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Old 05-24-2008, 07:30 PM   #1
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Need to improve a RV with a big block

Hi,
My daily is pretty good, I have a motorcycle, but I have an RV, it gets like 9 mpg.

We are taking it out west and plan on putting on 3600 miles.

Now, if I can improve it's gas milage by just 2mpg the gas savings will be huge!
It has a 454 chevy V8, with TBI fuel injection and a 4 speed auto trans with torque converterlock up.

Any ideas on how to improve the gas milage?

Use a wideband O2 to run it leaner?
Improve the exhaust ( headers etc)

Any other tricks?

thanks
Keith
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Old 05-24-2008, 07:48 PM   #2
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I think a custom tune could really benefit, as well as some technology upgrades to the fuel injection and transmission control.

At 9mpg, your trip will be 400 gallons. At $3.80, that's $1,520. At 11mpg you'll use 327 gallons, at a cost of 1,243. So, if you can get 2mpg for $300, it will pay for itself on that trip alone.

Can you post specifications for it? Weight, dimensions, HP and torque at least.

In your application, you probably could benefit from exhaust improvements but it won't pay for itself, at least not on your planned trip. You can almost surely benefit from additional tire pressure, if they're not up to their stamped maximum already. Common hypermiling driving strategies can help, though some might not be safe driving an RV -- and others are part of driving an RV safely anyway.
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Old 05-24-2008, 10:33 PM   #3
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For the money I would start out with the best synthetic oil in the rear end, tranny and engine that you can get, you will want to change the oil in all of this before a big trip any way so the added cost will be very little.
What is the model and age of this beast?
What is making you choose to do this?
Driving just fast enough that over drive locks in is also most likely give you the best mileage.
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Old 05-25-2008, 12:43 PM   #4
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Hey thanks for the help. I wasn't sure if I would get completely flamed for driving the thing in the first place!

It's 21foot class C, the kind with the bed over the cab.
it weighs 10,000 lbs and is built on a chevy 1 ton van chassis. I'm not sure what HP / torque it has.
It has an OBD1 compliant computer and I have an ALDL cable so I can at least monitor the engine.

I am doing an oil change so will switch to synthetic, allong with new plugs air filter etc.

Rv's are perfect to drive slowly, I plan on following all the hyper miling ideas I can.

About the exhaust, I have a set of headers I can use, and I can do all the work, so the cost is minimal. It is a big job though. then I'd have to replace the rest of the pipe to.

The big question is will headers improve gas mileage or hurt it?
If is good for milage I'll do it, but not if it hurts mileage...

Anyone know where to get a mileage improving custom tune??

Thanks
Keith
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Old 05-25-2008, 02:02 PM   #5
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Any of the aero mods we've done on our cars could be done on the RV with the exception of the grill block, since your ICE is working all out just to be able to move all of that mass and aero drag. If you are handy with tools you could do a smooth underbody panel, rear wheel well covers, wheel spoilers in front of the tires, wheel boattails behind the tires, fairings around the A/C modules and other RV stuff sticking out of the top and sides, smooth hub caps. The biggest single mileage improver would be if you could build a boattail of the back of that thing, either mounted on the reese hitch or built onto a small trailer. The interior of the boattail could serve as additional storage space. Anything you can do to make the shape of your RV more closely resemble a teardrop would help to improve the mileage.
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Old 05-26-2008, 07:27 AM   #6
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I am not confident that wheel spoilers/fairings/boattails will make a measurable difference in this case. They would be impractical in any useful size, as a class C is bound to use a lot of suspension travel and get low sometimes, and campgrounds can be very rough.

Completely smooth wheelcovers will also provide an improvement that's difficult to measure, at best. More importantly, if they're REALLY completely smooth they may affect brake cooling, which is especially important in a class C. It may be very easy to put in wheel skirts though, and you could probably even easily do it so they don't look out of place.

All these little things can add up enough to be worthwhile and measurable when you're talking about a 50mpg subcompact, but on this scale I don't think you'll ever notice.

Fairings/boattails for the various stuff sticking off the top could probably help a little. The front of them is generally pretty decent, but the rear is usually not. A measurable difference might even be had from those combined with semi-smooth wheelcovers and the underbody panel. The boattail trailer will be a huge aero improvement but is likely to be a big investment of time and money; I'd recommend it if it's feasible. The part that sticks out over the cab is probably flat-fronted and maybe could use some improving with a fairing.

What model year is it?

Driving style is important, but there's probably not much room for improvement in the way you drive it. You can't start flying around corners. You're probably already using pretty wide throttle openings (because you NEED to just to go). Pulse & Glide probably won't work too well with all that aerodynamic drag, but it's worth a try -- just don't forget what you're driving and pulse to excessively high speeds. You can certainly get away with driving abnormally slow or having big fluctuations in speed, people expect it anyway. If you're a good RV driver and have lots of practice, you probably ALREADY look and plan far ahead and avoid any extra stopping and accelerating, such as by trying to synch with timed traffic lights and getting off the gas as soon as you see a stop in the distance. You probably already need to use engine braking a lot, so if your PCM can do DFCO then it is certainly getting used.

