improving mileage
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
I have the same questions. I have a 1990 IDI that does not have a turbo. It has a 5 speed manual transmission, and it has 4.10 gears. I receive 16-17 just putting around and 19 on longer trips as long as I don't push it much over 65 mph. This pickup is a 4 door long box, and it is a 4x4. I also have a 1989 IDI, but it has an ATS turbo installed on it. It has a 3 speed automatic. It is a 2 wheel drive dually 4 door long box. It also has 4.10 gears. My problem is the dually. With it, I get around 14 mpg no matter whether I'm towing anything or not. The biggest problem is the transmission. It raps the engine up to around 2300-2400 at only 55 mph. I'm ok with the fuel mileage I get out of the 1990, but I'm not ok with the fuel mileage on the 1989.
Here's what I'm thinking of doing, and I'm definitely open to suggestions if you have any. The 89' with the turbo will pull tree stumps. I tow around a 44 foot dually flatbed, and this pickup handles it with ease. I'm thinking about putting 235 85R 16's on it replacing the stock 215 85% 16's. This will help a bit, but really not that much as there's not a huge difference in the height. The biggest reason for doing this is because the 235's are so much more common around here anyway. Then, I want to replace the 4.10 gears with 3.55's. I don't need to travel 70+ mph, but I'd at least like to travel the speed limit which is 60-65 around here on the highways. Here's my question for all: how much power am I going to sacrifice going to the 3.55's? The way this pickup is set up now, it will hold its own with the new diesels up to 55 mph before I get run over because I'm not comfortable rapping my diesel over 2300-2400 rpm. Am I going to lose so much torque that I'll regret going to the 3.55's when towing? I guess I should give a little background. This pickup rarely ever is just driven. It was bought specifically for towing, and that is about all I use it for. I just want to be able to bring the rpm's down around that 2000 range and hopefully be able to drive the speed limit. Thanks for any input.
Here's what I'm thinking of doing, and I'm definitely open to suggestions if you have any. The 89' with the turbo will pull tree stumps. I tow around a 44 foot dually flatbed, and this pickup handles it with ease. I'm thinking about putting 235 85R 16's on it replacing the stock 215 85% 16's. This will help a bit, but really not that much as there's not a huge difference in the height. The biggest reason for doing this is because the 235's are so much more common around here anyway. Then, I want to replace the 4.10 gears with 3.55's. I don't need to travel 70+ mph, but I'd at least like to travel the speed limit which is 60-65 around here on the highways. Here's my question for all: how much power am I going to sacrifice going to the 3.55's? The way this pickup is set up now, it will hold its own with the new diesels up to 55 mph before I get run over because I'm not comfortable rapping my diesel over 2300-2400 rpm. Am I going to lose so much torque that I'll regret going to the 3.55's when towing? I guess I should give a little background. This pickup rarely ever is just driven. It was bought specifically for towing, and that is about all I use it for. I just want to be able to bring the rpm's down around that 2000 range and hopefully be able to drive the speed limit. Thanks for any input.
Your dually seems to be doing very well for what it is considering the low gearing. Word of caution about going to 235-85 tires on a dually, is they may rub together when you are loaded. This makes heat, and that will cause a blow out under moderate or extreme conditions. Not worth the risk, IMO.
Swapping from 4.10s will affect your low speed pushing or pulling capacity on steep inclines. I can still drag a boat up the launch in high range easily, but if I had to go down forward, and then back the same load up in reverse, it may not do it. Those situations are rare, but what you need to understand is these automatics are VERY poorly geared in reverse, and the ratio is just too tall for hard core towing.
You will not be going all the way to 3.08s and might not get the taller tires because of the DRW setup, but its best to avoid heavy loading in reverse with a big trailer.
Based on what you said so far, I would suggest leaving the tire size as is. But go with either 3.73 or 3.55 gears and keep the 4.10s as a fall back if you aren't happy with the results. Once you are rolling and can get the RPMs up, your acceleration is no different and top speed will be higher. Just don't expect it to hold on to that higher cruising speed as well as at 55 MPH. This is not because of the change in gearing, but because the faster you go, the more power is lost to wind drag.
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
Overall it would be better to get a gear splitter, but can be pricy if you can't find a good used one. Certainly a good option if you have the cash for it.
