366 gmc milage questions?

captainkf · 01-05-2007, 12:37 PM

Hello all. I am seriously considering switching the bus over to regular gasoline. The trip to BC (very, very large mountain passes) loaded with moving stuff averaged 2-3 km's per litre running on propane. This is too crazy! I have had enough of not using my bus because the milage hurts so badly. So I am thinking of switching the bus over to run on regular gasoline.

edit: I did the math and came up with aprox 6.4 mpg (us gallons) based on 2.5 km's per litre. This does not seem so bad in relation to what others on here have posted. Is my math sideways? This is the site I used: http://convert.french-property.co.uk/

To do this I think I need to attach the tank, fuel pump, fuel lines, gas gauge, switch carbs and remove all the propane stuff. What I am missing? Can a 366 run off normal gas? This engine has aprox 15,000 km's on it since it was installed. It's new and I don't want to mess it up. Do I need to reset timing or anything else? Should I get a mechanical or electric fuel pump?

What milage are people getting with this engine? Is it worth it? I don't really want to go through the added expense of running a dual fuel engine.

Thanks in advance.

-Richard

hoser · 01-06-2007, 04:55 PM

My 1987 366 came from the factory running off gas, has a Holley carb.

captainkf · 01-08-2007, 12:00 PM

What kind of milage does it get? What kind of Holley carb?

-Richard

captainkf · 01-29-2007, 10:29 PM

So can anyone make a suggestion about increasing the MPG I am getting? I keep reading about people able to get 9 - 12 mpg and it is driving me crazy

.

I have a gmc tranny (i think) with 9r22 tires. Is it worth switching to dual fuel and running gasoline, or getting larger tires, or changing the rear gear ratio, or getting a 2 spd rear end, or building a spoiler on the front? What have you all found that made a substantial difference?

-Richard

the_experience03 · 01-30-2007, 01:35 AM

The 9-12 is most likely from a diesel rig....unless you're talking about some goofy rig like Steve's with his possessed 345. My 6.6 diesel only gets 8 mpg normally. I got 6.5 going across North Dakota. It doesn't matter which way you're going in North Dakota...the wind is always in your face.

KevinCoughlin · 02-05-2007, 12:25 PM

I've got a propane powered IHC with a 392. I'd kill to get over 6 mpg. I get 3.25 - so unless I find out what is seriously wrong I'm buying a diesel. At 6 mpg I would have a 400 mile range on one tank.

If you do go over to gasoline, you will need to change the timing. Propane LIKES to be advanced - it is a high octane fuel and can handle it. If you run "dual fuel" you will either need to set up compromise timing (set for gas and suffer for propane) or have a retarding ignition system that lets you switch on the fly. You can replace the throttle body of your propane mixer with a gas carb so that the propane mixer sits on top of it like a "hat".

If you run propane only and won't change - maybe you could try to increase your engine compression? Deck the heads, or add a turbo, and increase your power. It may still not yield huge gains - but it might be more fun, right?

captainkf · 02-05-2007, 07:20 PM

well, it's a brand new engine. We replaced the entire thing so I am reluctant to replace the heads. However I am intruiged by a turbo. Do you or anyone else on this forum have any info on turboing an engine like this? I don't have any experience with turbo's, but I like the idea of increased power under load or faster exceleration.

How much work and/or money would be required to put a diesel into my bus? Or would it be more usefull to get bigger tires and a different rear end?

-Richard

the_experience03 · 02-05-2007, 09:16 PM

Turbos can be confusing when you start reading about wastegates, blow off valves, etc but the layout really doesn't need to be that bad and I thikn you could do it relatively cheap and simply, but only if you're welling and able to do some fabrication. I'm not talking about horrible stuff, but you would likely have to make your own manifolds and run some intake plumbing, etc as I've yet to see a bolt on kit for the 392.

If you'd like to pursue the idea further, I'd be happy to direct you to some information.

You do need to decide which way you want to go before you start digging into things. I've seen many people start building a normally aspirated engine and drop lots of money to get the compression up to 14:1 so that they have an unbelievable normally aspirated engine....but they're men so it's not enough and end up going with forced induction. Unfortunately, a forced induction motor versus a high compression alky motor tend to be polar opposites in terms of setup (cam profile, compression ratio, etc).

I agree with the idea of getting the heads cut down a little as being a relatively simple means of getting some more power out of that propane engine. More power means less pedal and less pedal means you might get better mileage. Basically you'd be taking better advantage of the fuel you're already burning. Most machine shops can take a little off for cheap. You do need to do some math to figure out what your ratio will be at when you're done and to make sure you won't me mashing valves. A digital ignition like a DUI or MSD dizzy with a box will give you a nice hot spark for that high octane fuel and will give you some more adjustability for the timing.

Are you making what feels like sufficient power now? A drop in RPM's at cruise is always a winning way to get some mileage as long as you're making more power than you need anyway.

