Check out these graphs

Discussion on Data Loggers, how to read your logs, what to improve, etc.

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CHampshire
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Check out these graphs

#1 Post by CHampshire » Wed Nov 18, 2015 2:22 pm

I have been chasing 60 ft times in the car for a while and finally got frustrated enough to purchase a logger. Attached are screen shots. While the car 60 fts consistent it is slower than I feel it should be. We are just bracket racing, and the car is consistent when the track conditions are cool, but during the summer time not so much. I have a few ideas with what the logger is telling me. I believe it to be spinning the tire, hooking, spinning, and hooking. Also, looks like it spins on the shift.

I have tried the 4 link all over and have played with the shocks a lot also. While I was able to get the extension of the shock to increase as I loosened them up, the compression never went below 5/16 of an inch.

Some info on the car:
588 BBC
2600 Lbs with driver
6200 Stall converter
4.56 rear gear
1.80 ratio first gear power glide
15x15x33 stiff sidewall hoosiers
No nitrous or power adders.

Car went 8.13 @ 167 on this pass.

I am looking for some insight as to what the logger is telling me. I am new to this logger thing, and have some ideas of what I think, but am always open to hear others ideas.

Driveshaft Vs G-Force
https://www.dropbox.com/s/vd5vyqo2jrly0 ... F.jpg?dl=0

Engine Vs Driveshaft
https://www.dropbox.com/s/9073a7hww6yqn ... S.jpg?dl=0

Rear Shock Graph
https://www.dropbox.com/s/okcwi9x7jnp6f ... S.jpg?dl=0

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John_Heard
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Re: Check out these graphs

#2 Post by John_Heard » Thu Nov 19, 2015 3:52 pm

You can certainly see a little spin early in the graphs. What I can't really see from the data is what the front end is doing? Do you have a good video from that pass? It's quite possible part of the issue is front shock timing / travel.

If the shock travel data is scaled correctly, 1" of extension isn't really all that much. Course that could be just where it broke loose and on a dead hook run it extends further. I have a feeling it's still a bit tight for those conditions, when it rehooks it doesn't stretch them out much.

CHampshire
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Re: Check out these graphs

#3 Post by CHampshire » Thu Nov 19, 2015 4:39 pm

Hi John,

I didn't think of posting video of the run at the time, So here is a link to that:

https://www.dropbox.com/s/cb2r12qdm1e3p ... M.mov?dl=0

I don't have travel sensors on the struts at this time. I can tell you that they are set on full loose to try and get some weight transfer. I believe that the graphs are scaled correctly, but could be wrong as I am new to this data logging thing. There is no scaling option or anything that I have found inside the Racepak to change these values. I could be wrong though.

For the record, the car has never dead hooked and carried the tires any sizable distance. I have videos of it picking up and setting the front tire up and down a couple times before 60ft.

Rear shock settings were on 2 on comp and 3 on ext on this pass. 1 being loose and 10 being full stiff. The car has strange double adjustable on the rear and strange single adjustable for front struts.

Take a look at the video and let me know what you think.

Thanks for your time.

CHampshire
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Joined: Thu Oct 01, 2015 12:36 pm

Re: Check out these graphs

#4 Post by CHampshire » Thu Nov 19, 2015 5:57 pm

Slow motion of the same video I posted earlier. Things happen quick, always good to be able to slow them down and see what is really going on.

https://www.dropbox.com/s/rspf5c53ly5vu ... M.mov?dl=0

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Re: Check out these graphs

#5 Post by John_Heard » Thu Nov 19, 2015 10:39 pm

Can't really see the car unhook in that video, tires were wrinkled in every frame best I could tell. I would probably try and tighten the front shock extension up a bit, you're using all of the travel up very quickly. I'm not used to looking at those big slicks, but it really deforms the tire, have you tried more tire pressure? How much travel do you have in the front? Looks like maybe 2 to 2.5 inches or so?

