Concensus on why the gen 2 24v's bombed or not get less mileage than a bombed 12v
05-25-2004, 09:41 AM
#17
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Originally posted by BigBlue
Something ain't right there. I can do a 100 mile trip in my truck (3.54 geared auto with 35" tires) and only burn an 1/8tank. Run around town all week, and drive a 100 miles back that week. Over 400 miles on a tank.
Something ain't right there. I can do a 100 mile trip in my truck (3.54 geared auto with 35" tires) and only burn an 1/8tank. Run around town all week, and drive a 100 miles back that week. Over 400 miles on a tank.
05-25-2004, 10:22 AM
#18
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Well Infidel, you would be upset to drive my truck.
@ 1/8 tank im a 420 miles, and I fill er up to the neck every time. It usually takes about 26.5 gallons +/- a gallon.
I havent straight piped it yet. So Im gonna try that and see what if it helps.
@ 1/8 tank im a 420 miles, and I fill er up to the neck every time. It usually takes about 26.5 gallons +/- a gallon.
I havent straight piped it yet. So Im gonna try that and see what if it helps.
05-25-2004, 05:28 PM
#19
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PK, straight piping does not affect mileage positively in my truck, if anything, it might add to a little more heavy pedal usage to irritate the occasional ricer that pulls up next to me with his thump thump cranked up, or the idjit that you have to follow for 10 miles in traffic with his cell phone attached to his ear and his mind out in right field....
Gary
Gary
05-25-2004, 06:35 PM
#20
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HID: interesting about the cam timing. There are other reasons to retard the cam timing, though, besides lowering the TQ and reducing emissions. Retarding the cam give more top-end HP. I suspect that the cam in the Dodge application is retarded to coincide with the higher RPM redline of the Dodge application. Aren't the commercial engines governed to lower rpm? i though they ran like 2600rpm max, while the Dodge runs to 3200. If so, this might explain the retarded cam timing.
Boldt's: good post. I don't quite have a grasp on why the 24V seems to get lower mpg, but I suspect that it has a lot to do with the attempt to extend the RPM range of efficiency. When the 24V was introduced, one of the advertising points was that it had a broader RPM range, with more upper RPM power, and a more usable torque range. Indeed, your post confirms that the 24V has a much wider usable (efficient) rpm range in stock form than a stock 24V does.
If Dodge wanted to, they could tune the CTD so that it gave REALLY good mpg, even in a heavy Ram. Yes, it's possible to hit 28mpg. But to do so would require an incredibly narrow efficiency range-- maybe 300rpm (say, from 1500-1800rpm). This narrow powerband makes for an almost useless towing engine and a horrible driving experience. You'd need an 18-speed to make it work well! Not too cost-effective in a pickup.
Consider this: What's the mpg of a class 8 rig making 2500lb-ft? I've heard of rigs like that getting 6mpg hwy. Not great, but consider that they make ~5 times more tq (stock) than our little 5.9 does. if you take their 6mpg and multiply by 5 to compare it to the little ISB5.9, you're looking at 30mpg...
BTW- Cams are generally advanced for more low end and retarded for more high-rpm power. A cam with a narrow lobe separation angle will have a narrower, peakier powerband that makes big torque. A broader lobe separation angle (LSA) means a broader powerband with less peak tq.
Justin
Boldt's: good post. I don't quite have a grasp on why the 24V seems to get lower mpg, but I suspect that it has a lot to do with the attempt to extend the RPM range of efficiency. When the 24V was introduced, one of the advertising points was that it had a broader RPM range, with more upper RPM power, and a more usable torque range. Indeed, your post confirms that the 24V has a much wider usable (efficient) rpm range in stock form than a stock 24V does.
If Dodge wanted to, they could tune the CTD so that it gave REALLY good mpg, even in a heavy Ram. Yes, it's possible to hit 28mpg. But to do so would require an incredibly narrow efficiency range-- maybe 300rpm (say, from 1500-1800rpm). This narrow powerband makes for an almost useless towing engine and a horrible driving experience. You'd need an 18-speed to make it work well! Not too cost-effective in a pickup.
