Engine RPM and gearing
#11
09-13-2007, 04:27 PM
Originally Posted by allan5oh
Correction:
1700 rpms is too high of a cruise RPM to try to get decent fuel mileage. 
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#12
09-13-2007, 05:01 PM
Something is not right. An engine truning 1700 RPM, with 22.5 low profile tires, and a .73 overdrive ratio, which is most common, should run 73 MPH.
Your speedometer may be off. Your combo should turn 1550 at 65 MPH, if you have the same spec as above. If you have 11R22.5 tall rubber, then you would run around 67.5 MPH at 1550. As for the blowby, some Cats have quite a bit, just as some Detroits will look like they are on fire, but not burn much oil. It the smoke is fairly steady, then you are probably OK. If you are getting large puffs, then you could have a bad cylinder. If the oil consumption is not too bad, try ignore the smoke.
#13
09-14-2007, 02:03 AM
Originally Posted by stranger
Something is not right. An engine truning 1700 RPM, with 22.5 low profile tires, and a .73 overdrive ratio, which is most common, should run 73 MPH.
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#15
09-14-2007, 07:44 AM
If he had a 10 spd. direct and 24.5 tall tires, the truck would only run appx. 57.5 MPH at 1700.
The truck has to have an OD trans. If he would get the trans model off of the tag on the side, then I could get the exact OD ratio, although most anything since the 80's has a .73 or .74 OD ratio.
#16
09-14-2007, 11:40 AM
Alright, heres what I have........ 10 spd o/d with a rear axle ratio of 4.11, And I have 22.5 tires. This is according to the sales paper I have in my hand. Now the salesman that sold it to me said it had 3.73, either way im running 1650 at 65 mph. And to tell you the truth, with 620,531 miles on it, it still runs very well. It fires up quickly and has plenty of power. It only smokes out the breather tube when i'm pushing it hard. When i'm idiling it puffs out a little. It goes away after I let her cool down a little bit. But it still has the smell all day long. When I do an oil change, how much oil does it take? Is there anything I can add to the oil to help the seals and rings? Im getting around 6 mpg, is that good? Whats the norm? Thanks again.
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#17
09-14-2007, 12:14 PM
10 spd o/d with a rear axle ratio of 4.11, And I have 22.5 tires.
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#20
09-14-2007, 01:10 PM
Originally Posted by dteam270
I have a 15 direct with 3:70 rears and Im thinking about dropping down to 3:55 rears. Runs 1800@70mph kills me in fuel. Plus dont like running that high rpm's.
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