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Old 02-06-2015, 09:22 PM   #1
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Tranny swap or engine repower?

allison 542 swap or not?
I know this is an old thread but it seemed like good advice being thrown around.

however i didnt understand several of the terms used except jake brake tranny etc.

perhaps someone can define some of the terms above like spicer etc.

So,

I have a 35' coach on a diesel pusher spartan chassis. Actual weight is 22,500 lbs.

it is powered by an dd 8.2t or 500-t with 230hp and approx 450 ft lbs of torque. max engine speed is approx 3200 rpm. This is mated to an allison 542 w/o parking pawl. I don't know the eaton axle gear ratio.

tire OD size is about 37"

engine is ultra reliable, purrs like a kitten, never had a problem.

Heres the problem:

top speed is only 68 on a straight. with virtually no additional passing power ability.

Only had it to about 83 once and only once during a cool evening, however i found out later that the alt belt was off. Lol having one less component to turn may have created an underdrive pulley effect freeing up hp or engine speed and when coupled with the cool air prob added some performance.

Even worse:

When I pull hills the rv can slow down to as slow as 20 mph which to me is ridiculous exp since a carbed 454 and 3 sp chevy tranny in a 31' p30 chassis in a coach of same mfg can do at least 30 on a similar hill.

I want to pull a 5000-6000lb vehicle and when on straights i can and do with a 5000 lb toyota 4runner atop a 1400 lb trailer. I dont even feel the load back there at all but when pulling a hill, i have to un hitch and have my wife follows up the hill an we re-hitch at the bottom. Kind irritating when i see vanhool and other diesel buses pull the hill without effort. Becasue of this i wont pull a tow vehicle right now. I also wont plan too my trips around mountain ranges.

So whats the cause? Not enough torque, power, or is the tranny losing power or torque via lack of a lockup?

I hear that the 542 has no lockup. If it the tranny, i was considering an allison 2000 tranny with standalone computer and throttle sensor etc. I was hoping to pull the tranny i needed from a chevy duramax truck or other donor vehicle.

I know i cannot raise boost due to bhg, but the 8.2 is not intercooler so i figure power can be had by adding an intercooler to cool the intake charge, adding an egt and a/f ratio gauge. Next, id like to add propane injection and possibly raise governor speed and somehow slightly increase fuel pressure. If i cant do the above id consider a repower to a 7.3 powerstroke, 6.6 duramax or cummins 5.9 or 8.3.

So which do u think is the culprit?
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Old 02-07-2015, 09:18 AM   #2
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JMHO: Before you start on any modifications, intercooler, trans changeup etc. Examine the cost, time involved and the possibility of reduced reliability. You may be far better off to trade up a number of years to get a coach with the capabilities your looking for.
Something to consider , you didn't mention your coaches year, but my 99 Freightliner chassis is only rated for 65 MPH; it will go faster, but it doesn't feel comfortable over 70; so trying to get an older coach to go faster that it's rated performance speed, could create a whole pile of trouble.
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Old 02-07-2015, 10:16 AM   #3
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tranny swap or repower

Thanks for your input. Yes I'm looking at costs and setting up a budget. This may involved purchasing a running donor vehicle will all parts needed.

My coach year is a 1988.

However my coach only has 51k miles and I specifically sought out my make and model and am otherwise thrilled by everything else so trading rvs isn't really an option. My big mistake was not doing more researach on the engine. My chassis was available with the cummins 5.9 but not in the same model and either 1 year newer or 1 year older. I'm more concerned about hill pulling and passing power than top speed. My thought was that the p30 chevy chassis was likely not designed for 80 mph speed either but again my family used to own one and it did hit that speed occasionally going cross country w/o issue. Maybe a little simplistic, but I'm thinking if a box truck chassis with lesser brakes and less rigidity and everything else could do it,perhaps a spartan chassis could as well.