Consider this: What's the mpg of a class 8 rig making 2500lb-ft? I've heard of rigs like that getting 6mpg hwy. Not great, but consider that they make ~5 times more tq (stock) than our little 5.9 does. if you take their 6mpg and multiply by 5 to compare it to the little ISB5.9, you're looking at 30mpg...
BTW- Cams are generally advanced for more low end and retarded for more high-rpm power. A cam with a narrow lobe separation angle will have a narrower, peakier powerband that makes big torque. A broader lobe separation angle (LSA) means a broader powerband with less peak tq.
Justin
05-25-2004, 11:21 PM
#21
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Originally posted by HOHN
HID: interesting about the cam timing. There are other reasons to retard the cam timing, though, besides lowering the TQ and reducing emissions. Retarding the cam give more top-end HP. I suspect that the cam in the Dodge application is retarded to coincide with the higher RPM redline of the Dodge application. Aren't the commercial engines governed to lower rpm? i though they ran like 2600rpm max, while the Dodge runs to 3200. If so, this might explain the retarded cam timing.
HID: interesting about the cam timing. There are other reasons to retard the cam timing, though, besides lowering the TQ and reducing emissions. Retarding the cam give more top-end HP. I suspect that the cam in the Dodge application is retarded to coincide with the higher RPM redline of the Dodge application. Aren't the commercial engines governed to lower rpm? i though they ran like 2600rpm max, while the Dodge runs to 3200. If so, this might explain the retarded cam timing.
The 13 speed Road Ranger was designed for the 300 rpm power band of Detroit Diesels. In the granny gears, lower five, the power band is not as important, 600 rpm. In the upper eight, the split is roughly about 300 rpm. Put over 1,000,000 miles on one transmission. Shifted a couple of times
I dream of a 913 installed in the ram, might do it one day. Could keep it in the power/economy band in all occasions and have double overdrive to boot, and never use the clutch to shift. With air shift splits while pulling a load, it just becomes automatic to the driver.
05-26-2004, 11:34 AM
#22
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[QUOTE]Originally posted by Haulin_in_Dixie
I dream of a 913 installed in the ram, might do it one day. Could keep it in the power/economy band in all occasions and have double overdrive to boot, and never use the clutch to shift. With air shift splits while pulling a load, it just becomes automatic to the driver.
On a Side note, when you do this, let me know. I'd love to have a REAL transmission to go along with my REAL engine.
Chris
Now to find a REAL truck to put it in.
I dream of a 913 installed in the ram, might do it one day. Could keep it in the power/economy band in all occasions and have double overdrive to boot, and never use the clutch to shift. With air shift splits while pulling a load, it just becomes automatic to the driver.
On a Side note, when you do this, let me know. I'd love to have a REAL transmission to go along with my REAL engine.
Chris
Now to find a REAL truck to put it in.
10-02-2006, 10:18 AM
#23
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thanks... this clarifies a few issues...
From stock Cummins engine fuel consumption figures (by Cummins) published in the TDR, the 12 valve is better from 1500 to 1700 rpm with a peak efficiency at 1600 rpm. The 24 valve fuel efficiency peaks at 2000 rpm and is better than the 12 valve at all rpm above 1750rpm. The peaks are 22.25 hp-hr/gal for the 12 valve at 1700 rpm and 21.9 hp-hr/gal for the 24 valve at 2000 rpm.
The fuel consumption lines cross at 1750 rpm. The unmodified 12 valve will have better mileage than the 24 valve at less than 1750 rpm, the 24 valve will have better mileage at greater than 1750 rpm. At over 2000 rpm the difference for stock timing gets much better for the 24 valve. (7.5% or lower fuel consumption for the 24 valve above 2200 rpm.)
The efficiency is probably largely affected by timing. The 12 valve has fixed timing and the 24 valve can advance timing. Larger injectors, bigger fueling plates, ar advanced timing in the 12 valve gets all the fuel into the cylinder faster and effectively increases the timing and increases fuel efficiency and mileage. Fueling and/or timing boxes does the same for the 24 valves.
The other side of this coin is that truckers observed that advanced timing might increase fuel mileage but also reduced peak torque for pulling grades.
Basically, with stock engines, the 12 valve gets better mileage if operated at 1800 rpm and lower, the 24 valve gets better mileage at over 1800 rpm.
