8.3 and 34' Performance

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8.3 and 34' Performance

June 04, 2019, 10:56:17 am

Just got back from a 3500 mile trip much of which was in hilly and mountainous terrain . The 8.3 did great. When we first got this rig I expected that the performance of the 8.3 would be a disappointment when compared to the two M11s we've had and that it might not handle as well. However, after driving this thing for 24,000 miles I gotta say, you don't give up really anything with the smaller coach and engine. I don't have any real data to back up my perceptions but here's what I think.

Performance: The 8.3 Cummins along with the 3060 transmission and the 34 foot's 5.13 gearing is a great combination. This rig performs as well or better than our 40' M11 (400 hp) rig and is close to our 36' M11 (ISM ). I think the ISM got off the line faster but that's about it. I should add that the only changes I've made to this engine is a new lift pump and replacement of the stock muffler with a 5" resonator.

Handling: I gave this a lot of thought on this trip and I gotta say this is the best handling of the four we've had. I really did not expect this. It tracks straight and true.

Anyhow, for those who are looking at Foretravels I would say you will be just as happy with the medium Cummins as with the larger engine.
jor

Re: 8.3 and 34' Performance

Reply #1 – June 04, 2019, 11:19:21 am

At 34 feet long, look at the length of the wheelbase. If a Vanagon or Porsche 911 can be on rails with their ultra short wheelbase, a 34 foot RV sure will be. So much for the armchair QBs and the unstable short rear engine RV theories.

8.3 Cummins now have 380 hp in several motorhome brands. I followed one upgrade out of Salt Lake City and it was quick up the hills, especially with the six speed where we were caught between ratios with our four speed.

Correct front end alignment and good shocks make for tracking straight regardless of length. Some drivers can never get used to the movement in the high seating position with really flexible sidewall radials and blame it on other things.

Pierce

Re: 8.3 and 34' Performance

Reply #2 – June 04, 2019, 02:16:17 pm

A lot of owners have regeared the rear axle to the later higher ratio.

Were you in the Rockies much?

Changing the fan drive controller to the 199 degree unit will free up to 50hp

Re: 8.3 and 34' Performance

Reply #3 – June 04, 2019, 02:51:52 pm

Following on John's 8.3 engine comments: we have never been disappointed on the steepest mountain, pulling our 5,600 lb Jeep Grand. For us, its 50mph in 5^th gear, 40mph 4^th, 30mph 3^rd and if going slow on very steep like a winding climb out of a Texas State Park, it could get down to 20mph in 2^nd.

We always manually downshift & upshift, never let tranny hunt, and always get to the top.

Our mechanical 8.3 is so simple, it only has two 12-volt cables, one for fuel shutoff solenoid and one for intake manifold pre-heat, that is other than the starter motor & King throttle/cruise.

Re: 8.3 and 34' Performance

Reply #4 – June 04, 2019, 02:54:29 pm

Quote from: Caflashbob – June 04, 2019, 02:16:17 pm

Changing the fan drive controller to the 199 degree unit will free up to 50hp

I know those fans are power hogs but has this 50 hp claim been dyno proven by any chance? That's a lot, especially when you've only got 300 (when new) to work with.

Re: 8.3 and 34' Performance

Reply #5 – June 04, 2019, 03:02:09 pm

Chuck,

I want back and pulled the engineering data from when I worked with Caterpillar Corp on this: ***Understanding Coach /RV Performance*** Full document clickable at the bottom of that page.

Fan HP demand depends on both engine RPM and engine size (yes, larger engines require more CFM's of air to keep them cool, so larger hydraulic pump and fan(s)).

The 50 HP number is likely close for an M11 at near governed RPM.

Smaller engine, less.

And, this is NOT a "net gain" number, as the fans do not go from OFF to HIGH. They go from LOW to HIGH, as you have to have air flow across the CAC, even if coolant temperature is not high.

Re: 8.3 and 34' Performance

Reply #6 – June 04, 2019, 03:38:39 pm

Thanks Brett, that is very interesting. Never been able to sense a point when the fan kicks to high, probably because even when climbing and towing (my guess is) engine is not near near max hp and temp generally peaks near 200 deg. I use Barry and Cindy's technique and shift points, kick back and enjoy the sweet song of the power unit under a manageable load. The resonator seems to have improved overall performance when climbing.

