Filled the Allegro up in preparation for my next trip this coming weekend.

It looks like I went 165 miles between "fills", and it took 40 gallons. So about 4 MPG. I did run the generator quite a bit - a bit over 5 hours and it sucks down about a gallon an hour. I also question my last "fill" because I know that when it's full it pukes gas out the top of the tank where it meets the filler tube. The gas station attendant (can't pump my own gas in NJ) insisted it was full but there was no leaks. Tonight it puked fuel out like it should have when it was full.

So, I'm standing by my 5 MPG estimate. And I'm not gentle with the thing. I have my foot in the 4 barrels quite a bit. 

The fun part was all of 3 of the gas station attendants (Indian immigrants in this case) took a tour of the thing. The one guy said it was bigger than his flat in India. He was blown away at the fact that I owned the thing and drove it around (he had asked how much it cost me to rent it). So it's big, old and ugly to some, but a palace to others. I feel lucky to have the luxury of owning it...for now. Until whatever breaks next :)

Views: 329

Tags: 454 chevy rv engine improvements, chevy P30 engine modifications, increased rv engine gas mileage, rv engine modifications


You need to be a member of Good Old RVs to add comments!

Join Good Old RVs

Comment by Casey Chinook on June 25, 2015 at 12:00pm

The above site has some manuals for newer and older RV, may want to check it out.

Comment by Casey Chinook on June 25, 2015 at 11:01am

If you go with a OD trans which is probably your best mileage improvement, and your torque curve will allow for the taller gears at a lower RPM, then you just have to determine how many miles to get the cost of the transmission to pay for itself. You are extending the life of your engine since it is not in the rpm stratosphere and more important, is that you are reducing emissions!

Comment by Rich Thomas on June 24, 2015 at 11:25pm

PS It's a 77 chassis with no pollution crap at all. 

Comment by Rich Thomas on June 24, 2015 at 11:21pm

unfortunately they'er about the same LOL. the Palace weighs 7,700 pounds according to the paperwork. I have no clue what the rear end ratio is but it's rated for 7900 lbs  the front 3,900 total  G.V.W.R.  is 10,500. it's a G-30 cutaway RV chassis. 350 no air and I assume a TH 350.  It's 23' over all. it has the infamous Q - Jet that for reasons I can't explain works flawlessly. runs on 91 octane only. It seams to handle the task with ease it will cruse 60 easy all day long but 7.7 a rough 8 gallons per mile not so good. headers and open pipes in the future but want to get all the little things up to snuff first. almost there now but I want to add roof air and a small inverter / gen set before I get into tinkering with things that are not broke.I  like a good winter project though and the fuel delivery might be something worth looking at. I'll dig around some and get the info you mentioned maybe you can give me some ideas short of engine swapping. not really opposed to that but it just turned over 20k last month LOL

Comment by jeff york on June 24, 2015 at 8:27pm

Rich, more details. What is your weight, rear end ratio, transmission ? I mean RV weight. LOL. Do you have fuel injection. Lots of variables.  If you have much weight and mass I am guessing you are way under powered and working that 350 way to hard. Years ago Toyota built a a chassis that had a 2.2 4 cylinder engine that several motorhomes were built on. Great motor and later the platform in like 1987 or so came with a V6 engine. The bigger V6 got better gas mileage then the small 2.2 , 4 cylinder.  I have compared with some people that have shorter Airstreams that are powered by the 350. I get better gas mileage then they do. Ok, yes I modified my engine a lot but, they get pretty bad MPG . Its not always better mpg just because you have a smaller motor. As I mentioned earlier, my background (side hobby) was racing planes and getting maximum power under 3400 RPM and preferable below 3000 rpm. So, I applied that to my motor-home because we will never see 4000 to 6500 RPM and thats the sweet spot of the power-band of most motors. So, build it to get your power-band in the rpm range you realistically use. 

Comment by Rich Thomas on June 24, 2015 at 7:33pm

Wish you guys was talking 350's I'm getting 7.7 mpg's on the Palace just a couple weeks ago. I know it's cammed up a bit for an RV, you can hear the lope at idle but I have no Idea about what I have other than it's unaltered from new. any way It's been very interesting following your thread. 

Comment by jeff york on June 24, 2015 at 11:41am

I might also add that my bore and stoke is different then a stock 454 crate motor. So maybe that's why with may have went with a slightly different duration on the intake side of the cam. My bore was .60 over and the stroke was 4.250 or .250 additional stroke making my motor a 496 cubic inch motor. So, you have me curious, so I am going to go look at my build sheet and extensive notes related to the cam selection. The idea was to build for torque on the low side and a very flat torque curve. It was not to build for horsepower, we are trying to move a heavy object, who cares about horsepower when we are talking about a heavy load.  Since I was going for torque, that is why I stroked the motor as well. Since I have never been able to determine if a 454 in a car of that era was any different then a 454 in a P30 / truck / motorhome, I went with the assumption that my 454 was built to specs for torque and horsepower of that of a car equiped 454. Those specs were at that time on a large torque curve resulting in max torque being far past an rpm range any of us could get to. I believe it was 4500 to 6000 rpm and the torque ratings in our 2000 to 3500 rpm range were abysmal. To me, this explained why these motors got horrible gas mileage because they could never run in their designed sweet spot. No amount of add on would really get reasonable results. Remember, I tired and failed at bolt on fuel econ improvements with a previous Ford 460 powered motorhome. ( I know, different engine all together, but the concept was the same) Yes, that new 454 crate motor looks perfect for us, but those specs were not available to our coaches back in the 70's and 80's. So, my best suggestion is to build to them or buy the crate motor. 490 ft lbs of torque coming on at 1750 to 2000 rpm is exactly what I think we need in a motorhome. It also allows the motor to run in its sweet spot all the time and thats when you can start getting the kind of gas mileage I am getting at 12 mpg at 60-65 mph. I think I am going to get that up to just over 15 mpg with the OD trans because I am going to lower the cruise rpms down to 2200 rpm. I dont think you need the roller cam and you dont need to bore and stroke your motor like I did. I think a 200.00 cam change ( if you can do it yourself) will get you exactly where I am. But, I dont think bolt on's will help you one bit. Been there done that. I think I also said, dont go adding a K&N filter either unless you can re-jet your carb. You will cause your motor to run lean which may seem to improve fuel mileage but its going to do so at the cost of your motor. An engine running lean will not last long, it will run hotter too. Stay with a good stock air cleaner. Go with a K&N if you have fuel injection.   

