When to downshift?

[jokerl90]

2006 CH600, 427 AC engine (recently rebuilt), Eaton 10 speed. Usual gross weight between 78,500 and 80,000

When pulling a hill, is it better to downshift at 1200 rpm or 1400?

The story

I have been downshifting at 1200 when pulling hills. Trucks with 350 Cats, even ones that have been turned down,castrated, will just walk by me on hills (same loads,trailers.etc.). On flat land, the truck I drive will fly, would do 80mph all day long if I let it. It also gets pretty crappy mileage, like 4 or 4.5 mpg. This truck is famous at our company for being a "fall on it's face when it see's a hill" POS.

Yesterday, running with a buddy, he says start downshifting at 1400 even 1500 if it's a real hard pull. I started keeping up with him a lot better.

Have I been wrong???? Is it meeeee??????? hahaha

Thanks

[other dog]

That's what I do too. They recommend letting the Paccar engine pull down to 11-1200 rpms, but i've found that it shifts a lot easier and performs a lot better if I shift it around 14-1500.

[Green Dash]

I drive a '14 Pinnacle with an MP7 that cruises at it's governed speed of 65 mph at about 1425 rpm and downshifting above 1225-1250 is to soon for this truck. This is subject to debate but my opinion is to keep it in the operating range where it will perform at it's best while pulling a hill, without pegging the needle of course.

[DCR]

When I had my E7 460, if I down shifted at 1200 it was four ways on and everyone past me; downshift at 1400 I held my own and no four ways.

[Green Dash]

I've tried downshifting sooner in my truck but end up shooting myself in the foot. The Detroit powered Sterling I drove prior to this pulled well when downshifting at around 1300 and got better fuel mileage than the Mack.

[jokerl90]

Thanks for the replies!

All I could find, including the sticker on the visor said 1200. 1400 made a real difference, gonna try it for a while. I'm wondering about fuel mileage, will see if the 1200 vs 1400 makes a difference for good or bad.

[Timmyb]

I reckon it comes down to personal preference. mind you, my dad taught me to drive, and he always told me not to take it under 1400. This was in n14 and isx cummins. Guess I got me technique from my dad.

[dondiesel444]

1

Edited October 13, 2015 by dondiesel444

[Keffer inc]

Ive been down shifting at 1200 too. Go about 25 mph up sandstone mountain in WV. Im going to try 1400 too

[Swishy]

When try n to get the best power to the ground pulln hills etc

best to drive flatout up to govonors change cog n when wot the rev counter sez is tell n U when to down shift

eg: 3rd gear max out to govonor... change to 4th take note of the revs when back into it = wen to change down

jist my 2 cents worth of info TAX FREE

LOL

cya

§wishy

[mack mhe9]

this is where a 13 or 18 would be nice. the little engines can pull nice but sometimes you to high to down shift with a 9 or 10 spd. you start building up heat so you just have to back out of it to drop a gear. game over then. ive always like to pull hills with more RPM 1450 to 1650 light on the fuel. keeping the EGT about 850.

[TorresTransport]

I've got a 2005 CHN613 427 and I downshift at about 1400 rpm and it pulls like a champ even with 22-23 tons on my back with ease on any uphill

[dondiesel444]

1

Edited October 13, 2015 by dondiesel444

[rsb502]

How the hell.do you guys drive a truck by the guages, feel the truck in your hands and feet and do what it wants, anybody that uses a tach to shift is wasting fuel in my opinion. If your on flat ground you shift at a lower rpm than on a hill if your loaded a higher rpm, add wet roads and curves and it cha yes again. If you can't make yourself "feel" the truck your never gonna get it right. Oh and I can tell you your running too many rpm just from your fuel mileage, you should get over 6mpg no problem on the highway with an 06 model. Off the soapbox!

[jokerl90]

How the hell.do you guys drive a truck by the guages, feel the truck in your hands and feet and do what it wants, anybody that uses a tach to shift is wasting fuel in my opinion. If your on flat ground you shift at a lower rpm than on a hill if your loaded a higher rpm, add wet roads and curves and it cha yes again. If you can't make yourself "feel" the truck your never gonna get it right. Oh and I can tell you your running too many rpm just from your fuel mileage, you should get over 6mpg no problem on the highway with an 06 model. Off the soapbox!

Well, I don't drive the truck by the guages, I do have to look at the road every once and a while.... Using the numbers from the tach gives a reference. Don't think asking, do you guys downshift when the motor makes a chugga chugga ping sound or when it's a ping ping chugga sound, would get me too far.

This truck is very quiet and smooth. The only time I can tell a difference in the motor is around 1100 rpm . Thats just too low, or is it?

The last time I had it at a Mack dealer, I was getting 5.4mpg, I thought it was low, the mechanic said the best you could get on these motors was between 5.5 or 6mpg.

I may have the answer about the low mileage. Asking that question in another thread.

Truck seems to like 1300 a little better than 1400, to me anyway.

[Green Dash]

I don't watch the tach or speedo at every up/downshift but when the truck was new I did want to familiarize myself with how it responded at various shift points. For that I used the gauges.

[Lmackattack]

Most trucks I drove (besides a 5 speed)you kept your rpm up at 1800 and when it falls back around 1500 downshift. At some point you will find a gear that it can hold at 1600-1800. This is the rpm I like to pull at because it keeps EGTs down and of I have to let out of it I can drop a few rpm and then pick it back up.

Now that being said 1200-1400 is where most diesels make their most torque.but they also make higher EGTs down there.

[Ezrider]

my e-7 460 likes to be kept above 1350-1400 or it falls on it face.

[RedBullDog]

my e-7 460 likes to be kept above 1350-1400 or it falls on it face.

+1, and the 18 makes it easier

I've actually been studying this on my end too lately. I've been running the same run 2 or three times a day for a month or so. This has allowed me to try something different each time across a hill or through the same area again and again. Before I bought this truck, most of my driving was behind a yellow motor, so "lug it down and stay in that hole" was what I got used to. The E7 seems to really find its stride at an RPM that the yellow motor was kinda wound out at. Mack seems to make good power around 1400 to 1650, and it seems like running it up to 17-1800 before shifting in the taller gears really helps too. Keeping it around 1600 cruising in tall gear seems to make better fuel mileage too, as opposed to the 1500 I was originally trying to run the thing at. I split a gear going up hill at 1400 but that only runs it up to 1650 or a little less, If I grabbed a "whole" gear pulling hills, probably wind down to 1300. When I was bs'ing with some guys at the mack house The other day while truck was in, they acted like 1600 rpm cruise speed was about right and fuel figures seem to bear that out. Hope this wasn't a hijacking, just a brain dump

[Dirtymilkman]

My most favorite motor I have is my 460. It grosses 81,000lbs has 3.86 rears and it pulls better than any big kitty I had. Up a hill it also can pull ahead of my mp10 which I dont understand. Only thing done to it is stage 2 injectors and a valve set every 250,000 miles