Turbo Guys

[Custom Rx1]

Ok you might get this a lot but I can not get a stright answer.
I want to put in a turbo but I run only ride trail. I am looking for any one that knows what gas milage is like running pump gas at right boost for trail ridding. I have heard that it is like 10 to 12 MPG and than I hear it is better than stock gas MPG. So I am lost.
Thanks For all the help. Ryan

 

[BlueByYou2000]

It really depends on how much you are in the throttle. Very much like a stocker. I know this is vauge, but count on 8-13 MPG.

 

[lakercr]

Ok you might get this a lot but I can not get a stright answer.
I want to put in a turbo but I run only ride trail. I am looking for any one that knows what gas milage is like running pump gas at right boost for trail ridding. I have heard that it is like 10 to 12 MPG and than I hear it is better than stock gas MPG. So I am lost.
Thanks For all the help. Ryan

Ryan - it's a loaded question, but I'll try to help you out. Assume for this explanation that we're talking about a 'trail turbo' running on pump premium, and making 7-8 lbs of boost.

We'll get the big stuff clear right away - your engine is an air pump. Let's say a stock 1000cc Yamaha motor pumps about 165 CFM (cubic feet/minute). Obviously, you need to add a proportionate amount of fuel to this to maintain the correct A/F ratio, or desired BSFC (brake specific fuel consumption). A turbocharger is also an air pump. In this case, it is an air pump driven by a 150HP motor. At 8 lbs boost your pressure ratio would be:

PR = 14.7 + 8/14.7 = 1.54

Your new CFM would be:

1.54 x 165 = 254 CFM.

That's close to a 60% increase in airflow. To maintain the same A/F under boost, you will clearly need to add fuel. We could stop here and conclude that yes, turbos are much harder on fuel than the same motor naturally asperated. The reality is that you will spend very little time at your max. boost level. 8 lbs boost on a stock motor, stock gearing is somewhere around 130 real MPH. These are not trail speeds where I ride.

Most of the time you are trail riding, you will only be making a very small amount of boost, or might not be making any boost at all. Accelerate, and yes, you might see 8lbs on your gauge (turbos are load-sensing), but reach a steady-state again and the boost reading will immediately drop down.

For the purpose of this explanation, lets say that 8lbs boost = 220+ HP. You will need to add (a lot) of weight to your primary to keep off the rev limiter when under full boost. I've suggested that as a percentage, the amount of time you will spend at full boost is very small. This means that for a reasonable amount of the riding you do, the extra weight in your primary will keep your revs lower that they otherwise would be. Lower RPM = lower fuel consumption. Additionally, if you gear the sled up a bit you would again lower the engine RPM to maintain the same trail speed.

To sum it up, drive your (turbo) sled at moderate trail speeds, and you will see fuel consumption levels close to stock. Play with the throttle (you will, believe me) or poke it on some lakes along the way, and you'll need to find the pumps quicker than you did before. The other people that have been giving you feedback are both right. turbos can be close to stock MPG, or they can be a lot less, it all depends on conditions, and how it is driven.

Hope that helps.

 

[millstreet]

well said! bottom line - the more fun you have - the more fuel you will use
I've seen well under 10, but I enjoyed it!

 

[lakercr]

well said! bottom line - the more fun you have - the more fuel you will use
I've seen well under 10, but I enjoyed it!

Yeah, that about covers it. I run straight VP C16, so fuel economy isn't one of the things I monitor too closely.

Old adage, but very true - "Speed costs money, how fast do you want to go"?