.82 or .64 OD
Team Owner
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From: altered state
St. Jude Donor '05
The real truth is a motor gets the best MPG in its efficiency rpm range.
Been driving my DD (late Silverado) in 3 due to trans issues 3.73 gear 4l60e last few weeks
Up to 60 mph or so meaning 2500+ on the fwy the mileage is identical to using the OD.
So even with a bone stock motor (least in this case) unless youre 65mph or better its a waste and lugging the motor in the meantime. Add cams etc you get the picture
Last edited by cv67; Mar 27, 2014 at 12:05 PM.
Racer
Joined: Feb 2014
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Good post
Been driving my DD (late Silverado) in 3 due to trans issues 3.73 gear 4l60e last few weeks
Up to 60 mph or so meaning 2500+ on the fwy the mileage is identical to using the OD.
So even with a bone stock motor (least in this case) unless youre 65mph or better its a waste and lugging the motor in the meantime. Add cams etc you get the picture
Been driving my DD (late Silverado) in 3 due to trans issues 3.73 gear 4l60e last few weeks
Up to 60 mph or so meaning 2500+ on the fwy the mileage is identical to using the OD.
So even with a bone stock motor (least in this case) unless youre 65mph or better its a waste and lugging the motor in the meantime. Add cams etc you get the picture
Yep, my 2013 Chevy truck gets better fuel economy at 68 mph over 60 or 65, due to the rear end and so on.
D
Race Director
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From: South Western Ontario
Ya, the Silverado truck starts at 2000lbs more than a C3 and go up from there. They're also a rather square brick compared to a C3. Sounds like the perfect vehicle to compare...
My C5 gets great mileage running in the 40-50mph range still using 6th gear.
My C5 gets great mileage running in the 40-50mph range still using 6th gear.
Last edited by lionelhutz; Mar 27, 2014 at 01:21 PM.
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From: San Jose CA
It does, of course, have more frontal area.
Weight is a big penalty, as well as tire size, brake size, transfer case (on 4WD vehicles), etc.
Racer
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Im not comparing directly, but it has 3.42 gears and is still happier at a higher speed. Pushing anything through the wind still has a sweet spot
You compare your C5 to a C3 ........ good one
DW
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From: South Western Ontario
Did I say anywhere I'm comparing the C5 to a C3.
I'm just saying, a truck may have a better mileage at a higher rpm and/or a higher speed but that doesn't mean every vehicle does.
Safety Car
Joined: Nov 2008
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From: Seattle Washington
Obviously the General is putting these overdrive transmissions in new cars for a reason, namely emissions and mileage. One would think that better emissions equals better mileage but lets not start another subject.
I also have a 02 HD Silverado, and a C4 LT4 ZF overdrive. Interesting the LS modern truck engine at 300 HP gets maybe 14 mpg on the Highway. The Old school 330 HP Vette gets 26 + on the Highway. Ok so where am I going with this. Well one thing that is the same between the two, they both use overdrive transmissions, and they use them for the same reasons.
I also have a 02 HD Silverado, and a C4 LT4 ZF overdrive. Interesting the LS modern truck engine at 300 HP gets maybe 14 mpg on the Highway. The Old school 330 HP Vette gets 26 + on the Highway. Ok so where am I going with this. Well one thing that is the same between the two, they both use overdrive transmissions, and they use them for the same reasons.
Safety Car
Joined: Jan 2009
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From: New York
First number I found for cD for a Silverado is .43(2007 MY, the new ones are more slippery, around .40), which puts it ahead of every production C3 (the 80's got .44).
It does, of course, have more frontal area.
Weight is a big penalty, as well as tire size, brake size, transfer case (on 4WD vehicles), etc.
It does, of course, have more frontal area.
Weight is a big penalty, as well as tire size, brake size, transfer case (on 4WD vehicles), etc.
A motor with a carb is very limited in its ability to meter fuel in a way that is efficient enough to run tall rear gears with a tall O/D gear.
So c-5 / silverado ... It is like comparing a Modern jet fighter to a ww2 fighter
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Racer
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A fuel injected computer controlled motor can run any ratio it wants.
A motor with a carb is very limited in its ability to meter fuel in a way that is efficient enough to run tall rear gears with a tall O/D gear.