I have done engine swaps before but never in an rv or something this large.
It would seem to me that assuming that the tranny is ok that a propane inj kit might be the most effective and least intrusive approach.

Hoping to get some parts and pieces answers and input on this forum as well.
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Old 02-07-2015, 12:41 PM   #4
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Good advise above. No matter the reasons you wish to keep this RV you will be money ahead by trading for a coach with the capabilities you desire.


Propane injection sounds like a great way to overstress engine components that were never designed to produce that level of power.
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Old 02-07-2015, 03:51 PM   #5
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If every thing is working properly I would just learn to live with it. Otherwise you might hurt the old Detroit, or end up spending more money than the coach is worth putting a different trans in it. Detroits do well when you keep them wound up on the hills which means you'll have to manually downshift. They don't have the torque of a cummins or cat.

Maybe an Over/underdrive would do the trick?
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Old 02-07-2015, 10:08 PM   #6
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Let's face it. Your old Detroit Diesel is just an old generation, low horsepower engine.
My 2003 7.3 is new technology, but it's still two generations behind current diesels.
If your engine was more current, you might get a tuner to reprogram your fuel injection and transmission programs. But your unit is not modern enough where that's possible.

I would suggest you find a really good diesel shop with an older, experienced diesel mechanic. He might can send your fuel injection out to an injection shop to get the horsepower turned up. It'd also be nice if they had a chassis dyno to find out where you presently stand.

Otherwise, I'd suggest you trade or sell and go something more modern with a larger engine.
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Old 02-07-2015, 10:18 PM   #7
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I think you have a fine rig that you can run for a long time.
Coming up last on a hill has no shame. You will be right behind the "winners" at the next traffic light!
Be patient. Downshift to keep it about 2000 rpm on that grade.
Be proud that what you have is more than enough!
But if you wanna tow heavy, ya gotta upgrade. Put physics and $ in your favor.
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Old 02-08-2015, 08:23 AM   #8
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1. If you add the cost of any required updates to achieve what you are asking with the coach you have now (parts and labor), to the price of what you can sell your coach for today, I'm betting you can buy a coach that meets your new requirements. Further, it will do that with a degree of reliability not available with the mods.

2. The coach you have now will not sell for one dollar more after the mods than it would sell with them.

Put my vote with the others saying make the best of what you have, without the drive train mods, or update to a coach that meets your new criteria.
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Old 02-08-2015, 09:51 AM   #9
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Another thought...way different angle but works.

Time is money.

So it takes longer to get up the hill.

If your time was worth 100 bucks an hour and you removed 10 minutes from climbing the grapevine time you saved 10 bucks.

But how often do you climb grapevine?

But then get stuck in traffic anyway...

It would easily cost 10K on the low end to gain any real hp or torque and that would equate to 1000 trips up the grapevine if your time was worth that 100 bucks...

I was a fast driver...always in fast lane and looking to gain time on gps...usuall did but lookling for CHP is pain.

Drive slower now and get way better distance due to mpg up to 22 mpg from 18 (in the old jeep) and I still can gain a bit on the gps so I was not really saving that much time overall but was spending too much gas money and brain work doing it.

Enjoy the ride as it is.

The engine is likely capable of more hp but given that it makes it very strong in its current state so just drive it.
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Old 02-08-2015, 06:15 PM   #10
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Thank you for your initial input.

I should say short of finding a 40' version of my coach in better condition ( which after looking for 6 years), its unlikely i will be changing coaches in the next 10 yrs.

I don't expect to get a return on investment as automobiles are poor investments in that regard. RVs and boats...even worse.

I appreciate the advice of those who tell me to live with it which is what im currently doing, however i just avoid towing and destinations with lots of hills.

Id like to not limit my destinations as that is kinda one of my reasons for rving in the first place.

Suffice it to say that if dont have a reasonable solution the unit will stay as is except i may still consider cooling the intake charge.