Comment by jeff york on June 24, 2015 at 10:49am

Jim, thats a great link to what looks spec wise to be a great motor home motor. The torque does come on at pretty much exactly where I would think a person would want their torque converter to come in. I looked at the specs and specific to the cam specs I am anxious to get up to my Airstream and pull my engine build sheet and compare. I am curious because the specs lists a cam lift that I think is spot on to mine but, I am thinking the duration they list is longer than mine and what I thought was at the far end of a duration for a low rpm high torque design. They list a intake duration of 211 degrees and I thought 214 is for mid range torque not low rpm torque and I thought my cam was well below 211 degrees. I am pretty sure my lift is at .51 just like the crate motor. I would say that GM engineers certainly know more than I do so if anyone out there was going to build their 454 I am thinking I would copy the 454 crate specs. Actually, I thought I did when I built mine because at 490 LBS of torque on the crate motor that is what I think my 454 was set up to do. So, maybe my cam is the exact same. Thats why I want to go look at my build sheet. Its also why I felt no reason to go diesel if I could build a gas motor with those specs. However, I do not have roller rockers which I didnt feel were needed since I was only planning on max RPM of 3500-4000. Why do roller rockers for that ? The website that your link you provided goes to has options for a OD trans 4L85 and a controller but, there is no link on the trans when I tired to see what it was and how much. I am still not sure what stall speed to go with on a 700R4 OD trans. I think I want something different then my TH400 stall rated converter because first gear on the 700R4 is lower then first gear on a TH400. I am not sure that my trans rebuild sheet has the stall rating on it. I will look. I am going to toss in another big love of my conversion from the mechanical fuel pump to the electric fuel pump that I just did. It makes my big over built 454 a kitty cat to start and acceleration is instant. No luggin on acceleration and simple touch the key starts just like a modern fuel injected engine. Its on my list as a must do for all you guys out there still running a mechanical fuel pump. Get rid of your mechanical pump and have the confidence that your 454 will start instantly with an electric fuel pump. Make sure to add a fuel pump pressure regulator so that you dont push to much pressure past your float bowl needle. DO THIS conversion, you will love it when you are done. 

Comment by Casey Chinook on June 24, 2015 at 10:25am

Jim & Jeff


Here is the calculator link.

Comment by Casey Chinook on June 24, 2015 at 10:24am

Jim &  Jeff,

Here is a link that a RPM tire size final drive, and transmission specs and a calculator.



  •         How To Links 

-Search Good Old RV's

-Start a New Group 

-Roof Repair Photos & Products

-Repair an RV Roof

-Pick Roof Sealer   

-Understanding RV Electrical Systems 

-Get RV Insurance   

-What to Look For When Buying a Used RV

-Jack Installs Fuel Injection in his Dodge 



 Artist Roads                                              



If you love classic and vintage RVs then come Join us. Come on in and have some fun. JOIN HERE NOW


Update for my fuel injection

Started by Jack Wasmuth in RV Repair & Maintence Jul 18.

Systems monitor

Started by Laura in RV Repair & Maintence Jul 14.

78 Dodge 440-3 Timing solutions needed 1 Reply

Started by Tony Levero in RV Repair & Maintence. Last reply by Jimco_W001 Jun 27.

Blog Posts

Quandary about tire pressure

Posted by CH Smith on May 19, 2021 at 5:43am — 1 Comment

Third time is a charm!

Posted by S.Heins on March 31, 2021 at 1:14pm

Newbie Fireball

Posted by Kenneth C on March 9, 2021 at 10:25pm


Posted by Linda Lee Toepfer on January 18, 2021 at 1:40pm

1982 Chevrolet Travel Mate Class A

Posted by Barb Stanley on December 17, 2020 at 9:15am — 1 Comment



  • Add Videos
  • View All


If you love classic and vintage RVs then come Join us.

 Come on in and have some fun.      

 Dedicated to a simpler, more rewarding and fun way of life in a Good Old RV... 

Vintage Travel Trailers, Vintage Campers, Camper Restoration, Bus Conversions, Vintage RV Forums, Old RVs, Tiny Homes, Boondocking

A work of art by member Paige Bridges


 Disclaimer - Please Read it

Enjoy this site and use it totally at your own risk.

By using or viewing this site YOU agree to Hold Harmless anyone associated with it including other members. Also, YOU agree that YOU are solely responsible for ANY and ALL actions, results or damages. Members "opinions" are just that and any repair or alteration comments or recommendations are by folks who are not licensed repair  or mechanical professionals. Any repairs or modifications you do totally at YOUR OWN RISK. Use licensed professionals for all work to avoid possible serious injury or damage. Use  banks for purchases.  Have fun!

Copywrite & Trade Mark Registered GoodOldRV© ,GoodOldRVs©,©,©,GoodOldRV.Com©

© 2021   Created by Russell E Johnson.   Powered by

Badges  |  Report an Issue  |  Terms of Service