donny

I think my tach is wrong. At 60 mph in 5th gear my tach is reading about 2700 to 2800 rpm's. Seems high..
What do you guys see.

billyrohm

I dont remeber the rpm at 60mph but I know that at 80 it is just under 3k. Dont know if it'll help, I would check but my car isnt done yet.

Trexthe3rd

2700 is correct. 60mph in 5th would translate to a top speed of about 160mph, so it is correct.

Unless you have a different diff than everyone else there is no way you can be under 3K at 80 mph. If it is accurate, it means you car can reach 206mph top speed. How much do you want to sell it for??

billyrohm

dude I dont know what you're smoking but the 3rd gen was never rpm limited on top speed. Its 158mph top speed was drag ie power limited. Remeber our cars will do about 143 in 4th gear and I think that they are geared to do over 200.

billyrohm

dude I dont know what you're smoking but the 3rd gen was never rpm limited on top speed. Its 158mph top speed was drag ie power limited. Remeber our cars will do about 143 in 4th gear and I think that they are geared to do over 200 Its just they wont due to drag/lack of power.

Snook

iTrader: (12)

2,250
Saw the thread earlier and tried it on the way home

reminder to all fd drivers...do not take wide turns the way you do at a roadrace on the street while it is raining...

jimlab

What size are your tires? With the stock P225/50-16s, at 60 mph in 5th gear with the stock 4.10:1 differential ratio, you should be at about 2,400 rpm.

Tire height in. = (((Tire width mm x (Aspect ratio / 100)) x 2) / 25.4 mm) + Wheel diameter in.
Tire circumference in. = 2 x Pi x (Tire height in. / 2)
RPM = (((Vehicle speed mph / 60 min.) x 63,360 in.) / Tire circumference in.) x Differential ratio x Gear ratio

(225 mm x 0.5) x 2 / 25.4 mm + 16 in. = 24.86 in.
2 x 3.14159 x (24.86 in. / 2) = 78.09 in.
63,360 in. / 78.09 in. x 4.10 x 0.719 = ~2,392 rpm

With P275/40-17s, a common upgrade, substitute 80.62 in. for the tire circumference.
63,360 in. / 80.62 in. x 4.10 x 0.719 = ~2,317 rpm

Keep in mind that the circumference measurement assumes a perfectly round tire which is not the case in the real world, and wind resistance (although not much of a factor at 60 mph) isn't factored in either. Therefore rpm can easily vary by +/-50, especially since tachometers aren't always perfectly accurate.

Still, 2,700-2,800 rpm at 60 mph in 5th sounds high. Are you sure you're not talking about 70 mph? With the stock P225s, 70 mph is about 2,790 rpm in 5th. With P275/40-17s, it's about 2,703.
1.16 x 63,360 / 78.09 in. x 4.10 x 0.719 = 2,790 rpm
1.16 x 63,360 / 80.62 in. x 4.10 x 0.719 = 2,703 rpm

If it really was 60 mph, the only thing (besides a slipping clutch) which might put you at around 2,700-2,800 rpm in 5th gear would be 4.70 gears in your differential.

Snook

iTrader: (12)

double post forum sucks again

Trexthe3rd

My bad, I was typing 5th gear but thinking 4th. Sorry.

donny

I have a Power Fc on the way so I will just compare its reading to the tach.
I had pulled the needle off a while back and I must have not put it back on in the same place. I already had to move my speedo needle once because it was wrong.
FYI: If you remove your speedo needle make sure you put it back on while there is power to the gauges or it will read about 20mph while you are doing zero...

Herblenny

iTrader: (13)

jimlab.. thanks for that calculation.. I'm going to use it to find out what the RZ tranny 5th gear verification..

Fd3BOOST

iTrader: (7)

Way to much info IMO..
5th gear at 3Krpm you should be doing 80mph
..That should be enough info to get you there

Thats on stock rims.