Let me first add that in looking at the factory detroit diesel service manual (november 1986) it states the following sae hp and torque values for the federal 1985 and up 230 hp 8.2t:

230hp @2800 rpm (max engine speed is 3200)
510 ftlbs of torque @ 1700 rpm
injectors are 4b75 units (which are in other higher regarded older detroits)

So the torque on this motor is higher than i previously noted.

Also, my rear axle is an eaton 16123 ( spartan or DD #MH426dd4)
36 tooth spline and 1.85 spline diameter (still looking for the ratio)

Now,

I agree that based on the desires that I have outlined,especially hill pulling that a more powerful or more modern power plant is a definate and expensive solution.

On the other hand,
There are others who report that when equipped with 8.2t and allison 542 with @ 28,000 lb weight they have been able to achieve just under 90 mph when in cool air (no intercooler). ( I feel comfy at 83)

That suggests to me that to increase top speed from say 67-68 mph to 80 mph in a 22,000 lb vehicle and for this to take place " with cool air" that simply adding a cool intake charge would def increase power and does not kill the 8.2.
A min 10 mph increase with a 22.5klb.. in order for that to happen some modest power or torque gains were def generated and without increasing boost pressure engine speed. In doing my research, adding an intercooler in minimally invasive and inexpensive if done yourself considering the gains expected. I already have a very large intercooler from another project that i can use. (Whats stopping me is the max hp and torque limits of the transmission and lack of lock up torque convertor.)

Detroit must have recognized this at the factory since they were able to add an intercooler and change turbo from a switzer unit to an AR unit and increased injector size to larger 4b80 units (also from other detroits) and raised engine speed setting. This motor is sometimes called the 8.2ti or 500ti and is rated at 250hp@3000 rpm.

http://www.goldcoastpower.com/brochu...ochure%201.jpg

Then again, Detroit realized the engine was suitable and increased the hp again to 300hp

http://boatdiesel.com/Engines/Detroi...1193685&Page=1

Johnson & Thomas an aftermarket boat outfitter did the same thing and took intercooled 8.2s and created their own 300hp.

It just sounds to me like this can be done to generate modest hp power gains w/o hurting the engine. In this last case, a 70 hp increase.

Sounds like i could combine your advice with my findings and lower my expectations and leave as is or shoot for no more than 70 hp increase while making sure my transmission can handle the increase based on factory specs. Otherwise I a repower with a more modern motor like a cummins 8.3 or another coach would be in order.
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Old 02-08-2015, 10:48 PM   #11
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Tony,

Great analogy. Clever and insightful.
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Old 02-09-2015, 02:36 PM   #12
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Boatdiesel is a great site with tons of knowledge about marine applications. How that translates to over the road vehicles I am not sure.


I was a commercial fisherman for many years and have a great fondness for Detroits. They are loud and leaky but they are extremely dependable and commercial boats used them because they were rebuildable in frame, meaning you did not have to remove the engine which is a big plus when removing it requires cutting open the deck.


In my experience the vast majority of them were the lower horsepower versions simply because the highest power versions were far less reliable and reliability is awfully important in the north Pacific with a single engine boat. I guess you could roll the dice but there is no free lunch. Detroits are not a very torque motor for a diesel and to get the increase you are looking for will likely mean it is also less reliable, which is it's biggest asset. Good luck with whatever you decide. Certainly the intercooler will be cheap enough and may get you a couple miles an hour but probably not much more.
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Old 02-10-2015, 01:01 AM   #13
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Quote:
Originally Posted by dulobast25 View Post
Thank you for your initial input.

I should say short of finding a 40' version of my coach in better condition ( which after looking for 6 years), its unlikely i will be changing coaches in the next 10 yrs.

I don't expect to get a return on investment as automobiles are poor investments in that regard. RVs and boats...even worse.

I appreciate the advice of those who tell me to live with it which is what im currently doing, however i just avoid towing and destinations with lots of hills.

