N/A EJ25 power limits
12-03-2002, 11:39 PM
#62
NASIOC Slut
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Originally posted by N/ABeast
You can also gut your car and have a lightweight, N/A Impreza that eats many cars for breakfast like I plan on doing!
You can also gut your car and have a lightweight, N/A Impreza that eats many cars for breakfast like I plan on doing!
12-04-2002, 10:37 AM
#63
Big Baller
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Ok, there is something you guys are missing.
A high compression N/A motor with big cams and all that will give great power. But if you add any type of FI stuff (turbo or blower) You will get more. You might get turbo lag, but it's all relative. Text book turbo lag is on 8:1 compression cars that need the turbo to create any power. On a high compression turbo motor, sure there will be turbo lag, but you're lagging up to 400HP, instead of no lag to a whoppin 300HP.
See the difference?
Also, an N/A motor with big cams and High compression will have it's own lag and major loss of low end power when you go with bigger cams. Good Torque and throttle response are the product of a strong fuel signal. This is created by having high intake charge velocity. A 300HP N/A 2.5L engine WILL NOT have a high intake velocity at low RPM because the intake will have had to be ported out to a larger diameter to support the flow required for 300HP.
Larger ports=lower velocity= poor torque and throttle response<2k RPM
Stock size ports=higher velocity=good torque and throttle response<4k RPM
Sorry guys, but your dream (N/A) motor DOES NOT EXIST without running 13:1 compression and race gas.
The closest you'll get will be a high compression, SUPERCHARGED 2.5 with COBB ported heads, Equal length headers and a 2.5" exhaust.
Lastly, a N/A 2.5L will never have a higher power potential than a F/I 2.5L.
period.
A high compression N/A motor with big cams and all that will give great power. But if you add any type of FI stuff (turbo or blower) You will get more. You might get turbo lag, but it's all relative. Text book turbo lag is on 8:1 compression cars that need the turbo to create any power. On a high compression turbo motor, sure there will be turbo lag, but you're lagging up to 400HP, instead of no lag to a whoppin 300HP.
See the difference?
Also, an N/A motor with big cams and High compression will have it's own lag and major loss of low end power when you go with bigger cams. Good Torque and throttle response are the product of a strong fuel signal. This is created by having high intake charge velocity. A 300HP N/A 2.5L engine WILL NOT have a high intake velocity at low RPM because the intake will have had to be ported out to a larger diameter to support the flow required for 300HP.
Larger ports=lower velocity= poor torque and throttle response<2k RPM
Stock size ports=higher velocity=good torque and throttle response<4k RPM
Sorry guys, but your dream (N/A) motor DOES NOT EXIST without running 13:1 compression and race gas.
The closest you'll get will be a high compression, SUPERCHARGED 2.5 with COBB ported heads, Equal length headers and a 2.5" exhaust.
Lastly, a N/A 2.5L will never have a higher power potential than a F/I 2.5L.
period.
12-04-2002, 02:06 PM
#64
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Well, I'm sure we know there is a limit of what can be done with 2.5L of displacement - it's the reliability factor that's up in the air. An N/A beast making 250hp to the crank is probably just the same in terms of reliability as a turbo EJ25 making 280hp to the crank (very low boost needed), and I'm sure I would spend a heck a lot more for 250hp to the crank with an N/A setup. I'm not sure you will be able to keep at least the same amount of torque in the low end though... sure with N/A it's nice and natural (because there is no variable valve timing), but I ponder about the loss of torque as you go for the 250hp to the crank. And no, this is my street car so I don't think I will strip it down.
12-04-2002, 11:09 PM
#68
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Originally posted by ImprezaRSX
See the difference?
See the difference?
Yes, we all KNOW how much more power turbo charging and supercharging gives, but that is NOT THE POINT!!! NOW STOP!!!
12-06-2002, 01:54 PM
#70
Big Baller
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Originally posted by Kostamojen
Would you just stop already!!!
Yes, we all KNOW how much more power turbo charging and supercharging gives, but that is NOT THE POINT!!! NOW STOP!!!
Would you just stop already!!!
Yes, we all KNOW how much more power turbo charging and supercharging gives, but that is NOT THE POINT!!! NOW STOP!!!
Fact is people keep speculating about what can and can't be done. I'm just saying that people think you can get a drivable 280HP+ out of the 2.5 Naturally Aspirated.
This thread is N/A EJ25 Power Limits.
So I stated that you CANNOT get those power numbers N/A Like so many people are fantasizing about without race gas and high compression. AND Even if you COULD get those numbers N/A you would have a car with NO low end and it wouldn't be very drivable. You could have a drag RS but that's it.
I was also stating that many of the uninformed people are using Turbo lag as their #1 reason for not going F/I. And that on a properly tuned engine turbo lag would be almost unoticable, the car would be drivable AND you could get the power numbers WE all crave.
