Top Speed (no wind resistance)

[Bogie]

It's the engineer in me, but I do wonder about such things. We know the SKY is drag limited in terms of speed, with a theoretical limit between 140 and 150. But what if drag didn't factor in? What would our stock baby do without wind resistance, with just the electronic engine redline limiter to get in the way?

Someone correct me if I'm wrong (and I may well be as I'm not an auto engineer), but I do believe the relationship between speed, gear ratio, and RPM is linear, right? I don't need to factor in differential ratio and what not if I've already got a speed baseline, right? Engineers like linear presumptions...because it makes things easy....in fact we even linearize non-linear systems to make things easier....and it works.....sometimes. I digress. If I'm not right about the linear relationship (and I'm sure someone will come along an enlighten us if I'm not), everything below is rubbish. I'm sure there might be a small difference in drive train losses as function of gearing, but I'll "assume" those away as "negligible" between fourth and fifth gear, without really having a clue as to their true negligibility. And friction will take it's toll as well, but we'll assume those differences away too.

Youtube has a nice dyno run for a SKY Redline, which shows a pic of both speedometer and the Tach redlining at the top end. Dyno runs are performed in fourth gear (where the gear ratio is 1:1). The run shows the SKY redlining at engine electrical cutoff at a speed of 130 mph. The fifth gear ratio is .73 for the manual. If the linear relationship holds, a 130 mph limit at a ratio of 1 will map to a 178 mph limit at a ratio of .73.

So there you have it. The stock computer limited no drag limit: 178 mph. Of course, you can't test it unless you can somehow eliminate wind resistance...which maybe you could do drafting some beast that can actually punch through 1 atmosphere at such speeds....like a Z06 or Lambo.

Edit: Actually, I guess you could test it by redlining on a dyno in fifth gear.

[BigSkyCountry]

I think you're dead spot-on with your math. The reason why drag plays such an important role is that I think that drag coefficients are somewhere in the 4:1 ratio. That means, for every 10% in speed, drag increases 40%. It's either that or you need 40% more horsepower to increase speed by 10%. Damn, I wish I paid more attention during physics and less time studying the girl in front of me.


Nah.... Ray

[puggsleyssky]

Gosh I was always under the assumption that according to the laws of gravity, whatever goes up must come down. However I have not the inclination nor the authorization to report an such a sudicious subject at this particular time, so I shall put it off until a later date! This car is addictive and so are the people on this forum! I wish I was smart enough to have been able to take physics!! ..... Puggs

[Deuce]

I notice that the added weight of my wife, say 150 lbs, adds a lot of drag to my car. For some reason it just seems to run faster without her in it. Is it me and not her added weight or what? (hee hee)

[lorennerol]

Originally Posted by Deuce

I notice that the added weight of my wife, say 150 lbs, adds a lot of drag to my car. For some reason it just seems to run faster without her in it. Is it me and not her added weight or what? (hee hee)

Careful there or you'll find her posting about how much better she sleeps now that you've been evicted from the bed to the sofa due to her taking offense at things you've posted here!



L (married 16 years now)

[Bogie]

I did another theoretical number crunch at 6200 RPM, 0.73 5th gear, 18 inch tires, and 3.73 final drive train ratio and came up with 187.0, which compared to the original 178 is probably within the error range of the excluded variables. If you want a nice rounded "no drag" number to throw out, I would just round it to 180.

Said another way, if you turn an engine at 6200 RPM, geared at 0.73 and 3.73 through the differential to an 18 inch wheel, you will be spinning the wheels at a rate that propels the vehicle at about 180 mph.

Again, this is purely analytical. All the SKY horsepower will be swallowed up overcoming drag at around 140 mph.

By the way, anyone know why some of the spec charts indicate a 6200 cutoff and others sources identify a 6300 cutoff? Maybe the 6200 is the max you can sustain at 100 increment resolution, with 6300 being the actual cutoff trigger? If so, I guess the true max is 6299 perhaps?