Bamboo Cowboy · 07-26-2009, 02:31 PM

Hi....

I have a 366 gasser and got 5.35 mpg over a 1500 mile trip. Engine uses about 1 quart per 400 miles! So either rings are worn and/or valve guides worn. This was a heavy haul, about 22,000 lbs AND also hauling a Subaru station wagon! That is a lot heavier than a bare bus.

Oh I forgot to mention I installed a shade deck on top of the bus (hurts gas milege... increases air drag).

I installed a vacuum guage and drove the entire trip trying to stay above 6.5" mercury. That is where the power valve in the carb opens, and you lose gas mileage once it opens and richens the mixture over that of the jetting. And never turned over 3800 rpm.

Of course, with this very heavy rig, I could only maintain 6.5+ inches of vacuum on flat roads or declines. Any uphill grade at all and whoops, you are into the power valve.

By the way, I added cold air scoops feeding into the air cleaner for the trip.

I plan on doing a compression check someday. A fresh engine should be good for about 20% torque and mileage improvement, if the current engine is worn out.

Russell · 07-27-2009, 07:13 PM

I havent really taken my 366 G.M.C. 60 pass bus on a serious road or mileage run yet, its got a non lock'in converter Allison trasnmission , Holley carb 10.20 tires single speed rear gears. I'm wanting a two speed rear end and multiport E.F.I. and a vacume gauge to monitor the engine with, along with a tachometer. Ive just transplanted T.B.I. into my 73 chevy 1/2 ton pick-up, after driving it for a week I gave every carb. in my shop away, and I had alot of Q-jets and Holleys. Im thinkin I will get me single plane manifold 8 injectors a computer and start building. And then again ai mite find a bolt on system and turn the key, ether way I'm finished with carbs. It could cost a bit doin it that way but its best way Ive found to stay away from the pump, You can spend your money there are you can put it in your tank and burn it. I wanna drive my skoolie. May the farce be with you . Russell

the_experience03 · 07-27-2009, 07:38 PM

http://www.bgsoflex.com/megasquirt.html

Russell · 07-28-2009, 09:25 PM

Thank you Mr. Eexperience thats what I'm talk'n about, engine managment system , the 21st century. Russell

the_experience03 · 07-28-2009, 10:18 PM

Just be ready for some head scratching frustration and a true sense of accomplishment eventually.

Will · 06-28-2010, 08:45 PM

High compression gasoline , turbocharger gasoline, schoolbus--not good bed fellows.

Mostly it's about duty cycle. A pickup might take 50hp to push it down the road at a given speed and a bus might take 100hp. On hills or an any acceleration you are going to see 100%--sometimes for several minutes. A pickup might need only 40% on the same hill. Going across Wyoming in a bus into that wind, you might be at 80%+ for hours or 100%. It is designed to take it. The compression was lowered, the displacement is reduced (A 460 down to a 470 or a 454 down to a 366), the heads have reduced port and valve sizes to increase low rpm airspeed and improve low rpm cylinder filling. Due to the duty cycle, the exhaust valves are usually sodium filled to help take heat away from the head. The sodium turns to liquid when it gets warm and circulates heat up the stem. The cooling passages in the heads are generally larger, the water pump, radiator hoses and radiators are larger. Usually the distributor shaft is thicker because it drives a larger oil pump. There may be a mechanical governer built itto the distributor as well. The blocks usually have added webbing and the cranks are steel. I don't know if the 366 has all of these, but I've had a 361FT and a 413 truck engine and they were both like this.

It might be tempting to try and squeeze more out of the gas engines in these, but I wouldn't. If you increase the compression ratio, you may induce detonation that you won't notice in a bus. In a car or truck you drive around using 20% so if it has detonation, you are rarely at full power so it doesn't matter. And on a newer engine there is probably a knock sensor to retard the ignition. The best thing you can do with a bus motor is maintain it.

I think 6mpg is what those get. In a high load application they get 1/2 what a diesel gets. The difference is less in a low load application.

the_experience03 · 06-28-2010, 11:09 PM

The 366 has a few differences. It does have a steel crank and good rods in it, but they're not balanced well. It also is a tall deck allowing for an additional ring on the pistons which also have a thicker head and are obviously longer from crown to skirt. I don't know of any real specific differences with the distributor other than the length of the shaft.. The pushrods are longer to make up the height difference, but I don't know them to be larger diameter or thinner, both of which would make them stiffer so pushrod flex could be an issue with any real head work. The water pumps are different so don't expect a parts store to stock them. A regular Chevy water pump could probably be made to work, but there is a reason they're different. The cooling system is enormous and the TD Chevy motors make use of two thermostats. Most parts stores will stock one... There is room to grow on these engines, just the same as the diesels so long as you keep things reasonable.

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