Hi all,
I've been reading, reading, reading out here for 2-3 weeks now, trying to decide where to go and what to do. I bought a '04 Silverado HD extended cab/long bed w/LLY Duramax and Allison 6-sp. The truck is essentially stock - has nerf bars, ventshades, and that's it. I'm seeing 15.5 - 17.8 mpg, but hoping/expecting to improve it significantly. I'm not interested in a louder or stronger or faster truck... just a more efficient one. I'll take the stronger/faster as a nice side-benefit. :)

I'm planning on doing the following, hoping things will improve:

Lockable folding tonneau cover (improved aerodynamics)
4" exhaust (assume the best approach is turbo-back, but ???)
Cold air intake/???
Some type of chip/programmer I'd be interested in thoughts on a) which mod is likely to yield the most mpg bang for the buck, b) other mods I should consider, and finally c) any specific recommendations on the mods I've listed above? I'm trying to research all of the options, but this forum and others have so much anectdotal information and marketing glitz that making an informed decision seems daunting if not real, real tough.

Randy

Tonneaus seem to work for around 1 mpg or so....

Any programmer will/should increase it a bit too...

Dont expect any gains with a cold ait intake kit...

Get a Predator..... I increased 3 to 4 mpg.. The exhaust and cold air will not increase your milage.... Due to the nice sound and extra power, your foot Will be heavier. I use to get the same numbers you get...

Is there conventional knowledge on cat-back v/s turbo-back from a performance and/or noise perspective? Which option typically yields the most performance improvement? For an old fart not interested in rattling windows, what's the best option to pursue?

I've read a lot of in-depth information regarding cold air. Based on what I've heard/read out here, I just replaced my stock air filter with another AC Delco. But... I've been trying to determine if the opinions out here stating there are no benefits to non-stock filters were based strictly on OEM replacement filters or if there were any cold air or other non-OEM stock box filter options that actually improve performance. I don't need more turbo whistle, and I've got better things to do than showing off the stuff under my hood.

Are there other mods I should consider? For example, what is a boost stick? This is my first diesel... so I'm pretty much clueless... any guidance would be greatly appreciated.

Randy

The predator, new, is around 300 bucks. By far the best bang for your buck. I got mine on Ebay for around $140.

Randy, you dont need a boost stick. You also dont need an EGR blocker plate. I never ran either on 2 different model year trucks.

I dont think a Predator can or will give you 4 mpg...I think thats a bit far fetched....A couple, at that is best but then again, you're adding 40-100 h.p. and you actually think you're not gonna use it from time to time?

I've run an AFE stage 2 intake kit on my 04 LLY. I didnt notice any performance gain or mileage increase. Is it worth $350? For some maybe whom are after a bit more turbo whistle....Dont expect any power gains with it though because generally, the stock intakes flow well enough....Now, if you plan on making serious h.p. (which it does not sound like that to me) then the stock intake is fine...I may actually throw in a dry AFE drop in to see if that does anything here in the near future...

Exhaust...It really depends on what you want...The stock muffler is way more restrictive than any cat. converter thats welded under there. I've run a full 4" turbo back on my LLY and it did sound great and had lots of turbo whistle....A full 4" system will generally yield around 25 h.p....And I think thats shooting a little low......Exhaust systems tend to really wake up these motors....After I traded in, I chose to run a cat back for sound mainly...Its barely louder than stock and has a nice throaty rumble to it and I picked up 10-15 h.p. in the process and maybe a mpg...

The funny thing is that none of these trucks are the same...What worked for me, didnt work for other people with the same year or similar mods...Some of us got 22 mpg off the showroom floor and others got 11. Some of us see a dramatic mileage increase at a certain mileage and others dont...Some see alot of black smoke with certain programmers and some dont...

Its generally tough to say what will work for you but the facts are that, any exhaust system will be a gain for your truck, either cat back or turbo back. Intake kits can go either way. $350 is alot to spend in my opinion for 1 mpg. A programmer is probably your best bet but now there's a whole 'nuther discussion to get you started on that....

DiabloSport Predator?

