10-Speed Peterbilt 379 - Save Fuel with 13-Speed Upgrade?

Im sure we are talking the modern 13 speed. 13 directs ad the rtoo double over are ancient history.

 

I still see them in some trucks for sale. I know they are old and ancient but they are nice. I have driven one that was put into a F-350 with an old mechanical 5.9 cummins in it to. Throws you for a real whirl the first time you drive one with that bass ackwards gear pattern they have.

 

Hills, wind direction, driving habbits, shape of the truck, turbo, air to air and rear end gear ratio for the region your driving in. How many gears means nothing.

 

If you wound it up to 2100 and then split to 1850 they yes it would burn more fuel but if you take it to 1300 split to 1050 its more efficent than a hole gear at a time. A 13 or 18 if split properly will ALWAYS get better fuel econemy than a 9 or 10 shifting hole gears. A 13 or 18shifted like an idiot will get just a bad of milage as a 9 or 10 shifted like an idiot. Im not saying a 13 or 18 will get tons better econemy but they will get a 10th or two better if you in a situation where you are doing a lot of shifting. Cruzin' down the interstate at 65 for 11 hrs you wont see any difference. Buy the way if you think skip shifting with a 9 or 10 save fuel you realy confused. Maby bobtail or empty down hill a little but if you any load at all a skip will lug the engine to the point it will burn a hell of a lot more fuel than if you just shif normal. Excessive RPMs either way ( high revs or lugging ) burn fuel. Keeping the rpms in the peak torque range make good fuel milage. This is what a 13 or 18 speed dose.

 

I run mine up to about 1400 then split down to roughly 1200 and do that through the gears. 14-1500 is in my opinion the highest you really need to wrap the truck up to atleast the C-15 I drive. It has all the power you need within that few hundred RPM range.

 

what i can say about this thing above

here manufactures wants driver that shifts fewer possible

and skip as many as possible gears

thats why they now trying to force buyers to buy 12speed gearboxes instead of 16speed (1.285 vs 1.205 between gears)

mercedes wants to skip full 2gears ( 2.13 ratio differences)

so mercedes wants driver to start in 2H gear shift it in to 4H 6H 7H 8L and 8H

and it works

some trucks dont like shifting from 4-6 as full 2gears but only 1.5

also automated gearboxes works on this way and it is good

some of trucks have only 3timmes shifts from standing to top speed

also performing downshifts mainly like this

downshift 1/2 gear before hill and than let your engine to lug down at 1000rpm and depending on situation shift it 1.5 or sometimes 2gears down scania and volvo less because their manual gearboxes have larger ratios differences .....

i also trying to drive that way my father use as less as possible throttle and he is trying to shift gears to keep engine in 1000-1500rpm( also going uphill he shifts lot of speeds without skipping)

my fuel economy is better
but in our job this produce lot of heat and stress on engine it use lot of oil so in this summer months i am trying to drive like him

once he said to me not only reason for oil/heat but also he used to to this because he has habit from 40-50year old trucks he used to drive he says they were much more sensitive on heating and dont feel happy to rev outside of their sweet spot

my brother is careless on fuel he now works in company with very big demands on him ( time and delivery schedule) so it is ideal for him

 

Actually the 9/10 spd trans is better for fuel economy than a 13/18 in normal operating conditions. It has something to do with less gears and other things turning in the trans.

 

Thanks for the post John. Much kinder and more eloquently said than i could have done...

 

Normal is different for everybody though. I run mostly mid west which is normal for me but a person that runs regional out of say the knoxville area has more hills and stuff like that then I do.

I do agree about the 10/9 speeds having less moving parts and all and it just takes more out of the truck to turn everything in the trans on a 13/15/18 speed trans.

I would have to say out of my knowledge of diesels that a 13/18 speed would be better. This is just my personal opinion and the sense it makes to me. Lower RPM means lower boost #'s which means un burned fuel out the pipe and higher EGTs. If you have a 10 speed and lug the truck down to 1100 on a C-15 and then down shift bringing it back to what 1450-1500 RPM is a very drastic change where as with a 13/18 you could drop a gear at 1200 RPM and have it go back to 1400 and that 200 RPM range is IMHO is the most efficient power range on a Cat motor while still keeping most of the power. This is just my personal preference and I'm not disagreeing with you because the splitter box is extra moving parts especially with a double over with even more and I believe an extra counter shaft in there to turn.

 

I agree a 13/18 is my choice also I was just telling you the professionals opinion. I don't necessarily agree with it either.