Id like to not limit my destinations as that is kinda one of my reasons for rving in the first place.

Suffice it to say that if dont have a reasonable solution the unit will stay as is except i may still consider cooling the intake charge.

Let me first add that in looking at the factory detroit diesel service manual (november 1986) it states the following sae hp and torque values for the federal 1985 and up 230 hp 8.2t:

230hp @2800 rpm (max engine speed is 3200)
510 ftlbs of torque @ 1700 rpm
injectors are 4b75 units (which are in other higher regarded older detroits)

So the torque on this motor is higher than i previously noted.

Also, my rear axle is an eaton 16123 ( spartan or DD #MH426dd4)
36 tooth spline and 1.85 spline diameter (still looking for the ratio)

Now,

I agree that based on the desires that I have outlined,especially hill pulling that a more powerful or more modern power plant is a definate and expensive solution.

On the other hand,
There are others who report that when equipped with 8.2t and allison 542 with @ 28,000 lb weight they have been able to achieve just under 90 mph when in cool air (no intercooler). ( I feel comfy at 83)

That suggests to me that to increase top speed from say 67-68 mph to 80 mph in a 22,000 lb vehicle and for this to take place " with cool air" that simply adding a cool intake charge would def increase power and does not kill the 8.2.
A min 10 mph increase with a 22.5klb.. in order for that to happen some modest power or torque gains were def generated and without increasing boost pressure engine speed. In doing my research, adding an intercooler in minimally invasive and inexpensive if done yourself considering the gains expected. I already have a very large intercooler from another project that i can use. (Whats stopping me is the max hp and torque limits of the transmission and lack of lock up torque convertor.)

Detroit must have recognized this at the factory since they were able to add an intercooler and change turbo from a switzer unit to an AR unit and increased injector size to larger 4b80 units (also from other detroits) and raised engine speed setting. This motor is sometimes called the 8.2ti or 500ti and is rated at 250hp@3000 rpm.

http://www.goldcoastpower.com/brochu...ochure%201.jpg

Then again, Detroit realized the engine was suitable and increased the hp again to 300hp

http://boatdiesel.com/Engines/Detroi...1193685&Page=1

Johnson & Thomas an aftermarket boat outfitter did the same thing and took intercooled 8.2s and created their own 300hp.

It just sounds to me like this can be done to generate modest hp power gains w/o hurting the engine. In this last case, a 70 hp increase.

Sounds like i could combine your advice with my findings and lower my expectations and leave as is or shoot for no more than 70 hp increase while making sure my transmission can handle the increase based on factory specs. Otherwise I a repower with a more modern motor like a cummins 8.3 or another coach would be in order.
To get the rear axle ratio, next time the vehicle has the rear wheels off the ground, put a chalk mark on the driveshaft and one on a rear tire. With the vehicle in neutral rotate the tire one full revolution and count the number of times the driveshaft turns, you will get an approximate number like 4 and a quarter turns, see what axle ratio correspondes with that and you will know your ratio. You may be able to get more speed and better milage with a lower numbered gear but you will lose torque.
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Old 02-10-2015, 01:24 AM   #14
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tranny swap or engine repower swap?

Quote:
Originally Posted by easywind View Post
To get the rear axle ratio, next time the vehicle has the rear wheels off the ground, put a chalk mark on the driveshaft and one on a rear tire. With the vehicle in neutral rotate the tire one full revolution and count the number of times the driveshaft turns, you will get an approximate number like 4 and a quarter turns, see what axle ratio correspondes with that and you will know your ratio. You may be able to get more speed and better milage with a lower numbered gear but you will lose torque.
I have heard that trick before. My brother and i were just talking about lowering the gear to pull the hill but hurting my top end, just about 1 mins ago. I guess im burning the candle on both ends. Seems like more work to pull the hill than to gain a little in top speed. I suppose a gear vendor could help but not at a small cost.
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