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OK. From my other post, you can see the raw footage I had to work with. I spliced together a bunch of scenes from the first 3 videos to make one shot from start to finish. Might not be 100% professional or time line accurate but this was my first attempt at movie editing.
As before, crank up the volume and enjoy!
See below for final edited version
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87 IROC-Z
All engine, no power adders! Bests: 9.348@144.71
Last edited by Stephen 87 IROC; 10-08-2007 at 03:04 PM.
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very cool stephen! i'm gonna half to figure out how to mount one in my car now. though a 12 second car isn't near as exciting to watch as a 9 second car. only thing cool i got going for me is my exhaust note is pretty cool:
(fourthgen in video had cutouts, that's the blat blat sound, yuck)
Since no one has gone into my other thread, here's the video from there Just a simple night run at the track going against the car I worked on all week and kept me from working on mine. Friend doing the filming missed the burnout grrr Click here
I did a capture and slow motion of my launch. It doesn't launch the way I want and my 60' times are not as good as they should be. I've posted this on a racing site to get comments on the launch from other racers.
That's almost what I'm thinking. I have another version on my own computer that's been brightened up to see the tire more. I played it in a loop at least 20 times. As soon as the transbrake releases, the tire rotates about a 1/4 of the way around before grabbing. It looks like the rim is being hammered down into the ground, squashing the tire. You can see the back end drop almost just before the front end starts to rise. As the tires start to dig in, you can see the back end starting to go back up and the front end comes down.
In the tower shot, I can see the tire almost going 180* around then digs in briefly enough to stop the rotation before starting to spin again. The MT on the side of the tire can clearly be seen stopping. It shows up on the replay tach as the rpms come down with the bog just after launch.
I think I need some double adjustable shocks so I can control the compression and rebound. I may also lower the rear ride height a bit. Tire pressure experimentation is also required. I was running 8 psi all weekend except the first run where I had 10 psi and a 1.50 60' time. It's possible I may have to drop the pressure down as low as 5 psi but didn't think I needed to with the stiff sidewall tires. Best traction is normally the most air you can get in the tires until the 60' times start to go back up.
Looks like it`s hitting the tires too hard almost or not enough air, I was thinking after watching it the first time it was squat but it`s all in the tire, maybe try moving the IC forward, shocks look good to me. All in all I think besides the porpusing it looks really good
some tire spin is normal right after dumping the brake, the rear suspension extends a bit and seems like it upsets the applecart, right after the rear extends it looks like it unloads the tires (the brighter movie might look diffrent this is really dark) what have you tried as fas as instant center and bar locations, maybe you should keep the video guy at the track and keep reviewing, also from the rear sometimes you can see things you dont from the front, if they will let you shoot from back there, you should probably get some shots from the rear before making changes, hey i got it put the cam under the car looking at the suspension and tire ..that would be something
Watching a lighter version over and over, I can really see the rear suspension unloading. When the transbrake releases, I can see the rims being driven into the ground. As everything starts to lift, it looks like the back wheels are trying to jump off the ground (wheel hop).
There's 3 things I need to adjust. Adjust the shocks to make sure the rebound is on the softest setting, More tire pressure. Move the IC back about 10" and up slightly.
I thought about mounting the camera under the car but I'm borrowing this one. Once I get my own, I'll try different shots. I'd like to mount it of the outside also somehow.
im not trying to be a pain, after you installed the anti roll bar did you equal out the upper bars? also i disagree, i would lengthen the ic about say 10 inches or so, tighten the rebound, and like you said add air pressure (not that many people read it but the rec. min is 8 psi anyway isnt it?) i know you have moved the ic around before where did you start out, and what direction did you go, adding the anti roll bar should have helped some of the things you were crutching with the 4 link, it looks like the front is extending ok but the problem is the rear , again just my opinion but thats why we race right, if everybody knew the best way we wouldnt need to prove it lol
Original IC was way back and up similar to my old ladder bar setting. I could feel the car hopping off the line with that setting.
