Chevy and GMC Duramax Diesel Forum banner

Lly fyi

4K views 20 replies 12 participants last post by  DMVet 
#1 ·
The entire time I owned my LLY I loved it, but I would always hear that the LBZ was so much faster and better on fuel with the six speed. I bought an LBZ next and it was no faster and no better on fuel economy. Now I have an LMM and love it as much as the LLY, but the fuel economy still isn’t as good as the LLY (3mpg less). I just wanted to express my opinion
 
  • Like
Reactions: ALLY Cat
#2 ·
Good to hear patrick. I bought my 04.5 LLY at a decent price because it was "just a LLY and not a LBZ" so that's one more good thing about the LBZ,,, its popularity helps keep price of our LLY trucks more affordable. LoL
 
#3 ·
Nothing wrong with an LLY. Mine is used mostly to tow our 5th wheel for over 10 years now. Never had any issues other than the usual water pump, front wheel bearings and fixing the injector harness/connectors. Beefed up the trans, just because.... When I got it, first thing I did was the turbo inlet mod and DIY cold air intake. 5 speed is all that's needed for towing anyway... No DEF, no DPF, no CP4, no problem!!
 
#12 ·
Hi Ally just wondering if you can expand on the front wheel bearings you mention my LLY is making a slight whinning noise from the front area yet the wheel bearings do not feel really hot to touch
Have replaced the idle rollers
Thanks
 
#4 ·
The biggest difference between the 2 was the 5 speed (same ratios as the 6 speed just an extra OD...big whoop), the LLY had an atrocious intake system and the headgaskets will go. LBZ was just the year that they got everything right from the early models, and it didnt have the dpf on it that the lmm got.

Classics just look better then the lmm though so :p
 
#5 ·
That’s why I made the post. Everybody says they got it right with the LBZ, but they have their share of issues as well. I never blew a head gasket on the LLY. I had a turbo back exhaust, ppe programmer (that I really hammered on often), and the upgraded turbo inlet. The only issue I had on the LLY was the wiring harness pulling too tight and causing a limp mode. It was an easy fix with a ice pick. LBZ had an issue with the fuel rail relief valve before it hit 100k miles.
 
#7 ·
I agree, never got the hype of the lbz over the lly.
83mph......@2100 Rs. marx
 
#9 ·
83 at 2100 isn’t that big of a deal. Mine got
great fuel economy at 80 mph and it wasn’t loud. I always thought that extra gear would be amazing until I bought trucks that had it. All of the Duramaxes are awesome, but the LLY is way better than people give it credit.
 
#10 ·
Its crazy people want $30k for 2007 LBZ with low miles... I have a really nice LLY and actually applied to buy an LBZ guy wouldn't come off $30K but my truck is paid for and couldn't justify selling mine and having $30k payment for 12 year old truck best or not for $10k I put in to my paid off it will spank on almost anything... But the LBZ is awesome just over priced now...
 
#11 ·
Too bad they didn't put externally accessable injectors on the LB7......
 
#14 ·
Love my LLY but Im considering the 6speed valve body from Duramax tuners. Anything over 69-70 mph and my milage goes down quite a bit. I can get 17.5 staying in that range. I think they said that extra OD is geared 15% higher so I should be able to run 80mph at the same RPM's. At $1500 and I can put it in I don't think it will take long before the savings in fuel pays for it.
 
#15 ·
You will not get much higher mileage at higher speed no matter the number of gears. It takes the same amount of power to overcome the drag. As your speed increases the drag is an exponential increase. The increase you may see in mileage will be very small. I don't know how much the conversion is but it may take 100,000 miles to recoup your investment. Now if you do the conversion and stay at the same or less speed you will realize a much greater increase in mileage.

Just because you turn lower rpms doesn't mean you will necessarily get better mileage as the amount a fuel needed to produce the power you need will be substantially the same.
 
#16 ·
I looked into the 6 speed conversion years ago and calculated that it would never come close to paying for itself over any length of time, especially since I do a lot of towing. . Most 6 speed owners tell me they do almost all their towing in 5th gear anyway.
 
#17 ·
From my experience the lb7 and lly trucks get about 3 mpg better like you said, I believe it's mostly because of the 17.5:1 compression ratio vs the lbz/lmm trucks 16.8:1 compression ratio. And like these guys are saying you don't really need 6th anyways..
 
#19 ·
If your only getting 17.5 in a lly you either have large tires or a mechanical problem, most I have seen get 19-22 on the highway at those speeds. A mechanic buddy of mine got 22 hand calculated at 75mph driving from alabama to Kentucky. That was with a superchip, straight pipe and a lbz intake elbow I believe. Best Ive ever got out of my lbz was 19 on 33" toyo mt's at 70-72 mph on Idaho rob's economy tune. Again hand calculated, I don't trust the dash calculator one bit.
 
#21 ·
I bought my '04 LLY new, put the bullydog tuner on it and stayed stock on everything else. I now have 340,000+ miles and do some pretty heavy towing(ag business), and have done nothing but normal maintenance.
I get an average of 21.3 mpg towing my 5th wheel, and 23.4 mpg around town. Great truck. I DO NOT baby it and work it pretty hard towing fertilizer trailers and such. I would never give up my LLY.
Buddy has a LB7 and gets decent mileage(19 or so) but my truck fits my butt.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top