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Old 05-06-2006, 08:53 AM   #29
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Kent, I'm surprised by the fact you mentioned regarding turbo kick in! Did you mention that to your mechanic? If you're turning 3000 rpms and the turbo isn't active something is amiss... IMHO!
I just did a quick (70-73) mph run to Hilton Head yesterday morning. Engine turned 3000-3300 rpms. Adjusted fuel economy for the tank included some city driving the day before but I got 8.9 mpg. The 454 turning these numbers at that speed is o.k. for me when I've got to get there.
As you know I'm always looking for better, but sometimes staying in my own bed rather than another night on the road is worth the early morning high speeds.
I generally keep it at 60-65 on the interstates for economy and safety but it's nice to be able to keep up out there. I agree with others that 55 can be dangerous to your health as you're likely to find someone attached to your bumper more often than not.
Check that turbo out and then let us all know what your rear end ratio is .... sounds like a very low rear end ratio to me. Great if you're pulling but that's not what you do.
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Old 05-06-2006, 09:11 AM   #30
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Hi Glen: I was riding with my Brother in a new White Freightliner when the turbo kicked in. I almost jumped out the window. These newer turbos do kick in and out. Mine, on my older diesel doesn't. CK had stated earlier that at 3000 rpm's he gets 55 mph. That's way to slow.
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Old 05-06-2006, 02:20 PM   #31
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U.S. Gear overdrive

We have a 1981 Excella that was equipped with a non-turbo 6BDI engine. The previous owner had installed a U.S. Gear underdrive to compensate for the non-turbo's lack of power. The engine lost its coolant on a steep grade and a piston burned. Rather than pay for an in-frame rebuild and end up with the same engine I decided to buy a new "crate" 6BGI-T turbo diesel engine.

The new engine is more powerful, smokes less and is quieter than the original. My problem is the same as yours; 55 to 60 mph at 2,900 rpm. 3000 is top limited and way above the peak hp and torque points of approximately 2,200 rpm. I plan to have the gearset changed to an overdrive, which will bring the peaks in closer to 60 mph. I like the U.S. Gear gearbox as it is built with beefier components than the Gearvendors unit.

We stay in Southern California during the winter and spring and in Ohio during the summer and fall. We have made two round trips with the new engine and like the improved performance and lower sound level but would be happier with it all happening at a lower rpm.
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Old 05-07-2006, 06:15 PM   #32
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Quote:
Originally Posted by dienst1

The new engine is more powerful, smokes less and is quieter than the original. My problem is the same as yours; 55 to 60 mph at 2,900 rpm. 3000 is top limited and way above the peak hp and torque points of approximately 2,200 rpm. I plan to have the gearset changed to an overdrive, which will bring the peaks in closer to 60 mph. I like the U.S. Gear gearbox as it is built with beefier components than the Gearvendors unit.

We stay in Southern California during the winter and spring and in Ohio during the summer and fall. We have made two round trips with the new engine and like the improved performance and lower sound level but would be happier with it all happening at a lower rpm.
We just returned from a short 200 mile all interstate trip and I really like what you are saying. Can you give me more info on exactly what you will be doing? I think you are the only one here who really understands what this engine is doing but is capable of doing.
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Old 05-07-2006, 08:39 PM   #33
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Kent, I'm still curious about the lack of turbo response. If the engine has peak hp/torque at 2200rpm when does the turbo kick in? If you get all the umph at 2200 you should be out of turbo at 3000.... Your turbo should be set to perform at peak output with the engine, or why else would you have one?
I'm looking for someone with some turbo knowledge to kick in here. My last experience with turbos was my 318 Detroit Diesel in a Ford Louisville tractor, so long ago... Seemed like the turbo was always on and the 13 spd od just cruised the loads up and down hills.
Then their was the Toyota turbo that I just couldn't fit into .... much as I tried.
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Old 05-07-2006, 09:19 PM   #34
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Engine RPM's

[quote=ralley]CH Kent: I'm just curious. At what RPM would your old engine give you 55mph?

Ck Kent: Excuse me if I re-state the obvious, but I'm puzzled at your problem--either your replacement engine has very different characteristics from the previous (hence, my question above) or your transmission may have a problem.

All diesels are governed in some way--otherwise they would self destruct by running full out, continuously. If 3000 RPM +or - is really your top governed speed, giving you 60 MPH, then your engine and trans are likely mismatched. The diffrence in RPM at any given speed between your new engine and old engine is what you need to decrease through modification. Whatever you do should bring the new engine RPM down to near the proper specs in the power curve for the new engine at, say, 50-60 MPH. The first step in the process of determining what to do is to compare the characteristics of both engines, and see if/where they are different, assuming that your trans is working properly. QED

Best,

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Old 05-16-2006, 07:27 AM   #35
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[quote=ralley][quote=ralley]CH Kent: I'm just curious. At what RPM would your old engine give you 55mph?

