How much horsepower to be comparable to WRX?

[Plays_with_Toys]

I'm just trying to go through the math, and correct me if I'm wrong on this.

WRX's come with 227chp, but to the wheels its about 165hp. They are also several hundred pounds heavier than my 96 wagon. Currently I've got a 140chp motor which is hopefully making 90whp on a good day.

I've got a motor combination I will be piecing together this year as part of fun and a bit of education for myself. A local dyno'ed his 2.5RS which had a stock motor, but full exhaust and intake with larger injectors running e85 at 145whp. He had unequal length headers. With this combination he says he can keep up with lightly modified wrx's.

I'm looking at a 2.5 block, dual port 2.2 heads, delta cams, OBX equal length header, a hi flow cat, ej22t injectors and a walbro fuel pump running e85. Because of the differences in the motors, I would port the intake/exhaust. With the higher compression motor, equal length headers, and cams, I should be able to put a good 25hp or more on what the stock 2.5RS made. The figures I've come up with is that I am looking at around 200-220chp, with AWHP in the neighborhood of 160. A few local car builders have agreed that these power figures are about right, but what do you guys think?

Do you think with my shorter gear ratios and lower weight, will this combination get me up into wrx speeds?

[Reason]

Did you see my dyno numbers? I like to know where this guy got 20+ whp of el headers and larger injectors??

http://www.sl-i.net/FORUM/viewtopic.php ... no+numbers (http://www.sl-i.net/FORUM/viewtopic.php?t=2980&highlight=dyno+numbers)

I had a perrin pulley, intake, stromung mid pipe and SPT axle back. Maybe a el header and highflow cat would have gotten his power up there. Very interesting....

[Wiscon_Mark]

Tuning can do a heck of a lot for an N/A motor. EL headers and cams just as much so. If you pull a lot of tricks, you can make an N/A EJ25 more powerful than a WRX motor (although it will take more peak HP to beat a WRX as they have a pretty good powerband with the turbo).

Using the EJ22E heads is a great way to get the compression up.
Finding a Forester tranny with the 4.44FD would make your car considerably quicker as well.

It gets expensive though.

[Plays_with_Toys]

http://www.youtube.com/watch?v=MB-rs3B83uc

Th e85 is where you get alot of the extra power from. It's a very good source for basically free horsepower, it is alcohol after all. I was saying that since equal length headers are good for something like 10hp over borlas, and this guy did not have cams or a high compression motor, my numbers should be about 20-25 more than his, especially since high compression motors need high octane fuel, and e85 is in the neighborhood of 105-110 octane.

[Kraziken]

I'm just trying to go through the math, and correct me if I'm wrong on this.

WRX's come with 227chp, but to the wheels its about 165hp. They are also several hundred pounds heavier than my 96 wagon. Currently I've got a 140chp motor which is hopefully making 90whp on a good day.

I've got a motor combination I will be piecing together this year as part of fun and a bit of education for myself. A local dyno'ed his 2.5RS which had a stock motor, but full exhaust and intake with larger injectors running e85 at 145whp. He had unequal length headers. With this combination he says he can keep up with lightly modified wrx's.

I'm looking at a 2.5 block, dual port 2.2 heads, delta cams, OBX equal length header, a hi flow cat, ej22t injectors and a walbro fuel pump running e85. Because of the differences in the motors, I would port the intake/exhaust. With the higher compression motor, equal length headers, and cams, I should be able to put a good 25hp or more on what the stock 2.5RS made. The figures I've come up with is that I am looking at around 200-220chp, with AWHP in the neighborhood of 160. A few local car builders have agreed that these power figures are about right, but what do you guys think?

Do you think with my shorter gear ratios and lower weight, will this combination get me up into wrx speeds?

That's about right, when I originally looked at doing Cobb spicy cams and heads, EL headers, intake etc. I remember I think I was calculating 230hp at the crank. You shouldn't be far off.

[StatGSR]

Th e85 is where you get alot of the extra power from. It's a very good source for basically free horsepower, it is alcohol after all.

you do know when e85 burns it creats much less energy than gasoline right? octane just resists knock.

[rougeben83]

That's the basic consensus among the NA tuning posters on the other subaru forums.

They basically propose the same basic setup; cams, el headers, full exhaust, intake, engine management, and that's good for around 200bhp and change.

Coupled with the lower gearing and lighter weight, it should be able to keep up with a stock wrx.

Especially if it's an autox/tight course, were the smoothness and torque of the NA motor will be an asset.

[Reason]

Th e85 is where you get alot of the extra power from. It's a very good source for basically free horsepower, it is alcohol after all.

you do know when e85 burns it creats much less energy than gasoline right? octane just resists knock.

I read the same thing

[Wiscon_Mark]

On an engine that isn't high compression and designed to burn that high octane, yes.

But what he's saying isn't unproven.

[StatGSR]

I read the same thing

yes thats because thermodynamics says so.... you need to burn about 1.5 times the amount of e85 to get an equal amount of engery to gasoline.

