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APR DTR6054 Direct Turbocharger Replacement System

riceburner

riceburner

Autocross Champion
Location
nice try PPNT
Car(s)
MK5 Best GTI
starsmith said:
OK so since yall speculated on where I'm getting these numbers, and I think this is valuable to discussions about when a given amount of power is useful or not, here is a detailed derivation of the absolute maximum power that a FWD car can put down at a given speed. This makes some simplifying assumptions, but is valid at the low (~45mph) speeds we have been discussing, where both drag and downforce are too weak to be important in any road car.

Assume the power of the car is P. Power is the rate at which mechanical work is done, and work is the product of force and distance. Since velocity is the rate at which distance increases, the rate at which work is done is the product of force and velocity, F * v, so P = F v and hence

F = P / v (Eq 1)

Assume now your car is at the absolute limit of its front wheel grip - the force of friction is F = μ F_N, where μ is the coefficient of friction and F_N is the force with which the tire is pushing against the surface. In this case, we assume F_N is equal to the fraction of the vehicle's weight on the front wheels, around f = 60% of the weight for a GTI. So the forward thrust provided at the wheels is

F = μ f m g (Eq 2)

Here m is the mass of the car and g is the acceleration due to gravity, 9.8 m/s^2. μ will be ~1.2-1.3 for the absolute best road tire in existence on the absolute nicest unprepped track surface in existence, whereas you can get more like ~2 in drag conditions. We are neglecting weight transfer here because we want a best-case scenario - in practice the car will lift off its front wheels, reducing f. This is what suspension setup can help with somewhat.

OK now equate F from Eqs. 1 and 2. We have

P / v = μ f m g

Solving for P, the maximum power you can put down is

P = μ v f m g

Plugging in μ=1.3, f=0.6, m=3300lb, g = 9.8m/s^2, and v = 45mph, we obtain a maximum power that can be put down of about 300hp. Remember, this is assuming 0 wheel hop, 0 weight transfer, and absolute top-shelf sticky meaty rubber on clean asphalt, so in practice it will be less. That's why tuned GTIs like to spin if you mash the throttle from a 40 roll in 3rd.
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quoted for epic context
 
oddspyke

oddspyke

Autocross Champion
Location
Delaware
Car(s)
2016 GTI, 2018 ZL1
starsmith said:
Thanks for sharing. Demonstrates what I was on about earlier in the thread - your 0-60 is no better than Stage 1 numbers because you are never exceeding the maximum ~.5-.6g afforded by your tires and suspension in street conditions, and Stage 1 can keep up with that amount of power to the ground. Past 60 is where you should really see the difference.
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.... Keehs?
 
CarbonDub

CarbonDub

Autocross Champion
Location
Silver Spring, MD
Speaking of rolls, I just pulled on some kid in an AMG GLE 63 S Coupe. He took off out of nowhere from a light so I wanted to see if I could catch him. To my surprise I slowly reeled him in, caught him at ~120 in 5th (sport mode), pulled past, and let off at some point around 130.

He was dumbfounded at the next light, rolled down his window as we exchanged big grins plastered to our faces and he shouted something excitedly (couldn’t make it out, but “holy shit”esque).

From a quick google search that SUV traps 115-118 mph in the 1/4. No idea if it has a speed governor at 130 or something, but even if it did I caught him prior to that. Definitely not a race, but if you want to chase randos down past 130 mph, you’re in luck…

(I need to get this Dragy and some verified numbers and chill TF out with the hot pursuit)
 
CarbonDub

CarbonDub

Autocross Champion
Location
Silver Spring, MD
bentin said:
It’s governed to 174mph.
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Jeez, definitely a number this car will never see. Well, maybe he’d have regained past 150 then haha.
 
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Subliminal

Subliminal

Autocross Champion
Location
Vegas
Car(s)
Slow FWD VW Hatch
he def gets on it again at 9secs, you can hear his exhaust as you pass by
 
CarbonDub

CarbonDub

Autocross Champion
Location
Silver Spring, MD
Someone just posted another DTR dyno video for a 2021 MK7.5 GTI, APR tune - 411whp/393wtq:


Definitely seems to be a disconnect between the peak dyno figures and real world performance with this kit. Not that the performance is poor by any means, just that the power figures seem to demand more.

My Dragy should be here today, stay tuned for more mediocre 1/4 miles and 60–130s :cool:
 
mrmatto

mrmatto

Autocross Champion
Location
Jacksonville, FL
Car(s)
2024 GTI DSG
CarbonDub said:
Definitely seems to be a disconnect between the peak dyno figures and real world performance with this kit. Not that the performance is poor by any means, just that the power figures seem to demand more.
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I think it's weird how obsessed the car community is with saying X power should produce Y time or speed -- and then use that logic to "disprove" claimed power figures. (Not saying you're doing this.) There are so many other variables like spool time, power curve, etc. You can have dramatically different power curves with exactly the same peak HP output.

For example, we shouldn't expect these 3 examples to perform the same, right? Even though they make the same peak/headline power, there are very real differences that would affect performance.

1657720035745.png

1657720044088.png

1657720015483.png

(third one is a just a silly sketch to illustrate an extreme example)
 
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