I hate to sound like a downer but it's hard for me to find much room for improvement. I suspect that headers would help, not hinder. I think a custom tune would help, especially with aggressive DFCO and low shift points (and then if you have a "Tow/Haul" button, you could obviously press it when you need more power), and whatever else they do to tune it for additional FE. You could reduce weight as much as possible, but it's tough to get the wife and kids to go along with it. Be sure to empty your waste tanks before driving and don't fill up the fresh water tank unless you do any dry camping. If you've got lots of batteries but don't do any dry camping, remove them. I don't think those weight reductions will help much, but maybe a little.

Hmm...RVs could really benefit from hybrid drivetrains. If it had GM's full size pickup hybrid system with two 80hp electric motors in the transmission, it could have a much smaller gas engine. While the weight on a class C is usually right near design limits for all the components involved, some of the batteries are already there. With aggressive regenerative braking....

For those who aren't familiar with class C RVs, they're the kind that looks like this:
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Old 05-27-2008, 05:29 AM   #7
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Do you know anything about the internals of that motor?

I have a big-block Buick, and I just installed a set of Rhoades lifters. I used to get about 14-14.5 MPG, and on my last tank (first with the new lifters) I got 15.8 MPG. That's only one tank and "one data point does not make a trend" however I actually expect gas mileage to improve even more after a few more tankfuls.

Unfortunately, the effectiveness of the Rhoades lifters depends on the cam you have, and that's why I asked about the internals. On my car I know exactly what the cam design is, and I looked at how it would perform with the Rhoades lifters, and I knew there would be a significant improvement. There will probably always be "some" improvement, but whether or not you get a 10% improvement will depend on the cam design that is already there. It would also help to know your cruising RPM, since the lower the RPM the more benefit the Rhoades lifters will have.

Usually, the hotter the cam the more the benefit, however I think in every case there will be some benefit. I suspect in an RV you have a fairly small cam, which would mean less of a benefit, but if you cruise at 1600-1800 RPM then you will see more of a benefit.

It took me a full day to install- you have to take the valvecovers & rocker arms off, and the intake, in order to access the lifter valley. But for me it was WELL worth it, I consider 10% fuel savings to be more than worthwhile (and the nicer idle helps too).

Total cost for me was about $160, including the lifters, shipping, a new intake manifold gasket, and valvecover gaskets.

-Bob C.
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Old 05-27-2008, 06:36 AM   #8
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I'll second the Rhoades lifters, I first built an engine with them back in 1980 (400 small block Chevy) and they definitely do what they say they do.
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Old 05-27-2008, 08:00 AM   #9
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Quote:
Originally Posted by 427v8 View Post
Hi,
My daily is pretty good, I have a motorcycle, but I have an RV, it gets like 9 mpg.

We are taking it out west and plan on putting on 3600 miles.

Now, if I can improve it's gas milage by just 2mpg the gas savings will be huge!
It has a 454 chevy V8, with TBI fuel injection and a 4 speed auto trans with torque converterlock up.

Any ideas on how to improve the gas milage?

Use a wideband O2 to run it leaner?
Improve the exhaust ( headers etc)

Any other tricks?

thanks
Keith
It would be to your benefit to put the headers on. It will decrease back pressure letting the exhaust get on out of there. Something I have done to my 1988 Escort is put a pcv enhancer on it. Just take a jar any size drill two 3/8 inch holes in the top go to Home Depot and get a piece of all thread pipe, I use lamp pipe and lamp nuts. Place a piece of the pipe in each hole, and a lock washer and nut on inside and outside and seal leaks with silicone. Fill it about half full of steel wool. Take the pcv hose off and get some gas line or heater hose whatever size you need and run one hose from the pcv valve to the jar and then a hose from the jar to wherever the other end of the original hose ran. Leave the pcv valve in the vehicle. This will filter out all of the liquid emmisions from the blow by and send the other burnable emmisions through to be reburned. Just check and empty the jar as needed. On my Escort I was getting 37-41 mpg before doing this. Since I put this on it I am averaging nearly 45 mpg. That's between 10 and 20% increase and only cost about $5. including the heater hose. I'm not sure it will help you that much, but even 5% would be 0.45 more mpg if you are getting 9 mpg. On a 3600 mile trip at 9 mpg and gas being $4.00 gal it would cost $1600. If you were getting 9.45 MPG it would cost you $1524. a savings of $76. or 19 galons of gas. Even if it didn't help mileage it will help keep your engine cleaner on the inside. My 1988 Escort is listed in the garage section with my mileage record if you would like to see what it is doing.
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Old 08-13-2008, 05:57 PM   #10
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Boattails and vortexs

You might try doing a few google searches. I've been looking at 'boattail trailers' lately. (I've got a 10' tall stepvan for doing craft fairs). From what I've read, enclosing the bottom of the RV and adding a boattail would give the best bang for the buck.

Based on various sources, you're still only talking 8-12% (based on class 7 & 8 heavy duty trucks @ 60-80,000#). However, my hope is since my van has the aerodynamic shape of a brick (or an old 80,000# 18 wheeler), and with only 12% of the loaded weight of the 18 wheeler, my "aero" load is much greater and that the 8-12% is just a starting point.

Ask again next year...
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