Saturn Sports Coupe Aerodynamics
 

I've been checking out the Saturn sports coupes lately (hey, the Geo won't last forever you know) and have been comparing the SC1 with the SC2. I like the SC1 because it looks just like the SC2, tends to be a lot cheaper than its dual cam version, better expected fuel economy, and it has its peak torque at lower rpm.

However, I noticed one large difference about the 2 models in terms of aerodynamics: the SC2 has a Cd of 0.31 while the SC1 has a Cd of 0.33!

Other than the wing mirrors being the same colour as the body with the SC2 the cars look virtually the same to me. Why would the SC1 have worse drag than the SC2?

SC2 & SC1:
Attachment 273Attachment 274

it could be a very small thing like mirors that can at some drag so if there is a lot of small things it can add up pretty quick. thats my guess on what it would be

Just some ideas
 

The side sills look different. Other differences could include the foglights creating different airflow, wheel size and/or vehicle height. Merely guessing...

I thought about the fog lamps and the different styled rims too. I think that rear spoiler creates more drag than if it was without one (forces the air upwards before separating from the car). Indeed the site says the spoiler is for looks and doesn't mention any aerodynamic improvement. Could you explain more about the side sills?

For starters, you could option any sohc s-series to look like its dohc sibling. My car is an SL but it has the appearance and interior of an SL2. It only lacks the rear taillight valance on the trunk.

The cars pictured show slightly different wheels and thats it. Leading me to believe the CD would be identical. The CD would however differ on the less option laden base model SC1.

The following is my personal speculation why the number is higher for the SC1.

Usually the SC1 is without a spoiler and has hubcaps on 14" wheels. The spoiler and wheel combo of the SC2 could contribute to a better CD. Also
SC2's are more likely to have fog lights thus blocking more of the bumper cover.

Those numbers could be for a previous year car.

Its is somewhat confounding to me that the SC2's CD is only .005 lower than my SL sedan's. It does after all appear to have a much nicer taper to the rear of the car.

If I were you I wouldn't rule out the 4 door cars either. I've seen some fantastic deals around here on more than one SL.

2001 SL2 5spd, 50k, $3900(saw it last winter) it was a steal.

2001 SC1 5spd, 55k, $3900 saw it last month.

I would stick to the sohcs as they have nice FE friendly transmissions. Don't get an auto there terrible. The 5speeds have long overdrives. I turn just under 2500rpms at 70mph.

I paid 5k for mine with 50k on it.

Ride height? Angle of the windshield?

Silver Illusion
 

Now that I looked at other models, the Silver SC1 in the pic looked to have a slight notch running at the very bottom of the door at the bottom of the body. It turns out they're similar except for the spoiler.

I was curious as to the SC's weight vs. the SL's:

SC1 = 2379 lb.
SC2 = 2437 lb.

SL1 = 2351 lb.
SL2 = 2403 lb.

Pretty similar and the 4-door costs less, and could be more practical. If you're looking to haul more cargo than passengers, then the hatch is the winner. Plan on taking you and 2-3 others comfortably? Then the SL is the choice.

For me, the Integra's ability to haul LOTS of stuff trumps a Civic 4-door for utility, but is heavier, and is a true 4-seater (or 2 -- sitting in the back stinks).

Could it be that the twincam has more airflow through the radiator, which upsets the Cd?

Yeah, 0.31 to 0.33 only changes drag by about 0.6hp at 65mph.

Does the site that you got that info from list other cars or only Saturns?

The site that I found lists only Saturn models. I thought that a 0.02 Cd change would be quite substantial (or at least noticeable in a car's physical appearance).

The only difference I see is the fog light area of the bumper. .02cd if pretty small.

Late sc1 are my favorite saturn model. It should be good for 40 to 50 mpg (or more if you are hardcore).

Peakster -

I thought those pictures looked familiar! That seems to be a "web capture" of a 200X Saturn website. I like that website for the specs I can pull off of it.

I went to the trusty Miata tire calculator website :

https://www.miata.net/garage/tirecalcold.html

And compared these 2 tire sizes :
P185/65R14 85S (Stock with Saturn SC1)
P195/60R15 87H (Stock with Saturn SC2)

Here are the tire size comparisons :

SC1 tire diameter : 23.5"
SC2 tire diameter : 24.2"

So the SC2 has slightly larger tires, leading to increased frontal area. If you want to go really hardcore, go to tirerack and get the specs on the original stock tire for these models.

Question : Is the wheel size taken into account for Cd calculations?

Also I agree with what other people said about the spoiler, I think it is just for show. Even though my 1997 SC2 had a spoiler, I think the aesthetics of the car are great without one.

Question : Would the addition of the 3rd door (which I love) increase the curb weight of the car? I would think yes. I have an original 1997 sales brochure. If I find it, I will post the relevant specs.

