Healthy RPM for DD?

Alphaelectric

Registered User
Hi,

I got a question about healthy shifting points during daily driving for a manual 90 SC.

If I don't want to give the engine any stress and go for it just by listening, I keep RPM for coasting in between 1.500 to 2.000 RPM and upshift between 2.000 and 3.000 (3.500 if I'm in a hurry).

What's your experience? What RPM ranges do you use in daily driving?

-Seb
 
There are a ton of variables in this question.

Up or down hill? Tire size? Rear gears? Boost ease? (MPX spin up boost very quickly)

I get better mileage shifting up around 2500 rpms then bogging it down around 1500, but it has 2.73s now, it was a bit better with the 3.27 as would be expected. This is with the stock rim and tires.
 
Hmm, I agree. Difficult to say.

Boost ease and MPX? I am not familiar with these terms.

My car is mostly stock: tires, gears, etc. Concerning the drive: Let's say flat country road, no wild curves. Mild ups and downs.

I'm asking because I can hear a slight rastling noise when pulling it out of low RPM (=< 1000) and I wonder if this is happens due to wrong shifting on my part.
 
I apologize. MPX is the larger opening Supercharge made by MagnumPowers. It creates boost with very little throttle as apposed to a stock SC.

1000 RPMS is pretty low and that will lug a stock engine. Can you feel the vibration through the shifter that matches the noise being made?
 
Ok, thanks for clearing that up. The Supercharger is still stock. I figured that this might be too low, because yeah, the engine doesn't seem too happy being dragged to higher RRM.

No, the shifter doesn't move. This sound is only audible when driving with closed windows. It sets in at lower RPM (~1000) and stays a while until it goes away when above ~1900.

It reminds me of the speed at which the valves must be moving. But there is no smoke or oil spills or anything.
A friend suggested exhaust manifold gaskets might be shot or worst case, a minor fracture in the manifold itself.

If this sound is normal coming from very low RPM, I'll just ignore it and use a higher shifting band (1500 - 2500).
 
Ok, thanks for clearing that up. The Supercharger is still stock. I figured that this might be too low, because yeah, the engine doesn't seem too happy being dragged to higher RRM.

No, the shifter doesn't move. This sound is only audible when driving with closed windows. It sets in at lower RPM (~1000) and stays a while until it goes away when above ~1900.

It reminds me of the speed at which the valves must be moving. But there is no smoke or oil spills or anything.
A friend suggested exhaust manifold gaskets might be shot or worst case, a minor fracture in the manifold itself.

If this sound is normal coming from very low RPM, I'll just ignore it and use a higher shifting band (1500 - 2500).

It sounds to me like spark knock / ping / detonation. What does the vacuum / boost gauge read in a typical time when you are running the engine from 1000 rpm to 1900 rpm?

What octane of fuel do you run in this car?

I think you may be shifting too early.
 
Oh man. Guess I have to learn a lot coming from a 72 Toronado to a Super Coupe. This is a totally different breed of a car. Thanks a lot for breaking ground here...
 
Oh man. Guess I have to learn a lot coming from a 72 Toronado to a Super Coupe. This is a totally different breed of a car. Thanks a lot for breaking ground here...

Just imagine that you put some high-compression heads on your smog-era 455 and tried to lug it the same way, while running 87 octane. I don't think it would like it too much either. Maybe not an exact parallel, but it's the same idea.
 
make sure you are running 91 octane minimum fuel. You can run lower, but you should pull the octane plug, or make sure you don't get into boost excessively.

With a positive displacement blower if you get into boost at low rpm, you are stressing the motor the most you possibly could. Load from the blower goes to the crankshaft, effective compression ratio of the motor increases greatly and the mechanical advantage at low rpm is just not there. Better to down shift to pick up rpms before hitting the go pedal.

All that said, if you have premium fuel in the tank and the car is running well you shouldn't get noise from the motor even if you do stress it. Stock timing is sufficiently cautious it shouldn't be an issue. You might run a key on engine on diagnostic with the motor to see if you throw a knock sensor message.
 
Problem found

The strange noise actually comes from the right side exhaust manifold. (I could swear the previous owner knew -_- )

I dropped the car off at the shop (which specializes in US cars) and they'll check if the manifold is warped and needs to be ....what's the word.... sanded, planed so that it attaches again smug to the block.

Worst case: Manifold cracked already or cracks in the process of removal. Codes demand a SC exhaust manifold and I don't have one. Checked the numbers: N/A ones won't fit.

Expensive alternative: Kooks Headers from Super Coupe Performance.

Any idea which ones I can use with the stock catalytic converters?

Thanks a bunch!!


Btw: Thanks for the good advice. Next time I'll opt for power plus and see how it performs.
 
maybe im just a hell of an aggressive driver but my supercoupes see as high as 5500 just daily driving to and from work
 
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