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Old 06-18-2006, 12:55 PM   #15
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Gear Vendor +++++

Just my H.O., I still have a Gear Vendor in a T.V., it first was used with a 454 chevy with a turbo 400. 150k miles later, I put it behind a 5.9 cummins diesel with a 4L80-e trans {now I run 2 O.D.'s} all of this in the same TV! I now have over 300k on the cummins and it still runs strong. I have never had a problem with the G.V. only the pleasure of driving trouble free and splitting the gears makes it all worthwhile.
The GV is all that you have heard! Shifting with full power [pedal to the metal] is nice. [and no I don't work for GV, just a very satisfied customer]
Good luck with your project, I know that you will be pleasantly surprised .

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Old 06-18-2006, 01:42 PM   #16
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[quote=noiva]Guys,


Guy99, I haven't heard about peak efficiency being where the horsepower and torque curve meet, but I'm certainly not an expert on this either. Makes sense in theory, but in my case it's impossible to keep the rpms low enough to get them to cross while driving down the highway. "

Horsepower and torque curves always cross at 5252 rpm. It has to do with the way they are calculated. Dyno's measure torque, and calculate HP from that and the engine speed. Peak efficiency is supposed to occur at or near peak torque, whatever rpm that is.

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Old 06-18-2006, 03:43 PM   #17
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Gee, I had this in physics. I used to know why they crossed at 5252... hmm... rpm x torque/5252 = hp? Or do I have that backwards? And peak horsepower happens when the slope of the torque curve drops under (steepens more than) something. I remember the teacher saying that peak efficiency had to do with several factors, but never when the torque and horsepower curves crossed on car or tractor engines - none of them would (or SHOULD he'd empthasize, glaring at all of us) be run at that speed.

The Taurus HO with the Yamaha engine was still out there a few years in the future. I'm going to see if I can find a graph for that engine and see if it's true.

Lamar
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Old 06-18-2006, 04:17 PM   #18
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All I said was that I read it, not that it was true

I did some checking and you all are correct , but then you already knew that.

Does anyone have a source for the efficiency curve for these 454's?
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Old 06-18-2006, 05:05 PM   #19
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Quote:
Originally Posted by guy99
All I said was that I read it, not that it was true

I did some checking and you all are correct , but then you already knew that.

Does anyone have a source for the efficiency curve for these 454's?
Guy,

I don't have that info., but don't feel bad about saying you read something. That's how I learned most of what I know. Anyway, I'm doing all this because I am trying to solve a very REAL problem. Semis don't have multiple gears for nothing. When it comes to heavy loads, more gears is better, especially when you can narrow the gap between each gear like the G.V. set does. I may not have all the math down to precision, but I do know when this 37-foot, 18,000 lb. vehicle is spinning the engine too fast.

Chipster,

Thanks for the encouragement. I'm surprised how many Forum folks have sent me PMs with the same basic info.

Best to all,
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Old 06-18-2006, 07:25 PM   #20
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I spent some time on the Gearvendors site again today Tim and am just wondering where I can find an extra three grand to follow you with...
Having the performance figures for the 454 sure would be cool if anybody can find them.
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Old 06-19-2006, 08:07 AM   #21
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Quote:
Originally Posted by GlenCoombe
...Having the performance figures for the 454 sure would be cool if anybody can find them...
Below are two that I have archived…





The First (white background) is for a 454 HO engine that I think is fairly representative (but a bit on the high side) of the 454’s (7.4 liter) engines in most of the mid 80’s MoHos. Note that max torque (about 500 ft.lbs.) occurs at about 3350 rpm – max horsepower (420 HP) is at engine redline of 5250.

The engine which was dyno'ed has a compression ratio of 8.75 to one, requiring a 92 Octane (Premium) gas rating from the manufacturer.





Compare to the second (black background) curve – a modern 8.1 liter FI engine installed in the Workhorse Chassis. Max torque of 450 or so is flat between 3500 and 3000 rpm. Max HP of 340 is about 4200 rpm.

Note that where the HP and Torque graphs cross are totally meaningless due to the differing scales on the y axis.

