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Comment by Stephen Evans on October 27, 2014 at 11:37pm

Comment by jeff york on October 11, 2014 at 1:30pm

Jim, If you are at 15,000 lbs, you are nearly 4000 lbs heavier than me. That is a significant difference and cause for extra fuel burn. If you are running 3500 RPM at 60 mph, that is another big difference. I am at a bit under 3000 rpm at a little over 60 mph. If my rough in the head calculations are correct, it takes your Allegro about 40%  to 46% more horsepower to move at 60 mph then my AS. That sounds a bit hard to believe so I am going to do some research. I know I am off a bit because I am thinking in terms of aircraft HP and power differences to move an aircraft at a given speed and given weight and its a different animal but, you get the point. The weight and the increased RPM of you motor would mean a significant higher fuel burn. The one thing we can not overcome and that I could not overcome when I tried this on my previous Fleetwood MH was the weight. It too weighed about 4000 lbs more than my AS Argosy. We can do what we can to reduce weight like making sure we do not carry water in our tanks and try to load light but, we both know that loading light can be a challenge. As a pilot, we are forced to watch and control weight to keep within a safe CG (center of gravity) to operate within FAA FAR regulations. 

That you allow your MH to climb to 70-75 mph is also going to cause a massive drop in fuel econ. 

AS i mentioned, I could not overcome the weight and blunt aerodynamic and parasitic drag issues on my Fleetwood Class C when I tried this before. I am not trying to be a na sayer here but, I am not to sure you can have much effect on something like an Allegro. Do what you can with the free'r flowing exhaust, open up the air intake and by the way, did you re-jet your quadrajet carb when you opened up your exhaust. If you didnt, your AF (air fuel ratio is way off). Thats the problem with carbs. No offense to the carb lovers but, its why newer engines can last much longer. Best ratio AF keeps valves, rings and the oil doing what they do best. ok, modern OD trans that would run our engines at 2200 rpm instead of 3500 RPM means the same motor turns almost half the turns and therefore lasts twice as long  just on that alone.

Comment by Jim Stoltz on October 10, 2014 at 4:24pm

I have a rebuilt Quadrajet that the rebuilder claims is correct for the application. I don't have any heat soak issues. Actually, it starts much easier when it's hot. Ignition is stock.

I'll have to check the sticker again, but I think the gross weight is around 15,000 lbs. I need to have it weighed soon for new springs anyway.

The only adjustment on the QJet is for idle. Off idle a/f adjustments are with the rods, which I haven't messed with. It seems to run great as-is.

If memory serves, it's pushing 3500 RPM at 60 MPH. I usually cruise around 60-65, and will push it to 70-75 on an as-needed basis. I think if I keep my foot out of the secondaries, and keep it around 60 MPH it would do better MPG-wise.

Comment by John "T" Nordhoff on October 10, 2014 at 9:58am

   Yo Jeff York,

   EXCELLENT ENGINEERING AND TECHNICAL COMMENTS WHICH I ENJOYED (being a fellow techy type) ...

 I'm an Electrical NOT mechanical engineer but it just seemed intuitive to me a Class C had to produce less wind drag than a huge front surface area flat box Class A going down the road. Id guess there just has to be less front end surface area (they aren't as tall for one thing) on a Class C Van then a flat front taller Class A?????????  HOWEVER I have no data whatsoever to back that up nor have I any measurements or experimental results or tests so I just cant say for sure.................

 FOR SURE I agree weight is a factor and Id guess a Class C to be lighter (subject of course to length and accessories and frame and chassis) which is why they can get better MPG

 ANOTHER FOR SURE  Speed is critical and if you keep it under 60 MPG improves.

 Way back when I ran carb engines on big block V8's Id send the carbs to Gerharty Performance RV in California along with the distributors and after he was done with both my MPG improved HOWEVER the upgrade to dual 2 1/2 exhaust pipes (versus a long factory run of single pipe) and headers in some cases seemed to do the most good.

