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wyattearp

General Cummins 12v Question

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What kind of modifications does it take to boost hp to 300? Which pump is better, the VE or P7100? What kind of fuel mileage can I expect with 37" tires and 3.73 gears?

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The P7100 is the most coveted pump. You can get a fuel plate to get you over 300. A gov spring kit is the way to go also. Both inexpensive mods. With those tires and depending on how you drive 18 to 20 MPG is what you can expect on the highway.

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I would back up elkslayer on this one unless of course you drive like muddy:lol:

but 16MPG out of a rig that is honestly putting 300 to the ground running 37s well that aint too shabby

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I gots to get the fuel leak fixed on my '92. Seems 16 or so is pretty good for the old girl in it's present 'tune'.

92FuelEcono.jpg

(I really don't think it leaks very much..... But we shall see.)

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You can see my mods and RWHP numbers in my sig and in 2011 I saw mileage for the year of just under 20 mpg in 50/50 mixed driving. Your right foot is usually worth about + or - 2 mpg. My truck happens to like 65 mph when on the freeways. I realize that IDs speed limit on freeways is 75 so that can cost you mpg.

BTW my dyno numbers were all run in Meridian ID.

Bob

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Catch me if you can... 21-22 MPG... Muddy and I know how to drive properly...

The thing is the tires will compensate for the gearing yes... But the extra mass on the axles will degrade the MPG's before you gain anything MPG wise...

Right now with my 31" tires (235/85 R16) they weigh a minor 62 pounds... Now my stock (265/75 R16) they weigh a nice 85 pounds per tire... Now the trick is for every 4 pounds of tire mass your going to need 1 HP more to keep the truck rolling.

62 x 4 = 248 pounds 235/85 R16

85 x 4 = 340 pounds 265/75 R16

340 - 248 = 92 pounds difference

92 /4 = 23 HP less required to roll 235's compared 265's...

This tire change gained me 2-3 MPG... Just something to think about...

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Im not challenging that you do get that milage smaller tires means less miles will actually be driven than counted. Im sure you adjusted for that. and thats good milage. but your number 23 horse power for 92 LBS of rolling mass please help me undertand that. Semis that are running 18 to our 4 tires and I think they are close to 37s and well over a 150 LBS apiece would need over 550 horse just to keep the tires rolling without any other resistance and I know they are not putting out full power all the time

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Of course my figures are rough guesstimates for our trucks...

Muddy proved to me when I gave him crap about beating him on the dyno. The next time he got on the dyno he pull the outer dualies off and gained about 20 HP and beat my old number. This is rather old but in was in 2007...

He rolled a 363/810 originally... Afterwards he was like 386 HP? I can't seem to find the old post on this...

I'd rolled 381/831 originally...

After pulling the outer dualies off he past me barely... Ask Muddy... Rotational mass / tire size does play bearing of what you output to ground.

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I understand that rolling mass and diameter requires horse power I just was wondering were that number came from. 22 hp to 93 Lbs if was a formula that was cut and dried or if you had dynoed and seen the difference and was just curious. gain 2 miles a gallon next time you see my truck it will be on mini truck tires.

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Of course my figures are rough guesstimates for our trucks...

Muddy proved to me when I gave him crap about beating him on the dyno. The next time he got on the dyno he pull the outer dualies off and gained about 20 HP and beat my old number. This is rather old but in was in 2007...

He rolled a 363/810 originally... Afterwards he was like 386 HP? I can't seem to find the old post on this...

I'd rolled 381/831 originally...

After pulling the outer dualies off he past me barely... Ask Muddy... Rotational mass / tire size does play bearing of what you output to ground.

indeed,,,, mikey is correct. did make a dif on the dyno. the dyno measures acceleration so getting those extra lbs to speed up robs power. as to mpg, when ya need to do the stop and go driving it would make a diff but less difference on hwy driving.

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Muddy is right here. Only thing I want to add is that there is a difference from one manufacture to another in the same type and size of tires. I have seen that proven time and time again!! It is wild that just by changing to a different design of tire (Same size mind you!) that you would see a difference in mileage figures. (I have a newer mileage chart that I should put up here.... I'm not sure the old '92 is avg. over 15 MPG...... Oh well.....)

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