I only had the coach for several months before the engine was replaced. I do not remember what the RPM was before or even what the top speed was before the engine was replaced.
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Old 05-16-2006, 10:03 AM   #36
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I'm no expert in this area, but is seems that if the engine redline gives 55 mph, then a lower gear ratio would give more tire RPM, and thus a higher speed. How you get there is a judgement call, as has been pointed out. But, one other cause could be some sort of engine speed limiting device, such as a governer. Maybe there is a "computer" setting that limits the RPM, since this is a new engine.
But for sure, higher speed will increase the air resistance or drag, which increases as the square of the velocity. This increases the horsepower required to move the vehicle at this higher speed, and will certainly increase the amount of fuel needed to move it.

All this is speculation, and if you do decide to modify the drive train, I'm sure we all will be interested in its effect.
regards
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Old 05-20-2006, 09:04 AM   #37
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Kent, it's obvious that 55 mph/3000 rpm is rather slow and I'm certain a bit noisy.
Your engine is designed to deliver it's max torque at much lower rpm. The turbo should kick in, and out, at certain points in the rpm range before max rpms are reached.
If the turbo isn't kicking in why would it be there?
I'd be asking the folks who installed it for you what they think.
So far it sounds like you're getting great economy but this could be better at lower rpms and as pointed out with a trade off of wind resistance at higher speeds.
I'm betting that your rear end ratio is 4:56 and that a 4:10 or even a 3:73 would be much better for the coach considering all the power available from your engine.
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Old 10-04-2006, 07:09 PM   #38
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Hello.people if the motor is red lined at 3000 rpm and the max speed is 55 to 60 mph the answer is with the turbo or with out the turbo YOU are geared TOO LOW !! realy simple change the gearing eather ring & pinion or over drive ,under drive..
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Old 10-04-2006, 11:22 PM   #39
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Gears turbos and gears

Hi, Chaplain Kent. This is an indirect answer to your concerns. There are two things to consider before you part with your money. Do you need it? or Do you want it? Also, no matter how fast or slow you go, there will always be a Yo-Yo out there. Don't let the Yo Yo's spend your money for you!

Bob
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Old 10-04-2006, 11:32 PM   #40
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Quote:
Originally Posted by 2airishuman
hi guy 99 and others



as i recall best mpg is at or near peak torque.....all other things being equal.



cheers
2air
Hi, 2air. As I recall, best mileage is at highest vacuum reading. Oh, I forgot, Diesels have no vacuum!
Sorry 2air. I couldn't resist temptation.

Bob
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Old 10-05-2006, 12:48 PM   #41
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Chaplain Kent

Why don't you take Chummy back to the shop that did your old diesel and ask them to change your transmission filter?

Steve
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Old 10-05-2006, 03:41 PM   #42
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ChaplanKent, I remember when you had your engine replaced and have since bought my first diesel. I am by no means an expert on diesels, especially Airstream diesels, but what you described doesn't sound like it is all working right. No matter which side of the 55 MPH fence one falls on, from what I have read the Airstream Moho's were never speed demons and your expectations may fall at the limits of your motorhome's range. I don't know if it is a matter of brake size to weight ratio or what, but from what I remember about 60-65 is the max most people get with theirs regardless of length. However, my limited experience with my diesel and the reprogramming recall that Ford did earlier this year, your mileage is great, but you should be able to get more than 55 MPH out of your coach. I would expect more than that out of one of the longest that Airstream made; I believe they were 37' and on a totally different chasis and drive train that was essentially a city bus configuration that wasn't designed for highway speeds. Anyway, your turbo should indeed be kicking in. Mine will kick in at all speeds if I push the accelerator pedal too quickly. My truck will also reach speeds way faster than I want it too if I get too busy talking and not paying attention to the speedometer (recently pulling my 30' Safari I looked down and was doing 80, I immediately set the cruise at a lower speed).

With a newer engine, you probably have a computerized control system. It may be programmed for use in another vehicle, (I don't know what semi, tractor?) and need to be reprogrammed for its current use. I would go back to an Izuzu trained service center and have them do a diagnostic on the programming and reprogram it for use in a 15,000# motorhome and see if it makes a difference. It may just be programmed for a different transmission or different rear end and reprogramming may be all that is needed. Then I would look at other, more costly, options. You may want to contact the engineers at Izuzu for advise on what those options might be.
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