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  #16  
Old 02-17-2005, 12:54 PM
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Should be around 2677rpm or so at 70mph with a 2.88:1 axle (25.3" tire on mine). That's where I cruise on the freeways always around here. Gotta remember we don't have lock up torque converters so that can and does vary from what the stock instrumentation reads. Perhaps there's a few percent of error within them like others?

With the 2.47:1 shows appx 2296rpm at 70mph with the same variables as previous. There looks to be about 62rwhp at 2300rpm and around 75rwhp at 2700rpm.

I still have a dyno chart I found on here from a 300D where the torque is pretty flat from 2000-2600 then tapers probably 20rwtq from 2600-3000rpm.

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  #17  
Old 02-17-2005, 12:57 PM
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20 year old tachs can't be trusted, they just give you a general idea of what rpm the engine is running.

Still 603's like to rev I don't think lower rpms would make them to happy.
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  #18  
Old 02-17-2005, 01:07 PM
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Quote:
Originally Posted by Hit Man X
Should be around 2677rpm or so at 70mph with a 2.88:1 axle (25.3" tire on mine). That's where I cruise on the freeways always around here. Gotta remember we don't have lock up torque converters so that can and does vary from what the stock instrumentation reads. Perhaps there's a few percent of error within them like others?

With the 2.47:1 shows appx 2296rpm at 70mph with the same variables as previous. There looks to be about 62rwhp at 2300rpm and around 75rwhp at 2700rpm.

I still have a dyno chart I found on here from a 300D where the torque is pretty flat from 2000-2600 then tapers probably 20rwtq from 2600-3000rpm.
2,677 Rpm..........Damn...I'm only able to tell within 50rpm or so how fast mine is turning.
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  #19  
Old 02-17-2005, 01:18 PM
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Quote:
Originally Posted by Hatterasguy
Ok now someone who is good at math lets figure out what rp's an SDL would be turning with a 2.48?

With the stock rear of 2.88 it runs about 3k rpm at 70.
Strictly speaking Mathematically, it should be doing 70mph at 2,583 rpm with the 2.48 rear end. That disregards other factors such as wind resistance, tire resistance, etc., but you get the idea.

So 300SDLs do 70mph at 3,000rpm? Wow... must be a lot more quiet on the highways than the 617s. 300SDs do 65mph at 3,000rpm. That has to be one aspect of this car I hate, truly hate. The highway noise. Lately, I've been playing book CDs and listening to some music during long trips in the 300SD and those make it impossible for me to even hear the noise of the engine, but when I decide to turn off all sorts of music for some peace, I wish I never sold my Toyota Avalon. Oh well.
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  #20  
Old 02-17-2005, 01:34 PM
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Quote:
Originally Posted by braverichard
Strictly speaking Mathematically, it should be doing 70mph at 2,583 rpm with the 2.48 rear end. That disregards other factors such as wind resistance, tire resistance, etc., but you get the idea.

So 300SDLs do 70mph at 3,000rpm? Wow... must be a lot more quiet on the highways than the 617s. 300SDs do 65mph at 3,000rpm. That has to be one aspect of this car I hate, truly hate. The highway noise. Lately, I've been playing book CDs and listening to some music during long trips in the 300SD and those make it impossible for me to even hear the noise of the engine, but when I decide to turn off all sorts of music for some peace, I wish I never sold my Toyota Avalon. Oh well.


What tire height did you use? I used 25.3 which is off my 205/70R14
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  #21  
Old 02-17-2005, 01:45 PM
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26.62 inches, from a 225/60R16 tire.
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  #22  
Old 02-17-2005, 01:52 PM
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Thanks for the links Whunter. You're always there when needed.
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  #23  
Old 02-17-2005, 03:33 PM
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My stock tire is a 205/65/15.

It runs just below 3k at 70 maybe 2,900.

