14-2003, 06:59 PM   #19
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Quote:
Originally posted by LinuxGuy


Didnt you know another 1000RPM will put you in Bonus Honda VTEC mode?

What a noob....



huh?

Kevin
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Old 08-14-2003, 08:46 PM   #20
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At redline, the STI's moving the piston at 60.5 ft/sec vs 67.4ft/sec on the 4g63. If the STI's redline is 8K, then the piston speed is at 69.1ft/sec. With a big bore piston, that is a lot of mass being throw around at a pretty good speed.

The 2.0 STIs have 8K redlines, don't they? I am not sure what the difference is between the US STI head and the non US STI head, but if the valves, springs,valve guides, retainers, and cams are the same, then at least the head is ready...
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