So c-5 / silverado ... It is like comparing a Modern jet fighter to a ww2 fighter
A motor with a carb is very limited in its ability to meter fuel in a way that is efficient enough to run tall rear gears with a tall O/D gear.
So c-5 / silverado ... It is like comparing a Modern jet fighter to a ww2 fighter
I agree about EFI, but many engines with a carb properly set up can also run at low rpms and fuel pretty darn good as well. I just dont like to run mine that low is all.
Ive proven this for years designing jetting kits for street bikes, though it takes allot of testing, and in some cases I can out perform fuel injection. I do fuel injection as well and after a year of R&D am very close to coming out with a new motorbike tuner , EFI SUPERTUNE PRO
As far as the truck thing, I was just mentioning in my case mine does better on fuel mileage because of the tall gear upping the MPH a little
I think the main thing is what every works best for you combination is all that matters
Reminds me of motor oil
Cheers DW
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Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
I have read these posts about 10 times and there appears to be an egual amount of votes for the .64 as the .82 and everybodies reason was well thought out and valid.
With respect to tire size I will be running P255 / 60R /15 which is a 26" tall tire. The engine is the GM 454 HO Create engine and I will be running Doug's sidepipes with the middle of the road inserts
The Hurst web site has a RPM Calculator which figures that the RPM drop of the .82 will be 500 rpm as opposed to the .64 which will be 1100RPM.
I do appriciate everybodies input. I commited to the .82 I will update the forum on the next important issues- delivery, product and installation
Happy Motoring
With respect to tire size I will be running P255 / 60R /15 which is a 26" tall tire. The engine is the GM 454 HO Create engine and I will be running Doug's sidepipes with the middle of the road inserts
The Hurst web site has a RPM Calculator which figures that the RPM drop of the .82 will be 500 rpm as opposed to the .64 which will be 1100RPM.
I do appriciate everybodies input. I commited to the .82 I will update the forum on the next important issues- delivery, product and installation
Happy Motoring
Racer
Joined: May 2008
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This thread left me scratching my head.
I debated this (with myself) quite heavily last year since my car is a nightmare on the highway. Driving on the highway is a royal headache. At 60-65mph, .82 would be just right to quell the din. But at 80mph+ down the highway, that just isn't enough of a drop. It's a bad gear for a highway cruiser unless you drive slow. What I really wanted was a T56, but with my cam, the typical .50 6th gear would have been stumble bump city. I cruise around town in 4th to keep it quiet, and just deal with the stumbles.
Now, with a dinky cam 454 crate motor, I can't imagine why a .82 would be appropriate unless the gear has purposes other than highway use. If not, the general consensus seems to be it's wrong. Perhaps the best test is to cruise around in 4th at the RPMs you would be turning with each gear. Then pick the one you prefer. With as much torque and power as that motor has, the higher speeds should not be an issue in terms of available speed/power.
I debated this (with myself) quite heavily last year since my car is a nightmare on the highway. Driving on the highway is a royal headache. At 60-65mph, .82 would be just right to quell the din. But at 80mph+ down the highway, that just isn't enough of a drop. It's a bad gear for a highway cruiser unless you drive slow. What I really wanted was a T56, but with my cam, the typical .50 6th gear would have been stumble bump city. I cruise around town in 4th to keep it quiet, and just deal with the stumbles.
Now, with a dinky cam 454 crate motor, I can't imagine why a .82 would be appropriate unless the gear has purposes other than highway use. If not, the general consensus seems to be it's wrong. Perhaps the best test is to cruise around in 4th at the RPMs you would be turning with each gear. Then pick the one you prefer. With as much torque and power as that motor has, the higher speeds should not be an issue in terms of available speed/power.
Last edited by ryanmh; Mar 28, 2014 at 11:55 AM.
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From: San Jose CA
Yes, although the programs for most computers(pretty much every LS based factory computer I know of) are designed to run stoich in closed loop and in open loop shoot for whatever the PE tables call for. You can program them to achieve a different commanded AFR , but the self-correction factor will go away and it will start to become more and more like running a carb (MAP/SD based solutions use very similar principles to carburetors).
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I have the .64 OD behind my 427ci small block and I love it. I get around 24mpg on the highway at 80mph.