 HOWEVER when I switched to TBI MPG improved and it improved more when I went to EFI and BOTH beat the pants off any carb engines I had.

 On the Ford versus Chevy big block, that's a personal preference but I just prefer the 454 Chevy as I've had better performance and luck.

 Final note:  Im NOT a flight or aerodynamic engineer etc but have owned all brands and shapes and sizes of Class A and Class C over 30 years (was a used RV dealer at a time) and despite the carb and distributor and exhaust tuning and TBI or EFI and Class C or Class A, 10 MPG is the best I ever got (with current Class C with Chevy 454 Vortec and OD tranny) and Id love to know how to tune a 454 (or any other for that matter) or what to do in order to get 12/14 MPG as Ive never achieved that and want to know the secrets and tip and techniques, I hope he can tell us all we will be most appreciative. Gotta love how we all help each other here, GREAT SITE

 Best Wishes n God Bless Jeff and all others

 John T  

Comment by jeff york on October 10, 2014 at 9:06am

Jim, yes, your Allegro sounds very sweet. I am curious what carb you have, Do you have heat soak issues restarting it when its hot ? I have also changed my ignition system and timing to gain fuel econ but, it makes it difficult to start when the motor is hot. 

My guess is your Allegro is substantially heavier than my airstream. Airstreams are built light and I have tried to get mine even lighter. I have not weighed mine but its suppose to be 11,500. As far as your carb and mine, my concern right now is that I may have leaned mine out a bit much in my search for fuel econ. I will feel better when I can switch to TBI/EFI and be able to monitor AF ratios. 

My AS has a Econ guage which is a glorified vac gauge. I watch it and monitor it constantly. Especially when I am pushing more on the throttle. 

What speeds do you drive at? It would seem that you are pushing a brick ( no offense) down the road. Whats your RPMs at 60 and at 65 mph ? 

It does sound good

Comment by Jim Stoltz on October 10, 2014 at 6:02am

I'm getting around 6 with my "new" 454 in my M31 Allegro. I haven't done anything to tune the new carb yet, so there may be some more MPG I can gain from doing that. It's a GM Performance crate engine, so I don't think it was built for economy. What's interesting is that the fuel gauge apparently hasn't worked for a long time. The previous owner wrote down fill up mileage and gallons of fuel it took in pencil all over the cab. Based on my calculations, he was getting around 7 MPG with the original engine.

Exhaust is aftermarket and 2.5" the whole way back. It's pretty loud but I like it that way. Mine sounds very similar to the OP's.https://www.youtube.com/watch?v=Ki3ucp2KMbo

Funny how time flies - that was May 3rd. It was filthy and I didn't even have license plates on it yet. I've had a blast with the thing between now and then!

Good luck with your Airstream - it looks like a keeper and sounds sweet.

Comment by jeff york on October 10, 2014 at 12:58am

I will take a bit of an issue with the idea that any class c is more "streamlined". If you are saying its more aerodynamic, well, again, I doubt it other than the newer Mercedes / Sprinters. As a pilot and engineer and as someone who builds racing planes, let me therefore infer I know a thing or two about aerodynamics. The parasitic drag caused by the area between the cab and the overhead section of a class C alone as well as the vertical areas between the cab sides and the motorhome box will create a great amount of drag. I doubt any manufactures have done any drag tests but, this makes me curious enough to see if I can model it in my aircraft software. 

You are correct, the wind load increases rapidly above 60 mph and this is true in more than just a motorhome. Keep your foot out of it and maintain 60 or less and you have a big impact on fuel econ. 

Weight is a big factor as well. In fact its a big factor in aircraft performance and econ as well. The lighter the better. My previous Class C Fleetwond weighed nearly 4000 lbs more than my Airstream Argosy. Drag from the underside of a vehicle is also a major factor in a vehicles drag. My Argosy has been extensively closed in to try and minimize this problem. My son and I race a sports car and have completely enclosed the undercarriage. 

