Downshift RPM
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From: Jamestown NY
Downshift RPM
In the short time I have been driving my '98 ZF-6 I have been surprised at how soon the upshift arrow appears. One of the first things I did was to disconnect the CAGS and do not always take the upshift suggestion but the motor seems to want to run at a RPM I would have said is close to "lugging". I think it tells me to get 6th at around 50 MPH. My question is what RPM do you not get below in normal street driving? The rear end is 3.33 but the 285/35-19 rear tires bring the ratio to 3.17 if I am doing the numbers right. Is my perception of lugging a wives-tale? Thanks
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There is no clear cut RPM at which "lugging" occurs.
1800 rpm in 6th while cruising down the interstate isn't lugging.
But mashing the throttle in 6th gear @ 1800 rpm and trying to accelerate would be.
I've never seen one of those lights either, but it is obvious that it was intended to "train" people to drive for best fuel mileage.
1800 rpm in 6th while cruising down the interstate isn't lugging.
But mashing the throttle in 6th gear @ 1800 rpm and trying to accelerate would be.
I've never seen one of those lights either, but it is obvious that it was intended to "train" people to drive for best fuel mileage.
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From: Jamestown NY
I should have written it down because it seems too low now but I think I was passing almost everyone on I-90 the other day at between 1200 and 1300 RPM. Would you always downshift if you were below 1000 RPM? I get the "train for best fuel mileage" concept, I am surprised how far they take it, that is a good thing, especially for a high torque low rev engine like the L-98.
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Maybe not completely accurate, but a good indication of fuel usage under load and coast conditions. I think that it meters the fuel return line for flow and calculates the difference from fuel pumped from the tank to the injectors.
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In the short time I have been driving my '98 ZF-6 I have been surprised at how soon the upshift arrow appears. One of the first things I did was to disconnect the CAGS and do not always take the upshift suggestion but the motor seems to want to run at a RPM I would have said is close to "lugging". I think it tells me to get 6th at around 50 MPH. My question is what RPM do you not get below in normal street driving? The rear end is 3.33 but the 285/35-19 rear tires bring the ratio to 3.17 if I am doing the numbers right. Is my perception of lugging a wives-tale? Thanks
Your excursions on I90 would be the only ones that you might see the need for a 6th gear selection.
Last edited by WVZR-1; Nov 23, 2013 at 12:43 PM.
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From: Rolla Missouri
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But to answer your question, it probably was accurate.
But think about what it is actually telling you?
At that "instant" you were using more fuel to go up a hill than downhill.
Pay attention to what your foot is doing on the accelerator pedal in that same situation and it is easy to see.
The instant reading can be fun to play with, but that is about it.
The "average" reading on the other hand is much more useful, especially if you let it run without resetting it for awhile.
The more miles you accumulate after a reset, the more accurate it becomes.
You'll notice when you first reset it, the numbers will change (up or down) quite quickly.
But the more miles driven, the changes slow down.
Over the course of several hundred or thousand miles, it should be pretty close to what you would calculate using the manual way of calculating fuel mileage.
miles driven/fuel used = mpg
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From: Jamestown NY
Have you corrected the speedometer yet for the tire sizes? The VSS controls the information to the ECM and would control the upshift lights etc. I would think in your area you would "next to never" elect to pick a shift to 6th gear. To get your acceleration back to the original "seat of the pants" would require a ratio of something near 3.49 so you would chose either a 3.45 or 3.54 to get that back. I'm sure that's not in the plans but that's what would be required to get the original "feel"! The MPG would suffer from inaccurate VSS supply also.
Your excursions on I90 would be the only ones that you might see the need for a 6th gear selection.
Your excursions on I90 would be the only ones that you might see the need for a 6th gear selection.
I do not find it mentioned in the FSM. Changing the rear end ratio would be way beyond the point of diminished return for me. Is there a disadvantage in shifting at the arrows suggestion? If I can get to where I need to go by burning a gallon of gas and shifting often that is better than using 1.01 gallons and staying in lower gears. Unless some day some mechanic says " What the heck did you do? Shift every time it told you to?" I'll just get the poly-brass left kneecap with the optional
grease zerk.
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From: Murphy NC
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BTW, anything below 1000 rpm is pretty much idle. I am at about 1800 cruising at 70 in 6th gear, that is about as low as I get rpm wise. (3:45 rear gear)
Last edited by lt4obsesses; Nov 24, 2013 at 02:27 AM.
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As RollaMo-LT4 said already, there is no clear cut number for a decent driver. As an example; I'll go 900 RPM in 6th if I am cruising/coasting with my foot off the gas. If I'm at WOT, I generally don't want to be below 3500 RPM...but that is b/c I'm seeking max power -not b/c I'm worried about "Lugging". As long as the engine pulls smoothly w/o bucking, lurching, surging or vibrating, it's not "lugging".
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No. It measures the pulse width of the injectors. It "knows" the size of the injectors, and the fuel pressure, and can calc how much fuel flow occurs during injector on time. Car has "no idea" how much fuel is flowing through the fuel lines, delivery or return.
As RollaMo-LT4 said already, there is no clear cut number for a decent driver. As an example; I'll go 900 RPM in 6th if I am cruising/coasting with my foot off the gas. If I'm at WOT, I generally don't want to be below 3500 RPM...but that is b/c I'm seeking max power -not b/c I'm worried about "Lugging". As long as the engine pulls smoothly w/o bucking, lurching, surging or vibrating, it's not "lugging".
As RollaMo-LT4 said already, there is no clear cut number for a decent driver. As an example; I'll go 900 RPM in 6th if I am cruising/coasting with my foot off the gas. If I'm at WOT, I generally don't want to be below 3500 RPM...but that is b/c I'm seeking max power -not b/c I'm worried about "Lugging". As long as the engine pulls smoothly w/o bucking, lurching, surging or vibrating, it's not "lugging".
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From: Jamestown NY
OK excuse my thickness, if it is running smoothly it is not lugging, I've not known it to buck,
nock or shudder. I would never open the throttle more than slightly at low RPM in a high gear without downshifting first. But is there any other car that can travel at near highway speed at near idle engine speed?
Where could one find instructions on resetting the VSS?
nock or shudder. I would never open the throttle more than slightly at low RPM in a high gear without downshifting first. But is there any other car that can travel at near highway speed at near idle engine speed?
Where could one find instructions on resetting the VSS?
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From: Rolla Missouri
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But is there any other car that can travel at near highway speed at near idle engine speed?
Lightweight + higher gearing (especially the 6-speed with its 0.50 overdrive) + high torque relatively low rpm V8 = low cruising rpm.
That is also the reason most Corvettes get much better fuel mileage than most people would believe.
