Fuel Economy, or lack thereof

[Jim Stoltz]

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 :)

[Jim Stoltz]

I found this link for GM's 454 HO crate engine:

http://www.chevrolet.com/performance/crate-engines/big-block-454-ho...

Obviously this isn't the one I have (mine's from 1990), but it's a relatively low compression, iron-head 454 that makes 500 ft. lbs. of torque. With the cam they put in it (specs are on the page) the torque curve is flat pretty much right off idle at 450 ft lbs. and peaks at 500 ft lbs. at 3440 RPM. 

The stock 81-86 454 was 230 HP and 360 ft. lbs of torque, but I couldn't find anything that showed the curve. I'd bet you're right, Jeff. While they had stopped putting 454s in cars by then, the truck-spec 454 was made for Blazers and HD pickups. Probably not optimal for motorhomes right out of the box.

[jeff york]

The guy with the Alison may have had a much lower 1st gear and a better spread of gears with a final OD gear at or nearly the same as a 700R4...maybe ? As far as the torque curve on the 454 its not flat and the stock torque power band seems to be way above our cruise RPM. But, on my motor I could not tell what the stock cam was and assumed it was in the standard 4500 to 6000 rpm. Thats why I changed the cam to match the power band to our lower RPM demands. I believe the cam needs to be high lift low duration. If you do it yourself, a cam swap is only about 200 bucks to get your motor in the right powerband. But, as I said, I have no  way to tell what cam was in the stock 454 but, I think all of us are lugging the 454 with a stock cam. 

Casey, as far as rebuilding a transmission, it really isn't hard at all. I watched and helped a few times back in high school on manuals and ten years ago I did my first trans rebuild of an automatic and I am still driving the car. The 700R4 has been upgraded and used in many big high horsepower muscle car applications. Our MH applications are a bit different simply because they weigh more but, we dont have the same horsepower. So, I believe as long as we use a deep trans pan with cooling and a large remote trans cooler, we should be able to use the 700R4 if built well. Heat will be the killer of the trans but if we keep it cool, it should work fine. 

My problem now is I don't want to take my Airstream down during the camping season and my business has me buried in work. Doing work on my As now means really late nights. 

[Jim Stoltz]

Actually mine's a 454 as well.

I wish I had talked to the guy with the Airstream longer at NASCAR last year. He had a P30 with a bolt-ons 454 with the Allison 6-speed and aftermarket electronic controller. I hadn't thought about how it would lug down in 6th gear, but he seemed to be happy with it. My impression was that the torque curve on the 454 is pretty flat, but I haven't checked out the truck spec curve.

The 700R4 is a good choice, too, and would also require driveshaft and crossmember modifications. An OD gear would be really nice. I'll have to do some research (and/or let jeff do the guniea pig work).

[Casey Chinook]

Hey Jim & Jeff,

The TH700R4 would be a great overdrive transmission. Would probably be good for Jim's application as well. I think Phoenix Transmission products has a full line of TH700R starting at about $1755.00. Jeff, if you are building the transmission yourself you are way beyond my capabilities.

Jim,

 The GM crate 4 bolt main 350 with vortec heads motor is a great motor. I put one in my brother's 69  3/4 ton Camper Special GMC. 300hp and it moves out well.

I was running a 750 Demon carb on my 383. When I detuned it, I went with a 650 cfm Holley Street Avenger. The gas mileage improvement was substantial. 800cfm is a really big carb on a 350

Thanks for the replies guys!

[Jim Stoltz]

I know nothing about my engine other than that it's a GM Performance crate engine with truck-spec heads. It had 25k miles on it and was installed in an antique toy hauler. The carb that was on it when I got it was too small so I replaced it with the correct, 800 CFM Quadrajet. I'm really pleased with the way it lugs the motorhome around. It seems like it will continue to pull up to redline.

[jeff york]

I would have to look through my build sheet to see what the grind was on the cam. It was a Crane Cam. My area of cam and torque experience is mostly in racing planes and that conceptual knowledge was what lead me to believe I could do it on the 454. On an airplane, you can not spin a prop at greater then 3400 RPM of the prop tips exceed mach 1. So, knowing we build combustion engines in racing planes to achieve max torque and horsepower below that 3400 rpm made me feel that a 454 could do the same. The problem with the 454 as I seen it was that it was never really designed or built specific to being a a luggy 12,000 lb motor-home. It was built for a shared platform from mid sized cars to light trucks and then shoe horned into mid sized flat bed and other trucks and in my case a P30 platform which was the basis for many various work duty trucks. But, the engine suffered from generic homogenization . In other words, it was never really designed for what we are doing with it or what the RV industry did with it. So, my idea was to bring it up to more modern engine design. Gathering resources and specifications, I didn't try to re-invent it, but to merely look at modern specifications and apply them. My previous try was with my Fleetwood motor home and a 460 Ford motor. I failed to achieve any improvements in fuel economy on that project but did feel I got better power performance. I failed because I simply did what everyone else does. I bought a lot of Bank Performance add ons. In fact, I bought 8 grand worth. But, I learned. The 460 is known to be a gas hog but, its a powerful motor and I take nothing away from Banks. Their products are outstanding. That 460 sounded like a powerhouse muscle car but, retained about 6- 7 mpg. 