So to sum this thread up:
300HP N/A.... reachable, but drag only and not streetable
250HP N/A.... sure, but you're going to need more than
I'll probably go with Cobb Mild Cams, Get a Link ECU to tune well, have a custom Intake Manifold and TB made, along with a Cobb Shortblock and Heads. I think this will put you close to 250 HP..
and that's it.
Of course, you could add nitrous.
12-06-2002, 04:03 PM
#71
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But, Im sure if you buy the cobb shortblock, heads, cams, Get a redesigned Intake Manifold, ITBs or a bored TB, and all the usual bolt on goodies and tune it well, It will be around 250 HP without sacrificing driveability due to a radical cam profile.. Who talked about using wild cams to achive Honda like HP with Hondaesque torque? I'm certainly not.. I would just like the benefits of the EJ25 without the negatives such as its total lack of high end..
12-06-2002, 11:13 PM
#72
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MAN, this thread wandered off on its own little tangent...
I posted this out of curiosity of what would happen if I did the upgrades to my car with the INTENTIONS of going F/I with a turbo setup like the old Minnam/Vishnu kits, but hadn't quite reached it. In other words, all the things I would do on a "normal" budget (think college student, but gainfully employed, with no rush) up to but not including the actual turbo kit. Which means, at most, intake, exhaust, headers, Cobb street cams, possibly a high flow cat and maybe fuel pump and/or return line mod. That's about it, other than maybe getting a tecIII before the turbo kit too. ImprezaRSX hit it on the head. Whether you guys want to believe it or not, a 4 cylinder car making 270+ hp at 6000 RPM and 105 ft/lbs at 2000 RPM is not very streetable. And yeah, Nitrous would work, but it's debatable whether or not one could call a juiced motor "normally aspirated."
Where was I? Oh yeah. Who cares how much horsepower a $7,000 dollar N/A motor would make, when it can't touch the peak power or drivability of $4,500 worth of bolt-ons and turbo. The only justification for pursuing that is just because you have the resources to waste and really want to see just what a N/A EJ25 can possibly do on a drag strip. What I believe we can achieve, relatively cheaply, is a N/A EJ25 that is the equal of pretty much any other N/A 4 cylinder car we would come across on the street.
I posted this out of curiosity of what would happen if I did the upgrades to my car with the INTENTIONS of going F/I with a turbo setup like the old Minnam/Vishnu kits, but hadn't quite reached it. In other words, all the things I would do on a "normal" budget (think college student, but gainfully employed, with no rush) up to but not including the actual turbo kit. Which means, at most, intake, exhaust, headers, Cobb street cams, possibly a high flow cat and maybe fuel pump and/or return line mod. That's about it, other than maybe getting a tecIII before the turbo kit too. ImprezaRSX hit it on the head. Whether you guys want to believe it or not, a 4 cylinder car making 270+ hp at 6000 RPM and 105 ft/lbs at 2000 RPM is not very streetable. And yeah, Nitrous would work, but it's debatable whether or not one could call a juiced motor "normally aspirated."
Where was I? Oh yeah. Who cares how much horsepower a $7,000 dollar N/A motor would make, when it can't touch the peak power or drivability of $4,500 worth of bolt-ons and turbo. The only justification for pursuing that is just because you have the resources to waste and really want to see just what a N/A EJ25 can possibly do on a drag strip. What I believe we can achieve, relatively cheaply, is a N/A EJ25 that is the equal of pretty much any other N/A 4 cylinder car we would come across on the street.
12-07-2002, 11:54 AM
#74
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The problem I see is that not many parts are re-usable between a N/A setup vs Turbo setup (power-wise). CAI? gone. Exhaust? Bigger piping needed. Headers? Maybe, if you get the really good ones that won't crack when you slap a turbo behind it. Cams? Definitely different. Port and Polish? Lots of labour and you won't see much difference till you mod the car to hell, N/A or Turbo. You can address fuel and engine management, but those net minimal gains without other power mods and at a much higher entry cost.
Anything to increase power, you basically have to decide right up front whether you to go full N/A or Turbo - nothing really in between. As for going N/A, if you pick your parts well, you might not lose any torque down low, but you certainly don't gain much down there either - most of the power gains will be up high. Now as you tune for more HP, the torque curve will become steeper, making the car not as street friendly as before.
Now if you're going to strip the car down to the bare minimum, then sure, you don't need that much power because you're improving the power-to-weight ratio mostly by weight reduction first. However, the car will become a dedicated track car, not a daily driver.
Personally, I want around 250hp to the crank, preferably 300hp. When you need that kind of power figure, I doubt the reliability will be all that much different, and in a sense, the turbo might be cheaper to do. Someone PLEASE prove me wrong, and that a 250hp N/A beast will be street friendly, and doesn't cost more than a turbo setup producing the same power figure if not more.