15.1 mpg w/ulsd

16.8 mpg using Power Service w/ celetene boost

21.0 when i added the predator

these are numbers based on 80% hy 20% city

Yep thats the one.... If you read up on it people seem to get along just fine with it. Other programmers are 500 +

Scott, I wasnt saying you're far fetched by any means. I mean no disrespect...I just dont see how it gives a 4 mpg increase. Do you hand calculate? Maybe I'm way off here, I dont know....I never got better than 19 and that was stretchin it out of my LLY and the norm was 17-18.


I agree on the Predator as well. Great performance product and by far WELL worth the $300 price tag.

Unit is right about all trucks not accepting aftermarket parts with favorable results. Horsepower and fuel economy will differ in wide margins....

I trust the D I C since I have stock tire size. I filled up tp the neck today and in 4 days I will have that hand calculation.

The problem is that once the truck is tuned, the fuel mapping is changed, therefore the DIC is no longer accurate.

So... let me ask a totally obtuse question. Is there any typical guidance on how to drive these things? I've been driving the truck real easy, yet out on the highway (to and from work) taking it up to 65-70 mph. Keeping my foot out of it I was seeing around 17.6-17.8. However, after 3-4 tanks driving like that (coasting where possible, accelerating carefully to keep from romping on it, etc), I was seeing the mileage drop. And... the truck seemed to be bogging down some. I kicked it down a few times (which sure feels and sounds great) and naturally DIC is telling me I'm down around 15 mpg. But... the truck is running better.

I suspect that you've got to run the truck hot enough to efficiently burn fuel, but try to keep it under 2k rpm otherwise you start dropping mpg. Does this sound right, or is there that much difference between fuel from station to station?

With that in mind (if there is considerable differences between fuel from station to station), is there a fuel additive I should consider using on a regular basis? Or... is what I'm experiencing a typical characteristic of the beast?

I'm reminded of the old 2-stroke motorcycle engines. A buddy had a hot running Suzuki 2-stroke 550 many years ago, and he virtually refused to romp on it from time to time - almost never wound the RPM's up, etc. As such, his bike was constantly loaded up and running pretty lousy. He fouled plugs like nobody else. Is there anything similar in nature I need to know about driving my LLY?

Randy

OH.... Boy, I was just about to sell my Honda Civic commuter car since it I thought my truck was getting only 8 miles to the gallon less..... I better keep that car until the hand calculation is done. Thanks

Randy, you're not doing anything wrong...Its your truck, drive it how you want...

You just have to know a few thigns first when it comes to owning, driving, and maintaining these things....

Fuel is critical...Its not anything like gas. Some stations will have better quality fuel than others...Sometimes your truck is gonna feel like its got alot of balls and other times it wont...I really think the quality of the fuel we're getting these days has everything to do with the performance of the engine and the mileage it gets in the process...

Now, your fuel filter is probably the most imporntant single piece of maintenance hardware thats often overlooked on a modern day diesel. If you're not changing it at regular intervals, something is wrong. Your owners manual shoudlk also tell you this...I change mine at around every 10,000 miles. Its too easy to gel up in cold climates and clog the damn filter leaving you stranded along the side of the road...

Additives...Getting off topic here but here's your answer...

If you're in a cold climate, it would be beneficial to you to run additives. Stanadyne, Howes, or Power Services are by far the most popular. I believe GM reccomends Stanadyne. I run it in every tank. To me, its a simple piece of mind to keep my fuel lubed and gel free in the cold, long winter months that we get up here...

I drive like you do. But once or twice a week I hammer her down... The Power Service i use helped with engine noise and lubes the injectors, i hope. Pay attention to the fuel additive study that Spicer is doing. His results will determine what I stay with or switch to.

Units right, Standyne probable is the right choice. Its not sold in as many places as Power Service. I like the quick and easy.

You need to run additives. This ULSD is filtered heavily to remove the sulfer. That process also removes the some of the fuels ability to lube the injectors.

Where can you find Stanadyne? Power Service?

There are a couple vendors here who sell that stuff....

http://www.dieselplace.com/forum/showvendors.php?