I don't like the plastic redesign of the S-Series (in year 2000?). My favorite is the 1997 to 1999. Very clean lines. I wish they had introduced the 3-door right off the bat (I love the idea of intelligent assymetry in a car, and a suicide door too!!!!!). That original coupe design is why I have a Saturn right now. You could get a sporty looking coupe with 28/40 MPG!?!?!?!?!? And it's American made?!?!?!?!?!? Whoda-thunk?

CarloSW2

But remember, the SC2 has a lower cd than the SC1, according to that site.

Yeah, I think it's the closest thing to a 'modern Fiero' I can find these days (without wasting mucho dinero on a Solstice). Sporty looks with great FE and body panels that don't rust! I've always wondered why the resale of these cars are so much lower than similar Japanese models, since almost every Saturn I find at the junk yard has well over 300,000kms on the odometer. They must be real reliable.

Peakster -

Oops :o !!! I'll have to go back and look at that some more. Maybe the SC1 tires are skinnier?

They have their share of manageable problems, but I think there were some good design concepts built into them that made them cheaper to maintain. I remember reading that the engine bay was designed for easy access so that an average Jane or Joe could change the fluids.

But they have always been poo-pooed in the press. Cheap interiors, not much pizzaz, and such. There is almost NO performance aftermarket for Saturns, so you don't see many of them tricked out. They were designed to compete on their own terms with the Japanese economy cars, and they came up short in the eyes of buyers.

Th one thing that really depressed me about the Saturns is that the Kit Car Culture didn't jump on them like they did the Fiero. I think the specific "space frame" shape of the Saturns may not have been conducive to what Kit Car junkies want, but the body panels were just *waiting* to be swapped out with aftermarket body panels, but no one ever did it.

CarloSW2

.6 hp saved is still good for an extra 1 mpg or so at that speed, assuming nothing else was changed.

Wow, you're right. I didn't think that 0.6hp out of 20hp or so that it takes to keep the car moving would make that much of a difference.

Just running some quick numbers, a BSFC (lb of fuel per hour per hp for the uninitiated) of 0.63 gives a 1mpg gain, but my modeling of the V6 in my car predicts a BSFC in that area, so I suspect the Saturns 4 would do better. If the engine is really slick and the BSFC is down around 0.32, that 0.6hp savings would be worth a 2mpg gain at 65mph.
Of course, this is all assuming the same BSFC for both engines, which is not true. Even if it was the same engine in both cars, the BSFC would rise slightly as you throttle back to reduce the output by that 0.6hp, so there are alot more variables, but the potential is certainly there.

Now try that same math for a .20 drag coefficient, which is well within the realm of possibility on a car that size while retaining the basic overall style.

Generally, BSFC increases. Sometimes as much as the gain in glider efficiency. Depends on the vehicle/engine, but it is something to consider. It's also why Erie Rogers can see a ~35% increase in fuel efficiency from tires, synthetic oil, and a odd looking wing, while MetroMPG only saw a ~30% increase from a grille block, wheel skirts, alternator/mirror delete, transmission swap, synthetic oil, tires at ~45psi, and an underbody panel. Given the same vehicle, I bet MetroMPG's mods could blow Ernie's out of the water, but MetroMPG has to deal with a much greater drop in BSFC compared to load than Ernie does. :thumbup:

edited for clarity

Yeah. But finding engine maps for specific cars hasn't been very easy, making it a lot harder to predict the effects of these modifications. I'd really love to see someone build a 40 mpg V8 land yacht priced like an Aveo. In theory, it is perfectly possible. THAT is what American consumers want, but there just isn't much profit margins in low maintenance, efficient vehicles, and you compromise all sorts of markets you can otherwise create by offering every tiny incremental step between present day and hypercar. To maximize profits, car companies ration out advancements as slowly as they can, so much so that it took 80 years for two companies to make and market an Insight and Prius to beat the 1921 Rumpler in drag coefficient.


Like the Ford Tempo, the Saturn SC2 could have been such a great platform for a practical, efficient car. But the manufacturers never make them the best that they can. Instead, we get a product that shows only marginal FE improvements over the norm.

Even a car with a relatively low .25 drag coefficient has a lot of room for improvement. Isn't the lower practical limit something around .11 for a road car?(eg. solar powered cars, ect.)


Even fullsize luxury cars, minivans, and SUVs with large engines could be consuming about half the horsepower at speed that they do today. This corresponds almost to a doubling of fuel efficiency at speed, but not quite a doubling since the lower engine load means lower thermal efficiency.

BSFC increases as you throttle back an engine. Higher BSFC = more fuel used per hp generated. The lowest BSFC is WOT at the peak torque RPM.
I think you meant that effeciency drops?

The greater % you throttle back an engine the worse the increase in BSFC, which is why big engines are bad for economy. It's not the extra displacement per se, it is because you have to restrict the engine so much to only make a very low HP number that it is producing power pretty ineffeciently at that point because of all the throttling losses and the resulting low cylinder pressures. This is why GM and Chrysler are using cylinder deactivation - cut out half the cylinders and now you can open the throttle alot more and produce the required power more effeciently.

