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Old 10-24-2020, 11:29 PM   #101 (permalink)
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It certainly did! Since it had been a few months I kept walking back over to the first side to remind myself of how I dealt with some of the binding and clearancing issues and to copy measurements. There were an unbelievable number of spots that would bind up in various interesting ways...

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Old 10-31-2020, 12:51 PM   #102 (permalink)
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Quote:
Originally Posted by aardvarcus View Post
Based off your numbers, it appears you are quoting figures off automobile catalogue, or a similar database, which the majority of are not measured but parametrically reverse engineered (shown as “estimated”). GM claims a measured CD of 0.45 for a generic GMT400 pickup truck, which while is not my exact configuration is the only measured CD I am aware of in open literature for a GMT400 platform. I personally trust this number more, but will agree to disagree on this point.

The transition from the GMT400 platform to the GMT800 illustrates the transition from detail optimization to shape optimization, which resulted in the loss of many very good aerodynamic details (flush wheel covers, flush/tight composite headlight to grill, flush door handles, etcetera) but overall a better tapered body shape.

There were not enough tweaks on the GMT800 platform over its 8 year run to cut the drag coefficient by over 40%, a 1999 GMT800 Silverado very closely resembles a 2007 GMT800 Silverado Classic aerodynamically. Many of the changes were for looks, not lowering drag. (e.g. use of the early 2500HD upper hood profile on later half tons).

Regardless, the stock drag coefficient will mean little after I cut and taper the rear of the vehicle.
it's incorrect an average 1995 chevy suburban 5.7l gets 10-11mpg

that is why it has a 42 gallon tank
about as great as a hummer H2 6.0l 4 speed the H2 is 0.57..

Tahoe hybrid is 0.34 gets 25mpg on the highway(round trip) on 100% ICE 6.0L 4 speed auto (with Super gear OD)
1050rpm at 45mph

48MPG on the downhill side and 15mpg on the uphill side is the best I ever done
i can't shake the 15mpg on the uphill side no matter what since its mostly in v8 mode


if I was able to get 20 or 25 on the uphill side i could get about 34~36.5mpg


there is other route i had not taken yet but it's going to be closed tell next spring(due to fire and winter) it's all down hill so i might be able to stay in EV mode for the 28 miles on the down hill side the speed limit is only 25-35 or so i would be able to stay at 29mph .... and stay in EV mode (would have to use the A/C to prevent the battery from overcharging)

Last edited by Tahoe_Hybrid; 10-31-2020 at 08:54 PM..
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Old 10-31-2020, 09:56 PM   #103 (permalink)
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Tahoe Hybrid,

I agree to disagree on the drag coefficient. All I know is the GM published figure for the gmt400 platform. You think it is higher, aerohead thinks it is lower.

I don't know about a 1995 with the 5.7, but the 1994 GMC Suburban K2500 i was driving with the 6.5 was returning 24-25 MPG consistently in normal use. These tanks were a mix of some city, some interstate, some hilly backroads, and some highway. Speed limits between 35 and 70. Often with significant loads in the back. Definately not ideal conditions. Also 4.10 gears in the diffs aren't helping, needs 3.42s.

It is a bit out of commission at the moment seeing how I cut it in half.

I also have many thousands of miles past experience driving a 1991 k2500 pickup with the 5.7, that would get 12-13 with the 4l60 and 15-18 with the early NV4500. Tire choice was the biggest variable there, 15 on the all terrain 18 with the street tread.
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Old 11-01-2020, 06:19 PM   #104 (permalink)
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Originally Posted by aardvarcus View Post
Tahoe Hybrid,

I agree to disagree on the drag coefficient. All I know is the GM published figure for the gmt400 platform. You think it is higher, aerohead thinks it is lower.

I don't know about a 1995 with the 5.7, but the 1994 GMC Suburban K2500 i was driving with the 6.5 was returning 24-25 MPG consistently in normal use. These tanks were a mix of some city, some interstate, some hilly backroads, and some highway. Speed limits between 35 and 70. Often with significant loads in the back. Definately not ideal conditions. Also 4.10 gears in the diffs aren't helping, needs 3.42s.

It is a bit out of commission at the moment seeing how I cut it in half.

I also have many thousands of miles past experience driving a 1991 k2500 pickup with the 5.7, that would get 12-13 with the 4l60 and 15-18 with the early NV4500. Tire choice was the biggest variable there, 15 on the all terrain 18 with the street tread.
That must be imagination land, if it was actually getting that they would have keep the design..

Really this forum needs a Fictitious story section...


what it really sounds like is a mis-configuration somewhere and was not recalibrated and again with 4.10 ratio = less gas mileage in it self...

so at about 75mph you will be getting about 5-7MPG 2500rpm engine speed
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Old 11-01-2020, 06:53 PM   #105 (permalink)
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Quote:
Originally Posted by Tahoe_Hybrid View Post
That must be imagination land, if it was actually getting that they would have keep the design..

