quote:

Originally posted by ski_dwn_it:

quote:

Originally posted by moparacer:
What's with the spin at about .5 on those runs. Looks like it dead hooks the tire and drives into a spin. When my car does that I am slow too. And there is a difference in trans pressure that shows up on the RPM too from what I see.

The car does that every time. It is the bias ply "getting up on the tire". They wrinkle up (first spike) and then spin about 3/4 of the turn (second hump). If you are not monitoring driveshaft or have a good video you would never catch it. Also there are two curves there overlayed if you look close. The problem does not effect the driveshaft which means the trans is not the problem. The chassis is doing the same thing - its a power issue. Hence the reason the rpms differ.

Another clue I found last night when again going thru the grid. I have an alert for a low crank sensor. But grid does not show when or how many times. I am rarely in the grid so if could be 6months old.

Right now I have a new crank sensor, and cable. Also ordered a new coil but not putting that in unless it is still acting up.

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Originally posted by team:
Do the slower runs typically happen when the car is warmer/more heat soaked, or when you are hot lapping it?

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Originally posted by ski_dwn_it: The only odd thing is the rpms difference .

I have the track getting me some measurements to verify the beams at the end. Which most are around 5.5inches. I may also rig up a camera and scale system to see where my front shocks are at the end of the strip to very stripe taker and beam measurements.

quote:

In the nutshell he feels the car is tripping the beams with the wheels sometimes and other times the stripe taker.

quote:

Originally posted by Goob:
I had to remove the factory air dam under my front bumper. I'd stab the brakes and be .02 under and a couple of MPH off when I know I killed at least 5.

Cost me $10K at Beech Bend.....that's my story and I'm sticking to it. Everything was rolling my way that day.

quote:

Originally posted by markemark:

quote:

Originally posted by ski_dwn_it: The only odd thing is the rpms difference .

I have the track getting me some measurements to verify the beams at the end. Which most are around 5.5inches. I may also rig up a camera and scale system to see where my front shocks are at the end of the strip to very stripe taker and beam measurements.

What’s the difference in rpm between the two graphs at 1 second into the run of this pic?

Consider just removing the stripe taker and leave the front wheels break the beams…. most consistent if front bodywork is taller than beams.

quote:

Originally posted by B KING:

quote:

Originally posted by Goob:
I had to remove the factory air dam under my front bumper. I'd stab the brakes and be .02 under and a couple of MPH off when I know I killed at least 5.

Cost me $10K at Beech Bend.....that's my story and I'm sticking to it. Everything was rolling my way that day.

I rip the throttle instead of using the brakes!

I have a 2nd Gen Camaro & it has approximately 31" of beak/bill. While I did have a stripe taker & used it/not used it very well. It was an added advantage when used properly or maybe it was luck.

2BKING

quote:

Originally posted by Lenny5160:
So your car was tripping the 594' beam with the stripe taker but not the finish line beam? And this has played out the same way at multiple tracks?

I'm skeptical that it's been solved, but glad your car was great this weekend!

quote:

Originally posted by B KING:
FYI, you aren't legal at 2.75" according to NHRA. I bring this up because someone protested my stripe taker & tech checked me out; I was legal.

2BKING

quote:

Originally posted by ski_dwn_it:

quote:

Originally posted by B KING:
FYI, you aren't legal at 2.75" according to NHRA. I bring this up because someone protested my stripe taker & tech checked me out; I was legal.

2BKING

yes - cars are also supposed to have a diaper and million other safety things that many do not have.

quote:

Originally posted by ski_dwn_it:

quote:

Originally posted by Lenny5160:
So your car was tripping the 594' beam with the stripe taker but not the finish line beam? And this has played out the same way at multiple tracks?

I'm skeptical that it's been solved, but glad your car was great this weekend!

