Author Topic: Fuel Usage (Read 6261 times)

Tbone07 · « **on:** December 13, 2013, 10:26:57 AM »

How much time are you guys getting out of a gallon of gas? And what size motor are you running? Type of riding?

Trying to gauge how long a stock fuel tank will last with my upcoming 350 Sphynx. With the local CRA Harescramble series lasting about an hour, wondering if i'll need to refuel. I don't want to set up a stopwatch and purposely run out of gas just to find out

F-Red · « **Reply #1 on:** December 13, 2013, 04:57:25 PM »

ESR 330, 38mm Airstryker, Sunoco 112. My fuel consumption is terrible. I haven't ran her low, (no reserve). I burn about 1/2 of a stock tank, in 45 min. blasting. :chargrined:

supernutt · « **Reply #2 on:** December 13, 2013, 05:27:30 PM »

Neil ported 310 on race gas trail riding with a big tank I can ride at least 4 hours. But it's definitely not sand dune riding....mostly forest fire service roads

Burns363R · « **Reply #3 on:** December 13, 2013, 10:54:04 PM »

CT 310 stock tank went 1.5 hrs XC racing. Riding hard. I switched to reserve on my last 12 min lap. There wasn't hardly anything left in the tank.
Stock 250 stock tank. 1 hour 20 min hit reserve on my way to the pits from the track. Probably lyrics cause I was on smooth ground. Aka no take slosh.

BDT 350 stock tank. Can't remember where the fuel was at but I did make 1 hour 20 min. Probably not much to spare. Fuel usage was close on all my engines.

Tbone07 · « **Reply #4 on:** December 14, 2013, 11:29:18 AM »

Looks like i'll definitely have to get the IMS 4.0 just to be safe

sameltoe · « **Reply #5 on:** December 14, 2013, 11:57:47 AM »

According to my buddies rzr we went 50 miles before needed to head back for fuel at the dunes.
340/40.5pwk

Quinnlt4 · « **Reply #6 on:** December 14, 2013, 01:02:35 PM »

Quote from: sameltoe;19880

According to my buddies rzr we went 50 miles before needed to head back for fuel at the dunes.
340/40.5pwk

Wow. I made it 47mi on michigan trails having to hit reserve to make it. Mild port 250cc with 38mm AS. Fast pace riding but not racing by any means. On the dunes I get about an hour of riding but that's a lot of WOT. Think I need to rejet....

supernutt · « **Reply #7 on:** December 15, 2013, 08:15:28 AM »

My non ported 250 with a 38mm v force and trx5 on premium actually used more fuel? Maybe because I had to run it harder due to much less power

Quinnlt4 · « **Reply #8 on:** December 15, 2013, 11:27:36 AM »

Wondering if I am running it harder at the dunes with the smaller displacement like you said.

Jerry Hall · « **Reply #9 on:** December 15, 2013, 12:35:40 PM »

Quote from: Tbone07;19810

How much time are you guys getting out of a gallon of gas? And what size motor are you running? Type of riding?

Trying to gauge how long a stock fuel tank will last with my upcoming 350 Sphynx. With the local CRA Harescramble series lasting about an hour, wondering if i'll need to refuel. I don't want to set up a stopwatch and purposely run out of gas just to find out

A two stroke with well developed pipes and ports will use about 400 ml of fuel for every HP produced in an hour. This is based upon an engine that has a BSFC of 280 to 300 gm/hp/hr and fuel with specific gravity of .700 gm/ml to .750 gm/ml

example:

A two stroke engine run for one hour producing 50 hp will consume the following amount of fuel:

(50 hp) x (400 ml/hp/hr) = 20,000 ml/hour

20.000 ml/hr = 20 liters/hr

20 liters per hour is approximately 5 gallons hour

This would be the maximum amount of fuel used if the engine was operated with it producing 50 hp. When you close the throttle fuel consumption is almost zero. Open the throttle ( let some horses out to run, you have to feed them) fuel consumption goes up.
As you can see the fuel mileage will vary with two riders with identical machines depending upon how hard you ride.

In the old days when we were using the 250Rs for desert racing, the 250Rs would get about 15 to 20 miles per gallon.

The big question is how much peak power does your engine produce and what is your average power being produced over the course of the race. If you do not have this accurate information it would be impossible to calculate your fuel consumption.

You need to pre-race the course to determine what size tank will be needed. If you just ride the course your fuel consumption will be low.

fast350r · « **Reply #10 on:** December 15, 2013, 12:45:52 PM »

Always very knowledgeable Jerry thanks

Pumashine · « **Reply #11 on:** December 15, 2013, 01:17:38 PM »

Quote from: fast350r;19930

Always very knowledgeable Jerry thanks

Another thanks from the site. I knew the answer had something to do with engine size. My riding groups run 250's while I have a 400. They only use a gallon at the same time I use 2.

RyanWsly · « **Reply #12 on:** December 15, 2013, 08:42:09 PM »

My fuel consumption usually stays somewhere around 3-3.5 gallons in 1.5hrs plus a lap. The displacement had less to do with how much it used, how they lay it out the track is the biggest deciding factor with what you are going to do. How open the woods are, how many field sections they add and how you ride the engine will be what you need to figure.

HAYESTRX250R · « **Reply #13 on:** December 15, 2013, 09:16:12 PM »

My 265 drinks roughly 1 gallon per hour during hard xc/trail type riding.

silverlake250r · « **Reply #14 on:** December 16, 2013, 03:36:07 PM »

Well Jerry, that makes complete sense. Say my 344 makes 55-60HP, aggressive dune riding I am on average producing a lot of of that power, lets say 50% to be conservative. That means my maximum usage per hour could be 6.3 gallons per hour at MAX hp, and 3.1 gallons at 50% power. And I am probably a bit rich, which should burn more. No wonder I can only make 3-4 aggressive laps around the dunes before feeling uncomfortable about how much fuel I have left (usually close to reserve). Realistically I could have to put it on reserve after only a half hour of very hard riding. Definitely switching to my 4 gal tank next year and not looking back.