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Old 05-29-2019, 09:22 PM   #31 (permalink)
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Quote:
Originally Posted by Hersbird View Post
It's not wierd, it's just physics. I don't think it's going to get
a 30mpg tank no matter what you do. Good aerodynamics are one thing, massive frontal aera is another. I think 25mpg at 60 mph and under would be possible but not 30. I've had a few Suburbans and although never one newer than 2005. I do know my smaller minivan with a very efficient latest generation v6 will only barely touch 30 mpg at 60 mph. Already lower, very clean underbelly, highway gearing, 6 speeds and only 2wd. We did have a 2003 5.3 4x4 Burb that would hit 22mpg around 60, my current 2500hd 2001 was getting only 15.2 mpg across Washington but running 70 mph with 7 people and gear and it has 235,000 miles on it and aggressive AT tires, the 6.0 and heavy duty everything. My 5.7 hemi Chrylser Aspen, slightly smaller than a Suburban but just as aerodynamic, with 5 speed and cylinder deactivation would just barely get 20 mpg at 55-60 and running 70 deactivation never happened and was more like 17-18 mpg. I do agree as full size real SUVs go, the Suburban is the way to go. A Tahoe does no better but gives up room and seems to cost more on the used market. The Fords just haven't been reliable, and Dodge just only made them a few years 2003-2009. The Toyotas are overpriced and do about the worst on FE for some reason. That said, craigslist or publicsurplus.com is full of under $1500 cars that will get 30 mpg all day. Suburbans will always be available when you do really need one and 2 years down the road the $1500 car will still bring $1500 and the same Suburban you sell will be $3000 less to replace.
I already brush mid 20's on the freeway at 55 mph. The newer Suburbans are much more aerodynamic plus we have cylinder deactivation which the older ones did not have. I will see if I can get low to mid 30's but you could be correct.

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Old 05-29-2019, 09:23 PM   #32 (permalink)
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Quote:
Originally Posted by Tahoe_Hybrid View Post
Hitting 40MPG in the city with my Tahoe RWD with the 6.0L engine
Running aggressive tires...

Hybrid of course as I have figured out how to game the system (ECU) to MAXIMIZE city MPG....
40 city US-MPG /27 US-MPG Highway


on the Sub vs Tahoe cost

it's down to the size and the ease of parking it that is why it's more popular (and why i bought one)


He is chasing a pipe dream... esp since 4x4 is an automatically a penalty MPG wise
At least it will be a fun pipe dream to chase!
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Old 07-10-2019, 02:48 AM   #33 (permalink)
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Quote:
Originally Posted by Hersbird View Post
CITY is the key, add a plug in charger and you could do unlimited MPG as they can go pure electric up to 30 mph for a limited time. The Hybrid Pacifica is a better choice as it can go up to 80 mph pure electric with a range over 30 miles and has the built in plug in charger that recharges in 2 hours on 240 volts. You could own a Pacifica and never put gas in it. They used the 6.0 in the hybrid GM because it runs on the Atkinson cycle so without the motor assist it makes less power and torque than the 5.3.
it's LS2 based far from being weak with the electric and ICE it's rated at 379HP /472fb-lb torque..

it has a slightly higher compression ratio then the

L76=10.4:1 AFM VVT 355 hp 384 lb-ft
LFA=10.7:1 AFM VVT 332 hp 367 lb-ft
LS2 =10.9:1 400HP 400 lb-ft


Horsepower (hp @ rpm):

LFA Hybrid 332 @ 5100*
LS2 400 @ 6000
L76 367 @ 5400
Torque (lb-ft @ rpm):

LFA Hybrid 367 @ 4100*
LS2 400 @ 4400
L76 375 @ 4400
we could assume the TRUE specs of the LFA is 375 HP and 390 lb-ft at the L76 rpm speeds just for the ICE..

it's obviously they watered down the TRUE numbers.\ because they line up slightly better to L76 numbers at the same rpm (because of the slightly higher compression ratio)
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Old 07-10-2019, 11:56 AM   #34 (permalink)
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Quote:
Originally Posted by Tahoe_Hybrid View Post
it's LS2 based far from being weak with the electric and ICE it's rated at 379HP /472fb-lb torque..

it has a slightly higher compression ratio then the

L76=10.4:1 AFM VVT 355 hp 384 lb-ft
LFA=10.7:1 AFM VVT 332 hp 367 lb-ft
LS2 =10.9:1 400HP 400 lb-ft


Horsepower (hp @ rpm):

LFA Hybrid 332 @ 5100*
LS2 400 @ 6000
L76 367 @ 5400
Torque (lb-ft @ rpm):

LFA Hybrid 367 @ 4100*
LS2 400 @ 4400
L76 375 @ 4400
we could assume the TRUE specs of the LFA is 375 HP and 390 lb-ft at the L76 rpm speeds just for the ICE..

it's obviously they watered down the TRUE numbers.\ because they line up slightly better to L76 numbers at the same rpm (because of the slightly higher compression ratio)
The biggest difference in power is due to tuning and camshaft. The numbers aren't watered down.