These guys keep this site running free and constantly upgraded.

15.1 mpg w/ulsd

16.8 mpg using Power Service w/ celetene boost

21.0 when i added the predator

these are numbers based on 80% hy 20% city

Are you hand calculating your mileage? You know that the Predators programming distorts the mileage on the DIC, right?

I have a Predator V2.02 also and I've never gained any mpg on any tune the Predator offers. If anything, I've lost a little mpg with it.

I trust the D I C since I have stock tire size. I filled up tp the neck today and in 4 days I will have that hand calculation.

Get ready for a surprise!! The DIC will be way over optimistic if you are running a Predator tune.

15.1 mpg w/ulsd

16.8 mpg using Power Service w/ celetene boost

21.0 when i added the predator

these are numbers based on 80% hy 20% city

Boy scott, these numbers are gonna fall down when you get the hand calc, tuning throws the DIC off just as these guys are saying.

Post #1 ...... 04 with a six speed allison? Nobody has questions about that ?????

First things first, CAI will scoop up some mileage on the cheap. Either fab one or buy one, we have an inexpensive yet effective kit to correct the stock box deficiencies.

Second, if you aren't towing heavy, ditch the engine fan and install a Fan Damn. Power will jump up bigtime down low as if you had a strong tow tune without adding more fuel, the engine fan will be forever silenced, and mileage will bump up.

CAI will net you around 1 mpg and a Fan Damn will snag you around 1 mpg as long as you don't run around mashing the throttle sampling the new power and responsiveness all the time. :)

You need to run additives. This ULSD is filtered heavily to remove the sulfer. That process also removes the some of the fuels ability to lube the injectors.

The lubricity of ULSD did not get left out in the cold.

http://www.clean-diesel.org/vehicle_performance.html

You shouldnt have to run additives if you are getting good fuel. I run Stanadyne in the winter and keep a bottle of it in the tool box. I also keep a fuel filter, strap wrench, and ice pick in the tool box. You never know when you are going to need any of them.

As far as CAIs go, I have been using the very cost effective that is sold at Coolmyduramax.com . I have been trying to get information on the new Banks with the "Ram Air" however it appears to not be available to the public, despite that a picture of it is in every diesel advertisement for Banks.

I wouldnt have any pre 06 Dmax with out a way to sheild the underhood temps from the intake.

Speakin of underhood temps...

Last week, using my Predator real time data....Highway cruising at 72, OAT's were 67 degrees and my air intake temp was 91 degrees....I thought that was a bit on the warm side cinsidering I was travelin at highway speeds and this 06-07 "improved" airbox is supposed to completely shut off underhood air from getting into the box...

Yeah, I hand calculate all my mileage and I did NOT get any mileage gane with the Preditor 2.02.... But I have to say the extra HP is going to KILL YOUR mileage! thats because your foot becomes HEAVY! It is a lot of fun but with tickets and more power less mileage :)

Speakin of underhood temps...

Last week, using my Predator real time data....Highway cruising at 72, OAT's were 67 degrees and my air intake temp was 91 degrees....I thought that was a bit on the warm side cinsidering I was travelin at highway speeds and this 06-07 "improved" airbox is supposed to completely shut off underhood air from getting into the box...

That 20* rise beats the heck out of the stock pre LBZ years. IAT can and does get into the 200ish range. That is why it is important to isolate the underhood air from the intake. When the fan engages, only part of the power loss is due to turning the fan, the rest is lost to IAT.

First... I can count, and I can tell you I'm counting 6 distinct gears as I accelerate from a dead stop (5 distinct shifts between 0 and about 60). I do know the engine is an LLY, which puts this truck as an '04.5, and I do know that the owners manual indicated I've got an Allison tranny. I've had a couple of other guys ask me about this - did the '04.5 NOT come with a 6 sp Allison tranny? Or am I missing something? Please be gentle... ;)

Second, there sure as shootin' isn't any isolation of the intake air for the stock air box in my truck. It just opens up wide toward the inside of the passenger fender... so I'm assuming it's getting whatever air happens to be under the hood, which I'd bet isn't all that "cold". It would make some reasonable sense to me that getting an outside air source piped into that box would improve things... yet I keep hearing people out here tell me it just ain't so. Since there's no additional sensors in my truck, I don't have any indication about IAT or EGT. Thoughts on what to do?