The 8.3C mechanical engine is simple, fuel efficient, reliable and adequate for the job. Lots of the higher hp coaches have a worse hp/weight ratio. It seems like an ideal engine for a light no slide coach.

Re: 8.3 and 34' Performance

Reply #7 – June 04, 2019, 03:55:25 pm

My 34' does not track as straight as I'd like. I think I have worn bushings in the rear axle.

The hydraulic cooling fans are controlled by the "mechanical" wax capsule. It doesn't turn the fans on/off, it varies them (as far as I can tell).

I changed the rear end gears (I have a thread about it). 68mph on the flat is like 1600 RPM. If there are rolling hills, I manually put it in 5th gear and leave it. Best upgrade I did on my RV.

The 34' bathroom layout is better than the 36. I love the 34'. I squeeze into some small east coast state parks and don't see how I could do it with a 36 and definitely not a 40'.

Re: 8.3 and 34' Performance

Reply #8 – June 04, 2019, 05:22:34 pm

Krush,

How about driving in a parking lot until the wheel is centered and then doing the string alignment from the back tires to the front? A little toe in keeps the coach pretty straight. Uneven front tire pressure can make it move around as well as one shock weaker than it's buddy. Some tires seem to wander more than others. Some all position tires don't do that well up front. Crush is a veteran but for some new folks, there are drive tires, all position tires and steer tires. You would think the designation "all position" would mean steer also but according to some tire shops, it's not the case.

I always figure on a 60 hp loss with the two fans in the high position on our 1993 U300. The 1992 U300s had a vertical radiator on the side with only one fan. Probably good for at least 10 hp less waste than ours. Even in the low speed position, there is still loss, just not sure how much. I know I've said it before but with all that wasted space up front, why oh why didn't they put the radiators up front like a Yangon or 911? Our GM bus had a PTO to drive the rear radiator fan with a thermostatic coupling. And the radiator was huge, not marginal like ours. No crazy and complex hydraulic fan system to go wrong and then have to worry about finding parts for it.

Horsepower should be the same or better than new with a used engine in good shape. You know the old racing saying, "they're the fastest just before they blow." I've found that true in several cases.

Is the Cummings electrical fuel solenoid normally open or does shut off the fuel when activated/powered? VW diesels need electricity to open the valve and let fuel to the injection pump. No juice, no run. Mercedes (300SD) uses vacuum to shut off the fuel and stop the engine. Nice to have an engine that will continue to run even without an electrical source.

Pierce

Re: 8.3 and 34' Performance

Reply #9 – June 04, 2019, 06:01:51 pm

BTW, we are never full WOT full throttle pedal to the floor, even when climbing. It takes some light feathering to not push more than we need to go faster. Watching tach & EGT pyrometer keep us from pushing down too much on the throttle.

On our hydraulic fan non-electric thermostatic control valve, when the two small hoses are flowing hydraulic fluid (valve open) our fans run a slow speed. We have a ball valve on one of two small hoses, and when manually closed, fans run at high speed. I do not think our fans vary their speed between slow & fast.

Re: 8.3 and 34' Performance

Reply #10 – June 04, 2019, 06:31:02 pm

Man, since we're essentially pushing half a billboard down the road with a flat nose coach, makes me wonder what hanging an auxiliary radiator and wind scoop (roof perhaps) would do. Seems unlikely, given the dirty aerodynamics, there would be much penalty. But would there be enough cooling to eliminate one fan?

Re: 8.3 and 34' Performance

Reply #11 – June 04, 2019, 07:18:04 pm

Quote from: Chuck Pearson – June 04, 2019, 06:31:02 pm

Man, since we're essentially pushing half a billboard down the road with a flat nose coach, makes me wonder what hanging an auxiliary radiator and wind scoop (roof perhaps) would do. Seems unlikely, given the dirty aerodynamics, there would be much penalty. But would there be enough cooling to eliminate one fan?

A little tougher than a GV with your flat front. We already have the grill and only need the radiators behind them. Toughest thing would be to bring the coolant from the back to the front as there is not much clearance below the floor before you run into the water and waste tanks.

A rear roof cooling system would have promise and not have to extend up higher than the ACs. I've seen some older U.K. buses like that. Would take advantage of ram air and even convection. Our solar panels go all the way to the back or I might investigate that possibility. No complex plumbing to the front either. 102 inches wide should be enough room for any radiator system. Scoop the air in below the flat radiators and duct it so it has to go up and then out. Electric fans could provide aux airflow for city use.