I need to reiterate my opinions stated in a previous post – the carbureted 454 does not have enough oomph to warrant the installation of a gear reduction unit in a large motor home….AND…thorough and complete gas mpg records (recording EVERY gallon of gas and mileage between fill ups) should be documented for a representative number of miles prior to installing the reduction gearing. A good record – before and after - of mpg and time to 60 mph or time to ¼ or ½ mile markers from a standing stop would reveal the real benefit (or performance loss) of an expensive gear reduction installation.
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Old 06-19-2006, 09:05 AM   #22
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Quote:
Originally Posted by 87MH
Below are two that I have archived…





The First (white background) is for a 454 HO engine that I think is fairly representative (but a bit on the high side) of the 454’s (7.4 liter) engines in most of the mid 80’s MoHos. Note that max torque (about 500 ft.lbs.) occurs at about 3350 rpm – max horsepower (420 HP) is at engine redline of 5250.

The engine which was dyno'ed has a compression ratio of 8.75 to one, requiring a 92 Octane (Premium) gas rating from the manufacturer.





Compare to the second (black background) curve – a modern 8.1 liter FI engine installed in the Workhorse Chassis. Max torque of 450 or so is flat between 3500 and 3000 rpm. Max HP of 340 is about 4200 rpm.

Note that where the HP and Torque graphs cross are totally meaningless due to the differing scales on the y axis.

I need to reiterate my opinions stated in a previous post – the carbureted 454 does not have enough oomph to warrant the installation of a gear reduction unit in a large motor home….AND…thorough and complete gas mpg records (recording EVERY gallon of gas and mileage between fill ups) should be documented for a representative number of miles prior to installing the reduction gearing. A good record – before and after - of mpg and time to 60 mph or time to ¼ or ½ mile markers from a standing stop would reveal the real benefit (or performance loss) of an expensive gear reduction installation.
Dennis,

Even though I couldn't get your graphs to display, I am trying to make sure I understand as fully as possible what you're saying. Of course, in my case the order has been placed. By "gear reduction" are you talking about only the underdrive? My problem really isn't lower gearing, but the need for a taller overdrive due to the 5.29 axle. It's impossible for me to travel above 55 mph without revving the engine and causing it to produce too much heat. I am looking for a "taller" gear for cruising at around 65 mph without putting such a strain on the engine, cooling system, and transmission. By going to the .78 overdrive the engine will run cooler, less strain on the rpms, and the transmission won't be as hot nor as stressed. Do you agree with this? I've gotten dozens of communications from people with all kinds of vehicles, including large carbed, 3-speed, MoHos, who use the GV overdrive and are full of praise for how much better their vehicles run.

Thanks,

Thanks,
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Old 06-19-2006, 09:35 AM   #23
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Dennis,
I, too, am unable to see the graphs.
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Old 06-19-2006, 11:03 AM   #24
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Graphs

Quote:
Originally Posted by noiva
...I couldn't get your graphs to display....
Sorry about the graphs - they were and still are visible in the original post on my access to the Forums....

They are re-posted below - the first, the white one, is a 454 HO engine (about a '91 Block design) with a carbureted intake design (4 bbl) - should be fairly comparable to the '80's engines except for the compression ratio.

The second (black background) is from the Workhorse site - new manufacture 8.1 Liter (494 cubic inch) engine.


Quote:
Originally Posted by noiva
...By going to the .78 overdrive the engine will run cooler, less strain on the rpms, and the transmission won't be as hot nor as stressed. Do you agree with this?
Tim:

No, I do not agree with your assumptions. On my '87 345 I have a VERY difficult time keeping the vacuum gauge in the upper teens on a level grade (LOTS of level grades in my part of Texas...Planet Houston)....this indicates to me that the engine requires a healty dose of 4 bbl almost all of the time. In addition, I have very low torque in the 2300 to 2500 rpm range - this is the range the torque converter in the transmission is "slipping" to convert engine rpm to a lower rpm going to the "inlet" of the 3 speed transmission. Above 2500 rpm the speed of the engine varies directly with the speedometer, below (or at) 2500 rpm the speedometer can drop lower while the torque converter permits the engine to stay at 2300 to 2500 rpm. Below 2300 the tranny will grab the next lower gear.