[Plays_with_Toys]

Th e85 is where you get alot of the extra power from. It's a very good source for basically free horsepower, it is alcohol after all.

you do know when e85 burns it creats much less energy than gasoline right? octane just resists knock.

sort of correct. e85 on a gallon for gallon basis has less energy than gasoline, but when you throw oxygen in the mix the e85 is more powerful. A big reason so many drag racers have alcohol fuels of some kind.

Speaking of thermodynamics... I have a test in it tomorrow, so I better get off the computer and start studying that...

[StatGSR]

but when you throw oxygen in the mix the e85 is more powerful. A big reason so many drag racers have alcohol fuels of some kind.


how do u figure, it only has one heating value. and drag cars use mostly nitromethane...

[scottzg]

It's a very good source for basically free horsepower, it is alcohol after all.

so... alcohol = good?




it seems like 25 heads would have a good advantage over the 22 heads for peak power production since they flow much much better. Can we assume your boy was running some kind of aftermarket engine management? If not, maybe the stock stuff just isn't providing enough fuel at w00t? That's a pretty significant variable, imo.


Especially if it's an autox/tight course, were the smoothness and torque of the NA motor will be an asset. the torque advantage would go to the turbo car. Which brings up the point that if the na car has the same peak power as the turbo car, it's almost always slower since the turbo car has a much fatter power band.

[Plays_with_Toys]

The 22 heads are what gets your the higher compression ratio, and that's why they are used, not for the flow of them. Also, the RS was running engine management to tune for the fuel flow of the e85 (you need 15-30% more fuel flow into the motor for the e85 to run right).

The advantage of this project as I see it is 1)no turbo lag, 2) cheaper build than going turbo or motor swap (<$1500), 3)it's more original, 4) $1.80/gallon to fill up

[Sarra]

so... alcohol = good?

As long as your engine is consuming it, yes. When it's in your blood, and you're driving, no. :smt023

E85 has a higher knock resistance, which means you can run more boost, and therefore, pump more of it into your engine. Basically, you can make more power, but you're going to use up a lot more of it in the process.

[Reason]

What if the 2.2 head are pNp, who would they compare to stock 2.5?

[Sarra]

What if the 2.2 head are pNp, who would they compare to stock 2.5?

IIRC, 2.2 heads + 2.5 stage1 block = 14.something:1 compression ratio. You'd have to get special headgaskets to make it work, or pistons, or you'd have to run race fuel all the time. I may be wrong, though. Might be 2.5 heads + 2.2 block = super high compression ratio... Stupid bipolar making my memory bad.

[Huffer]

14:1 comp ratio is ridiculous. Not even CAM2 would be able to handle that kind of detonation/knock.

I can tell you that 2.5 DOHC heads on a SOHC shortblock = 11:1 (approx), and that will require the running of at least 89 octane. Anything higher and you will need standalone EM to cope.

[Sarra]

14:1 comp ratio is ridiculous. Not even CAM2 would be able to handle that kind of detonation/knock.

I can tell you that 2.5 DOHC heads on a SOHC shortblock = 11:1 (approx), and that will require the running of at least 89 octane. Anything higher and you will need standalone EM to cope.

I did not know that. What about the later higher compression SOHC motors, or is the bump in CR in the head and not the block?

[Huffer]

AFAIK, the compression ration on the later model SOHC engines is still 10.1:1 - the difference is because of the cam profiles and the AVCS system.

They get a bump up from 165hp to 173hp.

[StatGSR]

= 11:1 (approx), and that will require the running of at least 89 octane.

dude 11:1 needs premium 91+ for sure.....

[Wiscon_Mark]

dude 11:1 needs premium 91+ for sure.....

Depends on the tune. To make the most of it, yes, you'd want to tune for premium.

[Sarra]

= 11:1 (approx), and that will require the running of at least 89 octane.

dude 11:1 needs premium 91+ for sure.....

Not necessarily. If you can get a piston designed for a higher compression ratio, then it shouldn't be a problem. Our Toyota T100 runs an 11.1:1 CR and runs on Regular gasoline.

If you're going to be running a higher CR, you may as well tune for 91 or 93 octane gasoline anyway. Take full advantage of it.

[camaroz1985]

Was this ever built? I'm looking to do basically the exact same thing for my Grassroots $2009 Challenge car.

[camaroz1985]

Any updates? I'm really interested to see how this turned out.

[Wiscon_Mark]

I don't think he ever did anything with this, no...

[camaroz1985]

Then I guess I'll be the guinea pig :D

[Sarra]

A 2.5 GT or 2.5 RS should be able to keep up with a WRX with less HP, up to around 75 mph. Gearing is your friend in a 2.5 GT or 2.5 RS. The WRX has long gears and is the great equalizer.

Though, there's a 2005 OBS I know of that has intake, exhaust and cams that is faster than my WRX. He's also running a PP6. Last I heard he had dibs on a COBB Accessport when they release them for NA applications. :D