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Old 04-25-2004, 10:03 PM   #1
LatentWagen
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Default v8 vs 4 banger

ive always wondered... i realize that there is "no replacement for displacement" when it comes to power... but what is the reason for this?

ie: why does a 300 horse v8 pull on a 300 horse turbo'd 4, if they are both pulling the same weight?

i know they "breathe better", and ive heard that used as an explination many times. i guess im looking for something more complete.

-ed

ps: hope im in the right forum for this question
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Old 04-25-2004, 10:12 PM   #2
pegdrgr
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Area under the curve. If you have more power over a range of RPM you will be faster regardless of peak power. It is the shape of the power curve that matters, not the peak.
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Old 04-25-2004, 10:30 PM   #3
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well said, power band is much greater
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Old 04-25-2004, 10:41 PM   #4
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that makes sense. still, why does my friends stock s4 pull on me like a demon after 80 mph when my stage II dyno chart beats the s4's no question?
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Old 04-25-2004, 10:54 PM   #5
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not enough info
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Old 04-25-2004, 11:13 PM   #6
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Don't forget gearing, and a broad torque curve give more usable acceleration.

The 4th and 5th gears in the WRX are not ideal for top end acceleration, they are optimized for gas milage. A car with a wider power band, can make use of a larger portion of the engines rpm range, and will have more surplus torque at low rpm to allow it to pull into its power band if you stomp the throttle at cruise.

If the WRX had a red line a few hundred rpm higher it could make much better use of its gear ratios. It also would not need the huge split between low and second that the USDM tranny uses.

Much of the gear ratio selection decision is driven by a need for the manufacturer to meet CAFE standards for fuel milage.


For example the Corvette takes advantage of its torque to skip shift the transmission at light accleration to get good around town milage. It leaves the stop light in low gear and jumps to 3rd gear I think on the upshift if acceleration is moderate. You can't do that without the broad low rpm torque characteristic of a large displacement NA engine.

Larry
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Old 04-25-2004, 11:15 PM   #7
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actually most V8's or V6's are significantly heavier cars than 4 bangers. I was reading some reviews of 0-60 and 1/4 mile times for V8's, V6's and 4 bangers.

Seemed as though the 4 bangers spanked the competition in a big way across the board.

The WRX beat the Porsche Boxster not by much but it did. If you guys don't believe me I'll post the article. The Rex was also on par with the S4 and close to the M3 when it came to 0-60 and 1/4 mile times.

AmRik.

Smokin' Ferrari's all damn day!!

Peace Audi
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Old 04-25-2004, 11:36 PM   #8
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thanks for the info hotrod, that helps. actually, the vette shifts from first to FOURTH... that 5.7 is a monster. in the vette, ive started on several occasions in third rather than first, and not noticed it!

i still feel like there are some cars that can just dig in after 100mph. the s4 is the best example i can think of that is comparable, power wise, to a slightly modded wrx. i know gearing is important, but is 4th really that weak?
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Old 04-25-2004, 11:40 PM   #9
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Quote:
Originally posted by asbWRX04


Smokin' Ferrari's all damn day!!

Peace Audi
what ferraris do you smoke?
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Old 04-25-2004, 11:50 PM   #10
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parked ferraris
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Old 04-26-2004, 12:06 AM   #11
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Default 5MT

Thanks for the confirmation it skip shifts to 4th, I couldn't remember for sure.

The gear ratios on the WRX 5MT are
3.454
------------- 56% split
1.947
------------- 70% split
1.366
------------- 71% split
0.972
------------- 76% split
0.738


As you can see the difference in gear split from 1st to second is almost 35% larger than the other gears. If that gap was closed up and 2nd, 3rd, and 4th moved down a bit, the car would pull much harder at highway speeds. As you can see 4th gear is an overdrive ratio.

Larry
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Old 04-26-2004, 10:17 AM   #12
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Quote:
Originally posted by hotrod


Much of the gear ratio selection decision is driven by a need for the manufacturer to meet CAFE standards for fuel milage.


Larry
Don't forget the 0-60 claims

I HATE first gear in this car. I've never had such a useless gear in any car. 4th is pretty ridiculous also.