Again, in my opinion, the lower effective gear ratio will put a higher work and thermal load on both the tranny AND the engine of any Classic MoHo.

Now, my '87 has almost ALWAYS carried close to 16,000 lbs all of the time, and, my 454 has close to 80,000 miles on it. Perhaps (almost certainly) a speed reduction unit would benefit other types of vehicles - it would be ideal for a vehicle that runs light most of the time, and heavily loaded just sometimes (as in a one ton pickup used for "commuter" service during the week, and then to tow a huge and heavy trailer during the weekends), when loaded, the speed reduction unit could effectively raise the rear end ratio and put less of a strain on the engine (let run it at higher rpm's for a given load) whenever the vehicle is required to carry a "heavy" (heavier than normal) load.

In other words, on my '87, at 16,000 lbs, the one-ton P-32 Chassis and drivetrain are maxed out ALL of the time, and by noting my rpm gauge, vacuum gauge, and the performance of the drive train at 55, 60, and 65 on various grades (there is a "sweet spot" between 60 and 63 mph - where the engine is turning over about 3000 rpm, give or take 100) I have inferred that the GM engineers have placed the correct final drive ratio in the chassis - I do not believe I could benefit by a lower ratio final drive.

On the mileage (mpg) question - I can only state that my mpg varies widely. I do not have an explanation for this variance - I try to drive consistently all of the time - 60 to 63 with one eye on the vacuum guage. I can only state that keeping track of each gallon of gas on each and every fillup is the only way to accurately determine overall efficiency and your true gas mileage. I hope others would post their mileage-gas used records over a long interval. One tank "snapshots" are not that accurate, in my opinion.

My opinion by my observations only, but I will also be very curious as to the outcome of any final drive ratio modification on the Airstream Classic MoHo's.

In all honesty, I find it unusual that none of the regular posters with MoHo's here (to my knowledge) has done such an installation.

Please let my know if the two pics have uploaded successfully - as I said earlier, the pics are visible in my original posting when I open it.

Luck.
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Old 06-19-2006, 11:45 AM   #25
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Interesting...

as I've always wondered what a "in between" gear would do for my TV with trailer. I have a Dodge B350 van with a 5.9L V8 and a four speed OD tranny. The rear end is something like a 4.19 (Dodge gears seem to be a bit different than Chevy's, but I digress). Although I don't have a tach, I know I spin probably around 3000 rpms at 65 mph, probably around 3500 at 70 in third. In OD (which I'm not supposed to tow in anyway) I can't tow with this gear at all, the engine bogs down, and speed drops. It won't pull even at 65 mph. I think the OD drops about 1000 rpms at 70. Downhill, the engine will pull fine at 70mph (dUH!) in OD.

I do wonder if I had JUST a tad lower gear (something between 3rd and OD) if that would let me get more miles to the gallon. I get 8 mpg usually pulling (9 if I really baby it). However, that 3rd gear pulls our 5500 # trailer around just fine. I do notice too that if I hit a hill at around 70 (turning about 3500 rpms) that I can get up it just fine. If I go around 60, I'll be shifting down to 2nd at 50mph in no time.

I never (knock on wood) have overheated even pulling at 65mph through 113 degree heat, or pulling up the Grapevine in that same heat (AC off though).

I guess Dodge did their homeowork, but I can't help but guess at what a slightly different gear might do.
Marc
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Old 06-19-2006, 12:05 PM   #26
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Guy,

Thanks so much for taking the time to republish the graphs (They came up this time), and particularly for sharing your experience and expertise in such detail.

My knowledge of the 370 is based on lots of research, but not that much experience. The general assumption about the reasoning for the very low axle of 5.29 (much lower than the 454s tended to come with) is that the Gillig chassis, extra weight, and load capacity (18,500 lbs. GCVWR) is why Gillig used such a low gear. It was also assumed that speeds were lower in the 80s, and there would be no reason to routinely travel at 60-65 mph, as there is today. My "sweet spot" is between 50-55 with vacuum readings around 12. Anything above that causes the engine to rev over 3000 rpms (even though peak torque is 2200), heat begins to rise, vacuum drops to 10 or below, and it's quite obvious the whole drive train is under stress. The RV shop that does the things I can't do (major mechanical stuff) has told me from the beginning that the only problem they could see with the 370 set-up was it needed one more gear (overdrive).