This time I started with a completely different platform. An Airstream motor home. Its 4000 lbs lighter then my slab sided fiberglass Fleetwood. Weight makes a tremendous difference. I learned that from racing airplanes too. But, the Airstream is a lot more aerodynamic. Although I have no coefficient of drag data, I know its a lot slicker then my Flat Fleetwood and with the big weight advantage, that helps. I dont have data to support it but, my 454 even though purpose built has no where near the power that Banks equipped 460 Ford had. In fact, 80 mph was easy in the Fleetwood (crazy to do it but I tried a time or two) and it could keep up with the run of the mill sedan on the freeway and pass trucks on any incline. The 454 will not do that. But, its not really built to run much over 3000 rpm and the target is really 2200 - 2500. 80 mph will not happen, its to far out of the power band.

As far as my OD transmission, I am building a 700R4 with stouter internals and clutches. My research makes me believe if built right, it will hold up and will be a free'er flowing trans with less parasitic power loss compared to the newer 4L80E which also requires a lot more electronics and a very expensive price. In my opnion, the Alison 6 speed is not an option. It would be a stretch to think I could use 5th gear but 6th gear would be far outside of my power band below my 2200 RPM and would lug the engine. Even with my 456 rear gears and 19.5 tires.

In my experience, there are no easy bolt on fixes for poor fuel economy. I spent 8 grand trying. Not to say a good tune up and such will not help a lot but also keep in mind this. If you have a older carb motor like my 454, dont think a free 'er flowing air cleaner like a K&N is going to help you. Its not. Unless you are going to re-jet your carb all you are going to do with a high flow air cleaner on a Carb engine is throw your A/F air fuel ratio way off. Good luck finding anyone who has the knowledge to know what jets you need for your Quad with a K&N. Its fine to do a K&N with fuel injection because you have a MAF and O2 sensors and a computer to reset your A/F. Stick with a clean stock air cleaner on your carb. You may find some racers that know how to re-jet your carb but, will that really apply to your 14,000 plus pound land yacht ?  

[Casey Chinook]

Hey Jim,

Thanks for putting me straight. If you have enough torque out of your engine and went with just a overdrive transmission and got those rpm's down to 2200 - 2500 at 60 - 65mph or so you would save a lot of fuel. Plus the engine would not work so hard.

When the torque comes on with the cam is why I was asking Jeff about his cam. It sounds like he did his due diligence in selecting his cam grind, plus he has high flow heads, and the exhaust to move all that air.

My 383 stroker in my old pick up was mated to a six speed trimec transmission. Even with the special grind cam I had to be over 1900 rpm's to even go into sixth gear on a flat road. That was about 75 to 80 mph. If I was going up hill , I needed to be at around 2500 rpm, to get into where the cam really came on in the torque curve and not lug the engine and have to down shift into 5th gear. So basically I just used 5th gear on the freeway. I put the six speed viper transmission in because you don't see any older pick ups with six speeds manuals. There is no explanation why car/truck guys do the things they do. Guess that's why I now have an old RV. Can't explain that, except I think the old RV's and old trailers are cool.

 RV's are lot heavier, and my point is that you have to be careful not to add more gears then the cam /engine/weight/ rear end gear ratio can handle.

 

[Jim Stoltz]

Casey I know your comment was for jeff york, mine was too. I just wanted to provide an MPG update. Seems to have stabilized in the high-4s.

I'd be curious as to what trans Jeff is considering. It's always easier if someone hoes the same ground ahead of you :)

[Jim Stoltz]

My RPMs are 3,000 on the nose at 55 MPH. Around 3,200-3,300 at 65. I don't like to push it any faster than that. I prefer 55 but that's dangerously slow in some 65 MPH zones. I'd like to move to an OD trans one day, preferably an Allison 6-speed. It will bolt right up. The driveshaft needs shortened and a custom cross member built, but it's been done lots of times.

Fill to fill on my Hershey trip I got 4.8 MPH with the generator running the entire 6 hours round trip. I had both air conditioners running full steam.

[Casey Chinook]

Amazing fuel improvement. As to engine wear, the SAE stated that 80% of engine wear is from cold starts after long periods of sitting. There was also another study done by one of the University's that said to was closer 90% wear from  engine starts after long periods of sitting.

There are prelubers on the market that allows you to prelube the engine prior to starting. If  I get my last major engine issue resolved I plan on looking into a pre luber. You can also use it to pump out your oil with a hose for fast oil changes while standing with a flick of a switch.

The balance and blueprint engine work you did will pay off in extended engine life without a doubt. As far as the cam, I did the same thing on a 383 stroker following a joint phone conversation with a guy from Comp Cams and the a engineer from AFR heads. I wanted the lower torque to come on because the engine was in a pick up and weighs more. It work out perfect. Horsepower is great, but torque is what moves things.

A couple questions, did you go with a roller cam on your rebuild? and also the cam grind you mentioned getting the lower torque to come on around 2200 rpm's should be right on the money I would think.

With that in mind, if you go to the overdrive transmission, what do think your rpm drop will be?