Yes sir. Only change was the 1" to the stripe taker. I have had it happen at other tracks. I have seen it in the 330ft vary also run to run where other parts of the track are dead on (even end ET within few thousands). The staff there this weekend said they set the height to 5.125" - qualified with as best as we can. Things like dips in the track and other factors obviously can effect things. I originally made the stripe taker to be at the same height as the spoiler that is behind it, further back from the tip of the nose. The tip of the bumper is only 8inches off the ground. The spoiler was 3.5inches from the ground. So its very conceivable that under power the car is lifted more than 2inches missing the beams. And when off the gas, or on the brakes it is tripping the beams 28" sooner(distance from tip/front of stripe taker to tire). I went arounds asking and measuring dragsters fronts and they were all 2.5-3" off the ground. So I put mine at 2.75" - made many passes this weekend in right lane and it never didn't trip it or not have 120.XXMPH. Prior the 330ft on all the runs even the 116 were within few thousands. That was the big tell when I spoke to Biondo despite the rpm difference in the graphs - which I still can not explain. The 330ft were all again within a few thousands as were the 60ft suggesting the car is making the same power run to run. If the timing were retarded like I had originally thought it would be further off. Biondo said his trans am does the exact same thing when on the brakes - they just are not allowed stripe takers.

Here is the other thing that ties:

Using the standard 66-foot speed trap:

116 MPH = 66 ft in 0.3879 sec
120 MPH = 66 ft in 0.3750 sec
Difference = 0.01293 sec

At an average speed of about 118 MPH (≈173 ft/sec), the car travels:

173 ft/sec × 0.01293 sec ≈ 2.24 feet (26.9 inches)

So the answer is:

A change of about 2.2 feet (27 inches) in where the timing system "sees" the car would be required to make 116 MPH look like 120 MPH.

quote:

Originally posted by Lenny5160:

quote:

Originally posted by ski_dwn_it:

quote:

Originally posted by Lenny5160:
So your car was tripping the 594' beam with the stripe taker but not the finish line beam? And this has played out the same way at multiple tracks?

I'm skeptical that it's been solved, but glad your car was great this weekend!

Yes sir. Only change was the 1" to the stripe taker. I have had it happen at other tracks. I have seen it in the 330ft vary also run to run where other parts of the track are dead on (even end ET within few thousands). The staff there this weekend said they set the height to 5.125" - qualified with as best as we can. Things like dips in the track and other factors obviously can effect things. I originally made the stripe taker to be at the same height as the spoiler that is behind it, further back from the tip of the nose. The tip of the bumper is only 8inches off the ground. The spoiler was 3.5inches from the ground. So its very conceivable that under power the car is lifted more than 2inches missing the beams. And when off the gas, or on the brakes it is tripping the beams 28" sooner(distance from tip/front of stripe taker to tire). I went arounds asking and measuring dragsters fronts and they were all 2.5-3" off the ground. So I put mine at 2.75" - made many passes this weekend in right lane and it never didn't trip it or not have 120.XXMPH. Prior the 330ft on all the runs even the 116 were within few thousands. That was the big tell when I spoke to Biondo despite the rpm difference in the graphs - which I still can not explain. The 330ft were all again within a few thousands as were the 60ft suggesting the car is making the same power run to run. If the timing were retarded like I had originally thought it would be further off. Biondo said his trans am does the exact same thing when on the brakes - they just are not allowed stripe takers.

Here is the other thing that ties:

Using the standard 66-foot speed trap:

116 MPH = 66 ft in 0.3879 sec
120 MPH = 66 ft in 0.3750 sec
Difference = 0.01293 sec

At an average speed of about 118 MPH (≈173 ft/sec), the car travels:

173 ft/sec × 0.01293 sec ≈ 2.24 feet (26.9 inches)

So the answer is:

A change of about 2.2 feet (27 inches) in where the timing system "sees" the car would be required to make 116 MPH look like 120 MPH.

It seems odd that the stripe taker would always hit the 594' beam but sometimes miss the 660' beam, assuming that the beams are at exactly the same height. The attitude of the car wouldn't be changing at that point in the run if it was WOT all the way.

But the math does check out to 4 MPH at 28", as you said. It would be an amazing coincidence if some other performance difference worked out exactly the same as the difference between the stripe taker and the tire.