Third, there's been much talk about the Kennedy mods for the stock air box, but I can't seem to nail down what that is and what it's supposed to improve. Any pointers and/or info would be appreciated.

Finally, I tracked down the Power Supply fuel additives and I'm on my second dose (first full tank). My inclination is to say I notice a difference, but it's probably too soon to really tell.

Randy, common mis-understanding ........that 6th gear (5th shift) that you are feeling is the convertor lock-up. The Allison will normally go to 'lock-up' once it is in 5th gear(overdrive).
I vote for Stanadyne.......good stuff!
I also vote for leaving the air box in stock form.
Good luck! Ed.

Post #1 ...... 04 with a six speed allison? Nobody has questions about that ?????


Good catch, Chris. I guess most of us don't read very thoroughly...

Maybe he has the Suncoast conversion!:eek:

Speakin of underhood temps...

Last week, using my Predator real time data....Highway cruising at 72, OAT's were 67 degrees and my air intake temp was 91 degrees....I thought that was a bit on the warm side cinsidering I was travelin at highway speeds and this 06-07 "improved" airbox is supposed to completely shut off underhood air from getting into the box...

Nick,

Most of the time (moving) my IAT is within 2° of the OAT on the mirror. I'm running TxC's CAI. It really does help.

First... I can count, and I can tell you I'm counting 6 distinct gears as I accelerate from a dead stop (5 distinct shifts between 0 and about 60). I do know the engine is an LLY, which puts this truck as an '04.5, and I do know that the owners manual indicated I've got an Allison tranny. I've had a couple of other guys ask me about this - did the '04.5 NOT come with a 6 sp Allison tranny? Or am I missing something? Please be gentle... ;)

Second, there sure as shootin' isn't any isolation of the intake air for the stock air box in my truck. It just opens up wide toward the inside of the passenger fender... so I'm assuming it's getting whatever air happens to be under the hood, which I'd bet isn't all that "cold". It would make some reasonable sense to me that getting an outside air source piped into that box would improve things... yet I keep hearing people out here tell me it just ain't so. Since there's no additional sensors in my truck, I don't have any indication about IAT or EGT. Thoughts on what to do?

Third, there's been much talk about the Kennedy mods for the stock air box, but I can't seem to nail down what that is and what it's supposed to improve. Any pointers and/or info would be appreciated.

Finally, I tracked down the Power Supply fuel additives and I'm on my second dose (first full tank). My inclination is to say I notice a difference, but it's probably too soon to really tell.

Like others here said, you're noticing the torque converter lockup (usually at about 50mph). Your Allison came as a 5-speed unless you've got the SunCoast $1800 conversion, which I doubt.

Get TxC's CAI (cold air intake)(http://www.coolmydmax.com). Helps the engine run a little cooler and runs more efficiently.

If your read much of this forum, you'll learn there's a ton of mods available. It's up to you to learn which ones are worth the money.

I've done all that you're considering, not so much for any fuel mileage improvements (but I have seen a slight gain), but more for functionality purposes.
I went with the Corsa 4" exhaust because I've always had great experiences with their exhausts on my cars. Top notch fit and finish, easily installed, but a little pricey...
I have the Fold-A-Cover tonneau, and in my opinion it can't be beat. It's functional, and quite durable. The kids put folding chairs on top of it and watch events, and it never hurts it.
The Predator is where I've seen the best MPG gains, and it has a number of useful features in addition to the power gains.
Chevy installed the LBZ Intake, and it seems to do the job.

Are you hand calculating your mileage? You know that the Predators programming distorts the mileage on the DIC, right?

I have a Predator V2.02 also and I've never gained any mpg on any tune the Predator offers. If anything, I've lost a little mpg with it.

Im runnig a hand calc. now... Ill see at the end of the week what I really get.