I put a five cylinder 300SD engine in my MBZ 406D van. The engine stuck out to where the radiator had been so I put one underneath at a bit on an angle. Worked fine but put a hoop around the driveshaft so it could not drop onto the radiator.

I think the biggest improvement would be to put a couple of big electric fans on the outside of the rear radiator. Not to be the primary cooling but in case of a hydraulic failure of one of the components. Normally, you are absolutely stuck as there is zero ram air and any attempt to drive will only get you a quarter mile or so before it starts to overheat. Electric fans would allow the coach to be driven at lower speed as long as you didn't have to go up any grades.

Years ago in San Francisco, a tour bus driver showed me the engine and steerable rear wheels of his bus. It was a flat six or eight and air cooled. There was a large electric motor driven fan above the cylinders that provided cooling for the engine when needed. It was idling and running the AC but convection kept the cylinders cool enough that the fan was not needed. The engine was modular so could be remove in twenty minutes (he said) leaving the fan in place as it did not touch the engine. The rear wheels also were steerable so parking was a snap. Wish I had taken a photo as I can't find it online anywhere.

Anyhow, it just seems shortsighted to design a vehicle that can't take advantage of ram air. Who wants to be SOL with any cooling fan system failure?

My take,

Pierce

Re: 8.3 and 34' Performance

Reply #12 – June 04, 2019, 07:54:50 pm

DEUTZ - Air cooled diesel engines
These Deutz air cooled engines are used on some ships as emergency generators, because they can be placed in the upper floors of the deck house, and it is not necessary to have sea water cooled heat exchangers, or big radiators.

Re: 8.3 and 34' Performance

Reply #13 – June 04, 2019, 09:04:33 pm

Quote from: jcus – June 04, 2019, 07:54:50 pm

DEUTZ - Air cooled diesel engines
These Deutz air cooled engines are used on some ships as emergency generators, because they can be placed in the upper floors of the deck house, and it is not necessary to have sea water cooled heat exchangers, or big radiators.

Those have been around for a VERY long time.

Watch the "Indiana Jones" movie and you will see the German truck which huge round fan in the nose of the truck is for an air cooled diesel Deutz engine!

Also, with no cooling jacket/block, VERY LOUD.

Re: 8.3 and 34' Performance

Reply #14 – June 04, 2019, 10:25:06 pm

Quote from: jcus – June 04, 2019, 07:54:50 pm

DEUTZ - Air cooled diesel engines
These Deutz air cooled engines are used on some ships as emergency generators, because they can be placed in the upper floors of the deck house, and it is not necessary to have sea water cooled heat exchangers, or big radiators.

This was a big flat pancake engine. I've seen a lot in Euro big rigs where they put the engine down low behind the typical cab-over configuration.

P

Re: 8.3 and 34' Performance

Reply #15 – June 04, 2019, 10:46:36 pm

We have the slightly newer 8.3 in our 34' and also do not have any complaints when it comes to performance. We have put a little over 3400 miles on our coach since we bought it . Now I don't have any real comparison to the M 11 or other coaches but when traveling with friends and SOBs we can leave them behind without any effort.

Re: 8.3 and 34' Performance

Reply #16 – June 04, 2019, 11:07:02 pm

Quote from: Eric & Alena + 3 – June 04, 2019, 10:46:36 pm

We have the slightly newer 8.3 in our 34' and also do not have any complaints when it comes to performance. We have put a little over 3400 miles on our coach since we bought it . Now I don't have any real comparison to the M 11 or other coaches but when traveling with friends and SOBs we can leave them behind without any effort.

Quote from: Eric & Alena + 3 – June 04, 2019, 10:46:36 pm

We have the slightly newer 8.3 in our 34' and also do not have any complaints when it comes to performance. We have put a little over 3400 miles on our coach since we bought it . Now I don't have any real comparison to the M 11 or other coaches but when traveling with friends and SOBs we can leave them behind without any effort.

Are you sure you have the 8.3? Think you have the ISL 8.9 400 hp 1250 ft/lb engine. Big difference. James T. has said that is the hot rod foretravel.