I think the travel sensors must be in the ballpark, there's very little extension showing. With the shock as loose as you have it, perhaps ladder bar/4 link adjustment to put a bit more hit in it might help some.


Looks like you cut a nice light BTW :-)

I assume from your posts that you're wanting to dead hook this car, that's not usually the quickest way down the track on those tires but it may be the most repeatable. Another thing you might want to think about in regards to making it repeatable and dead hooking it is to take some starting line ratio out of it. You are 8.20, with that tall tire it may not be all that deep, but a 1.69 or 1.59 gear in that glide would calm it down some - probably hurt the ET though. This is one of those deals, do you want it fast or repeatable? They don't always go together.

CHampshire
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Re: Check out these graphs

#6 Post by CHampshire » Fri Nov 20, 2015 9:42 am

I have watched the rear tire in the video over and over and I initially thought the same thing as you. It sure does wrinkle the sidewalls a lot. I actually sent the video to Hoosier tire to get an opinion on if I need more pressure. The fellow out there said no. That said I have been up and down on pressures and have not really gotten anything different other than less wrinkle/more wrinkle. I think I am going to try a MT slick next year just to try something different. It has been recommended that MT is a better tire for my application so I will give it a shot and see.

I have the front struts full lose to try and get some weight transfer. I agree it happens quickly and could certainly slow it down with an adjustment to them. I don't know if that would help or hurt but I will give that a shot.

What I see on the video, and have been chasing for some time is, what looks to me like, a bounce in the rear of the car. Looks to me like the rear separates, sets the tire, the car pitch rotates, front comes up and it starts driving out. On its way out, it can't keep the shock compressed and back comes back up. Looks to me like it bounces twice.

When I look at the shock graph, my main concern is that the shocks only compress 5/16 of an inch. What is really odd to me is this is with the shock on 2. When I had comp tight earlier in the day (8) it compressed right to about 1/4 of an inch. I don't think the rear is going down far enough to stay planted? I imagine that the softer the shock setting the more it should compress. As I loosened extension, the shock extended farther, and that makes sense to me. Is the rear shock only going to compress so far?

I want it fast and consistent of course! :mrgreen: I am taking the 4.56 gear out this winter, and replacing with a 4.29. It rpms too high for me to be happy on the top end. I already have them setup in another center section so it will be just a time thing to swap them. While they are out I plan on checking the shocks and see if they adjust like they should. I have looked at them in the past and all has seemed ok.

At the end of the day, it's a bracket car and I need it to xerox time slips. That is number one priority. It sure would be nice to get that 7.999 time slip though 8-)

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Re: Check out these graphs

#7 Post by John_Heard » Fri Nov 20, 2015 11:03 am

With those huge sidewalls, seems like 99% of the rear movement is the sidewall deforming massively. It never "gets up on the tire" - which if you're trying to dead hook it won't. Whats the tire marks look like it leaves? do they look like it's wadding the tire? I'd bet it does.

How much pressure range have you tried? Maybe you haven't made a big enough move? Back to the tire marks, have you ever got it to not show it's wadding? Assuming that's what it looks like.

The gear change will calm it down a bit for sure. I'd like to see a stiffer sidewall myself.

CHampshire
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Re: Check out these graphs

#8 Post by CHampshire » Thu Dec 10, 2015 11:18 am

Hey John. Thanks for the reply. I honestly can't tell you what the tire tracks look like. That is a great idea to look at them, and something I never think about doing. I will have to do that in the spring.

Tire pressure has been between 5-8 lbs. It is getting a set of sticky Mickeys this spring to try another tire. I am looking into rear spring pressure as a possible culprit to this problem currently. I think that the rear of the car should be able to compress more than 5/16 of an inch. I think the spring is too stiff and not allowing the weight transfer to occur. This could be why the tire looks the way it does. All the suspension movement is being transferred to the tire instead of the shocks. That is my theory anyways!

I'm going to PRI tomorrow with the intent of talking to different shock and spring companies to try and get some answers. It's the off season, so now is the time to do the homework and get it sorted out.

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