To the OP, I would suggest taking the tires to 40psig, we saw a measured difference going from 35 to 40. What year do you have? You might be able to get a Tahoe hybrid front air dam to fit and you would have a factory look.

Nvm, I see you have an '08, the air dam should fit if you can find one.
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Last edited by ksa8907; 07-10-2019 at 12:13 PM..
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Old 07-11-2019, 12:25 AM   #35 (permalink)
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Quote:
Originally Posted by ksa8907 View Post
The biggest difference in power is due to tuning and camshaft. The numbers aren't watered down.


To the OP, I would suggest taking the tires to 40psig, we saw a measured difference going from 35 to 40. What year do you have? You might be able to get a Tahoe hybrid front air dam to fit and you would have a factory look.

Nvm, I see you have an '08, the air dam should fit if you can find one.
Yes the tunning but it is a heavy duty crank shaft and cam as it has very strong for "high speed start ups" 1500-2000RPM is the typical start up speed..


it goes from 0 to 1500-2000RPM in under a second varies based on load
some people all ready have broken their I/O shafts on the transmissions

that is how strong the cam and crank shafts have to be..
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Old 07-11-2019, 08:11 AM   #36 (permalink)
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The first question is always:

What are the projected savings on an annual basis?

There’s a goal or there isn’t.

Thus, the first test:

1). Take to truckstop out past edge of town. Preferably 25 or more miles from cold start. Top off fuel tank to first auto shut-off.

2). Weigh vehicle on CAT Scale. Only driver plus gear kept permanently aboard (till the day it’s sold).

3). This is how tire pressure is set. Accurate numbers. Given that a cold (sat overnight) reading was done at home, use the tire manufacturer Load & Pressure Table to get CORRECT pressure value. Too much IS NOT correct for handling, steering and braking. This is truck. High COG. Don’t screw these up!

3). Take a 200-mile plus round trip via Interstate back to that same fuel pump. Refill in same manner to auto shutoff. Check tire pressure again on stopping. Should not be more than a 7% rise from adjusted cold read.

4). Engage cruise control before the end of the entrance ramp. 58/mph. Note rpm setting. . No higher. Do not cancel except to get slow passing traffic around you. At the end of the outbound run (choose a crossover WITHOUT any traffic), make your quick stop and going o the inbound portion. Don’t let it cool.

Glide on back. Avoid ALL pack formation. Watch mirrors and plan to get them around you fastest.

Ideally the brakes are used only when exiting. Same idea for manual use of throttle. Let the drivetrain do its job. You’re there to steer, primarily.

This loop will give a baseline that with by-the-book tire pressure and computer-control of speed can be easily replicated.

This number is as good as it will get. Aero is for the higher speeds of maybe 62-64/mph that commuting will keep you from being a rolling roadblock. Below the big trucks, yet they can pass you easily.

Without this basic info of what is possible one winds up where so many others do: fantasy.

— CAT Scale has a phone app. Directions of scale use on website. Go inside from diesel fuel island for your paper copy (if app PAY feature set up).

— Load & Pressure Table at tire website. Print a copy.

— This is NOT about mods in driving or the vehicle to get highest number. This is about a relaxed weekend morning drive letting things fall where they may. That anyone can replicate (no knowledge of desire for higher mpg).

From here is:

1). Annual highway miles expected.
2). Gallons consumed ($)
3). What percent savings will justify “spending to save”?

How can I make my 64-mph trip as fuel efficient as my 58-mph trip? Is the question now quantified.

(Removing roof rack just degrades utility. As does mirror change. (Thus, why own this Vehicle?).

FE is the maximization of steady-state. Until that is a given, other changes won’t pan out. IOW, I can run your truck “as delivered” at a higher highway mpg than you with your thus-far modest changes. All test parameters the same.

So what I’m trying to say is to “get the driver out of the way”. The desire for better mpg will effect the driver far more than vehicle changes at first. Will give inaccurate results.

Get the Baseline Highway MPG.

The only number that matters ISN'T the weekly out-of-pocket expense, but the annual percentage change to the Total Cost of Ownership when expressed as cents-per-mile. CPM.

The VAST majority see how low is that change to the CPM and just give up. But the more miles and years, the more important it becomes to establish new habits and to be sensitive to conditions of road, load, traffic and weather that effect an otherwise sound vehicle.

Only a beginner thinks it’s about “going slower”. There’s a great deal more to never stopping, never idling, all to maximize the Average MPH for a given vehicle.

So, find the engine hours. Compute the trucks overall average speed at present. Use that as gauge more than worry over fuel burn (as inaccuracies abound until a complete year is recorded). THIS will maximize your aero changes.

Your vehicle is better than you. Until one learns to give it exactly what it asks for (and no more), and has a baseline to work against . . .

. . the temptation to say, “oh, not today, I’m in a hurry” (HA! Sucker. The only guy who’s in a hurry didn’t plan his use well. Now will “abuse” vehicle to counter that — daily? — personal failure).

A plan based on real numbers. The willingness to acquire new habits and be disciplined about them. Safety over stunt driving. Longevity over stupid pet tricks with the drivetrain and tires. Etc.

.

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Last edited by slowmover; 07-11-2019 at 08:16 AM..
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