corvettesforevor

I have a 1984 corvette with a 4 speed manual with overdrive. If I was about to go on the highway, what RPM's should I shift at in 1st second and third gear? I am still somewhat a beginner to manuals.

Do you shift at higher RPM's 1-3 so when you go into 4th it is really low RPM? Or is that not how it works? OR should I just always shift at about 2500 for normal driving? I just want to get the lowest RPM possible at cruising speeds in 4th gear.
Or does none of this even matter because I have overdrive?

Tom400CFI

The lowest RPM that the engine will tolerate given the conditions (load, hill, engine temp etc.)

FOURSPEEDVETTE

Simple solution. Just put it in overdrive after you shift into 4th gear on the highway. Not many cars that can match such low rpms in 4th gear overdrive as a C4 with a 4+3 transmission. You should be able to average about 27 mpg with it in overdrive also.

corvettesforevor

I've been getting about 23 on the highway in my 84

FOURSPEEDVETTE

Try using your cruise control and set it at about 65 mph while in overdrive. If possible, keep it on for a lengthy drive and then re-check your average mpg. I bet you'll see a few more mpg's than 23.

cv67

Unless your foots really in it dont think it will make a noticeable difference (in town driving). Too much rpm is almost as bad as lugging the motor.
I get the same mpg leaving mine in D as I do using OD at speeds below60-65 mph. Taking it easy on the right pedal seems to help the most and keeping it in good tune.

FOURSPEEDVETTE

Klondike

An engine is most efficient when it's doing work; pulling a load. You just don't want to spin it too fast or lug it too slowly. Accelerate somewhat briskly up to your cruising speed and drop it into overdrive. The time you spend getting up to speed has a minimal effect on mileage if you make the engine work a little to get you up to speed without pushing too hard.

Tom400CFI

This^

Increased RPM = increased friction, which = wasted energy.

Upshift as soon as possible for the conditions. Depending on your driving conditions, upshifting soon can make a several mpg diff; all city driving, shifting has a meaningful impact. Getting on the highway to drive 450 miles in OD...how you get on the hwy will be pretty meaningless after 450 miles. impact depends on type of driving.

corvettesforevor

I can't seem to get my cruise control to work, I have it on the blinker ****. I flicked it to on, then pressed the button at the end of the ****, but nothing happened. Am I supposed to be doing anything else?

DGXR

I agree... somewhere around 30% throttle many/most engines have a sweet spot producing adequate useable torque to accelerate up to cruising speed and using fuel most efficiently without accelerating too quickly or too slowly... any more throttle would be potentially wasting gas, any less throttle would not be producing enough torque to accelerate enough and keep from pissing off other drivers. You can call me crazy but I've experimented with a number of vehicles and engines over the years. I used to think "the lighter the foot the better the MPG," but this is not true.

But just the idea of "excess acceleration" and wasting gas, in a Corvette, it seems wrong. I could coax the average MPG number up to 24 or 25 but I would not have much fun doing it.

corvettesforevor

bump

Wheel Stander

If MPG = Max Performance Group, I would recommend somewhere around 7,000 RPM.

:-)

Cliff Harris

You set the cruise control by pressing the switch to the "R/A" position. That stands for Resume/Accelerate. If you hold it in the R/A position the car will continue to accelerate until you let it go. If you hit the brake the cruise control will disengage but it will remember your speed. Pressing the switch to briefly to R/A will cause it to do whatever it takes to Resume the previous speed.

The button on the end of the stalk is used to decelerate. If you hold it in, the car will decelerate until you let it go.

You can "tap up" or "tap down" by quickly going to R/A and releasing the switch or quickly pressing and releasing the button. That will change the set speed by 1/2 MPH.

corvettesforevor

So get up to speed, flick it into R/A, let off the gas and it should be in cruise? Do I have to put in the clutch or anything?

Paul Workman

You do NOT push the clutch to engage the cruise control. In fact every time you press either the brake or the clutch, the cruise control is disengaged and (as Cliff said) the cruise is in a "standby" mode until the R/A button is bumped "on" again to resume control.

But, as far as MPG vs. shift points, generally the lower RPM will usually result in the best mileage. However, monitoring my instant gas mileage readout while cruising in hilly terrain did NOT always favor the higher gear/lower rpm!

So, if you have the "instant mileage" readout on your car, you can experiment with the gear/load/rpm and decide for yourself what gear will give the best mileage. It isn't always the highest gear, is my point! (but usually is)

corvettesforevor

So I just brought it up to 60 mph, had cruise switch on the "on" position, flicked it onto r/a, let go, let off the gas, and nothing happened.

Paul Workman

The system depends on manifold vacuum, working throttle actuator and the cruise control module, the CCM speed data active, and no blown fuses, of course. Time to dig out the Factory Service Manual (FSM) or if you don't have one yet (highly recommended you get one!!) maybe someone here has one for your model year that can walk ya through the steps.

Tom400CFI

That's because "R/A" doesn't SET it. All you did was turn the system on. To SET it, the proper procedure is to accelerate to your desired speed and move the switch one click to the right to "ON". Then, you press and release the button in the end of the turn signal stock once. This sets the speed. W/in about 2 seconds, the system should take over and hold the gas pedal down to maintain speed.

Pressing and HOLDING the button on the end of the turn signal stalk will put the car in to decel, and you can hold the button until the car has slowed to your desired speed, release and that will be your new set speed.

Pushing and holding the switch past "ON" on the "R/A" (Resume/Accelerate) will accelerate the car until you release that momentary position on the switch, then that will be you new set speed. Pushing and releasing that momentary position will accelerate the car ~ 2mph for each push/release. In addition, if you previously set CC, then disabled it by depressing the clutch or brake, you can press & release the momentary "R/A" position and the cruise should kick back on and accelerate the car back up to it's previously set speed.

All this is in your owner's manual

Paul Workman

I tried to edit and include this, but got kicked back several times for "improper server response"...WTF?