Senior User
Joined: Nov 2008
Posts: 319
Likes: 0
From: Western Australia
What revs will these engines sit on happily as a maximum. Mine is 7.3 factory turbo that is basiclly stock as far as i know. At 100km/h in o/d i am doing about 2000rpm. Not sure of tyre size or diff ratio. If I put it out of o/d to tow I can only do 80km/h. Can these engines handle prolonged running at 25-2800rpm for instance or is it ok to tow in o/d on flat country. I have found the auto starts to get warm on long trips towing in o/d.
Junior User
Joined: Aug 2009
Posts: 60
Likes: 0
This under over drive you speak, can you describe it? I just bought this dually in May, and I have only put a couple thousand miles on it. On the automatic shift lever, there is a black control with a button you can push up or down. I've messed with it, but it doesn't seem to do anthing. Maybe this is a control for an under over drive? If it is, it might not be working? I know this pickup was used exclusively to pull a camper before I bought it. It might already have something on it that I was unaware about.
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Junior User
Joined: Aug 2009
Posts: 60
Likes: 0
I have a C6. The button is definitely an add on as it just clips onto the automatic shift lever. You can easily see it's not something that is stock. However, I have played with it going down the road and it doesn't seem to do anything. What I'm asking is where would the wire from the add on button go? I've never traced the wire, but if it is an under over drive where would it go?
Lead Driver
Joined: Nov 2003
Posts: 6,900
Likes: 3
From: Campbell River, B.C.
What revs will these engines sit on happily as a maximum. Mine is 7.3 factory turbo that is basiclly stock as far as i know. At 100km/h in o/d i am doing about 2000rpm. Not sure of tyre size or diff ratio. If I put it out of o/d to tow I can only do 80km/h. Can these engines handle prolonged running at 25-2800rpm for instance or is it ok to tow in o/d on flat country. I have found the auto starts to get warm on long trips towing in o/d.
A large auxiliary cooler might help though. I know not all of australia is hot and dry, but looking at your photos, it seems that you are in a warmer region. When it comes to these transmissions, you generally want to get the biggest cooler you can find.
2500-2800 will not hurt anything in these trucks. They are actually a commercial engine that is rated for constant horse power @ governed speed (think yours would be 3000-3300 RPM). They were tested like that in the early 80s before they went into full production and the certainly can take that. Only catch is you might burn some more fuel. 2000 is a pretty good towing RPM though because of the torque range.
Something you could also try, is going to a slightly shorter tire diameter to bring the RPMs up a little.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
West Aussie,
IF you have 235/85-16 tires, with the E4OD 2000 RPM at 103 kph says you have a 4.10 gear.
Running at 2500 or 2800 or 3100 RPM all day long will only hurt your wallet.
I don't remember the numbers right now, but the IDI ran wide open at full load for an incredible amount of hours during development.
jedstamm,
Welcome to FTE and the IDI diesel forum.
What elevation and terrain are you in?
How much weight do you normally gross when towing?
IF you have 235/85-16 tires, with the E4OD 2000 RPM at 103 kph says you have a 4.10 gear.
Running at 2500 or 2800 or 3100 RPM all day long will only hurt your wallet.
I don't remember the numbers right now, but the IDI ran wide open at full load for an incredible amount of hours during development.
jedstamm,
Welcome to FTE and the IDI diesel forum.
What elevation and terrain are you in?
How much weight do you normally gross when towing?
Junior User
Joined: Aug 2009
Posts: 60
Likes: 0
I'm from SW Nebraska, so it's fairly flat where I live. Of course, we're not far from the mountains of Colorado. I'll never ever take a naturally aspirated diesel into the mountains again. I normally tow either a 20' goosneck livestock trailer which will be about 14-15 thousand pounds loaded, or I tow my 44' flatbed with a couple of smaller tractors or cars on it which will weigh in around 16-18 thousand pounds loaded up. My dually has no problem at all handling these loads. I just can't go very fast. I've been around diesels my entire life. I have semi tractors, diesel irrigation power units, diesel farm tractors, and diesel pickups. From my years of experience, it is never a good idea to run a diesel much over 2000 rpm's. We run diesel irrigation power units upwards of 20-30 thousand hours before overhauls. If you try to run them much over 2K, you'll never get over 10 thousand hours on them. So with this being said, I can only run between 50 and 55 mph trying to stay in the proper rpm range with the 3 speed auto and 4.10 gears. My 90' has 4.10 gears, but it is a 5 speed manual. It will run 65 at 2K. However, it's not a dually and it doesn't have a turbo either. I'll pull with it, but not nearly as much weight.