Really this forum needs a Fictitious story section...


what it really sounds like is a mis-configuration somewhere and was not recalibrated and again with 4.10 ratio = less gas mileage in it self...

so at about 75mph you will be getting about 5-7MPG 2500rpm engine speed
It's called the unicorn corral. How are you calculating fuel mileage based on rpm and speed?
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Old 11-01-2020, 09:43 PM   #106 (permalink)
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Quote:
Originally Posted by Tahoe_Hybrid View Post
That must be imagination land, if it was actually getting that they would have keep the design..

Really this forum needs a Fictitious story section...


what it really sounds like is a mis-configuration somewhere and was not recalibrated and again with 4.10 ratio = less gas mileage in it self...

so at about 75mph you will be getting about 5-7MPG 2500rpm engine speed
So is your accusation that I am lying simply because my 1994 Suburban gets better fuel economy than your 2008 Tahoe does? I can see how that would be frustrating for you.

Since you like looking up metrics, go to “fueleconomy.gov” and look up a 1994 Chevrolet K1500 Pickup 4WD 6.5L, 8 cyl, Manual 5-spd. (Note they don’t have the correct factory engine or transmissions for the Suburban, hence look up the K1500 so you can actually select the powertrain I am using and not a generic 5.7 with 4l60e) Note the highway fuel economy estimate (original MPG 21 highway, New 20 highway). Note that is the estimate for a stock vehicle (mine is highly modified at this point), but even if I hadn’t modified it getting MPG 14% higher than the original highway fuel economy estimate isn’t that spectacular… Perhaps I should be ashamed at only getting 24 MPG in a vehicle with that engine transmission combination…

There were many other reasons besides fuel economy that GM scratched the 6.2L/6.5L diesels (competing higher HP options), but the US Army kept them around long after that (e.g. 6.5 still being produced last I checked). Thus a variation of the 6.2/6.5 engines has been in continuous production since 1984 to now. Pretty good run in my book. GM did significant detail optimization for the GMT400 platform (1988-2002), but lost many of it’s good details in the transition to the GMT800 platform (1999-2007) such as flush door handles, tight fitting headlights to grill, available flush wheel covers, etcetera as those made way to revised styling and the “shape optimization” to get back to the desired cD to hit their desired fuel economy with the new LS engines. If you spent several hours crawling over a stock GMT400 vehicle with an eye to details, your opinions on the cD might change... but perhaps not...

My odometer readings have repeatedly been both GPS and Google Maps distance verified. With 235/85R16 tires they will spin 656 revolutions per mile, which at 70 mph means 834.9 times a minute, which with 4.10 gears means at 70 mph my driveshaft spins 3423.1 times a minute, and with my modified 0.643494 overdrive gears (22/38 cluster ratio, 51/19 gearset) means my engine will be turning 2202.7618 RPM when traveling at 70MPH. (With 3.42 it would only be 1837 RPM, but I am not ready to do that swap yet, need to finish my bodywork first) My odometer is reading off the transfer case FYI so only the tires affect it, which I account for as verified per above.

I have alluded that my vehicle is modified, I have a full build thread on here, but to help support my outrageous claim of 14% better than epa estimated fuel economy, the cliff notes for back when those fuel economy figures were set were are a 2010 6.5L Diesel GEP Optimizer running Naturally Aspirated, NV4500 with custom overdrive gears, mechanical injection system swap which included me completely rewiring the vehicle from scratch to eliminate the computer, weight reduction, Michelin Defender LTX 235/85R16 tires, electric fans, DOT legal LED headlights, Duramax alternator swap, roof rack removal, flush bumper swap, WT grill swap, rare large bore OEM cast iron exhaust log manifold, custom air intake, conveyor belt air dam, and many other small tweaks.

I also don’t know where you are getting 5-7 from at 70MPH, even my 2001 Chevrolet 2500HD tow pig with the 8.1L and Allison gets better than that... It get about 12MPG average. Or perhaps I am lying about the 12MPG…

Last edited by aardvarcus; 11-01-2020 at 09:48 PM.. Reason: Typo
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Old 11-01-2020, 10:17 PM   #107 (permalink)
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Quote:
Originally Posted by M_a_t_t View Post
It's called the unicorn corral. How are you calculating fuel mileage based on rpm and speed?
Matt,

I do not know how he is calculating his figures.

In overdrive at 70MPH per my BSFC Chart I should expect 0.405 lb/bhp-hr at WOT. Using that as an approximation for other throttle positions, 5-7 MPG would imply burning 14 to 10 gallons an hour, or about 98 to 70 pounds of fuel. Given the BSFC, that implies it would take 241.9 to 172 bhp to cruise down the road. Anyone familiar with the naturally aspirated 6.5L would know that is more HP than the engine makes total, much less at 2200rpms. I would basically have to install two engines to burn that much fuel in that time frame at that RPM at wide open throttle the entire time. This means that no GM vehicle ever produced with a 6.5L non-turbo engine would have ever driven 70MPH on flat ground, regardless of gearing as the road load would be to high.

