Maximum safe RPM for M1008 with 6.2 liter diesel engine?

[goldneagle]

Would like to know what the maximum safe RPM for the M1008 with the 6.2 L Diesel engine. I installed a tachometer to track the RPM. I will need it once I update the tires to HMMWV tires and rims.

 

[doghead]

Mine, with 37" radials runs at 2850 rpm at 65 mph.

I've run it for 20 hrs(including fuel stops) like that, several times. I've put about 30000 miles on it now.

 

[goldneagle]

DH thanks for that info. What did you do to LIFT the truck in order to use the 37" tires?


Mine runs at 3400 RPM at 55 MPH on the NAV system with stock tires.

 

[doghead]

I gained about 9.5mph at the same rpm with the 37" tires.

I used a 4" lift.

http://www.steelsoldiers.com/showthread.php?51504-M1008A1-Gets-a-Lift!&highlight=

 

[markg]

With the factory 235/85r/16 rubber and 4.56 gear i always kept my speed at 50mph max, i dont know what rpm that would be but the engine screams! im guessing 3k rpm. i installed 255/85r/16 on one of my trucks for a 10% gain over the stock tire. this gets me 55 at the same engine speed. i use the gps to check actual speed vs speedo reading. i would like to get 65mph with an engine speed of 3k. that big of a tire wont fit under the wheel well without a lift. maybe the hummer tire/wheel change will get you 20%? what do you think? thanks. mark

 

[doghead]

Before my lift, I had a set of 285/75/16 tires.

 

[goldneagle]

With the factory 235/85r/16 rubber and 4.56 gear i always kept my speed at 50mph max, i dont know what rpm that would be but the engine screams! im guessing 3k rpm. i installed 255/85r/16 on one of my trucks for a 10% gain over the stock tire. this gets me 55 at the same engine speed. i use the gps to check actual speed vs speedo reading. i would like to get 65mph with an engine speed of 3k. that big of a tire wont fit under the wheel well without a lift. maybe the hummer tire/wheel change will get you 20%? what do you think? thanks. mark

Since the HMMWV tires are either 36" (old) or 37" (new) I should get the same speed as DH gets with his 37" tires.

BTW the manual said max speed with stock tires should be 55 MPH. That is why I drive 53 to 54 MPH on the Interstate. Here in LA and MS posted top speed is 70 MPH on the Interstates.

 

[doghead]

I had always limited my top speed to 55 before the lift. 65 max now.

I did calibrate my tachometer with a kent moore tachntime.

I also recalibrated my speedometer(new gear) after the lift. http://www.steelsoldiers.com/showthread.php?51556-M1008-Speedometer-recalibration

 

[Recovry4x4]

I run my bambalance at around 61 MPH with 255/85R16 tires. Lets see if this copies over.

	235/85-16	255/85-16	Difference
Diameter inches (mm)	31.73 (805.9)	33.07 (839.9)	1.34 (34) 4.2%
Width inches (mm)	9.25 (235)	10.04 (255)	0.79 (20) 8.5%
Circum. inches (mm)	99.68 (2531.81)	103.88 (2638.62)	4.21 (106.81) 4.2%
Sidewall Height inches (mm)	7.86 (199.75)	8.53 (216.75)	0.67 (17) 8.5%
Revolutions per mile (km)	635.65 (394.97)	609.92 (378.9	-25.73 (-15.99) -4%

 

[Skinny]

I have no tach and have not corrected my speedo gear, running 4.56 with 37's. I will not go above 55mph indicated as regardless this is max speed the truck was intended to be in my configuration. Like everyone else, my actual GPS confirmed speed is more like 65mph due to the oversized rubber. I have plans to install a tiny tach and a corrected speedo just to know my limits. As stated, regardless of tire size, keep the speedo around 50-55mph if you haven't adjusted the speedo gear.

 

[goldneagle]

I have no tach and have not corrected my speedo gear, running 4.56 with 37's. I will not go above 55mph indicated as regardless this is max speed the truck was intended to be in my configuration. Like everyone else, my actual GPS confirmed speed is more like 65mph due to the oversized rubber. I have plans to install a tiny tach and a corrected speedo just to know my limits. As stated, regardless of tire size, keep the speedo around 50-55mph if you haven't adjusted the speedo gear.

Check my M1008 recover and restore thread. I list a small tachometer that I installed for $40 with free shipping.

 

[markg]

Before my lift, I had a set of 285/75/16 tires.

I have plenty of 285/75/r16 as well , i run them on my 02 crew cab. in that truck they give me 10% over the stock 245/75/r16 the truck came with. when i put the 285/75 next to the 255/85 they are very close to the same height. the only draw back to the 255 tire is the D rating wich i dont like. thanks. mark

 

[Skinny]

Check my M1008 recover and restore thread. I list a small tachometer that I installed for $40 with free shipping.

That is a nice tach, perfect size and rpm scale. I used to install those on Rovers because they use the alternator feed.

Thank you for that info, I will order that and a matching set of oil and temp gauges...hello winter project!

 

[truck1]

I own a 1028 with 37"s , 4 " lift, Tiny Tach and Gear Vendor. Otherwise it is stock configuration. At 70 MPH the Tiny Tach reads 2310 RPM. At 65 MPH , 2210 RPM. I keep my foot at 65 and get 17-20 MPH. The 6.2 seems very happy at these RPM,s. The motor was a new replacement at Fort Sill in '09. I run it conservatively on the freeway hoping it lasts a long time. This is my favorite all around truck . An accurate tach is a must with these rigs!

 

[markg]

I own a 1028 with 37"s , 4 " lift, Tiny Tach and Gear Vendor. Otherwise it is stock configuration. At 70 MPH the Tiny Tach reads 2310 RPM. At 65 MPH , 2210 RPM. I keep my foot at 65 and get 17-20 MPH. The 6.2 seems very happy at these RPM,s. The motor was a new replacement at Fort Sill in '09. I run it conservatively on the freeway hoping it lasts a long time. This is my favorite all around truck . An accurate tach is a must with these rigs!

the gear vendors makes that work. they are the way to go except they are a little pricey!! thanks. mark

 

[goldneagle]

I own a 1028 with 37"s , 4 " lift, Tiny Tach and Gear Vendor. Otherwise it is stock configuration. At 70 MPH the Tiny Tach reads 2310 RPM. At 65 MPH , 2210 RPM. I keep my foot at 65 and get 17-20 MPH. The 6.2 seems very happy at these RPM,s. The motor was a new replacement at Fort Sill in '09. I run it conservatively on the freeway hoping it lasts a long time. This is my favorite all around truck . An accurate tach is a must with these rigs!

Your RPM numbers don't sound right -unless your gear ratio is different than DH's truck.

 

[truck1]

My 1028 is stock as far as the differential gear ratios-4.56 front and rear. I don't know the specifics of Dogheads rig but if I don't engage my overdrive the RPM's would be about the same as what he mentioned in his reply to the posters question. The Gear Vendor drops the RPM's by about 500 give or take at 70 mph. I personally would not run above 55 without it regardless of 37's or not.

 

[wheelspinner]

Run it til it blows, then back it off just a little.