Help!! C15 twin turbo MPG...

Now that's great for you guys but a friend here saw the opposite. He went from a FL Columbia to a Classic and he mileage went up. Now I know it wasn't from the flat hood but it just shows my point that there are so many factors involved that blanket assumptions that aero = guaranteed fuel economy improvements doesn't work. I just see too many people spreading the 1mpg + claims (not pointing at anyone in particular). In my experience most of the HUGE claims have more to them than people will admit. Like "I went from 5.5mpg to 7 when I put some air tabs on the sleeper" then you find out they also went from pulling a flatbed with lumber to a dry van hauling potato chips. I guess the difference in the load they were hauling had nothing to do with the huge jump.

I would just love to take one of these high mileage OTR trucks and hook it to a RGN with a bulldozer or something with the same "brick" aerodynamics and watch the owners reaction when his mileage was no different from the 379, W900 or Classic that was pulling it before.

Another guy here (not a genius by any means) blamed his engine ('06 C15) for his horriable fuel mileage in his 379. He only owned it for less than a year but you couldn't convince him that it was because it was a long WB flat top pulling a van. Yea it was the engine, not the 4ft of trailer sticking above the cab and his lead foot that was responsable for it. Just saying there are too many factors to blame just one.

 

Your so right and owning trucks and having drivers you know that a throttle jock in any truck no matter what is gonna get crappy fuel mileage!

 

I agree, there are way two many factors involved to say one truck will get better fuel than another because it looks more aerodynamic. Thats said if everything else is equal than the more aero truck will get better fuel, the problem is "everything else" is never equal. And I think just because a truck looks slippery doesnt always mean it is.

Oh yeah... the classics, pete 379s, KW w900s, etc just plain look cool too.

 

NXS should have 120 gph head already. what filter# and brand is in primary position now?

Also, 1450 cruise rpm is way past best mpg for an Acert. above 1300-1325 mpg drops off quick

 

Talking about fuel economy, I have a 625 Acert I have been trying to improve the fuel economy on with little sucess.
Its T908 KW, B-double tanker, 62.5 metric tonnes, 4.11 diffs. Driver treats truck as Cat tells you to in their driver video.

Started at 1.51 km/litre, can be overtaken by pre Acert C15s # 550hp with mild fuel settings at the same weight and spec except 4.33 diffs.

First change was valve adjustment, set all setting as per spec except IVAs which were set a couple of thou loose, wastegate spec tightened up 1.5 turn, stretch fuel pump spring to get 100psi fuel pressure. This saw a small gain to 1.52km/litre and slightly better power, still getting overtaken though. boost maxes at 365-370kpa.

Second mod was fuel setting which I was told would give 20-30rwhp gain. Truck now gets 1.55km/litre, no longer being overtaken but cant pull away from pre Acert 550, boost in the 380kpa range.
At this point truck was PAR dynoed, came back as within spec, making 625hp, fuel rates within spec, no chances were made by PAR dyno.

Third was fuel settings supplied by DDS (many thanx), truck more responsive, jumps to 1.61km/litre, cannot overtake pre Acert 550s but can pull away on the hills, boost just gets over 400kpa.

Fourth mod was to remove the mufflers and swap for a set of donaldsons with the baffles cut out. truck runs much more freely, pulls a little better, especially down low. strangely is hardly any louder, even on the jakes. fuel economy has not been officially checked yet but driver works it out to be slightly worse but I am yet to confirm, and this was only a week ago so I need to give it some time, but there was certainly no big jump as I had thought there might have been. We are aiming to get to 1.75km/litre, his previous pre Acert 550 got 1.79km/litre. full boost now on tap at 1350rpm, easily over 400kpa (limit of the gauge).

Where to next.... we are going to fit dual primary filter system so the truck can still use the same filters as the rest of the fleet rather than go to a Davco. Going to wind the wastegate back to bring the boost down a bit. not sure where to go from there but I will keep everyone posted.

 

Jas, have you tried Fleetgaurd FS 1023 in primary position ? fit same head as Cat 256-8753 flows like crazy # 100 mic 400 gph screen type filter w/drain. the Davco flows 180 gph but 50 mic is largest availible. have a friend with 625 who had similar complaints.last he said was Cat fixed it and runs great. I will check to see whats been done and get back to you.

 

PaulE,

Cant put fleetgaurds on it, its on Cat Xtra service contract, gotta have cat filters for warranty, plus I work in dealer land so its much easier to get cat filters to try. the truck current runs a 1335673 which is a largish filter with a glass bowl on the bottom( cant find any flow specs for it though ), I have a couple of spares with bases and bowls laying around so I'm going to try a dual set up and see how it goes.

Thanks for the info.

 

I know part of his economy woes.

Look at the RPMs its turning. All the talk and literature i have seen on the Acert is that it wants a lower cruise rpm.
Pre-acerts ran on 4.11 for double, tell the driver to back it down 5 kph ( if he has the time on his run ). personally i would have suffered the performance loss on the hills and put 3.9's in from new.

The old c-12 was Ultra sensitive to rpms, running under 1500 rpm i could nett between 2.7-2.9 ( towing bogie vans ), yet once i fired it up the road, i would sit between 1650-1750 at highway speeds ( 4.33 ) and the best i saw was 1.7 with a bogie tautliner. ( had something done to ecu but never looked into what. ran 395hp to the tyres)

I think that the larger engine too would likley be happier with lower cruise rpms.

is the truck limited still? if the limiter is being played with then he can throw fuel out the pipes and forget about it.

 

I hope those fuel figures are in km per liter Agent
I wouldn't like people to think those were MPGs