Motor Home Mileage

[87MH]

There has previously been some discussion on what the 454 engined MH's should aspire to as far as mileage.

The following is an honest to goodness map of every gallon of gasoline that has gone into the Xepellin since purchase.

The anomaly at the last tankerage was anticipated, the fix has to do with getting sufficient air to the carb. If the mpg increase appears to be permanent, I will post photos of the modification.

I know that PeterH is out there waiting to jump in with an advertisement for Jacobs Ignitions, but I think that I will go the MSD route with an adjustable timing kit.

I will definitely post on what the effects (if any) the MSD gives me.

[87MH]

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[ViewRVs]

How big is your gas tank? I thought these had 80 gallon tanks. It would appear that twice you filled it past the max.

[87MH]

Fred:

Your quite right, several of the entries are multiple fills.

For various reasons, (weight, price, pocketbook), I did not fill the tank all of the way at all refills. (Sam's are notorious for cutting off the pump at $75).

However, I am confident that all gas going into the tank has been accounted for.

I do question the sixth to last fill, thinking that it may be one of those "credit card limit" stops, especially since the fill following it indicates a lower than average mpg. If you average the one above and the one following that fill, it comes out right in line with the rest of postings.

I thought they were interesting numbers, I didn't have enough room to put the dates on the gas purchases, but the middle third were purchases for the Forum Ralley at Heron Lake in Northern New Mexico this past June.

I hope to see numbers consistantly above 8.0 with the added airway. It sure felt as if it had more power over last weekends trip to Canyon of the Eagles.

[swebster]

Dennis,
Apparently I don't have the time (or attention to details) that you do ...but our 345 is getting between 7.9 and 8.4 based on my "back of the napkin" calculations from my trips.

I have wondered many times however if I have a 100 gallon tank. I guess I thought that my gauge is off but it sure seems like based on the distance and the mileage and the gauge readings that there is more than 80 gallons in there.

BTW – these are the things I wonder about on my 12 hours treks to see RV dealers in the middle of the night. Man I need to get a life.

[87MH]

Dennis,
Apparently I don't have the time (or attention to details) that you do ...but .......

Steven -- you can say it, I am anal retentive.

I am supposed to be on a 12 step program to help the problem, but every time I get to the sixth step I have to tell them how they could make the program better, and then they make me start over from step one!

That one fill at 4.0 mpg has me mystified. That was recorded at about the time I was really having problems with the genset, and about half of that tank was also through some fairly heavy rain coming back from Goliad State Park.

With the possible swings (highs and lows) of the mpg, I feel it is necessary to record each fill to get a good handle on how the engine is doing.

As I indicated earlier, the addition of the MSD equipment in steps will be a good test of the functionality of the devices --

[ALANSD]

You 345 owners should be happy, youhave 6 more feet in length than my 280 and my mileage is only a shade better
;0

[RonJudi]

I as a new owner am very much apprreciative of your detail info. Would you mind giving me any departures from standard on your unit like exhaust, or anything else so I can kinda figure out where I am at. My 93 33' unit has a modified Air Filter and that may be it. I appreciate all the advice I have been getting from everyone and would like to see a break down on how much each thing does to improve MPG. I understand for instance that the exhaust is one of the areas that can be impoved as well as new intake manifolds. Cost is a factor. Thanks

[87MH]

The intake is straight factory. I suspected a problem where the cool air intake plenum mated with the horn of the air filter bowl. They (the plenum and the air filter) come together right at the leading edge of the doghouse, and the plastic plenum appeared to be crimped, greatly reducing the available area for the intake air to move through on it's way to the carb.

I cut an auxilliary oval in the air filter bowl, and riveted a second horn through the oval I cut. From there, I ducted to the upper wheel well, away from the exhaust manifold. I am still pondering a prefilter to combat the dust problem at this location.

The exhaust system is a mystery. There does not appear to be a "standard factory" system. Mine has the "factory header" manifold. These are steel fabricated (not cast) with an expansion sleeve between the front pair and the rear pair of cylinders on each side. There is no "crossover", other than the internal crossover under the intake manifold. The rest of the system allows for pretty fair breathing. I'm guessing 2 1/2" OD tubing running down each side of the driveshaft, exiting on either side, just in front of the tires. Each side has it's own muffler, about 1' diameter X 3' long.

The popular "Banks" system addresses both the intake and exhaust problems. The Banks air filter is entirely different from the stock, and the header system is tuned for MH duty.

[swebster]

Alan - You could always trade up - er - longer!

Dennis - I'm anxious to see how your MSD does. I've been looking at these in the Jegs/Summit catalogs and wondering about them. Been planning my exhaust for a while now. I'm currently thinking about the following setup: MSD ignition/distributor, original "factory" headers, add a crossover pipe, series 70 flowmasters and move the pass side to exit on driver's side - and chrome tips (of course). I'm more than a little reluctant to remove the factory headers given the amount of "stuff" plumbed in and out of them and the idea or breaking loose 18 year old manifold bolts doesn't help either.

But - I think the chrome tips are good for an extra one or two ft-lbs of torque don't you?

[87MH]

Only if you get the ones with the Blue LED lights around the outside perimeter. The Red LED lighted Stainless Steel Exhaust Tips look a bit too much like rear tail lamps to add any horsepower.

[thenewkid64]

Originally posted by 87MH
Only if you get the ones with the Blue LED lights around the outside perimeter. The Red LED lighted Stainless Steel Exhaust Tips look a bit too much like rear tail lamps to add any horsepower.

You guys start bolting on that stuff and making them sound like an overwound blender and Airstream is going to ask for their motorhome back!

[swebster]

Only if you get the ones with the Blue LED lights around the outside perimeter. The Red LED lighted Stainless Steel Exhaust Tips look a bit too much like rear tail lamps to add any horsepower.

Is there another kind?

Oh - and don't forget the blue fluorescents under the coach.

[1367_345]

Just thought I'd chime in on my mileage as I too did an exhaustive log on my last trip from Denver to Lawton OK.

I have a bone stock 1989 345 and we averaged 6mpg on our trip.

I was really sad as I hoped for a bit better. It actually got worse at lower elevation which surprised me also - I guess it is tuned for our altitude.

[87MH]

1367_345:

I feel your pain, but I'm glad to know some actual numbers!

I've had so many people bragging about 10's and 12's I was beginning to think I had a seriously sick 454.

Anyone else have some documented numbers?

[ViewRVs]

My numbers ran 6.5 - 8 mpg while I tracked it. It varied based on speed and gen set usage. Most of my driving was in Florida and Georgia. Mine is all stock.

[thenewkid64]

I am averaging 7-9 MPG with a 2300 LB toad in Fla. If I run the genset it is more like 7. It really seems to be based on the speed more than load. This one rides so smooth I have to watch that I don't go too fast. I normally drive at 62-68 MPH.

Stock exaust, but a nascar-ed fresh air intake and a new Edelbrock Qjet carb. I am still tweaking the carb, the OEM carb got me closer to 10 MPG, but that was without the toad.

[donnall]

Headers make a big difference in milage and performance. I don't have such exact mumbers but I believe I'm getting about 20% better milage and alot more power.

Don

[thenewkid64]

my 76 Argosy had headers and I had more power for sure, the mileage with the same model Qjet was closer to 10, I know on our longest trip to Virgina I got close to 11 with no genset or dash AC required!

I also think that the timing on my 78 is off a bit, I just can't get it to perform like I "feel" it should and I know that will affect the overall mileage.

[toddster]

I'd be curious what sort of fuel economy some of the Isuzu and Cummins (conversions) diesels are seeing.

Happy Trails!!!!