I guess I'm having a tough time understanding why it won't be beneficial when I'm running above 55, keeping in mind that the GV can be cut on and off anytime. By the way, I do keep very close records on gas mileage, and my limited trips have produced widely varying figures, as you mentioned with yours. Tops has been 8.6, and low around 6. Frankly, however, my travel has been too limited to give a reliable average. I've put barely 2000 miles on the MoHo in almost 3 years, although it's picking up now that I actually own it.

Would you consider it possible that the 370, at least, may be the exception to your opinion that the Classics don't routinely need another gear? It is an odd set-up, so to speak.

Thanks,
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Old 06-19-2006, 12:39 PM   #27
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Tim,
You addressed your message to me but it was Dennis who posted this very useful information.
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Old 06-19-2006, 12:48 PM   #28
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Quote:
Originally Posted by noiva
...about the reasoning for the very low axle of 5.29 (much lower than the 454s tended to come with) ....My "sweet spot" is between 50-55 with vacuum readings around 12. Anything above that causes the engine to rev over 3000 rpms (even though peak torque is 2200), heat begins to rise, vacuum drops to 10 or below, and it's quite obvious the whole drive train is under stress....I guess I'm having a tough time understanding why it won't be beneficial when I'm running above 55, keeping in mind that the GV can be cut on and off anytime....on gas mileage, and my limited trips have produced widely varying figures, as you mentioned with yours. Tops has been 8.6, and low around 6...
Tim:

It's interesting that your Ford drivetrain turns 55 mph at 3000 rpms with a 5.29 rear end, and the P-32 delivers the same 3000 rpms at 60 with a 4.56 rear end.

Doing a little math results in the fact that you are turning about 3272 engine revolutions per mile, while I am doing about 3000 revs per mile -

5.29/4.56 = 1.16

3272/3000 = 1.09

Close enough taking into account the accuracy of the tachs and the "about" readings.

With your vacuum dropping off above 55, it indicates to me that the engine is fully loaded at this speed (at 3000 rpm), and forcing it to deliver the same horsepower at a lower rpm (by installing an accessory gear) will do three things -

First: - It will INCREASE the heat load to the radiator, since you want to produce the same horsepower at a lower rpm - this will require a more open throttle in order to pass an additional amount of gas to the engine at a lowered rpm. This will also lower the amount of water circulating through the engine (since the water pump will also be turning slower), all of this lowers your engine vacuum, and you are closer to "lugging" your engine with the higher specific horsepower requirement at a lower rpm.

Second: - It will also INCREASE the transmission heat and wear since you will be forcing the tranny to operate closer to the "torque multiplier" speed of 2500 rpm. - In other words, the transmission is doing more work at lower speeds, causing a higher specific heat buildup per mile travelled.

Third: - It will cause you to get WORSE mileage per gallon of gas. This is due to the fact that the gear reduction will PROBABLY cause your vacuum to drop, pulling the engine mixture to an "over-rich" condition, thereby lowering efficiency. This all falls in with the concept of requiring more horsepower (pushing the vehicle faster) at a reduced engine speed - given that the engine is probably loaded close to optimum conditions right now (you stated that any faster speeds rapidly drop your vacuum reading). The same power requirements at a lower engine speed will assuredly cause your vacuum to drop even lower at a lower engine speed with a higher horsepower output requirement.

Your range of mileage is about the same as mine, with my average about 7.2 mpg.

One good thing about the unit you are planning to install - you can always go back to the original gearing with the flick of a switch. I haven't used a Gear Vender or similar, but having driven split gear rear ends it took about twice as long to switch the rear end ratio as it took to grab another gear, so "split shifting" required quite a bit of time between clutch out to clutch out (power on to power on) - too much time to be beneficial when going up a steep grade.

Good luck on your installation, please post as accurate before and after performance numbers as possible. There are many of us interested in increasing the longevity and performance of our units.
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