Anti-roll made a big difference in how the car launches. It's always had poor 60' times with the 4-link. They've been close but never as good as the ladder bars and a 10.5 tire. Without the anti-roll, the car would twist and pull to the right. The anti-roll made both sides lift equally. Before I had to yank the steering to the left after launch to straighten out. Now I can just about let the steering wheel go it launches so straight. There is little to no preload on the upper right bar now.
According to my 4-link software, the car's CG is 60.6" out because of the nose heavy 60/40 weight ratio. With the bars in the current positions, the IC is 61.6" out and 4" up so it's just slightly ahead of the CG. I'm calculating the CG height off the camshaft being 19" high so the IC is 15" below that.
Using proper logic would say to move the IC out even more to put more lift under the nose heavy front end. I think I did try about 80" out once but wasn't happy with the results. That was also before I installed the anti-roll so maybe it was lifting fine but the pull to the right didn't make it feel right.
Reading through the 4-link software suggestions I just found this.
"Anti-squat values of 100% should accelerate the car without any pitch rotation (raising of the back or rear of the car). A higher AS hits the tires harder. IC ahead of the CG lift the front. IC behind the CG raise the rear." The software suggests a starting point of 43.2" which would be behind my CG and I know that isn't working.
From that bit of information, it looks like moving the IC forward would be the best suggestion. Keeping the IC high would hit the tires harder which I'm doing already at 34.2% anti-squat so move it forward and keep it low.
As for tire pressures, heavy cars don't normally like low tire pressure. Add in that I have stiff sidewall tires and don't use tubes and that adds another factor to what's the best tire pressure. Invest in the 32x14 radial slicks and you can run 25-30 psi.
Too bad all this information and video came right at the end of the season. Depending on the weather, I may get a bit more track time on Friday nights but that's about it until the track reopens in May/June.
yeah somewhere time gets away, are you lower bars parallel to the rockers at ride hight? and how high are they?
ladder bars are easier to tune (less choices) and usually work good on slick tracks, I do find it annoying when something thats supposed to make the car better actually makes it worse.
have you ever weighed the car on scales where you could raise it with a jack at one end to accurately calculate the cg? I dont know how people are around there but since the track is a road course maybe one of the road race guys would help you out with that, even if it costs a case of beer or something its worth it, i belive it would make the 4 link software more accurate then just an approximation, also dealing with a slick track is diffrent then a good track, seems all the tracks around here are slick lately lol, and i pull the fronts when nobody else is hooking good (luck me i got a good car for it) just another question, how are your front shocks set ( i have the same ones so you can just use turns from one end or the other) im thinking actually not hitting the tires as hard might work, im wondering if you have the front loose or tight cuse i might think about lowering the lower bar so it has more leverage and slow the front so it loads more progressive and stays loaded longer, just shootin ideas
Last edited by car_fixer; 10-10-2007 at 12:42 AM.
Reason: more info
Lower bars are down in the front. At the current setting, rear is 9-3/8" high and
front is 7.5".
Front struts are Koni SPA1 set on full soft.
I know the theory of lifting the front while the rear is on a scale to calculate CG height but have never got around to doing it. Changing the CG height only changes the anti-squat percentage number so I guess my AS numbers are only an approximate. Either way, keep the IC low below the AS line.
odd that thing should squat like hell like that...essentially the driving force (rear axle) pushes on the lower bars, with the front lower than the rear it will want to climb over , with the rear lower it will try and go under...ideally the bar should be straight on launch so that its not either pushing the rear out of the car or into the car. the axle pulls on the top bars createing the big triangle that more or less results in this instant center , their are so many opinions on how they should be set its not even fair lol after all this reading and stuff you really wont know why to do what lol
As we always tell people with LCA relocation brackets, the LCA should be parallel to the ground or down slightly in the rear. Of course this is also for a torque arm suspension but the theory is the same.
