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Discussion in 'PSI Superchargers Tech Questions' started by partel, Feb 18, 2009.
How high should the sensors be?
Believe it or not there are international standards for dragstrips. Here's the part about photocells:
All photocells at the start line should be set so that at the centre of each lane the timing beam operates between 30 and 60 mm(1.18"-2.36") above the track surface. In cases where there is difficulty achieving this, the 60mm height should take priority.
Photocells for 60 foot time should be 250mm ±20 mm(9.8") above the track surface.
All other photocells should be 150mm ±20 mm(6") above the track surface. All interval increments and quarter-mile finish lines are measured from the guard beam.
I have a PDF file of these standards(originally written for European drag bikes) if anyone wants one. Just shoot me an email and I'll send you a copy.
Yes, I found it too, UEM rules. And I hope they are correct.
Trouble is, that our local system is Raceamerica:
Pg 4 gives #5040 for finish line sensor, which, as pg 17 shows, is low level, i.e. for front wheels, like stage, not body nose. Put a brick under them?
Don't have a NHRA rulebook handy, I hope someone can clear it up!
Thanks for that other link. Don't have a rulebook here either so I'm really still in the dark. I know we don't have the photocells at those heights at Cape
Breton Dragway - I think ours are all around 3" or so.
Partel; I believe the above info is copied from the NHRA books.
Before this change to a 6" number, 1. there were dragster guys with pivoting nose and a weak spring to pull the back down after the car slowed. 2. bumpy tracks would not even see the front tire (tyre) if it jumped over, with the low setting. 3. Billy Meyer had a platypus lip for a front spoiler on an early body that would blow down and drag on the ground to be sure to get the beam before the tire.
They just stopped all the questions of what was legal by raising the finishline beam. They left it up to the racer if he wanted a sleek layback nose, or if he really didn't mind losing by an inch, even though he was ahead by 3/4"
P.S. Have you ever noticed how ugly the front tip plates of some dragsters are today, they belong to those who know how to play the game!
Shouldn't all of them be a maximum of 75mm since that is the minimum height for the front of a car, from the very front to 300mm behind the centre of the front wheels? If the 60' timers are 250mm off the deck they'll be triggered by the body.
Bob, thanks a million! Unexpected gap of know-how for me!
I've always thought that the body clicks it, never checked the obvious. What's the point of limiting front overhang then? And how do you do photo finish otherwise, when Pro Stockers MOV is 0.00000