3g hemi gas mileage

-
I talked with Dave Weber at modernmuscle.biz, and he said I've got things hooked up right, but the rear gears are whats killing my mileage. So I called a buddy of mine and he still has my 489 center with 3.23's. I'm gonna swap out the 742 with 3.91's and see what that gets me.

And yes, the speedo is right on, checked it against the wifes Iphone gps app.
 
That is just bullshit. Driving around town those 3.91's HELP your mpg. Didnt you say you were at 2,000 at 60 mph?

Justin (1wildandcrazyguy) got 17 mpg in his 340 valiant. Thats a 400 hp carb'd motor with a standard 833 and 3.73's. No overdrive. I calculated the mpg. Spinning over 3,000 rpm on the highway.

But go ahead and change the gears out and report back.
 
I keep getting conflicting advise on the gears, go 3.23, stay with 3.91, step down to 3.55, so on and so on. My head is gonna explode with all the advise.

I like the way it scoots now, and I'm sure I would be dissapointed with anything less. Gotta think about this before I waste time and money switching stuff around.
 
5.7 hemi said:
I keep getting conflicting advise on the gears, go 3.23, stay with 3.91, step down to 3.55, so on and so on. My head is gonna explode with all the advise.

I like the way it scoots now, and I'm sure I would be dissapointed with anything less. Gotta think about this before I waste time and money switching stuff around.
Click to expand...

IMO gearing is not your problem, if you do the math your cruise RPM in top gear will only change by a few hundred RPM if you swap to 3.23's which makes almost no difference in fuel consumption by itself. If you didn't have overdrive or were running shorter gears like 4.56's I would say 'MAYBE' but in this case I really doubt that will fix it; you'll just lose acceleration. Like Blue87D100 said, people have gotten better gas mileage from carb'd old-school engines without overdrive and similar rear gears.

I would first do like others have suggested and make absolutely sure the computer is doing the right thing. Get a wide-band O2 sensor and check the actual Air/Fuel ratio; even if the computer isn't throwing any codes it could still be running way rich. The fact that your O2 sensor was sooty when you pulled it should be enough evidence of that. Driving around with a pig-rich A/F ratio just washes oil from the cylinders wearing out your rings, and dilutes the oil making it less viscous and less able to lubricate highly stressed components. Not to mention it pollutes more, for no good reason...
 
MOPEkidD-3 said:
IMO gearing is not your problem, if you do the math your cruise RPM in top gear will only change by a few hundred RPM if you swap to 3.23's which makes almost no difference in fuel consumption by itself. If you didn't have overdrive or were running shorter gears like 4.56's I would say 'MAYBE' but in this case I really doubt that will fix it; you'll just lose acceleration. Like Blue87D100 said, people have gotten better gas mileage from carb'd old-school engines without overdrive and similar rear gears.

I would first do like others have suggested and make absolutely sure the computer is doing the right thing. Get a wide-band O2 sensor and check the actual Air/Fuel ratio; even if the computer isn't throwing any codes it could still be running way rich. The fact that your O2 sensor was sooty when you pulled it should be enough evidence of that. Driving around with a pig-rich A/F ratio just washes oil from the cylinders wearing out your rings, and dilutes the oil making it less viscous and less able to lubricate highly stressed components. Not to mention it pollutes more, for no good reason...
Click to expand...

Listen to this. With all the time and money you have into this a wideband is going to be extremely valuable and not too expensive http://www.ebay.com/itm/ws/eBayISAP...704+&item=250745191704&lgeo=1&vectorid=229466 I have had many friends buy from this seller,this is the best price you will find,and its a great WB.
 
Now that is gonna be money well spent, thanks for the link blue87d100.
 
MOPEkidD-3 said:
IMO gearing is not your problem, if you do the math your cruise RPM in top gear will only change by a few hundred RPM if you swap to 3.23's which makes almost no difference in fuel consumption by itself. If you didn't have overdrive or were running shorter gears like 4.56's I would say 'MAYBE' but in this case I really doubt that will fix it; you'll just lose acceleration. Like Blue87D100 said, people have gotten better gas mileage from carb'd old-school engines without overdrive and similar rear gears.

I would first do like others have suggested and make absolutely sure the computer is doing the right thing. Get a wide-band O2 sensor and check the actual Air/Fuel ratio; even if the computer isn't throwing any codes it could still be running way rich. The fact that your O2 sensor was sooty when you pulled it should be enough evidence of that. Driving around with a pig-rich A/F ratio just washes oil from the cylinders wearing out your rings, and dilutes the oil making it less viscous and less able to lubricate highly stressed components. Not to mention it pollutes more, for no good reason...
Click to expand...

I agree 100%

Once you've sorted this out, you could always sell the sensor..
 
Yeah I can't see the gears affecting much besides the trans shifting strategy. You should upgrade to an 04 PCM. You have to move a couple wires around in the harness But I have that all laid out already and I can send you the diagram if Todd can find it still. But then you can run a diablo and tune that bad boy.
 
johnparts said:
Yeah I can't see the gears affecting much besides the trans shifting strategy. You should upgrade to an 04 PCM. You have to move a couple wires around in the harness But I have that all laid out already and I can send you the diagram if Todd can find it still. But then you can run a diablo and tune that bad boy.
Click to expand...