Anything to increase power, you basically have to decide right up front whether you to go full N/A or Turbo - nothing really in between. As for going N/A, if you pick your parts well, you might not lose any torque down low, but you certainly don't gain much down there either - most of the power gains will be up high. Now as you tune for more HP, the torque curve will become steeper, making the car not as street friendly as before.
Now if you're going to strip the car down to the bare minimum, then sure, you don't need that much power because you're improving the power-to-weight ratio mostly by weight reduction first. However, the car will become a dedicated track car, not a daily driver.
Personally, I want around 250hp to the crank, preferably 300hp. When you need that kind of power figure, I doubt the reliability will be all that much different, and in a sense, the turbo might be cheaper to do. Someone PLEASE prove me wrong, and that a 250hp N/A beast will be street friendly, and doesn't cost more than a turbo setup producing the same power figure if not more.
12-07-2002, 12:39 PM
#75
Dork
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Car Info: 2005 STi, 2005 OXT
DUDE, ALEX! You know I'm on this board. I'm member number 3. HOW DARE YOU put a 5000 word limit on a post! 
Part 1.
Hello,
1. Horsepower is a function of the mean (average) pressure being exerted against the pistons in the cylinders.
2. A motor blowing up is a function of the peak (maximum) pressure exerted against the pistons in the cylinders.
2a. On certain Subaru engines, the head gaskets go before the cylinders (woah, novel concept, eh?
)
2b. Tuning determines peak cylinder pressure v mean cylinder pressure. Simple example: ignition timing is usually measured in degrees of crank rotation before the piston reaches the top of its stroke, on the way up toward the heads, when the spark plug fires. Too much advance and the flame front will propagate toward the piston and try to prevent it from reaching the top. If the flame front / expanding gasses push too hard, they crush the ring lands and pop the motor.
2c. Although not true in practice (timing of a single-point spark is not a good enough system), in theory you could continue to build power until you had many times more power than stock without ever changing peak cylinder pressure.
3. The engine doesn't care what creates the cylinder pressure (ignoring tuning-related pressure issues).
3a. Turbos and Superchargers force more air into the engine. The engine sensors (MAF and/or MAP depending on which Subaru we're talking about) detect the extra air and add appropriate fuel.
3b. More efficient NA engines draw more air into the engine. The engine sensors (MAF and/or MAP depending on which Subaru we're talking about) detect the extra air and add appropriate fuel.
So that's the story - it doesn't matter what setup you run, power is power. If you assume the tuning is the same (ie, both NA and FI systems are well tuned), then you can practically assume that peak cylinder pressures are the same and the reliability of both systems is the same, for a given power output. Two 230 hp cars, one NA and one FI, all else being equal, will be equally reliable internally.
Of course, once you get to higher outputs from NA motors, you typically need higher RPMs, which introduce a new unreliability factor...
PART II coming...
Joel
Part 1.
Hello,
1. Horsepower is a function of the mean (average) pressure being exerted against the pistons in the cylinders.
2. A motor blowing up is a function of the peak (maximum) pressure exerted against the pistons in the cylinders.
2a. On certain Subaru engines, the head gaskets go before the cylinders (woah, novel concept, eh?
)2b. Tuning determines peak cylinder pressure v mean cylinder pressure. Simple example: ignition timing is usually measured in degrees of crank rotation before the piston reaches the top of its stroke, on the way up toward the heads, when the spark plug fires. Too much advance and the flame front will propagate toward the piston and try to prevent it from reaching the top. If the flame front / expanding gasses push too hard, they crush the ring lands and pop the motor.
2c. Although not true in practice (timing of a single-point spark is not a good enough system), in theory you could continue to build power until you had many times more power than stock without ever changing peak cylinder pressure.
3. The engine doesn't care what creates the cylinder pressure (ignoring tuning-related pressure issues).
3a. Turbos and Superchargers force more air into the engine. The engine sensors (MAF and/or MAP depending on which Subaru we're talking about) detect the extra air and add appropriate fuel.
3b. More efficient NA engines draw more air into the engine. The engine sensors (MAF and/or MAP depending on which Subaru we're talking about) detect the extra air and add appropriate fuel.
So that's the story - it doesn't matter what setup you run, power is power. If you assume the tuning is the same (ie, both NA and FI systems are well tuned), then you can practically assume that peak cylinder pressures are the same and the reliability of both systems is the same, for a given power output. Two 230 hp cars, one NA and one FI, all else being equal, will be equally reliable internally.
Of course, once you get to higher outputs from NA motors, you typically need higher RPMs, which introduce a new unreliability factor...
PART II coming...
Joel