I am probably not as much a fan of the 454 as you are or many others. but, I tried this same experiment with my previous 460 Ford powered Class C and simply didn't get the results. Spent a lot of money to get little results. But, I think it pulled 4000 lbs more easier then my 454 pulls 4000 lbs less. 

As far as calculating my econ, I have previously described how as a pilot, we calculate fuel burn in route and we become extremely accurate at it. But, since there were doubters, I began using only full tank to full tank calculations.  With 3 engineering degrees and therefore a math major, I can assure you, my ability to figure fuel econ is spot on target. 

I am not offended by those who doubt, I had doubters that my racing plane could produce the speeds and fuel burn econ but, when I won national title's in 2010 and 2011, most of the doubters , doubted no more. The rest were just upset for getting beat. Those that are upset are the same ones who claim I must be cheating and also say I am an arrogant a$$. I don't try to be, in fact I am pretty humble. But, as an engineer, I back my claims with data. Yes, I am surprised at my results so far but, I have always been able to get more speed and econ be that my airplanes or sports cars . I am not the backyard BS'er.  There is no magic carb or additive, no If it helps, as I mentioned, I failed in my first attempt to do this with my 460 Ford. But, its why I chose a Airstream Argosy this time. Probably the best platform in a class A that I could get to reach the results I want. Its all for fun

Comment by John "T" Nordhoff on October 9, 2014 at 9:28am

  Pat, first off I ALWAYS got better MPG in a Class C (perhaps 1 more MPG) as they are more streamlined, catch less air, not as tall etc. The wind load increases like exponentially with speed and all that big flat front surface area in a Class A and I drive like 60 mph max which helps.  In a 26 Ft Class C with a 454 Throttle Body and 4l80E Overdrive Tranny Id get in the 8 to 8.5 range. Then when I moved up to the 454 Vortec and same OD Tranny I can get nearly 10 in PERFECT conditions and when not towing can get 9.5 pretty easy still in good conditions and I drive 60 mph mind you. This is ACTUAL MPG with me filling it to the same brim each time and using a calculator NOT rounding up. When I hear of 12 MPG in a huge Class A Gas powered rig caution flags always fly but if it can be achieved I'm happy and want to know how to do it myself lol

 Other things a body might do (I'm NOT admitting to anything lol) is decrease exhaust back pressure and let her breathe by adding dual oversize exhaust, perhaps eliminating a cat converter (Not meeeeeeeeee lol) use of an Overdrive (like my tranny) tranny BUT MOST IMPORTANT is to keep her under 60 mph and drive like an Old Man. Headers can also improve exhaust performance. I keep my engine perfect tuned as well and let her speed up down a hill to get a run for the next up hill.  

 John T

Comment by John "T" Nordhoff on October 9, 2014 at 8:26am

 SWEET, I'm also a Chevy 454 fan yayyyyyyyyyyy. I started with a carburetor 454, then moved up to a Throttle Body Fuel Injected, then currently to a 454 Vortec with the 4L80E Overdrive Transmission, AND EACH UPGRADE IMPROVED MY MILEAGE especially when I went to the Vortec and Overdrive Tranny..........

 In my 29 Ft Class C I can get close to 10 MPG, its hard to believe 12 in a large motorhome, Id have to see that to believe it woooooooooooo hoooooooooooo Keep on keepin on

 Nice rig, best wishes

 John T

Comment by jeff york on October 8, 2014 at 10:21pm

Thanks guys. I am pretty happy with the way it is turning out. I seen a guy with one advertised that admits his 454 Argosy gets only 6 to 7 MPG. I am now getting almost 12 mpg with the rebuild and mods during the rebuild. I think I have already mentioned previously the changes and mods. I really think I will hit nearly 14 mpg once I get the over drive trans installed. If not, I think I will get there once I get the EFI/TBI installed. 

Also, I met an older man from the factory just a few weeks ago. He was so happy to see my 1977.

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