Whenever I hit the highway I row through the gears until I hit 70mph and drop it into 5th and I am turning about 1800RPM, it's a really great feeling and with my engine I can still stomp on it in 5th and get going real fast in no time at all.
The way I see it is they made this .64od for guys who want to drive to the track with 4:10 rear ends. They don't have to trailer it.
The .82od was made for road racing for a good top end mph down straightaways.
Whenever I hit the highway I row through the gears until I hit 70mph and drop it into 5th and I am turning about 1800RPM, it's a really great feeling and with my engine I can still stomp on it in 5th and get going real fast in no time at all.
The way I see it is they made this .64od for guys who want to drive to the track with 4:10 rear ends. They don't have to trailer it.
The .82od was made for road racing for a good top end mph down straightaways.
Le Mans Master
Joined: Oct 2007
Posts: 7,456
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From: RI, Now Franklin/Nashville TN
I have the .64 OD behind my 427ci small block and I love it. I get around 24mpg on the highway at 80mph.
Whenever I hit the highway I row through the gears until I hit 70mph and drop it into 5th and I am turning about 1800RPM, it's a really great feeling and with my engine I can still stomp on it in 5th and get going real fast in no time at all.
The way I see it is they made this .64od for guys who want to drive to the track with 4:10 rear ends. They don't have to trailer it.
The .82od was made for road racing for a good top end mph down straightaways.
Whenever I hit the highway I row through the gears until I hit 70mph and drop it into 5th and I am turning about 1800RPM, it's a really great feeling and with my engine I can still stomp on it in 5th and get going real fast in no time at all.
The way I see it is they made this .64od for guys who want to drive to the track with 4:10 rear ends. They don't have to trailer it.
The .82od was made for road racing for a good top end mph down straightaways.
Does it "load" up on the highway at 1,800 RPM ????
Does it buck and surge on the highway in overdrive because its a "carb" car and not FI?????
What total nonsense!!!!
Its fine for people to have different preferences about what they want from an OD but misinformation and comments that are simply not true is another story………….
Last edited by jb78L-82; Mar 28, 2014 at 07:18 PM.
Safety Car
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From: New York
Ya he is going 80 why ?? Well so he can keep his block rpm up , most areas 65 is the limit so why run 1 to 1 at 50 or 65 just so you can run .62 at 80 ? Makes no sense for a street car ...
People can do what ever the chose to do , but be warned to tall a gear ratio with low rpm's causes a sluggish experience.
People can do what ever the chose to do , but be warned to tall a gear ratio with low rpm's causes a sluggish experience.
Le Mans Master
Joined: Oct 2007
Posts: 7,456
Likes: 977
From: RI, Now Franklin/Nashville TN
Ya he is going 80 why ?? Well so he can keep his block rpm up , most areas 65 is the limit so why run 1 to 1 at 50 or 65 just so you can run .62 at 80 ? Makes no sense for a street car ...
People can do what ever the chose to do , but be warned to tall a gear ratio with low rpm's causes a sluggish experience.
People can do what ever the chose to do , but be warned to tall a gear ratio with low rpm's causes a sluggish experience.
Who the heck drives 65 MPH???? Sluggish with a 454 HO???? with a .64 OD-you DON'T accelerate with an OD, especially with a manual trans-It is for cruising along at 70 -80 MPH. Last call on this issue.
Last edited by jb78L-82; Mar 28, 2014 at 07:32 PM.
Safety Car
Joined: Jan 2009
Posts: 4,000
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From: New York
Many people cruse at 65 .. You think 80 is the norm .. Maybe in your state it is .. But an O/D only good until you hit 80 is useless ..
With correct gearing for the street a O/D should be doable at 60 .. Your instance 65 is to slow or even 60 is laughable because driving is not exclusive to the highway .
With 3.92 rears my O/D ( automatic) Is perfect from 45 and up.
With correct gearing for the street a O/D should be doable at 60 .. Your instance 65 is to slow or even 60 is laughable because driving is not exclusive to the highway .
With 3.92 rears my O/D ( automatic) Is perfect from 45 and up.
Le Mans Master
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From: Tuttle OK
Cruise-In VIII Veteran
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