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Old 09-01-2002, 08:49 PM   #1
Patrick Olsen
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Default Dyno results: +36.5hp over stock, naturally aspirated

A group of us were up at Adrenalin Motorsport in Massachusetts for a Subaru dyno day. I've been to Adrenalin's dyno a few times already to do stock and modified runs. Adrenalin has a Dyno Dynamics Low Boy AWD dyno, which is an eddy current type load-bearing dyno.

A while back I did three stock runs on two different days - 100.3hp, 105.7hp, and 106.7hp = 104.3hp average. Since then I've added a full MRT exhaust, Cobb Stage 1 heads, Cobb Street cams, and an Injen intake. The last time I was at the dyno (about three months ago, with a used WeaponR intake rather than the Injen intake) I tuned my newly installed S-AFC and put down 132.5hp on the dyno. The AFR was a nice, flat 13:1 all the way through the RPM band. I haven't changed the settings since. However, I did remove the WeaponR intake, and went back to the stock intake with K&N panel filter.

Recently the engine just doesn't seem to be very happy. I've been noticing a ticking noise that I was afraid was an exhaust valve going bad (which has happened before, and led me to get the Cobb stuff). Sometimes the idle is rather rough, other times it will idle at 2000rpm when I first start it (when it's 85deg out, mind you), etc etc. I've been getting all sorts of conflicting indications. As an example, when I pulled the plugs a few weeks back they indicated the car was running quite lean, but when the dealer pulled the plugs earlier this week they were very dirty, indicating the car is running rich. The ECU pulls timing (which I've datalogged with a PocketLogger) which would make me think the car was lean, but the exhaust tip turns black. I've tried adding fuel with the S-AFC, and it didn't seem to make any difference as far as the hesitation went.

So, back to the dyno story. My first two runs yesterday looked bad - 129.5hp and 128.7hp, with AFRs running 14.5-15:1 up to 4000rpm , then 14:1 to redline, and torque way down across the board. Did the intake cause it to run that lean? (Keep in mind that when I tried out a used WeaponR intake, the car dyno'd just as pig rich as stock). Whatevah. Richened it up 5% across the board after the first run, then another 5% after the second run. On the third run AFRs were down to around 14.2:1 up to 4000rpm, then 13.6:1 to redline. The result - 140.8hp, about 37hp more than stock at the wheels.

Unfortunately, the computer hiccupped, so that last run didn't save properly. We saw it draw out on the graph during the run, and then shifted to the numbers screen and saw the big 140.8, but when Ami (Adrenalin's head dude/dyno operator) went back to try to save it to disk for me it was gone. The run that was saved as my third run was identical to my second run, so somehow that got hosed up. By the time we figured this out my car was already being pulled off the dyno, and since there were a few more guys waiting to go, and we had already had a delay due to technical difficulties, I didn't want to be a bitch and make them run it again. Oh well....

I was pretty happy to see that 140.8hp pop up there on the screen. Trey Cobb had told me an intake would help out quite a bit (when I expressed disappointment at the relatively small gains of the heads and cams), but soon thereafter I dyno'd with the WeaponR and saw zero gain. I really wasn't sure what to expect from the Injen, so I was quite surprised to see it pick up another 8hp. Not only does it sound sweet at WOT but it actually makes good power, too!

So, now we get to the age-old question - how much is it making at the crank? Honestly, I don't know. My guess is that I'm somewhere in the vicinity of 205hp, assuming my engine was making 165hp when I dyno'd it stock (with K&N and synthetics throughout). So, that's about 63hp drivetrain loss + 140.8 = roughly 205hp. There are some that say drivetrain losses are a percentage, but I think my results prove that isn't the case - at least not on Adrenalin's dyno. If you were to just use the ratio of (165/106.7) * 140.8 you get 217.7hp at the flywheel - only 10 less than what Subaru says the WRX puts out. But a stock WRX dynos at around 165hp on Adrenalin's dyno, which is 24hp more than my car dynos. So, either the WRX's advertised output is under-rated by Subaru, or a fixed drivetrain loss is a bit more accurate in this case. Who knows for sure?