Any affordable 6-speed options yet? Hopefully they get under 4k in the next couple years.
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Old 04-26-2004, 10:37 AM   #13
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Default Re: v8 vs 4 banger

Quote:
Originally posted by midnite_wrex
ive always wondered... i realize that there is "no replacement for displacement" when it comes to power... but what is the reason for this?

ie: why does a 300 horse v8 pull on a 300 horse turbo'd 4, if they are both pulling the same weight?

i know they "breathe better", and ive heard that used as an explination many times. i guess im looking for something more complete.

-ed

ps: hope im in the right forum for this question
are u serious? the replacement for displacment is technoligy. and i beat V8's that make more power than me all the time. because of my power to weight ratio and AWD, and gearing. and rarely do u have a v8 and 4banger the same wieght making the same power. i can beat the 390 hp cobra's and i make like 285whp and 270wtq.
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Old 04-26-2004, 10:42 AM   #14
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4th gear on the WRX does suck big time. On the strip, I hate the idea of getting into fourth, because the car would feel like it stalled and roll through. For the RA gears, it's a different story.
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Old 04-26-2004, 11:09 AM   #15
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replacement for displacement is forced induction. It is not the displacement, but the amount of air and fuel you can burn at once that gives you power. Now with forced induction comes a laggier powerband, so that means you have to rev higher to stay with the big boys, but you can indeed stay with them unless they start using the same tactics (i.e. modified 03-04 cobras).
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Old 04-26-2004, 12:59 PM   #16
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blackie, i am serious.

if you took the time to read my post instead of babbling about how fast your car is, then you would see that my example was ceteris paribus.

Quote:
Originally posted by midnite_wrex

ie: why does a 300 horse v8 pull on a 300 horse turbo'd 4, if they are both pulling the same weight?


notice the phrase "same weight"

also, all wheel drive doesnt help much when youre already moving.

but congrats on your power numbers. i bet my girlfriend is hotter than yours!
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Old 04-27-2004, 01:00 PM   #17
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I smoke Ferrari's mostly Enzo's!

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Old 04-27-2004, 02:34 PM   #18
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And don't forget the drag coefficient at higher speeds. The WRX has some ungodly number of .73 or something like that. 0-60 is nice, but then you see a loss in acceleration for equal gearing with a sexier looking car with a smaller Cd. Besides, they are probably more stable at high speeds without the need for a pizza-box wings.

I'll shut up now and go to bed.
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Old 04-27-2004, 03:39 PM   #19
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.73? Wow, that's awful. Luckily the WRX is no where near there - .33 sedan, .37 wagon for the slanty eyed variants. No doubt the bugeyes are a bit worse.

My money says the reason for the discrepancy is optimism in calculating the turbo4's flywheel horsepower.
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Old 04-27-2004, 04:56 PM   #20
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torque.

My mild 340 made 251 whp @ 4500, and 342ftlbs @3000
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Old 04-27-2004, 09:21 PM   #21
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I think top end has everything to do with air flow! I know my WRX really slows down at 100mph. WRX's are not very aerodynamic at all.

My WRX -- ------ ------ --- 12.8 @ 104mph
Corvette ZO6 at the track day I ran 12.8 @ 117mph
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Old 04-27-2004, 09:59 PM   #22
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PxLxAxNxK/33000

do the math
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Old 04-27-2004, 10:19 PM   #23
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im not familiar with those variables... or that denominator
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Old 04-27-2004, 10:25 PM   #24
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Quote:
Originally posted by MUGWUMP
I HATE first gear in this car. I've never had such a useless gear in any car.
Go drive a diesel or an older truck with a MT and a "granny low" and then you will discover the most useless 1st for most situations. However, when towing that "granny low" is your friend.

On another note: "Boost #1 replacement for displacement" "Revs #2 replacement for displacement"
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Old 04-27-2004, 10:34 PM   #25
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I love it when people want simple answers to comples questions. First, in it's simplest terms, and engine is just an air pump. If you pump more air, you make more power. Big engines pump big air, but turbos make small engines pump big air, but not at low rpms, but small engines rev higher, but... Next, the area under the curve is a key. Take calcusless. A good example of this is electric motors. Torque line, not curve. You can drive a passenger car with a 15 HP electric motor. Do not try this with your lawnmower engine. Lastly, gearing. If you have better gearing, you can sty in the sweet spot of the power curve longer. In the 80's Mercedes were DOGS off the line, but highway passing was a dream. That is because they had three usable gears from 50-100 mph. The best solution would be a continously variable transmission, if only someone could make one as strong as the Suby gearbox. (sarcasim intended, but it is also true)
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