4104 Repower???

[zimtok]

A question was posed to me last night at the gig by my co-owner of the bus.....

What would be the best combination of engine / transmission / rear-end for our 4104 if we were to re-power it? I'd like to hear your thoughts on everything from a rebuild of the stock engine, adding turbo, engine replacement transmission and dif replacement. I like my manual transmission but am not opposed to having an automatic.

Some background on how we use the bus.....
We take it to every gig. We currently are doing 4-5 gigs a week. Most of the gigs are local, but we do get a few gigs that take us on round trips of about 1000-1500 miles.

The future of the bus is that we would like it ready for more frequent longer trips. 1000-3000 miles stopping to do several gigs over a couple weeks tour.

We want a good reliable combination that has over the road power, speed, and fuel economy. Top speed is currently 60mph-65mph I would like to have at least the capability of 70mph even if I would not use it except for passing.

[gmpd4104]

sell it and buy a new bus is probably the smart move

[Airbag]

If fuel economy and performance is what you want then get a MC5 with a 8V-71 and four speed manual.

10 mpg and you can find yourself at 85 mph if not careful.

[lostagain]

I don't think a re power is worth the money and time.

I just overhauled my engine to turbo specs, and that is great. Went from 65 injectors to 75, after cooler, new rad, dry air filter from oil bath. A lot more torque lower in the rpm range. Very noticeable going up hill. I now go up hills one to two gears higher, (5 speed manual Spicer). Top speed is still 60 mph at 2500rpm, but that is fast enough for a motorhome. So far I get 11 to 12 Cdn. mpg (9 US).

I agree with gmpd: if you want a more modern power train, get a newer bus with a four stroke and automatic.

JC

[Dallas]

You may be better off to find a newer coach, if you were so inclined, but, if you are determined to keep the classic lines and looks of the 4104 as a calling card of your band, consider rebuilding the 6-71 back as a 6-71T, raise the differential ratio from 4.125:1 (what it is now) to as high a number as you can find, somewhere in the 5.X:1 and drop in a VS2-8.

You could also do the Detroit 50 series swap with a VR731R and the almost impossible to get 4.10:1 differential from an RTS.

[luvrbus]

A good repower for the 4104 is the  DDEC inline 671 330 hp makes a rocket out of the 4104 and will get in the 10 to 12 mpg range.        good luck

[TomC]

The easiest way to obtain more power and fuel economy is to turbocharge and air to air intercool the engine.  By keeping the same injectors, you'll get a bit better fuel mileage, your performance will be the same in altitude and smoking will not be an issue (with 65 injectors, will have 244hp and 730lb/ft torque).  By going up to 80 injectors you'll bump the horsepower from 210hp (60 injectors) to 300hp.  The torque from 554lb/ft to 900lb/ft torque (the 4spd manual is rated at 1200lb/ft torque).  You'd have to add the air to air intercooler (most put them in the right engine door), change the air cleaner and radiator. But-without a change in the rear end ratio-the same top speed.
If you were to change out the entire engine/transmission, the most common change I've seen in 04's is to go with a 6V-92TA and a V730 Allison automatic.  Then you'd have up to 350hp and 1150lb/ft torque.  This would involve also changing to a bigger radiator, muffler, air cleaner, changing the rear end for a different driveline angle-but-you'd have a real hotrod.
Turboing would be in the $8-10,000 range-total engine trade pushing $20,000.  With that in mind, and the fact that there are an abundance of used converted buses on the market, and that the 4104 is over 50 years old, maybe best just to get another bus.  Good Luck, TomC

[uncle ned]

Just wait to you see Don and mine 12v71 twin turbo powered 04. Will be removing the hot 6v92 and replacing it.

Will place the 12v on its own Wheels like a cement truck and run the drive shaft to a turned over t drive axle.

Will cruse at 90mph and get 25 mpg.

If i tell a little lie i might as well go all the way

Great minds at work on this board

uncle ned

[Don Fairchild]

If you like the bus you have then the lest expensive way is to turbo the 6-71. You can find a 6-71TA either MUI or DDEC
and rebuild it. If you go with a 6V92 then that is a tight fit and will be pron to overheating. Ask Uncle Ned. You can also look back in BCM magazine and see one that was done here in Bakersfield, they did a real nice job but it runs hot also.

If you go with a 6-71 TA and change gears you would pick up road speed the way you want. It you bus but for my money I would turbo the 6 turn up the rpm and change gears. Good millage good road speed and a fun coach to drive.

Hope this helps.

Don

P.S. If you go the 6-71TA let me know and I will help you find one and work with your mech. to see that it is put together for the best overall performance.

[RJ]

Zim -

I agree with Don - 6-71T or TA would make for a sweet ride with great dependability, if you want to keep the classic '04.

You'll still be saddled with 65 mph, tho, unless you can find one of the VERY rare 3:55 axles.  And I mean VERY rare!  You could pick up maybe 5 mph by going to 11R24.5 tires that turn 470 revs per mile, rather than the stock 495 rev/mile size.  That would be less trouble than trying to find a 3:55, and a whole lot easier on the clutch, too!  Don could help you set it up for a couple hundred rpm over the recommended 2100 rpm engine speed, which would also help you pick up some road speed.

Another thing to consider:  Even tho the transmission is rated for 1200 ft/lbs of torque, the bevel gears hung off the end are not.  GM discovered this while doing development work on the 4106 with it's 8V71.  That's why the '06 and all later production GMC manual transmission coaches have the bevel gearset between the clutch & transmission - to handle the torque.

And no, the bevel gears are NOT interchangeable between the models.  Different ratio, too. The '04 and earlier are straight 1:1, whereas the V-8 models use a slight overdrive 0.808:1.  Which is why a 4106 and later GM highway coach will easily run 70 mph right out of the box.

But bottom line:  Unless, as Dallas said, you want to keep the '04 as an advertising gimmick for your band, a newer coach with an automatic makes a whole lot of sense (cents!)  And there's a BUNCH of good deals to be had on fully converted units right now!

Sounds like you and your band mates have some serious cuss/discuss coming on!

FWIW & HTH. . .

[johns4104s]

I know lots of people that have gone with 671TA, kept there 4 speed, they love the power and get better milage. Don may have a 3.55 high rear end in the parts he is getting. Or i will be parting out a 4104 with a good 3.55 pumpkin that got me to 73mph with the 671 at 2300 rpm.This ratio rear end is slow on the hills, but changing to the 671TA will compensate.
Note you will have to upgrade the radiator to dissipate all that extra heat.( rad mod $1000.00)


John

[zimtok]

Thanks for ALL of the input. We know that a new(er) bus would be the best choice and maybe even cheaper in the long run. A new bus may be the way we go. I guess that if the band really starts to take off and we are doing more longer tours it only makes sense to get a different bus.

We do not have any plans to sell this bus as it does have some family/sentimental connection to the co-owner Eddie Smith. So we will always have this 4104 for the local gigs and personal use.

Our intention here was to see all the options and the degree of modifications needed to perform the swap. I don't think we want to modify the bus extremely so our best option at this point may be to stick with a 6-71 with turbo and possible upgrade to the rear end ratio.



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