I was bored the other day and since I finally finished on the wheel and tire package that I'm getting (haven't got it yet but FINALLY decided on what it'll be https://www.rx7club.com/forum/showth...hreadid=156436), I figured it would be nice to show you guys what kinda power it takes to get speed in an FC. Here's some stats first off...

Frontal Area of the FC (S4/S5...stock ride height and body) is 22.997916" (height 49.8" and width is 66.5"). Drag coefficient is either .31 or .29 (I show you both numbers) and rwhp is roughly...

S4 N/A 121.6
S5/NA 133.3
S4 TII 151.6
S5 TII 166.6

Okay now here's the rwhp you need to hit each speed (notice how important aerodynamics is when trying to get speed...) shown with the .31 Cd on left and .29 Cd on the right side...

0-60 10.779/10.084
0-70 17.117/16.013
0-80 25.551/23.903
0-90 36.381/34.003
0-100 49.905/46.985
0-115 75.889/71.003
0-120 86.236/80.673
0-125 97.471/91.183
0-130 109.642/102.568
0-135 122.786/114.864
0-140 135.940/128.105 *
0-145 152.143/142.327
0-150 168.430/157.564
0-155 185.841/173.851
0-160 204.412/191.224 **
0-180 291.048/272.271
0-200 399.243/373.486
0-231 615.154/575.467 ***
0-241 698.552/653.485 ****

The aterisks are at 140 because that's my goal for my FC, 160 because I consider that the holy grail of speed (I'm not a fan of much more than that because it gets pointless quickly), 231 and 241 because those are the McLaren F1 numbers in case you wanted to see what it'd take to get an FC up to that level of top speed (not acceleration). Of course gearing has to be taken into account since no stock tranny has gearing for those speeds (the max is 190+ I do believe). Anyway this is just something to show you guys why speed is so hard to get notice that at 60 you only need about 11rwhp, but at 100 you need almost 50 (5 times as much), and at 140 you need about 140 nearly 3 times as much as 100. This will also hopefully make people think twice about ridiculous claims of top speed that we see far too often (not neccessarily on this board). Oh yea in case anyone is wondering I've calculated a top speed of between 156-157 for the top of the line RX8 and 148 for the base model.

DON'T FORGET to take into account that if a car is lowered then the frontal area changes again (for instance my FC is 3/4" lower so the frontal area is only 22.651562") which is important to remember. It also changes the Drag Coefficient (Cd), but that's too hard to estimate w/out a wind tunnel or doing those ridiculous coast tests.

 

Damn...I tried to space that out some so the numbers wouldn't be so close together. Sry

 

that is some nice info. thanks man.

 

So can having a lower car increase top speed noticably then? That would be interesting to know.

 

It would atleast increase downforce, which would allow a safer top speed.

 

Yes it can increase your top speed, I wouldn't say significantly like you might be thinking. But here is an example...

FC with a 2" drop (height is now 47.8) and the same width (66.5")...F/A is 22.074305"

To hit 160 with the Cd .31 you only need 196.203 rwhp and 183.545 for the Cd .29 as opposed to 204 and 191.

But remember that when you lower the car that also changes the Cd. to a lower number (thus the front air dams on racing cars). But either way that's a vague look at how it would change the power needed to get certain speeds.

 

Only the 86-87 Sports with its factory aero package and flat rear spoiler had a CD of .29

 

If I am not mistaken the Vert had drag coefficents of .33 with the top up and .38 with the top down.

Could you calculate those #'s?

Let all us vert owners know how much more we suck!

 

yes please inform us heavy *** verts heheh

 

Ha, I'll do the vert numbers at lunch time. I am aware of the difference in the Cd. between the Aero package cars and the normal FCs. To be perfectly honest the Cd of .31 is actually a measurement of the base car with the 14" wheels. The 15" wheels don't really change it, but either way it's still a tad bit higher (nothing drastic though). Like I said I'll hook the vert guys up this afternoon after the exam I have to take (MAYbe earlier). Hey badboy, any pics of your car?

 

also you might want to include other areas that will affect besides just aerodynamics. such as tire width and grip, gear oil, etc. you also have to figure out at what rpm you will be at 140, which gear and the hp you will be making at that rpm in the selected gear. peak hp doesn't necessarily mean you are going to see this top speed if the band isn't wide enough or in the gearing to put it down.

 

could you use these numbers to get an idea of how stock 7 is performing?

i used to do high speed runs on the freeway after work at night here in phoenix and almost always hit what the speedo said to be 138mph.

this is in an '86 with removed precats and stock rims and tires.

by your calcs id need about 130rwhp, and id imagine i prolly have 150fwhp(if everything running right).

so my guess would be that my car is in decent shape and that my speedo reads about 5mph higher than it should.

does all this sound close to correct?

 

I would say that's a reasonable asessment.

 

Jeremy, I've taken into account the fact that just because you have a specific rwhp doesn't mean that you can hit a specific speed. I didn't state the relationship between the gearing and the rpms that you will fall to (after you shift), just because I wasn't giving a full on speed lesson, just what power you would need to hit a specific speed. I don't really wanna get into the rpms that you will be at and all that good stuff simply because I really don't have that much time right now. Thanks for pointing that out though...

Also tire width as far as aerodynamics is taken into account, the handling at that speed is not .

 

3engineRex, that's is definately a fair estimate. Also note that if anyone has dyno sheets you could calculate your top speed (since you can see where the lowest amount of rwhp is) by finding the lowest point of rpms after you shift (into 5th of course) and finding out what the rwhp is at that point and so on.

 

Okay all you vert lovers here's you numbers...

RWHP/Cd .33/Cd.38

0-60 11.475/13.213
0-70 18.221/20.982
0-80 27.200/31.321
0-90 38.728/44.596
0-100 53.125/61.174
0-115 80.796/93.038
0-120 91.800/105.709
0-125 103.760/119.481
0-130 116.716/134.400
0-135 130.707/150.512
0-140 145.775/167.862 *
0-145 161.958/186.497
0-150 179.297/206.463
0-155 197.831/227.806
0-160 217.600/250.570 **
0-180 309.826/356.769
0-200 425.001/489.395
0-231 654.841/754.060 ***
0-241 743.620/856.290 ****

...ummm well at least you look cool when you're driving. Just don't try to do any top speed runs because remember it's a vert so everyone can see you .

 

If I waxed my vert real good would it's Cd improve? What if I rubbed vaseline on my face?

 

those speed numbers are good. And I had guessed that a stock s4 would have about 121-122 hp. Woo hoo! I was right. Now it's time to put that intake and exhaust on my car so I can get those top speed #'s up a very small amount.

 

LMAO

 

Hey hey now...only if you use baby oil! Seriously though DO NOT FORGET that just because you have the rwhp to reach a specific speed means you can reach that speed. It has to do with the gearing (what rpm do you make that rwhp at, and when you shift are you at that rpm???) also. But if you do have that power and the rpm (gearing) to do it, you're all set. ALSO DO NOT FORGET that just because you can reach a specific speed you should do it, what about your tires (can they reach that speed safely...don't do this with S rated tires), how about your driving ability (don't be overly optimistic...you could wind up dead that way).

Also if you get some lard just before you lube her up with baby oil I hear it'll drop the Cd by almost 8/10 (.30/.25)!!!