Coefficient of drag, frontal area and curb weight of RMW?

[TheFleshRocket]

My Ebay CAI should be showing up either at the end of this week or the beginning of next. I happen to have an Auterra ( www.auterraweb.com ) OBDII monitoring tool, and one of its features is a road dyno. I'm going to run the RMW before and after doing the CAI to see if it actually nets any measurable power gains. But in order to do it, I will need the following:

Coefficient of drag.

Frontal Area.

Curb weight (including 200lb driver).

If any of you guys have that info handy, please let me know. I'll post my results and impressions after getting the CAI.

 

[Buffman]

I always thought the CD was about .34 or something.

 

[MrBuick (Magnum)]

Those are some veeery good questions. The frontal area would be nearly the same as that of a Caprice sedan(not a roady sedan). The weight, I wanna say is about 4550 lbs. The info I found on the car put the curb weight between 4500-4600.

 

[tyler711]

Curb weight is also in the manual I think, if you have that in your glove box!

I'd get mine, but the walk to the lot from the dorm is a long one...

 

[TheFleshRocket]

I don't trust the manual's numbers for weight, given that who knows if that's dry weight (no fluids), wet weight (with all fluid except gas, or even with gas) or with any passengers. If you look on your door jamb, you might see a GVWR (or some acronym like that) listing some number that is absolutely positively a lot more than the car's real curb weight.

Actually, I'm going to go squint at the RMS review that Stuart posted--it should at least have an accurate curb weight in it.

<edit> My squinting suggests 4240lbs. Car & Driver's curb weights are with a full tank of gas and a driver. So how much more is the RMW? I figure it can't be more than 100lbs extra.

Here's the pic again--check it and see if my eyes were accurate:

 

[tyler711]

I see 4240 as well, but I don't know about 100 pounds more... the tailgate, longer roof, roof rack etc. I know you don't like what the manual says, but it does have weights listed for both the sedan and wagon. Maybe you could use gm's difference in weight there? I dunno.

 

[MrBuick (Magnum)]

The wagon's about 300lbs more!!!!!

 

[TheFleshRocket]

The wagon's about 300lbs more!!!!!

You think the difference is that much? The wagon has the rear seats which the sedan doesn't.. which maybe add 50 lbs? There is additional roof metal but not a whole lot, once you consider that the roof metal on the wagon is at least partially duplicated in the trunk on the sedan. Rear glass probably weighs about the same on both.

I'm not saying the difference couldn't be as much as 300lbs--just that I'd be surprised if that was really the case.

 

[TheFleshRocket]

I guess the Roadmaster wagon is indeed a fat(ter) pig. According to this site: http://consumerguideauto.howstuffworks.com/1991-to-1996-buick-roadmaster-6.htm

RMS: 4211 lbs.
RMW: 4572 lbs.

Wow, what a huge difference. I have no idea where that extra ~360 lbs comes from, but apparently it is there! All that extra weight in the back would certainly improve traction and make burnouts more difficult.

I'm not sure if those numbers are wet or dry, and with driver or without, but assuming both vehicles were measured the same way, the difference in weight is still probably accurate.

 

[TheFleshRocket]

I found the coefficient of drag of the Wagon here (http://www.theautochannel.com/vehicles/new/reviews/wk9342.html) and the frontal area of a Cadillac Fleetwood here (http://myweb.accessus.net/~090/cfb.html). I figure the Fleetwood is close enough for this testing.

cD: 0.35
Frontal Area: 25.9 square feet

That, along with the curb weight, should be enough information to get my Auterra to produce SOMEWHAT accurate dyno numbers for this beast. Guess I'll go play with it today and see what it comes up with.

The Auterra recommends making dyno runs in fourth gear for stick shift cars as that's usually a 1:1 ratio which should produce the most accurate numbers. However, as we all know, the speed limter cuts off the fun well before redline in fourth gear and even in third gear. Second gear, on the other hand, will hit redline. And putting the transmission in second not only prevents it from downshifting to first under full throttle (this surprised me) but also prevents it from upshifting at redline.

Theoretically the Auterra can compensate for being in a lower gear, as it measures your speed and RPM to calculate your gear ratio before making a run, but in my experience when testing this with my Cobra, the numbers in the lower gears were less accurate. (I don't remember whether they were too high or too low as it's been a good 9 months since I tried it.)

 

[Roadmonster]

Hey guys.

I can email better pics of the C&D article to you.

Just send me a pm. 🙂

Stewart

 

[Roadmonster]

Just re-read this entire post.

You're right, the wagons are about 4500 pounds.

I recently had a '95 RM Wagon, and it felt heavier than
the sedan.

It felt, to me, like a bigger and heavier vehicle than the sedan.
It must have a lot more weight in the tail.

It felt like a RM sedan with a heavy load in the trunk.

I know that the tailgait is a pretty heavy sucker 😉

My .02 FWIW.

Stewart