Pat Olsen
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Old 09-01-2002, 11:15 PM   #2
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Actually, by your own numbers, you should be pulling 192.59@ the crank. (using the percentage for drivetrain loss)

Wheel HP was 104.3, stock crank is 165, so the percentage of loss is 36.787878787878787878...%. Take 140.8, multiply that by 36.7879%, divide by 100 and you get 192.59. It's grade school math......And it only took me 20 minutes to figure that out.

[Edit] If you think about it, assuming that the MRT full exhaust will gain you 14.4 HP to the wheels, your power output would roughly be at 184Hp to the crank. Somethings smells fishy about your run. The cams + full exhaust should've placed you well over the output your at.

Last edited by obyone; 09-01-2002 at 11:22 PM.
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Old 09-02-2002, 12:35 AM   #3
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Quote:
Originally posted by obyone
Actually, by your own numbers, you should be pulling 192.59@ the crank. (using the percentage for drivetrain loss)

Wheel HP was 104.3, stock crank is 165, so the percentage of loss is 36.787878787878787878...%. Take 140.8, multiply that by 36.7879%, divide by 100 and you get 192.59. It's grade school math......And it only took me 20 minutes to figure that out.
And in that 20min you still did it wrong. If it makes you feel any better, you made the same mistake that most people do when they try to apply a drivetrain loss percentage to figure out flywheel horsepower. You calculated the loss as a percentage of flywheel horsepower, which is correct. Then you multiplied that by my new wheel horsepower, which is wrong. Here, let me show you how to derive the equation:

First, WHP = horsepower at the wheels, while FWHP = flywheel horsepower. So...

WHP = FWHP - drivetrain loss
WHP = FWHP - (X) * FWHP ....... where X is some percentage
WHP = (1-X) * FWHP
Therefore FWHP = WHP/(1-X)

So, using the number you calculated (36.7879%) we get
FWHP = 140.8hp/(1-0.3637879) = 221.3hp
(When I did my calculation I went with the most conservative numbers, in other words, the smallest drivetrain loss, so I used the 106.7hp run. That's why I got 217.7hp in my original post).

Note that there's a big difference between calculating FWHP the correct way, and calculating FWHP by multiplying WHP by some percentage. Dividing by (1-X) is quite a bit different than multiplying by (1 + X/100). I see guys do it the wrong way all the time. Why is my way the right way? Well, we start with flywheel horsepower and lose some portion of it before we measure it at the wheels, so it makes sense that the drivetrain loss is some percentage of FWHP. We don't start with WHP and somehow create power to get to FWHP, so it does not make sense to define drivetrain losses as a percentage of WHP.

Quote:
Originally posted by obyone
If you think about it, assuming that the MRT full exhaust will gain you 14.4 HP to the wheels, your power output would roughly be at 184Hp to the crank. Somethings smells fishy about your run. The cams + full exhaust should've placed you well over the output your at.
That's exactly why I was disappointed by my first dyno runs with the Cobb heads and cams on the car. I went from 114hp at the wheels to 127hp - not exactly earth-shattering numbers. However, if you read Cobb's site, they say, "Depending on parts used in conjunction with this Cylinder Head package, power gains are potentially 25-35HP...." Based on that, I'm actually slightly ahead of the curve right now. Adding the S-AFC and Injen CAI allowed me to optimize the combo a bit, picking up another 13 or 14hp.

I'd love to see what the car would put out with all of the current mods but with stock cams, or all of the current mods but with stock heads. With the stock heads and cams would I have picked up another 13 or 14hp with the Injen and S-AFC? Who knows. Until I make lots of money and decide to spend it all on dyno testing I won't know just how effective the Cobb stuff is.

Pat

Last edited by Patrick Olsen; 09-02-2002 at 12:41 AM.
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Old 09-02-2002, 01:31 AM   #4
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Interesting... I just saw stankfootz run on a simular type of dyno (IE not a dynojet, a full blown real dyno at Vishnu) and he got 126whp with just a cobb intake, MRT header/midpipe with a stromung muffler, plugs, and magnacore wires...

Those 128-130's without the tuning are interesting... We calculated stanks car at about 174hp or so crank? Doesnt seem like the cams really do to improve that does it... Maybe up to 180 or so?