Checking my numbers, 70 MPH at 24 MPG (which I never claimed, but for arguments sake) is 2.91 gallons, 20.416 lbs diesel, implying 50.41 bhp assuming constant bsfc, or a bit under 1/3 throttle to maintain speed on level ground. In real life efficiency is slightly less at fueling less than WOT, my 70MPH stretches would be lower MPG than the average, but in general that level of road load seems about right to me.
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Old 11-01-2020, 10:35 PM   #108 (permalink)
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Quote:
Originally Posted by aardvarcus View Post
Matt,

I do not know how he is calculating his figures.
I was hoping to pick his method apart and figure out how he might have came to the wrong conclusion.

My best in my van (close to the 5.7 4l60e config with a 4.3 4l60e) was rated 15 city and my best was 24 mpg. So 14% over is definitely possible. I don't understand why it would be questioned.
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Old 11-02-2020, 12:29 AM   #109 (permalink)
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I was hoping to pick his method apart and figure out how he might have came to the wrong conclusion.
(Consider the source)
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Old 11-04-2020, 01:26 AM   #110 (permalink)
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Quote:
Originally Posted by aardvarcus View Post
So is your accusation that I am lying simply because my 1994 Suburban gets better fuel economy than your 2008 Tahoe does? I can see how that would be frustrating for you.

Since you like looking up metrics, go to “fueleconomy.gov” and look up a 1994 Chevrolet K1500 Pickup 4WD 6.5L, 8 cyl, Manual 5-spd. (Note they don’t have the correct factory engine or transmissions for the Suburban, hence look up the K1500 so you can actually select the powertrain I am using and not a generic 5.7 with 4l60e) Note the highway fuel economy estimate (original MPG 21 highway, New 20 highway). Note that is the estimate for a stock vehicle (mine is highly modified at this point), but even if I hadn’t modified it getting MPG 14% higher than the original highway fuel economy estimate isn’t that spectacular… Perhaps I should be ashamed at only getting 24 MPG in a vehicle with that engine transmission combination…

There were many other reasons besides fuel economy that GM scratched the 6.2L/6.5L diesels (competing higher HP options), but the US Army kept them around long after that (e.g. 6.5 still being produced last I checked). Thus a variation of the 6.2/6.5 engines has been in continuous production since 1984 to now. Pretty good run in my book. GM did significant detail optimization for the GMT400 platform (1988-2002), but lost many of it’s good details in the transition to the GMT800 platform (1999-2007) such as flush door handles, tight fitting headlights to grill, available flush wheel covers, etcetera as those made way to revised styling and the “shape optimization” to get back to the desired cD to hit their desired fuel economy with the new LS engines. If you spent several hours crawling over a stock GMT400 vehicle with an eye to details, your opinions on the cD might change... but perhaps not...

My odometer readings have repeatedly been both GPS and Google Maps distance verified. With 235/85R16 tires they will spin 656 revolutions per mile, which at 70 mph means 834.9 times a minute, which with 4.10 gears means at 70 mph my driveshaft spins 3423.1 times a minute, and with my modified 0.643494 overdrive gears (22/38 cluster ratio, 51/19 gearset) means my engine will be turning 2202.7618 RPM when traveling at 70MPH. (With 3.42 it would only be 1837 RPM, but I am not ready to do that swap yet, need to finish my bodywork first) My odometer is reading off the transfer case FYI so only the tires affect it, which I account for as verified per above.

I have alluded that my vehicle is modified, I have a full build thread on here, but to help support my outrageous claim of 14% better than epa estimated fuel economy, the cliff notes for back when those fuel economy figures were set were are a 2010 6.5L Diesel GEP Optimizer running Naturally Aspirated, NV4500 with custom overdrive gears, mechanical injection system swap which included me completely rewiring the vehicle from scratch to eliminate the computer, weight reduction, Michelin Defender LTX 235/85R16 tires, electric fans, DOT legal LED headlights, Duramax alternator swap, roof rack removal, flush bumper swap, WT grill swap, rare large bore OEM cast iron exhaust log manifold, custom air intake, conveyor belt air dam, and many other small tweaks.

I also don’t know where you are getting 5-7 from at 70MPH, even my 2001 Chevrolet 2500HD tow pig with the 8.1L and Allison gets better than that... It get about 12MPG average. Or perhaps I am lying about the 12MPG…

a 1995 is a square brick stock
https://www.fueleconomy.gov/feg/Find...n=sbs&id=12447

it's only rated at 12 combined with the 2008 rating
Original MPG

13 combined


that is babying the throttle were going by fuelly which is realistic driving conditions out in the wild. minus the "junk information"



under normal driving conditions I easily get as little as 9MPG with this 6.0L engine.[in 4 speed mode] just by driving how "everyone else drives" CVT,V4 and Autostop Disabled [Transmission gear ratio (4th=0.73] 3.08 RPO:G80 Locking Differential..

the speed limits in my area are upto 60mph 40-45 is the most common.. so you can bet if i hit every single red light its going to guzzle gas


there is no choice but to move to smoother air based vehicles.... obviously..... where did you get the conveyor belt ? i'm having trouble finding one reasonably priced .. plenty of low hanging fruit to aero mod on this hybrid


Last edited by Tahoe_Hybrid; 11-04-2020 at 01:56 AM..
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