03 5.7 ram owner here, never posted, just come here now and then to look at all the cool projects. I'm running a diablosport tuner with custom tunes on my 03 ram, so the diablo does work on the 03. You can't tune the trans, raise the idle or rev limit on the 03 with the diablo though, but it will run custom tunes.
 
Belgiquebasterd said:
03 5.7 ram owner here, never posted, just come here now and then to look at all the cool projects. I'm running a diablosport tuner with custom tunes on my 03 ram, so the diablo does work on the 03. You can't tune the trans, raise the idle or rev limit on the 03 with the diablo though, but it will run custom tunes.
Click to expand...
Your 03 probably uses the NGC pcm then because there is no diablo for the 03 with the older pcm.
 
Looked at tuners today and saw diablosport released a replacement for the predator called "intune" looks like a great unit, will be a few months before I fire my motor though.
 
My demon has a 2004 ram computer that was tuned by B & G.With the custom tune he turned off the down stream o2 snesors . Im running 3.55 gear and a stock 833 4 speed with no over drive and a 27" tall tire. On a 300 mile trip doing 70-75 mph i averaged 19.0 mpg.
 
Gdemon said:
My demon has a 2004 ram computer that was tuned by B & G.With the custom tune he turned off the down stream o2 snesors . Im running 3.55 gear and a stock 833 4 speed with no over drive and a 27" tall tire. On a 300 mile trip doing 70-75 mph i averaged 19.0 mpg.
Click to expand...

Gdemon, what are you revving at 70-75? must be 2500+
 
I would put a cat on after the first O2 sensor but before the second one, without the cat the 2nd o2 sensor is sensing that the mixture is too rich because with no cat there theres no difference in oxygen between the two O2 sensors and its messing with things, pull your spark plugs and see what they have to say if you know how to read plugs they will tell you more then anything they should be almost as clean as a new plug being that your running factory efi
 
Well I pulled the o2 sensor, and it looked brand new. So I'm sure it's not running rich anymore. I also pulled out the 91 octane tune and went back to the stock tune. I'll check mileage in a few days to see whats going on.
 
if that doesn't work I would look at adding a converter and putting 3:55 gears in, since most newer chryslers run 3:55 from factory it may help fuel milage, I don't think I would go with much higher gears then that, idealy 1750-1800 RPM at 60 MPH would be great
 
johnparts said:
Hemi Equiped cars run 3.23 gears and get 20mpg
Click to expand...

exactly my point IMO 3:91 is too steep for the computer to handle it and give the best fuel economy possible. 3:23 or 3:55 would give great throttle response and good milage too
 
On another note you most likely won't want to hear but my 90 chevy p/u with its T56 six speed gets 22 mpg with a 129,000 mile engine. In sixth gear with 3:42 gears at 70mph, I'm running 1300rpm using 235-60-15's. I'm changing motors soon to an LT1 and will be sure to get 2 or 3 more mpg.
Your gear ratio can be altered slightly with a bigger tire and possibly bring it to 3:70's range if you do the math running your 3:91's

My Signet though light weight with its newer 360 gets 16 around town with 3:55's and a 727.. Knowing gear ratios and tire sizing is very important when searching for mileage.
 
Here's an example, number not exactly pertaining to you yet this will work in either direction using your rear end ratio..

Right now you have a 3.73 gear and a 28 inch tire.
You want to know what a 27 inch tire will act like compared to your 28 inch tire.

Current tire diameter = 28 inches
New tire diameter = 27 inches

28 divided by 27 = 1.037037

Current gear ratio = 3.73

1.037037 X 3.73 = 3.868148

Example: If you put on a 27" tire it will act like it has a 3.86 gear ratio compared to a vehicle that has a 28" tire and 3.73 gears.
 
66plyValiant said:
exactly my point IMO 3:91 is too steep for the computer to handle it and give the best fuel economy possible. 3:23 or 3:55 would give great throttle response and good milage too
Click to expand...

I drove a Ram with 3.91 gears, 545RFE, and it turned 2000 rpms doing 70 on the highway. Data logging on a tool would really tell you what your engine is doing. It's where I would start if your past efforts were in vain.
 
Did you swap out the 6.1 injectors for some 5.7's? That should help the most. The gears won't do anything. Well they will but very little, most ram trucks came with Eather a 3.55 or 3.92. My 6000 pound 4door 4WD ram gets 15.8 with my really aggressive driving. Down the highway cruise set at 80mph I can turn high 19's for fuel economy. So installing correct injectors and start there. Once that is done drive it for a week and calculate your fuel economy and report back.
 
Yeah I already went back to the 5.7 injectors, put the stock tune back on, new o2 sensor (upstream only), and I just reprogrammed the speedo. Something very interesting about the speedo....once I finished with the programming, the trip jumped from 23.8 to 53.8....wtf!!! So we'll see what happens in a few days.
 
Tincup said:
Gdemon, what are you revving at 70-75? must be 2500+
Click to expand...

Yes its about 2500 rpm. Im using a factory tach and a tach adaptor so im not sure how acurate the tach is. But the speedo is within 1 mph. Before i got the custom tune you could smell how rich the car was . Never checked the milage with the factory tune but performance was alot better after the tune.
 
You must log in or register to reply here.
-

Back
Top