But what I really would like to see someone get the higher reving cams and ACTUALLY move the redline and dyno it!!!
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Old 09-02-2002, 01:44 AM   #5
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pat i understand your frustration, that's alot of money spent and not too much in the way of results...and yes the intake makes a difference...where did you guys get a 36% drivetrain loss?? cobbs dyno seems to support a 26% drivetrain loss, that's why i asked. as for my 2 cents on this issue, unless you've done a FULL port job like the one done to Whitewag's CRX that i put together for him then you really won't see too much in the way of gains on the heads.

Jeremy
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Old 09-02-2002, 03:04 AM   #6
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Quote:
Originally posted by HndaTch627
where did you guys get a 36% drivetrain loss?? cobbs dyno seems to support a 26% drivetrain loss, that's why i asked.
What kind of dyno is cobbs?
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Old 09-02-2002, 03:33 AM   #7
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Quote:
Originally posted by Kostamojen

What kind of dyno is cobbs?
mustang dyno...i just can't see that kind of discrepancy between one kind of dyno and the next

jeremy

p.s.: IIRC
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Old 09-02-2002, 07:04 AM   #8
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Quote:
Originally posted by HndaTch627
i just can't see that kind of discrepancy between one kind of dyno and the next
Well, to put it simply (and hopefully without sounding like a jerk), you need to learn more about dynos, Jeremy. This type of difference has been brought up here a number of times (pretty much every time someone posts dyno results). Up to a 15% difference has been proven based on the type of dyno alone.

Pat
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Old 09-02-2002, 01:23 PM   #9
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Quote:
Originally posted by Patrick Olsen

Well, to put it simply (and hopefully without sounding like a jerk), you need to learn more about dynos, Jeremy. This type of difference has been brought up here a number of times (pretty much every time someone posts dyno results). Up to a 15% difference has been proven based on the type of dyno alone.

Pat
i guess i can accept it, and i know dyno's have discrepancy but a 26% drivetrain loss as opposed to a 36$ drivetrain loss that's incredible. anyhow i hope you get things worked out. and i guess i should my car on the rollers sometime soon.

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Old 09-02-2002, 01:30 PM   #10
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I think dyno's are nice for tuning your car, but I would be more interested in 1/4 mile times or something. I would think you would be able to run low to mid 14's with those mods....
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Old 09-02-2002, 06:59 PM   #11
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Quote:
Originally posted by HndaTch627
i guess i can accept it, and i know dyno's have discrepancy but a 26% drivetrain loss as opposed to a 36$ drivetrain loss that's incredible. anyhow i hope you get things worked out. and i guess i should my car on the rollers sometime soon.

jeremy
See, I'm just the opposite - I think the drivetrain losses coming from Dynojets are way too small for an AWD drivetrain. From what I've read here, stock WRX's normally dyno around 185-190hp at the wheels on a Dynojet, which works out to about 18% drivetrain losses. That's not much more than the number most people use for manual transmission 2WD cars (Mustangs, Camaros, etc) - generally people throw out 15% for those cars. An AWD car has two extra differentials, two extra axles, and CV joints thrown into the mix - all that stuff has got to account for more than another 3% loss. My guess is that the Dynojets show such low drivetrain losses because really only half the drivetrain is being used - one set of rollers is just a "dummy" set. Just a guess, of course...

Quote:
Originally posted by nomorefocus
I think dyno's are nice for tuning your car, but I would be more interested in 1/4 mile times or something. I would think you would be able to run low to mid 14's with those mods.
The nearest dragstrips are all about 3hr away. It's just not worth the trouble to drive all that way for maybe 90sec of "racing". I went to the strip once with my first 2.5GT, and found that it was about as exciting on the strip as watching paint dry. I'm moving out to Hawaii in a couple months, and there'll be a strip much closer there (kinda hard for it to be far away ). I imagine I'll do more drag-racing out there, but I'd be more inclined to do it with my Mustang - much more exciting.

Pat
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Old 09-03-2002, 12:40 AM   #12
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Well,I dyno'ed in at 123.4whp in my car

I have a brullen header back,Lightweight pullies,K&N filter,and 80,000 miles.

If your're pulling only 20 more horses for almost 4 grand more worth of items then i think something is definitly wrong.

Of coarse,The stock ECU may not bne able to support the amount of mods you are running even with the SAFC.

