Run Data Question - Engine RPM

Got out to the track for the first time this year last Wednesday for Test & Tune. Car ran good, no problems. Data for one of the runs is attached. On the graph, engine RPM is flat for about a second just after launch. Then climbs. I would expect to see some kind of RPM increase for the first second.
What do you think? Why is engine RPM flat for that time?
60 ft = 1.372, 1/8 mi = 6.312 et/107.68 MPH
93 Daytona, aprox 2600 lbs, Back-half, 4-link, 4.88 rear, Mild 377inch R3/W8, powerglide 1.76, 6K convertor

Looks like it spun a bit at the hit then dead hooked. Since it's flat at the same rpm it drops on the shift, I'd say the converter had it. Nothing weird about it. Just too much wheel speed for the motor to maintain.

As long as I'm flapping my gums, I'd offer this too. The motor looks like it pulls all the way up to 7200 or so where I'm guessing you're crossing the stripe. I'd loosen the converter, leave harder, and make the first shift at 7200 instead of 6500, or wherever you're shifting. I think it would go a good bit faster.

Just making that shift higher would help I think.

We have found shifting 500 RPM over Peak horsepower with a Glide has been the fastest way down the track.. tuning the flat spot out of first gear is very difficult with a Glide.. do you know where you make Peak power and Peak torque..

I don't have peak HP or Torque numbers. I was thinking about putting it on a dyno but dropped it in the car instead. Left at 4800, shifted at 6800. Is a 1st gear flat spot typical for cars with a glide? I'll try leaving/shifting a little higher & see what it does.

I can't see the data on my screen very well. Do you have a driveshaft speed sensor? If you have both engine rpm and driveshaft rpm then you can start to see what the transmission is doing.

I can't see it very well either. Damn glad I'm not the only one who is losing his vision.

I don't have an answer but I can tell you mine looks almost identical including the driveshaft rpm. Its a 727 3450 lbs runs 9.60's. Have not had time to investigate it - don't know if it started with the new carb or not. Have not looked at my old data yet.

If you only have A.2 magnet pick up on the drive shaft that can be a normal look at the hit.. it can appear as wheel speed.. do you have the grid.. we add timing in the first gear where the converter is trying pull the motor down.. don't be afraid to add three or four degrees of timing for the first one to two seconds of the Run.. also adding timing at shift recovery will help ET as well

Good idea. Perhaps upgrade to a 8 magnet setup on the driveshaft so you can get more resolution. I've seen some guys doing that are even more. There was also a setup where a guy was using the teeth on the parking brake in a 727 trans as a reluctor wheel for the driveshaft speed. That would provide some decent resolution since there are a lot of teeth on that wheel.

What is your stall on it.. looks low to me..
you need to be up in the revs to launch hard

Looking at the data it flashes to 5900 and drops to 6000 at the shift.. so the actual stall speed is probably 6000.. he can probably get a few hundred RPM more out of it with timing.. I'm betting the converter is too tight.. but without Dyno sheets we will never know

Here's a bigger pic.
It is a 6K stall convertor. Not a Grid, older MSD Digital 7. I think timing could be adjusted per gear. I'll have to look at that.
Drive shaft sensor only gets 2 pulses per rev.

The stall speed will drop for the same torque input as the vehicle starts moving. What you're seeing is normal. The converter torque multiplication changes as a function of the speed ratio of the converter (engine speed to turbine speed). The torque multiplication is dropping as it is no longer at true stall (0 turbine speed).

As Whitedart mentioned, adding timing will reduce the drop.

Looks to me like the car doesn't start to move until the 1 second mark. Is that correct? So the first second of this data log is you sitting on the line with the engine at 5000 rpm? And then at the one second mark you release the brake and the engine speed goes up and the driveshaft speed starts to go up? If that is case then I guess I don't see an issue.

That's it exactly. First second is the car staged with rev limit at 4800, brake releases & engine RPM goes to convertor stall of 6000 RPM, driveshaft RPM goes up. It ran good, 6.31, 6.34 & 6.35 1/8 mile times, all at 107.xx MPH.
I just expected to see engine RPM climb after the brake release rather than sit at stall speed for a second.

If you release the brake and still sit there you
have a conv problem if there is no delay in it

I'm interested in what the little dip in the driveshaft speed is from. If the tires are spinning it seems like driveshaft speed would go up but about 1/2 second after you launch the driveshaft speed have a dip in it.

What are the other lines on the display? There is one that is steady across the top and one that goes up at launch and then goes down the rest of the time.

The red line would be a g meter.. the line across the top is probably voltage it appears to be steady around 12 volts..

Pulled it right back to stall on the shift. It will go quicker upping the shift.

It looks like you have some tire spin between 1 second and two seconds on your chart, did you feel it?
Does your car do a wheelie leaving the starting line?

You can always Right-Click on every image on Moparts and let it show in its full resolution.
The Moparts forumsoftware downscales any images that are larger than a certain size.

Here is the full size link of the image;
https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/330588/filename/Run3.JPG

I think the dip shows the tires were spinning a little & then hooked. Track was not the best & it was hot & sunny.
The line at the top is battery voltage. The one that goes up at launch & then down is G-meter.

I did not feel it on that run. I did feel some spin on earlier runs. It just lifts the front tires a few inches at launch. Not a big wheelie.