Edit: One more piece of Gwhiz; the max horsepower at fifth gear is produced at an RPM that is pretty close to what the engine can turn at the drag limit, in consideration of drive train loses. A higher gear buys you nothing without more horses.

[puggsleyssky]

Thanks Bogie! and keep the info. coming. You need to be paid to accurately predict the ratings of the modded vehicles for forum members. Or for supplying just the information needed so that others can try to intrepret on their own the power of say a 2.4 sky with a 275 lb. operator, cai, cat back, hi-flow converter, ecu tune, and manual transmission. You make this forum most interesting!!!...Puggs

[Bogie]

Originally Posted by puggsleyssky

Thanks Bogie! and keep the info. coming. You need to be paid to accurately predict the ratings of the modded vehicles for forum members. Or for supplying just the information needed so that others can try to intrepret on their own the power of say a 2.4 sky with a 275 lb. operator, cai, cat back, hi-flow converter, ecu tune, and manual transmission. You make this forum most interesting!!!...Puggs

How's this for interesting. A 2.4 running at 7000 RPM in 5th gear will bust 200mph...no mods required.

[SKY-DOGY]

GoodYear tire specs. 245/45/18 F1s: Revs per mile = 786 divided by 5,280 ft equals a circumference of 80.6106 "
Or......................
tire diameter of 26.6 inches times 3.14 equals a circumference of 83.524"
Take your pick!

[puggsleyssky]

WOW NOW!! Well I'd better see someone.. Vector? about that tune!!!! awesome, Puggin Puggs

[Sky Hi]

Originally Posted by Bogie

How's this for interesting. A 2.4 running at 7000 RPM in 5th gear will bust 200mph...no mods required.

The 2.4 is geared a little lower than the redlines. Final ratio is 3.91 for the 2.4 where the 2.0 redline is 3.73. I calculated what the speeds would be while operating at maximum power RPM. Ideally you would want the car geared for max power to equal the wind resistance and loss load if you are to attain maximum top speed.

Redline max 260HP @5300RPM => 151 MPH

2.4 max 177HP @ 6600RPM => 180 MPH

2.4 Stage II DDM 280HP @ 5300 => 145 MPH

I doubt the Redline will actually reach 150 MPH, No way a 2.4 will reach 180!, (maybe it will go faster in 4th gear), but I suspect a supercharged stage II DDM would reach 145MPH. What are the Redline "racers" seeing???

[JRinKY]

Sky Hi : The 2.4 is geared a little lower than the redlines. Final ratio is 3.91 for the 2.4 where the 2.0 redline is 3.73. I calculated what the speeds would be while operating at maximum power RPM. Ideally you would want the car geared for max power to equal the wind resistance and loss load if you are to attain maximum top speed.

Redline max 260HP @5300RPM => 151 MPH

2.4 max 177HP @ 6600RPM => 180 MPH

2.4 Stage II DDM 280HP @ 5300 => 145 MPH

I doubt the Redline will actually reach 150 MPH, No way a 2.4 will reach 180!, (maybe it will go faster in 4th gear), but I suspect a supercharged stage II DDM would reach 145MPH. What are the Redline "racers" seeing???

Because you are looking for terminal velocity, you also have to pay attention to engine torque and its multiplication through the drive train.

[RickyD]

I thing we need to find a very long (unused road of coarse)!
and see just how fast these things can go!

Please let me know when and where

[puggsleyssky]

The question of top speed is one that I have wondered about, and one of the things that I have not seen addressed on this or any other forum. I'm not concerned about speed as much as I am "quickness" and agility performance. It is fun to see and read about it as you guys compute and discuss the possibilities.Keep the Gwhiz coming! BTW, I am seriously contemplating the purchase of the DDM Stage II S/C. ....Puggs

[Bogie]

Originally Posted by puggsleyssky

Keep the Gwhiz coming! BTW, I am seriously contemplating the purchase of the DDM Stage II S/C. ....Puggs

Note most of my Gwhiz in this thread is pure mathematics divorced from reality. From a practical standpoint, my numbers cannot be achieved in the real world. Why do I do this? I'm an engineer. I like to toy with the mathematical LIMITS of things. It helps define a boundary, and gives me a better understanding of the first order mechanics. Then I can start backing out friction, inertia, drag, etc.

