I like to find all possible means of good performance and gas mpg whether gas or diesel . Tell your upgrades and modifications .

Tags: Fuel Mileage, RV Exhaust System, RV Gas Mileage, RV carberator

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  Jerry, having owned countless motorhomes especially in the eighties and nineties (was a used dealer then plus used them) and always wanting to improve MPG, experience taught me the VERY FIRST THING TO DO was improve/modify the exhaust system to include true dual 2 1/2 minimum exhaust pipes with free flow mufflers and no resonators etc. and shorten them and run them out the sides versus allllllllllll the way back to reduce back pressure and improve free exhaust air flow. THAT ALWAYS IMPFOVED MPG in all the motorhomes I owned, it may or may not in yours.

 The next thing I did was to improve the incoming free cooler air flow pressure by doing something like using aluminum clothes dryer vent piping covered with fine mesh brass sreeening tilted slightly down so any water drained back out and running it from the air cleaner intake to the front of the RV so as to stuff that incoming 60 MPH cooler air under some pressure into my air cleaner assembly. I also tried high performance air filters such as K N etc.

 In the day I sent my distributors to Gerharty Performance RV & Automotive in California for improved advance curve set up especially for RV's.  I also kept the engine perfect tuned with plugs and quality plug wires, and of course, timing. I also sent him some carbs for modification, but regardless if I tried a 2 or 4 barrel or a Holly or an Edelbrock etc etc I never saw all that much difference in MPG despise all those variations. 

 Finally, I drove like an old man. I kept speed to 60 max with soft slow starts.

 Other things in later years that really helped were OVERDRIVE be it an auxiliary box or differential gear ratio changes or an automatic equipped with OD etc. However my current 454 Vortec fuel injected Chevy with the 4L80E Overdrive Tranny beats any older carburetor set up of any brand I ever owned as far as improved MPG.  

 Those were modifications which worked for me at a relatively low cost, I'm sure other things may have worked for other people on their particular RV's, so I hope they add them to the list for all our benefit.   

  John T in Indiana

In most vehicles I owned overdrive was never installed it was just a 3speed auto. My wife says I drive like an old man anyway but fuel injection sounds good . Thank You

Overdrive doesn't do much good on a vehicle with an automatic transmission unless it has a lock-up torque-converter.  In fact, adding OD to RVs that lack a lock-up will sometimes lower MPGs.  It can just make the torque-converter slip more and waste more fuel making heat instead of pushing you down the road.   On my 1988 Toyota Minicruiser - there is a four speed automatic with no lock-up and OD.  Basically a 3 speed with 4th as the OD.   In 3rd it can get 16-17 MPG @ 55 MPH.  Same conditions in 4th OD it gets 15-16 MPG but is quieter.   There are many published road-tests showing the same drop in MPGs with OD for many RVs. It has a lot to do with how your RV is geared and how hard it's workking to maintain highway speed .

 Ifffffffffff there's an overdrive and if a torque converter is indeed slipping more as a result, that creates heat and inefficiency and the gains (or gearing changes) an overdrive might provide can be in effect canceled out grrrrrrrrrrrrr lol. In all the years and all the different RV's I owned air flow and exhaust and timing and gearing, be it OD or lock up converters etc. etc., indeed helped my MPG. Still, my later model RV's with EFI and/or lock ups and/or overdrives etc still do better in MPG then in my old carburetored days, but those improvements were welcome and a fun hobby in the day.

 Very fun chat and I sure enjoyed (and still do) squeezing our every inch of MPG possible..

  John T

I've had several vehicles that got worse fuel mileage with OD.  Here's a road-test of a Toyota 20 foot RV with a auto trans, OD, and no lockup.  Got 19.5 MPG @ 55 MPH with the OD turned "off."  With the OD "on" it only got 18.5 MPG.  I have a similar rig with the same results.  That test was on a flat road with no wind.  Mileage drops even worse in OD if pulling a grade.  Obviously - if you have an RV with a huge engine and geared so it wants to rev 4000 RPM at 55 MPH - adding an OD might help assuming it does not make the engine work harder to maintain speed.  My 88 Toyota drives much nicer with the OD "on" while on flat roads.  Kind of shame it drops the MPGs though.


 I sure hear that, it depends on the RV and engine and its gearing and lock up torque converters or manual trannys and the overdrive gearing and the road conditions (hilly, windy) etc. etc. as to mileage. I always experienced improved MPG using overdrive, but again, there are so many variables and sizes and types of RV's and engines and gearing its hard to say how one particular unit may fair.....

  Love RV chat, thanks

  John T

Hello , i have a 85 chief 33' chief 454 . I installed a banks power kit. It is headers, good ones, muffler, 3" exhaust , single,cold air intake,. the power increase is very good . i can fly up any hill , pulling a trailer with a jeep. no less then 30 mph on any hill. just driving the motorhome alone it flies . I was hoping for better milage but i still think it increased by 2mpg . but for pulling stuff it really helped . sounds good also.

  Ronald, I'm a believer in Banks engineering, although I haven't yet shelled out the bucks for one. Still, the theory of improved intake and exhaust air flow (what your Banks system involves)  represents the same home made modifications I have made. As I understand it (electrical NOT mechanical engineer) cooler air is denser which is the reason it can improve performance and in some RV's I rigged an aluminum dryer vent hose attached to the air breather intake and ran it down below the engine compartment (fine brass screen cover) so cooler air was sort of forced/stuffed under some pressure (driving down road at 60 MPH direct into it) like a poor mans blower system. My current fuel injected 454 Vortec with the 4L80E Overdrive Tranny still blows the doors off my earlier carburetored 454's as far as both power and MPG. Id like to also hang a Banks on it someday wooooooooooo hoooooooooooooo 


  John T loves RV performance chat

Hey John, yes the banks cold air intake is like that and they give you a little end piece that goes in front of the radiator . but they did make a nice alum. air cleaner .  but pretty easy to modify your old one .  

Hi Jerry, 

I have a 1985 35' Pace Arrow. We get 6 mpg with the wind behind us. I have checked into a fuel injection system by Holly (Throttle Body) and that is just about $2000 with me installing it. Not worth it, in my world. I do have dual exhaust with 2 1/2 inch pipe dumped behind the rear axle with Turbo Flow Master mufflers. I have a cracked exhaust manifold and looking to replace both with headers. I believe that the only way to improve mpg is the big exhaust, good air flow with a K&N filter w/housing and perfect maintenance (and driving like Grandpa).

I also have 4:56 gear, Chevy 454 and a turbo 400 transmission. Thought about changing the gear but I think I would never be able to pull my car with that.

I am a retired over the road truck driver and was taught years back to save fuel just as a driver, keep your foot out of the throttle and go slow. Hope this helps you out    

I doubt adding an electronic throttle-body kit would give you any gains in fuel mileage.  In fact, it might even drop a little with it.  Many cars and trucks when first equipped with throttle-body EFI got worse fuel mileage then the previous carbed versions. But they drove better.  No " sluggish cold starts" or  "lean" situations.  Newer rigs with somewhat more efficient engines have gains based on much more then just a electronic-monitored "water pistol" shooting gas into what used to be a carb.   Lower friction parts in the engines (e.g. roller cams), variable valve timing, higher "mechanical" compression ratios, higher "effective" compression ratios, etc. 




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