I know for a fact that my car runs pig rich throughout the RPM range.
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Old 09-03-2002, 01:49 AM   #13
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But if you boost it you could raise HP from 98 stock to 233 at the wheels like I did

Anyways, I always figure a 25% loss for Subaru, so I use the following

WHP = Fly HP x 0.75
FHP = WHP x 1.33
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Old 09-03-2002, 08:14 AM   #14
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Hi Patrick,

Remember a while back when we did a spin down "Drivetrain Loss" calc with my car.

I posted a dyno chart with a spindown calc based on a Dynojet, not a dynapac. The spindown resulted in a 27% driveline loss?

Anyways, with the dyno chart and the drivetrain loss calc, mine dyno'd at 208HP at the crank.

I'll try to dig up the old thread. I think 36% is a little high for drivetrain loss. Did the dyno you used have a spindown test for drivetrain loss? It would really clear up the speculation.

Thanks

Ah, here it is:
http://forums.nasioc.com/forums/show...highlight=Dyno
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Old 09-03-2002, 04:51 PM   #15
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Pat, either the dyno is having some issues or your car is. Your analogy between the WRX whp and fwhp is a good one. With just stage1 cams, pulley, intake, high-flow cat I was giving stock WRXs a run for their money (I'd lose at higher speeds but it was close). Now I'm running a full header and proecm and am definately making more power, WRX results are more in my favor now (still get beat by the occaisonal quick stocker though). Your heads and SAFC should imply you've got a nice chunk of juice on my setup. I've figured I'm running 210-215 fwhp (depending on weather) using hp/weight ratios of the WRX and the GM6 RS. You might want to get your hand on another dyno, or even a g-tech (I know they are pretty inaccurate but average a bunch of runs and you should be pretty close) to determine the accuracy of Adrenalin's dyno. Also, you may want to upgrade your tranny/diff fluid prior to your next dyno tuning session to see if it helps.
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Old 09-03-2002, 07:17 PM   #16
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Default Re: Dyno results: +36.5hp over stock, naturally aspirated

Quote:
Originally posted by Patrick Olsen
I tuned my newly installed S-AFC and put down 132.5hp on the dyno.
How does one go about tuning a vehicle with a S-AFC? Does the car need to be on a dyno to tune a S-AFC?

Chieh
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Old 09-03-2002, 11:50 PM   #17
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You guys are killin' me here. There's nothing wrong with Adrenalin's dyno, nor is there anything wrong with the results I've seen. I've already quoted Cobb's website once, do I need to do it again? The gains I've seen are exactly in line with what they say one should expect from the Stage 1 stuff. Is there more to be had from my setup? I'm sure there is, but I think it will take a custom ECU reflash to get there.

Quote:
Originally posted by jetfan8178
Well,I dyno'ed in at 123.4whp in my car

I have a brullen header back,Lightweight pullies,K&N filter,and 80,000 miles.
OK, great. Now come the two mandatory questions when it comes to this discussion: (1) what type of dyno? and (2) what was your stock baseline? For all I know you car only put out 120whp stock and your results are from a Dynojet. Comparing raw numbers from different dynos is worthless, comparing gains from different dynos is not. That's why I always mention what type of dyno all of my runs were done on, and I mention what my stock results were.

And for the record, my engine has 114,000miles on it, with 60,000 of those coming in the last 21 months. In that 60,000 miles the head gaskets have blown twice, I've burned up an exhaust valve, done dozens of auto-x events, and done 17 (I think) track days. The entire short block is still stock. My compression numbers are still good, but I think my leak-down numbers are a bit high (albeit still within Subaru's specs).

Quote:
Originally posted by jetfan8178
Of coarse,The stock ECU may not bne able to support the amount of mods you are running even with the SAFC.

I know for a fact that my car runs pig rich throughout the RPM range.
I concur, and that's exactly why I mentioned that the engine just doesn't seem to be very happy. I'm sure the ECU is struggling a bit, and I'm hoping I'll be able to get the ECU reflashed before the Navy moves me to Hawaii in October.

