Treeshaker
Nitro Member
- Joined
- Jul 31, 2006
- Messages
- 478
- Age
- 77
- Location
- South Carolina
The rev limiter portion of the timing box activates at around 2.5 seconds into the run. They were changed twice towards the end of last season and again right before the start of this season. The competitors that use the system have gotten the spec sheets of where they are set and when they activate.
Today's tune up is 8300 to 8500 rpm at the hit, pull the motor down to 7800 when the clutch locks up and right on back to just below the rev limiter. They have 52 lbs of boost at the hit and 60 in the lights. If a cylinder goes out the boost goes up approx 5 lbs per cylinder, i.e. 65 lbs w/1 out, 70 lbs w/2 out, etc. The key is to know when you are going to hit the magic rev limiter setting and have the fuel system adjust as quickly as the timing is being retarded. The units retard the timing in a set pattern so this can be calculated. Most times a dropped cylinder is from a lack of load for the amount of fuel (rich condition) but can also be caused by a lean condition. When a cylinder drops all other cylinders go leaner (extra boost) which will cause others to drop. There have been 3.80s ran with the rods in the pan at 800+ feet because of dropped cylinders and extra boost.
To accomplish all this, an accurate clutch curve has to be established. The teams use traction control devises in testing to see where their limits are and to come up with these clutch curves. Sometimes the teams forget to remove them after testing, but that is for another thread.
The bigger valve heads are helping the teams create higher speeds at the 1/8th mile where the 1.000' speeds actually come from. The cars only take about .8 of a second to go from the 660' to 1000' marks and the speed gained in that time is limited. And the faster they are going by the 1/8th mile the less time it takes to travel that distance which gives less time to accelerate for more speed.
One of the biggest races at an event is to the tire trailer to select the biggest tires available. They are sold on a first come basis at each event. Initially big tires ran at low pressures will stretch the most and give the fastest speeds at the top end. But they are the most likely to shake at the 60' to 100' mark. Used tires will be 3" to 5" bigger circumference than they were when new.
Unseen development is rampant in the nitro categories, and the more rules the more development that is needed giving the bigger teams more of an advantage.
I hope this gave some understanding of what is taking place and answered a few questions.
Today's tune up is 8300 to 8500 rpm at the hit, pull the motor down to 7800 when the clutch locks up and right on back to just below the rev limiter. They have 52 lbs of boost at the hit and 60 in the lights. If a cylinder goes out the boost goes up approx 5 lbs per cylinder, i.e. 65 lbs w/1 out, 70 lbs w/2 out, etc. The key is to know when you are going to hit the magic rev limiter setting and have the fuel system adjust as quickly as the timing is being retarded. The units retard the timing in a set pattern so this can be calculated. Most times a dropped cylinder is from a lack of load for the amount of fuel (rich condition) but can also be caused by a lean condition. When a cylinder drops all other cylinders go leaner (extra boost) which will cause others to drop. There have been 3.80s ran with the rods in the pan at 800+ feet because of dropped cylinders and extra boost.
To accomplish all this, an accurate clutch curve has to be established. The teams use traction control devises in testing to see where their limits are and to come up with these clutch curves. Sometimes the teams forget to remove them after testing, but that is for another thread.
The bigger valve heads are helping the teams create higher speeds at the 1/8th mile where the 1.000' speeds actually come from. The cars only take about .8 of a second to go from the 660' to 1000' marks and the speed gained in that time is limited. And the faster they are going by the 1/8th mile the less time it takes to travel that distance which gives less time to accelerate for more speed.
One of the biggest races at an event is to the tire trailer to select the biggest tires available. They are sold on a first come basis at each event. Initially big tires ran at low pressures will stretch the most and give the fastest speeds at the top end. But they are the most likely to shake at the 60' to 100' mark. Used tires will be 3" to 5" bigger circumference than they were when new.
Unseen development is rampant in the nitro categories, and the more rules the more development that is needed giving the bigger teams more of an advantage.
I hope this gave some understanding of what is taking place and answered a few questions.
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