[QUOTE=LT1GMC;235085]My SS hasn't came in yet, I am wondering what the rpm is at 60 mph in 5th gear?

I checked mine out today to see how they matched the chart:
2nd 60 mph @ 5500 rpm

3rd 60 mph @ 3900 rpm

3rd 65 mph @ 4000 rpm

4th 60 mph @ 2900 rpm

5th 60 mph @ 2300 rpm

5th 80 mph @ 3000 rpm

Looks very close to the chart.

 

Thanks for taking the time to doublecheck it, FastedSS!

 

I crossed 600 mile make on Saturday. Sunday morning while pulling out on US1 a slow Suburban was in front of me on the on-ramp. It was early and there was no traffic on the hiway. I couldn't resist. I opened the SS up and pulled out around the Suburban. I lifted at 110 @ 5500 RPM in 4th gear. It get there fast and is stable. It might actualy get to that 150MPH.

 

I kind of wonder whether RPMs are being misread a bit due to the small tachometer. It's either that or I am missing some part of the calculation I don't know. Anyway, here's what I was thinking...

Tire Circumference of 225/45R18s: Overall width is 225mm * 45% Aspect Ratio = 101.25mm sidewall height * 2 (top + bottom) = 202.5mm. 18" * 25.4 = 457.2mm + 202.5mm (sidewalls) = 659.7mm tire diameter. tire D*pi = ~2073mm circumference. Of course, the tires won't sit perfectly round, since they'll be loaded with weight, but I imagine that should be fairly small. ~2073mm / 25.4 = ~81.59".

MT5 final drive ratio is 4.05.
MT5 forward gear ratios:
First: 3.38
Second: 1.76
Third: 1.18
Fourth: 0.89
Fifth: 0.70

Here are my assumptions, which might be missing something, so if anybody knows one way or the other please chime in...

I think Tire RPM = Engine RPM / Final Drive Ratio / Gear Ratio, but let me know if you think this is wrong.

*If that formula is right*, then the MPH at 5,500 RPM in 4th is as follows:
5500 (Engine RPM) / 4.05 (Final Drive Ratio) / 0.89 (4th Gear Ratio) = ~1526 Tire RPMs * Tire Circumference = Rolling IPM * 60 min/hr = Rolling in./hr / 12 = Rolling ft/hr / 5280 = 117.9 Rolling MPH, about 8 MPH above Fast Ed's reading.

Going the other way, you would determine the Engine RPM based on the 110 MPH in Fourth as follows:
Rolling MPH = 110 MPH * 5280 = Rolling ft/hr * 12 = Rolling in./hr / 60 = 116160 Rolling in./min / ~81.59 Tire Circumference = ~1424 Tire RPM * Final Drive * Gear Ratio = 5131 Engine RPM.

Does this need transfer case gear ratios? Wheel slippage maybe? I can buy misreading by a few RPM from the small tach, especially during quick acceleration. But 5500 vs. 5131 RPM is kind of pushing the limits enough to make me wonder. Maybe the final drive and gear ratios are not exact, but even using 4.0549 instead of 4.05 and 0.8949 instead of 0.89 wouldn't account for nearly that much difference.

 

I think you can only calculate speeds to a certain accuracy. Because in real life you have wind speed, road grade, tire pressure, the ever present human error, and probably several others.