I have often wondered, if you have a car with a very low CD, would it be effecient to have two engines? Shut off the 500hp one on the highway and run a 35hp unit to cruise on. When the driver hits the gas, the big motor fires up and you go! Hybrids have really developed the technology to quickly and seamlessly start and stop an engine so this might be possible. A 35hp engine running at near WOT would be quite effecient...

Exactly what I meant. :o

Regarding a drop in drag coefficient, like anything else, there are plenty of reasons why manufacturers don't bother with it. There are probably more, but they include
-Aerodynamic instability at high speeds
-Building great EV gliders
-Small increase in efficiency
-Interbrand pressure
-Lower cost to maintain
-Etc...
To take advantage of the increase in glider efficiency for gasoline engines, they need to drop in a taller OD gear, or use a CVT. The problem with a taller OD gear in today's automatic cars is the balance between having the tranny kickdown, or stay in gear with more throttle for better efficiency. Toyota/Lexus went to an 8 speed automatic with some kind of intuitive learning so the car could get better mileage, but most Corollas aren't going to get an 8 sped auto tranny. Even the Prius' CVT doesn't spin at the optimal rpm for fuel efficiency at ~55mph, since it still has to rev up in order to have what most consider to be acceptable passing power.

BSFC maps are generally pretty simple. NA diesel have a pretty even distribution of ovals.
https://www-personal.engin.umich.edu/...s/image016.jpg
As do TDI's. with the large drop at the bottom being associated with the turbo dropping out of it's efficiency band (turboed gasoline engine probably has the same deal).
https://home.earthlink.net/~rps1976/I...ion%20Map.jpeg
A DOHC NA gasser looks like this.
https://www.v6performance.net/gallery...0805_Fig11.gif
With the difference between the dotted and solid lines probably attributed to better control of ignition and possibly better fuel injection control. A VVT-whatever engine would have even larger BSFC ovals with the peak BSFC pushed a bit to the left... And an Atkinson cycle gas engine has near diesel BSFC ovals. I think a SOHC may have the peak higher, or at the same place depending on the cam (i.e. it may not let in as much air as early, pushing peak BSFC farther down), and carbed engines can probably have some odd maps, since they don't meter fuel linearly, or as precisely as a fuel injected car would, unless I'm at the right rpm.

2001 Saturn SC1 EPA ratings: 28mpg city / 40mpg highway / 33mpg combined
2001 Saturn SC2 EPA ratings: 27mpg city / 38mpg highway / 31mpg combined

However get a load of this:
I wonder what fuel economy improvement someone would see if the SC2 transmission was swapped with a SC1 transmission? Perhaps the SC2 does have better aerodynamics and more efficient engine, but it's hampered with a shorter top gear, thus decreasing its FE? I'd like to find the actual final drive ratio differences between the SC2 and SC1.

Peakster -

Yes, the S?2 drivetrains have what is called an "MP3" transmission, while the S?1 drivetrains have an MP2 transmission.

I think the only question is whether or not the ECU/PCM would get upset. Otherwise they should just swap right in.

This is a saturnfans.com quesiton. It must have been asked before. Maybe I will ask it again.

CarloSW2

Are you talking about a manual or automatic transmission? If it's a manual, I can't see any reason that the ECU would know the difference as long as you have the right signal for the speedometer.

For an automatic, it would depend on how much GM integrated the powertrain and engine controll modules. If the trans controller is seperate from the engine controller, that would likely need to be swapped along with the trans to get the right shift points and then communication issues might come up.

He is talking about the manual trans. In saturn s-series cars you often have to swap trans and the matched pcm together. I'm not sure on the particulars I ran into similar issues while looking into cruise control. Apparently the pcm monitors VSS and engine RPMS to make sure there's no funny business.

Peakster -

I found my 1997 Saturn brochure (another victory for packrats!). Here is the Cd info :

Attachment 342

I am going to post all the vitals in a later post.

CarloSW2

Interesting. Yet another source that says that the SC1 has higher drag than the SC2.

Eureka! The SC2 has a more aggressive spoiler
 

I think I found the main difference between the SC1 and SC2:

SC1:
Attachment 378

SC2:
Attachment 376

My question is why is it that the SC2's spoiler (which appears to separate the rear air flow higher than the SC1) is more beneficial for Cd?

One reason I suspect is that the 'kick' in the SC2 spoiler does a better job at eliminating/reducing vortecies at the rear departure by allowing more side air to tumble underneath.

Also, by being higher up the rear spoiler will probably help increase the pressure on the rear window = less drag. Basically it would 'trick' the air into seeing a shallower taper at the rear.

Hmm. Makes sense. So basically, if a person wanted the higher MPG SC1 and wanted the lower drag of the SC2, it's just a matter of changing spoilers.

It seems that way, unless someone can find a notable difference in the nose. I can definately see the right spoiler making a up a 0.02 difference in Cd. Actually, the right one can make much more...

At 2001 Saturn SC1 Specifications It shows the 2001 Saturn SC1 and a drag coefficient of .31

Zombie Thread! RUN!!! :D