The 12 valve does have the advantage(?) that it does not have the flat torque curve of the 24 valve. The 12 valve will have peak torque at about 1600 rpm where the 24 valve is just getting started. Unfortunately, this also results in much clutch trouble in both the automatic and manual transmissions with the 12 valve engines.
The fuel consumption lines cross at 1750 rpm. The unmodified 12 valve will have better mileage than the 24 valve at less than 1750 rpm, the 24 valve will have better mileage at greater than 1750 rpm. At over 2000 rpm the difference for stock timing gets much better for the 24 valve. (7.5% or lower fuel consumption for the 24 valve above 2200 rpm.)
The efficiency is probably largely affected by timing. The 12 valve has fixed timing and the 24 valve can advance timing. Larger injectors, bigger fueling plates, ar advanced timing in the 12 valve gets all the fuel into the cylinder faster and effectively increases the timing and increases fuel efficiency and mileage. Fueling and/or timing boxes does the same for the 24 valves.
The other side of this coin is that truckers observed that advanced timing might increase fuel mileage but also reduced peak torque for pulling grades.
Basically, with stock engines, the 12 valve gets better mileage if operated at 1800 rpm and lower, the 24 valve gets better mileage at over 1800 rpm.
The 12 valve does have the advantage(?) that it does not have the flat torque curve of the 24 valve. The 12 valve will have peak torque at about 1600 rpm where the 24 valve is just getting started. Unfortunately, this also results in much clutch trouble in both the automatic and manual transmissions with the 12 valve engines.
10-02-2006, 01:16 PM
#24
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I consistently get 20-21 mpg with a best of 22.6 with my current set-up. With Mach 3s,a drag comp and a quicker spooling charger I was only getting 18 and 19 mpg on the highway. I usually get my best mileage at 1900 rpm which is around 70 mph with 285s.
10-02-2006, 09:26 PM
#25
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I believe neither the 12v, 24v, and CR engines have any leg up on the next with mileage. Non really seem to out do the other two.
For every guy that gets 23mpg out of a 12v, will be matched with another guy getting 23 out of CR truck.
It goes the other way too, I've seen plenty of threads with 12v guys complaining of low mileage.
I get 15/23 with my 24v.
I think the biggest difference is each truck, much less than the motor that it has, as mileage varies so much between the same trucks, before you even talk about 12V vs 24V.
For every guy that gets 23mpg out of a 12v, will be matched with another guy getting 23 out of CR truck.
It goes the other way too, I've seen plenty of threads with 12v guys complaining of low mileage.
I get 15/23 with my 24v.
I think the biggest difference is each truck, much less than the motor that it has, as mileage varies so much between the same trucks, before you even talk about 12V vs 24V.
10-02-2006, 10:14 PM
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10-02-2006, 10:27 PM
#28
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Same here I might get just over 400 miles per tank and fill with 25-27 gallons mostly city driving with some 7000lb TT hwy towing but not much TT towing.
Best tank ever was 17.8 mpg in my stock 02 auto with 3:55 gears
10-02-2006, 10:58 PM
#29
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I believe neither the 12v, 24v, and CR engines have any leg up on the next with mileage. Non really seem to out do the other two.
For every guy that gets 23mpg out of a 12v, will be matched with another guy getting 23 out of CR truck.
It goes the other way too, I've seen plenty of threads with 12v guys complaining of low mileage.
I get 15/23 with my 24v.
I think the biggest difference is each truck, much less than the motor that it has, as mileage varies so much between the same trucks, before you even talk about 12V vs 24V.
For every guy that gets 23mpg out of a 12v, will be matched with another guy getting 23 out of CR truck.
It goes the other way too, I've seen plenty of threads with 12v guys complaining of low mileage.
I get 15/23 with my 24v.
I think the biggest difference is each truck, much less than the motor that it has, as mileage varies so much between the same trucks, before you even talk about 12V vs 24V.
10-03-2006, 03:49 AM
#30
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With the new injector pump, I got 20.3 mpg ( hand calculated ) last tank with mixed city/highway driving . I don't usually go faster than 70, allergic to speeding tickets ! The overhead is waaaaaay off now though, used to be pretty close .