Pat
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Old 09-04-2002, 12:49 AM   #18
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Quote:
Originally posted by BOY
Pat, either the dyno is having some issues or your car is. Your analogy between the WRX whp and fwhp is a good one. With just stage1 cams, pulley, intake, high-flow cat I was giving stock WRXs a run for their money (I'd lose at higher speeds but it was close). Now I'm running a full header and proecm and am definately making more power, WRX results are more in my favor now (still get beat by the occaisonal quick stocker though). Your heads and SAFC should imply you've got a nice chunk of juice on my setup. I've figured I'm running 210-215 fwhp (depending on weather) using hp/weight ratios of the WRX and the GM6 RS. You might want to get your hand on another dyno, or even a g-tech (I know they are pretty inaccurate but average a bunch of runs and you should be pretty close) to determine the accuracy of Adrenalin's dyno. Also, you may want to upgrade your tranny/diff fluid prior to your next dyno tuning session to see if it helps.
I think you are a liiiiiiiiiittle too optimistic about your car...

Im sure you could run high 14's with a good 60 foot time with that set up, but you still wont be making stock WRX power numbers.
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Old 09-04-2002, 06:56 AM   #19
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Quote:
Originally posted by Kostamojen
Im sure you could run high 14's with a good 60 foot time with that set up, but you still wont be making stock WRX power numbers.
I don't think that's what he's claiming. If you read it again, BOY just said that he could stick right with a WRX in acceleration, which makes sense. I was cranking through the numbers the other day after I got back from the dyno and found that an RS with my engine would be pretty damn quick. The pounds-per-HP of a 205hp 2850# RS is almost exactly the same as the pounds-per-HP of a 227hp 3140# WRX. Unfortunately, my 2.5GT is about the same weight as a WRX so I'm not as quick.

Pat
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Old 09-04-2002, 10:01 AM   #20
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Pat, right on. My concern is your engine should be making more power on the dyno as vehicle weight is irrelevant. All I'm suggesting is a comparison test series to confim/deny the dyno numbers. Either way, you have a great setup and even if the ##'s seem low you've still got a screamer.

Kost, the dyno numbers on the stock WRX's are all over the place, some are dramitically quicker than others. I've run enough to know that I'm right in the middle of their performance range. using 227hp as a baseline I calculated my hp to weight ratio, factoring in weather conditions (mind you I live in Texas right now but the car has been all over the country) in 100deg heat 205 is probably reasonable, however, when weather conditions change (65-80, moderate humidity) my car absolutely screams, hence the higher 215. I'm in there somewhere, and 10hp is pretty much unnoticable to the butt dyno. And to your comment about running high 14's, yup WRX's run high 14's stock, I run with WRX's... do the math.
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Old 09-04-2002, 02:06 PM   #21
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Boy,
Do you have any idea what your 1/4 trap speed is vs a WRX? Thats really a better indicator of power/weight than ET.
My RS with street cams, intake UDP and catback trapped at 87.75mph IRRC the WRX's were trapping 90-92 mph.
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Old 09-04-2002, 03:17 PM   #22
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Midway, unfortunately I will not full-up drag the car until I work on the clutch/fw. I just finally replaced a blown center diff (driving on it blown for ~8 mos) and I don't want to go through that again. You do have a good point though on the trap speed but also remember the gearing, the redline, and the cd are quite different between the two cars, we actually need a bit more hp/w to get the same trap speed. I can tell you this the runs I've made (usually onto highways, on highways, etc) have been up to 100, usually if I get beat it is around 90mph when our drag kicks us in the boys.
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Old 09-04-2002, 03:38 PM   #23
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I understand not wanting to drag launch. But IIRC the launch doesnt affect trap speed much, so you can take it easy and still get a good trap. Oh well. I wish I had a baseline on my car.
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Old 09-04-2002, 03:56 PM   #24
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BOY, isn't the RS tranny more aggressively-geared that the WRX tranny? this is helping us RS guys as well.

peter
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Old 09-04-2002, 04:07 PM   #25
BOY
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Location: Ft Wayne, IN
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99 RS-T RIP
02 Forster-S

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depends how you look at it. 1 extra shift will take away from your overall ET and trapspeed. The biggest problem is the damn cd. Its like taking a football vs a shoebox, the shoebox is lighter but you have to throw it a lot harder to make it fly like a football. I remember a couple of years ago I was messing around on the highway with a mustang (tweaked v-6 if you can believe that) and he had me on top speed BUT if I drafted him I'd get the needle well past 120 until I'd try to shoot around him then the car felt like it just hit the brakes, aero sux.
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