With the big race coming up soon and so many teams that may not have any experience with this race I thought that a thread offering some of the hard learned lessons from the more experienced people might be in order. Any and all are encouraged share or ask questions. Disclaimer - there is always more than one way to do it. If your way is better then go with that.
As for me - our team has been in 5 V2R's. Two in UTV's and three in 7200 including Vegas 2 reno the long way in 2009. To be honest we have had our struggles with this race but we always learned a lot and had a great time doing it.
First tip - beware of vapor lock !!!
Because of the altitude and temperatures encountered at this race the likelihood of vapor lock is much greater here than any other BITD race. If you are not proactive in setting up your fuel system you will probably suffer from it. Racers that have never had a problem with it ever before will see it here and do not let anybody tell you that vapor lock only affects carburetors not fuel injection. that is just not true.
The simple explanation of what causes vapor lock is the reduced atmospheric pressure due to the altitude and temperature causes the fuel to boil at a lower temperature than normal, just like water. Under race conditions if the fuel in the fuel line or fuel rail reaches that temp then the boiling will stop the fuel from going to the engine and you are stopped until it cools down. Usually watching all the guys you just passed in the last 100 miles go by.
So what can we do about it?
A careful examination of your entire fuel system with the thought of trying to reduce the transfer of heat to your fuel is crucial. This may entail rerouting fuel lines, the use of high tech insulation designed for this and even fuel coolers.
The design of your fuel system also plays a part. Return systems (the excess fuel that your engine does not burn is returned to the tank) are generally better because the fuel does not have as much time to sit there and preheat prior to being used. Return systems if not factory do require a fuel pressure regulator and some plumbing but overall it is a better setup. Even a factory return system would benefit from a good quality regulator for consistent fuel pressure.
The down side to the return system is that as it recirculates the unused fuel it returns to the tank a little warmer each time until the fuel is nearing its boiling point just prior to being sent to the engine. Thats why once you get a vapor lock the next one will be much sooner. We have had the truck come into the pit with the fuel cell hot enough to be uncomfortable to the touch.
So if after you have done everything you can to prevent vapor lock and you are still concerned or if you have a problem what else can you do?
Thermal mass- The fuel itself is the mass so by choosing what pit to fuel at you introduce cool fuel to the entire system and ward off the potential of vapor lock at the times that are most likely to produce it. See there is more to pit strategy than just range.
The first time I saw this was some Trophy truck teams stopping for fuel at pit 2 Bonnie Claire that is less than 60 miles into the race. When I asked about it they said they were just changing their pit timing as to be fueling at less crowded pits but then I saw that they were only fueling from dump cans and the cans were sitting in bins of ice. It took me a little while but I figured it out.
Our last line of defense was a small Co2 bottle but you need to be careful about very cold on very hot.
Some people believe in using avgas because it is formulated to raise the boiling point for aircraft use but in my experience it is not a good race fuel as it was designed for a completely opposite set of parameters (constant and low RPM) and the vehicle needs to be retuned for it.
I was inspired by badassmav to share things that could help others.
Tim
hope it was not boring.
more tips to come
As for me - our team has been in 5 V2R's. Two in UTV's and three in 7200 including Vegas 2 reno the long way in 2009. To be honest we have had our struggles with this race but we always learned a lot and had a great time doing it.
First tip - beware of vapor lock !!!
Because of the altitude and temperatures encountered at this race the likelihood of vapor lock is much greater here than any other BITD race. If you are not proactive in setting up your fuel system you will probably suffer from it. Racers that have never had a problem with it ever before will see it here and do not let anybody tell you that vapor lock only affects carburetors not fuel injection. that is just not true.
The simple explanation of what causes vapor lock is the reduced atmospheric pressure due to the altitude and temperature causes the fuel to boil at a lower temperature than normal, just like water. Under race conditions if the fuel in the fuel line or fuel rail reaches that temp then the boiling will stop the fuel from going to the engine and you are stopped until it cools down. Usually watching all the guys you just passed in the last 100 miles go by.
So what can we do about it?
A careful examination of your entire fuel system with the thought of trying to reduce the transfer of heat to your fuel is crucial. This may entail rerouting fuel lines, the use of high tech insulation designed for this and even fuel coolers.
The design of your fuel system also plays a part. Return systems (the excess fuel that your engine does not burn is returned to the tank) are generally better because the fuel does not have as much time to sit there and preheat prior to being used. Return systems if not factory do require a fuel pressure regulator and some plumbing but overall it is a better setup. Even a factory return system would benefit from a good quality regulator for consistent fuel pressure.
The down side to the return system is that as it recirculates the unused fuel it returns to the tank a little warmer each time until the fuel is nearing its boiling point just prior to being sent to the engine. Thats why once you get a vapor lock the next one will be much sooner. We have had the truck come into the pit with the fuel cell hot enough to be uncomfortable to the touch.
So if after you have done everything you can to prevent vapor lock and you are still concerned or if you have a problem what else can you do?
Thermal mass- The fuel itself is the mass so by choosing what pit to fuel at you introduce cool fuel to the entire system and ward off the potential of vapor lock at the times that are most likely to produce it. See there is more to pit strategy than just range.
The first time I saw this was some Trophy truck teams stopping for fuel at pit 2 Bonnie Claire that is less than 60 miles into the race. When I asked about it they said they were just changing their pit timing as to be fueling at less crowded pits but then I saw that they were only fueling from dump cans and the cans were sitting in bins of ice. It took me a little while but I figured it out.
Our last line of defense was a small Co2 bottle but you need to be careful about very cold on very hot.
Some people believe in using avgas because it is formulated to raise the boiling point for aircraft use but in my experience it is not a good race fuel as it was designed for a completely opposite set of parameters (constant and low RPM) and the vehicle needs to be retuned for it.
I was inspired by badassmav to share things that could help others.
Tim
hope it was not boring.
more tips to come
! Tell me about it. The ambient temp was already 110* to start with, so there isn't much room for poor fuel plumbing layout/design. It was 18-22 minutes of down time each time it vapor locked, before it cooled down enough to get going again. By the time we lost the motor around RM 400, we vapor locked no less than 4 times.