Re: 8.3 and 34' Performance

Reply #17 – June 04, 2019, 11:48:08 pm

Quote from: Pierce & Gaylie Stewart – June 04, 2019, 05:22:34 pm

Krush,

How about driving in a parking lot until the wheel is centered and then doing the string alignment from the back tires to the front? A little toe in keeps the coach pretty straight. Uneven front tire pressure can make it move around as well as one shock weaker than it's buddy. Some tires seem to wander more than others. Some all position tires don't do that well up front. Crush is a veteran but for some new folks, there are drive tires, all position tires and steer tires. You would think the designation "all position" would mean steer also but according to some tire shops, it's not the case.

A quick measurement (done two weeks apart) shows I have about 1/16" toe in. A year or two ago I added a bunch of toe on old tires and it helped a lot....I just added toe and didn't measure. The tires feathered some (I didn't care because they were getting replaced in the future). After the scrubbing I removed some toe and measured and it was about 1/8 to 1/16.

I have brand new toyo m177 long haul steer tires all around. The front end isn't the cause of the wander. Oh, redhead rebuilt steering box too. Years ago Josam's in Orlando added a tiny bit of right caster with a wedge. It works out and the RV doesn't pull in the right lane, but it sometimes pull slightly in the left (depending on the crown of the road).

The wander comes from the rear or when the weight shifts. It's almost like the weight shift causes one or both of the axles to move, changing the steering angle. It's weird and the only thing I can think is the bushings in the swing arms.

Re: 8.3 and 34' Performance

Reply #18 – June 05, 2019, 04:26:35 am

Front and back the coach has 10 arms and 40 bushing halves,your bushings are probably as hard as a rock.

Re: 8.3 and 34' Performance

Reply #19 – June 05, 2019, 09:52:31 am

Sounds about right on the toe in. Wonder if you could have a bad or weak rear shock on one side? If I can get my wife interested, I like to be under the front of a vehicle and have her rock the steering wheel back and forth.

Pierce

Re: 8.3 and 34' Performance

Reply #20 – June 05, 2019, 01:57:15 pm

I know you're in recommended range for static toe in measurement. As long as you have a super tight front suspension. Easy enough to add some and see if it helps. I was never satisfied with recommended.

Rear axle, seems like hard acceleration and backing off would make it dart if bushings are shot?

Re: 8.3 and 34' Performance

Reply #21 – June 05, 2019, 02:09:44 pm

Quote from: Chuck Pearson – June 05, 2019, 01:57:15 pm

Sounds really minimal for static toe in measurement. Unless you have a super tight front suspension. Easy enough to add some and see if it helps.

Think he did but got feathering on the edges. 1/4-3/8" would seem OK to me. Like you say, easy to add some and try it. Several good videos on YouTube on how to do it. Steering box play and not enough toe make for constant attention and driver fatigue.

Pierce

Re: 8.3 and 34' Performance

Reply #22 – June 05, 2019, 02:56:28 pm

When my Michelins aged out I recently replaced with Toyo M177 as well. I measured toe at that point, realized I'd been running 3/8" on the Michelins and reset it to 1/8, thinking that the strong directional ribs on the Toyos wouldn't need as much toe. I'm now incrementally adding it back in.

I couldn't discern any wear patterns on Michelins after 40K miles with prior setting. Could be I didn't know exactly how to inspect, but it'd take a lot of scrub to wear a tire out before it ages out. Going to DWMIDG (do what makes it drive good.)

Re: 8.3 and 34' Performance

Reply #23 – June 05, 2019, 07:46:47 pm

The scrubbing on the old tires could also have been some weird wear from before I owned the RV. I'm just a little more careful with the toe-in now that I have brand new tires up front. The wander is not really coming from the front. I'm not able to play with the RV for a few months, but I think the next step is a go-pro mounted on the rear axle to observe what's going on when I swerve.

Re: 8.3 and 34' Performance

Reply #24 – June 05, 2019, 08:40:50 pm

Brett all the 97's have the same cooling system and hydraulic controls as far as I know.

Fan on low until 165. Then ramps up to full speed at 180. So warmed up it's full speed.

As the 8.3 revs higher my thought it uses more power than a lower rpm m11.

My 50hp comment stands. Maybe more

Mine is now idle at 185 then ramps up to full at 199.

The rest of the biz uses the same 199 if hydraulic side drive late model

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