For example, I noted that if a 2.4L can turn 7000 RPM in fifth gear, it can go 200 mph. Well, a 2.4L stock will never turn 7000 RPM in fifth gear because drag, inertia, friction and a host of other "real world" things will never let it get there. Because in order to spin it that fast against nature you probably need about 600 horsepower. The 177 HP will pretty much get max'd out at around 120 or 130 mph.

[BlueSkyRL]

Originally Posted by Bogie

Note most of my Gwhiz in this thread is pure mathematics divorced from reality. From a practical standpoint, my numbers cannot be achieved in the real world. Why do I do this? I'm an engineer. I like to toy with the mathematical LIMITS of things. It helps define a boundary, and gives me a better understanding of the first order mechanics. Then I can start backing out friction, inertia, drag, etc.

For example, I noted that if a 2.4L can turn 7000 RPM in fifth gear, it can go 200 mph. Well, a 2.4L stock will never turn 7000 RPM in fifth gear because drag, inertia, friction and a host of other "real world" things will never let it get there. Because in order to spin it that fast against nature you probably need about 600 horsepower. The 177 HP will pretty much get max'd out at around 120 or 130 mph.

I'm an engineer too and find your "on paper" calculations fun and accurate enough if we could drive in a vacuum void of every force known I have had or know of someone very very close to me that the RL will do 147+ on a good day with a tail wind...but I'll deny I ever said that

[GreenDevil]

Originally Posted by BlueSkyRL

I'm an engineer too and find your "on paper" calculations fun and accurate enough if we could drive in a vacuum void of every force known I have had or know of someone very very close to me that the RL will do 147+ on a good day with a tail wind...but I'll deny I ever said that

Yeah, I "know someone" who had their RL going 145 on a roadtrip through Wyoming. It was shaking like a jackhammer....so I am told.

[Bogie]

If you're interested in speed and horsepower, this vid does a good job explaining the relationships. It also has some really neat engineering stuff. One of my favorite lines: "At this speed, the tires wear out in 15 minutes.....but that's OK...because the fuel runs out in 12". The part where it "hunkers" down is pretty cool too. Top Gear does an excellent job with the choreography and sound track.

YouTube - Top Gear - Bugatti Veryron 253 mph

Edit:
And here are some Gwhiz numbers for what a SKY needs:
60 mph: 17 HP
100 mph: 81 HP
120 mph: 140 HP
144 mph: 240 HP
168 mph: Stock RL Tire Rated Limit
200 mph: 640 HP
240 mph: 1120 HP
288 mph: 1920 HP

[RedHeaded RedLine]

Originally Posted by BigSkyCountry

...drag coefficients are somewhere in the 4:1 ratio. That means, for every 10% in speed, drag increases 40%. Nah.... Ray

"As speed doubles, aerodynamic resistance squares"
As for your wife's weight: 100# is ~.1sec in the ¼ mile.
As for tire diameter discrepancy: the tire deflects under load, so its static diameter is different from its dynamic diameter. -J

[blackmod]

lets see some real numbers

just my two cents - being north of the boarder in canada, mph and psi really frustrate me. I'm always trying to do the converison, especially with the turbo.

My max speed is 235 kph / 146.03 mph with more in it, ran out of road
this was done in clear weather 12 celcius, altitude 1049 meters, 6 km strip of road decline at the start and slight incline for last 1.5 km

my turbo spikes at 125 kpa to 130 kpa momentarly and I have know idea if tHAT IS GOOD OR BAD?

I have added stuff sinse and waiting for snow to dissapear so i can try again. i'll take a picture of the speedometer this time if i have the chance...
top speed in snow 173 kph WWWeeeeeee