I have finalled had a chance to get my GTA out on the open road (non city freeway). I have never driven a big block before and was surprised that the first thing I noticed was that the engine appeared to be reving a bit high for my speed. My car has a standard 390/C6 combo with a 3.25 diff, at 60mph the engine was reving at 2700 rpm. The second thing I noticed was that my factory installed Tacho does not have a redline. What should the redline be with such a setup and is my engine reving too high for the speed? What sort of maximum comfortable cruising speed should I stick to (I know this one is subjective)?
cb1368
If you just want to cruise at hiway speeds 75-80 you will have to change to a 2.80 rear ratio. The 390 has plenty of torque to pull this gear at 1800 -1900-rpm. i have had several with this set up and really liked it for hiway driving. lose a little at the stop light drags however. 390 not much for quick acceleration anyway. Gary
RPM @ 60 sounds about right to me. Don't worry about running out of RPM on the top end. In a vert, you will back off from getting your brains beat silly by the wind long before that happens. At 110 mph, the interior of a vintage Mustang vert is an aero nightmare that will just about suck you out of your socks.
your tire diameter is about 24" I am guessing and 2700 would be right. Taller tires will bring it down a couple hundred rpm. 3.00:1 gear would drop it 200rpm or you could install an AOD and then you would run about 1900rpm
Myself I just purchased tires that are 25.5" tall and ordered 3.80:1 and purchased an AOD. Once installed I will be able to melt the tires but at 70 mph 2400pm
Myself I just purchased tires that are 25.5" tall and ordered 3.80:1 and purchased an AOD. Once installed I will be able to melt the tires but at 70 mph 2400pm
Yep, those are sure reasonable freeway speeds. It's a public road, not a racetrack.
If you're running that fast on the street you're an idiot. If you're building a race car to run at that speed and using a 67 390/C6 'vert, you're still not quite that smart...
But back to the redline issue, the car was designed when the speed limit was 70, it won't hurt it at all to run it at 60/2700. Comparing it to a newer car with overdrive is a apples and oranges excercise. The 390/C6 wasn't designed as a freeway cruiser. On the freeway your mileage will suck, but not as bad as in the city. But "redline" is over 5000 assuming a stock 390 and no rebuild and improvements.
As noted, if you keep in in D its going to limit itself unless you can't tell you're pushing it way too hard (like 110 for a long period of time).
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