My car is very quite on the highway for a diesel MB at least, the sunroof makes more wind noise then the engine does. (I need to fix that)
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  #24  
Old 02-17-2005, 04:00 PM
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I've often wondered if my SD has LSD. On the rare occasion I get the rear tires to spin(wet pavement, gravel, ect), it seems they both do.
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  #25  
Old 02-17-2005, 10:41 PM
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Quote:
Originally Posted by braverichard
Strictly speaking Mathematically, it should be doing 70mph at 2,583 rpm with the 2.48 rear end. That disregards other factors such as wind resistance, tire resistance, etc., but you get the idea.
I'm sorry, but I don't think that things like wind resistance or tire rolling resistance have any affect on how many rpm's the engine is turning at a given speed. It's pretty much a mechanical linkage, if the engine is spinning at 2,583 rpm's the car will be going 70 mph irregardless of wind resistance or rolling resistance. What the wind resistance and rolling resistance will affect is how much fuel the engine is consuming to get to and maintain 2,583 rpm. Or, I'm wrong
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  #26  
Old 02-17-2005, 10:52 PM
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Just like you don't think so (meaning you don't factually know so), I think that those factors affect rpm. But I don't know this for a fact, I'm just going off seeing my car doing 65mph at around 3,200 rpm when it is extremely windy on the highway instead of the usual 3,000 rpm. Maybe someone who knows the facts can chime in here.
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  #27  
Old 02-17-2005, 11:09 PM
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Our 83 does 70mph at about 2900rpm according to the tach.....I think mine is probably a little higher. I love the sound on the freeway! Hearing the engine purring along is music to this addict's ears. In the fall I will be commuting a lot (probably 2-3 times a month) between the very top of MI, Sault Ste Marie, to GR a lot....305ish miles each way.....my SD is gonna love it.
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  #28  
Old 02-17-2005, 11:33 PM
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Unhappy Resistance = RPM is higher for lower speed.

I drove in Hurricane Hugo's 135 mph wind, engine full throttle screaming, and looked down to see max speed was eighteen too twenty mph...

Hurricane Hugo Sept. 10-25, 1989 Max. winds: 160 mph.
SUSTAINED WINDS: 135 mph
PRESSURE: 934 Mb./27.58 inches.
STORM - SURGE: 16 - 20 feet above Mean Tide.

http://www.geocities.com/hurricanene/hurricanehugo.htm
http://www.wunderground.com/hurricane/hugo1.asp
http://www.clemson.edu/special/hugo/
http://www.hurricaneville.com/hugo.html

http://www1.ncdc.noaa.gov/pub/data/images/hurricane_hugo_1989_goes_ir_3.gif
http://www1.ncdc.noaa.gov/pub/data/images/hurricane-hugo-radar-chs.gif
http://www1.ncdc.noaa.gov/pub/data/images/hurricane-hugo-ir2.gif
http://www1.ncdc.noaa.gov/pub/data/images/hurr-hugo-19890921-n11rgb.jpg
http://www1.ncdc.noaa.gov/pub/data/images/hurricane_hugo_1989_goes_ir_1.gif
http://rsd.gsfc.nasa.gov/rsd/images/HugoPersp.html
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  #29  
Old 02-18-2005, 12:06 AM
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Quote:
Originally Posted by Chris Bell
I'm sorry, but I don't think that things like wind resistance or tire rolling resistance have any affect on how many rpm's the engine is turning at a given speed. It's pretty much a mechanical linkage, if the engine is spinning at 2,583 rpm's the car will be going 70 mph irregardless of wind resistance or rolling resistance. What the wind resistance and rolling resistance will affect is how much fuel the engine is consuming to get to and maintain 2,583 rpm. Or, I'm wrong

Quote:
Originally Posted by braverichard
Just like you don't think so (meaning you don't factually know so), I think that those factors affect rpm. But I don't know this for a fact, I'm just going off seeing my car doing 65mph at around 3,200 rpm when it is extremely windy on the highway instead of the usual 3,000 rpm. Maybe someone who knows the facts can chime in here.
First of all, the engine rpm of a vehicle with a manual transmission traveling 70 mph with 225/60/16 tires and 2.47:1 gears will be 2187 rpm. This has nothing to do with wind resistance or tire rolling resistance or whether the vehicle is going uphill or downhill. If the vehicle is traveling at 70 mph, the engine will be turning 2187 rpm. Period.

Now, the variable that is not mentioned is the automatic transmission and the torque converter. Once you add the torque converter, you don't have a rigid coupling between the engine and the drive wheels. So, when the engine turns 2187 rpm, the vehicle cannot go 70 mph anymore because there is some "slip" in the torque converter. This slip can be as little as zero, if the vehicle is going slightly downhill and the vehicle needs just a touch of power from the engine to maintain the vehicle speed. The slip can be as much as 1300 rpm (estimated) if you stand on the brakes and mash your right foot on the floor. The engine is turning at 1300 rpm but the wheels are stopped! Most of the time, M/B with their high stall torque converters will be slipping about 300 rpm on level ground at 60-70 mph. So, if you want to maintain 70 mph in an automatic with 2.47 gears and 225/60/16 tires, you will need to have an engine speed of somewhere around 2487 rpm. You will need more than this rpm to go uphill and you will need less than this rpm to go downhill. This is why you see different tach speeds for the same vehicle speed.

Hope this makes some sense.

Last edited by Brian Carlton; 02-18-2005 at 09:53 AM. Reason: more thoughts
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  #30  
Old 02-18-2005, 07:19 AM
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Dont tires also "grow" at high speeds ? futher throwing off the speed ratio calculations...

(though I would agree if it were a negligable amount)

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