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.

You ever try to take that out? When my car dead hooks, and doesn't do that its way quicker overall. My wheel speed looks like a nice smooth rainbow. When everything is right I can lay 2 or 3 runs over each other and they are identical.

Mines 2 oe 3 slower on 60 ft when I get that hump.

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

quote:

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?

Car is always at the same exact temp - trans, water, etc. I heat soak it first startup to 195* to ensure the water is out of the oil, drain it, and catch can stays water free the entire day. Maybe a tsp of oil.

I did change the crank trigger and cable to - grounding the cable inside the grid as that is something I did not originally do.

I also had a very good conversation with Peter Biondo over the weekend when he called to discuss various items. In the nutshell he feels the car is tripping the beams with the wheels sometimes and other times the stripe taker. His transam is built similar. Also the car is way to consistent up front and at 330 to be gaining and loosing that much ET/MPH. The only odd thing is the rpms difference otherwise I would have been looking here to start with.

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.

I did also rephase the rotor, which was not off much but did require a little adjustment because I used to run more launch retard. But again can not see what being the issue.

I will be at $20k event this weekend at same track as prior anomalies, so we will see.

Appreciate the suggestions and will let you know. Hopefully with big check as verification.

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:

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

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 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 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.

That is the million dollar question. That is what I am trying to figure out. Everything leans to a timing retard or change.

Yet the 330ft is nearly dead on...

I am loaded up and heading to a 20k event this weekend. I will keep you posted on if things improve, stay the same, etc. Same track.

Should also address that I can not simply take the stripe taker or spoiler off. The front of the car is only 9inches off the ground and part of the spoiler is molded into the "bumper". The soiler itself is only 3inches off the ground. My stripe taker expends that to the tip of the car. In theory the stripe taker always should hit the beam....again in theory whether on the brakes for the gas. peter has the same problem with his trans am, but they can not run stripe taker. Not running a stripe taker cost me 10k 15years ago. Since I have always had one. Just recently is started showing in the MPH - hence the concern.

This message has been edited. Last edited by: ski_dwn_it,

My opinion for what it is worth. Yes the front bumper could be a small part at finish line but I would not think THAT much. Can not see it making 4 MPH difference so that makes me think electrical or mechanical. So we look at data logger.

Your driveshaft looks same on those two runs but your engine RPM is higher especially at stall and before gear change. That makes me think stall converter. Driveshaft RPM basically is your MPH and that appears to be real close? Mathematical, if the driveshaft RPM is X at finish line and tire growth is same or very close the finish line MPH should be the same.

Right after release of transbrake looks like driveshaft (tire) RPM spikes up pretty high and drops back too much. Maybe some tire spin or lots of tire wrap up maybe too low air pressure. But after that it is same after the spike.

So that makes me wonder. This may be reaching but was the differences in SAME lane? We used to have a local track where MPH was about 5 MPH faster than any other tracks (both lanes)around but also the ET difference between Right and Left lane was significant and you had to dial for what lane you had or be sure to dump.
Does anyone else at that same track have similar problems? I have seen MPH, ET and reaction times different from left lane and right lanes. Even still 4 MPH is a lot and I am assuming you are having problems in both lanes.

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

Ripping the throttle in my car does nearly nothing to the ET, unless I start at about 450 feet.
Squeezing the brake pedal without lifting on the throttle has always been the best method, when I can make myself do it.
My low power junk isn't making ET at the finish line, it's just riding.

Ok problem solved.

Went to money race this weekend and first run 116mph in right lane where problem was last time there. Went to left lane and car went 120mph.

Came back and added 1 inch to stripe taker. Went back to right lane. Car went 120mph. Car was unreal all weekend long. Went to 5th round of 20k and lost a really close race. Sunday took both entries to 4th round and car never moved lane to lane, run over run more than .008sec. I lost two races by less than .002sec. bad when you loose with a 11pack, and 7pack. Sometimes it just isn't your day.

So in the nutshell the car was missing the beam by less than 1 inch. Why the rpm looks different on that one trace is beyond me. That is what threw me for a loop. Guess I have a backup crank trigger and second run crank trigger cable should I ever need one to plug in quick.

Thanks everyone for the help.

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!