Putting the bottom bar in both lower holes puts the rear at 8-3/8" and the front at 7-1/2". Moving the front hole up one puts it at 8-1/2" which is now pointed upward slightly.
The amount of IC points are less and are more spaced apart forward of the CG leaving less choices or more drastic changes in IC position.
sounds like your on the right track with those lower bars. made sense to me that the LCA's on our stock cars need to be parrallel or the rear end lower than the front for best traction as the car will push the rear down with that setting.
hey wait i just reread something, and your front brackets are not in the right place,if i understand that correctly, at ride hight they should not be that different with the rod in the same hole???? unless you have really long bars that seems like alot to me, i think i will go to your page and check out the pics to see , by the way your site is pretty cool..
oh ok after reading the captions, you put them low on purpose...I should do a page on mine..its interesting to compare things in other cars and say hey i should , or im glad i did this, just need to talk the wife into borrowing the camera..........
I asked about where the best place to position the front mounts before I installed them. The best answer I could get was to have the bottom hole anywhere from 6-8" off the ground. There is no 100% correct answer but after installing the mounts, I can see where having them positioned differently can give much different IC points. It's almost like you need to plot out all the IC points before welding in the brackets. Since the holes in my brackets are 1" apart, you can basically go up or down in position 1" before you're back to where you started.
As for the angle of the rear bars at rest, it will really depend on what the rear suspension does when it launches which depends on where the IC is situated as well as spring and shock settings.
If the car launches and the back end rises up and the diff is being forced down, the shocks are extending. This bring the front mounts up higher. If the car launches and forces the chassis down compressing the shocks which raises the diff up higher into the body, the front mounts will drop lower when compared to the axle mounts.
The video isn't that great to see what's actually happening. I can see the tire being squashed as the rim is being driven into the pavement. The front end starts to come up and the rear is dropping however what it actually looks like it's doing is rotating around the axle. Watching the fender opening around the tire, it's hard to see if it's going up or down in relation to the tire. Assuming the body is being forced down compressing the springs, the front mounts are also going down. If the bars are already angled down at the front then this angle is increasing. I'm going to have to re-edit the launch shot. Enhance the image so it's not so dark and remove the zoom and pan left option.
Now on the other hand, the front end is rising. It goes up and when the front wheels come back down, the front end stays extended all the way down the track. See the picture in my sig going down the track. A huge amount of space under the front spoiler and over the front tires compared to when it's at rest. This means going down the track, the chassis is sitting high and if the lower bars and angled down at rest, they should be parallel while going down the track.
I've been told a probable cause to the rear unloading after the initial tire hit is the single adjustable shocks. They have 3 adjustments to control rebound (extension) and I need a double adjustable shock to also control compression.
Off to re-edit the launch video. Shouldn't take long.
yeah a quartering rear shot would be the best to see all of that together but would probably be in a shadow, worth a try though, i am going to try to set a tripod up in a few weeks at the track , and see how this one looks at launch, i havent seen it from the outside lol, guess you havent seen yours from outside yet either lol
Outside video shot shows more than you'll ever know if you only sit in the car. Just this one shot of the launch is telling me so much about what the car is doing.
yeah much better to see the wheel and tire, the back does come up kinda looks like two times...I also go down track with the front way extended, i am thinking about changeing to stiffer front springs to see if it rises less down track, and i am definitly adding limiters (might need to replace more than just collectors next time) I still think a longer ic with the lower bar straighter will help, and you may need to tighten the front shocks to control the rise (i ran out of adjustment lol) and definatly get double adjustable rear shocks, preferably external and easy to get to, you might want to recheck all bars to all equal lengths and start over with the notebook, sometimes its too easy to get tied up in what you already did to think straight (also why we make notes right?) there are alot of ways to do things on the same car to get the same results, just who can find it, for example if you watch jason line and gregg anderson side by side you will see that lines can picks the front up higher and carries it longer than anderson, but they usually run similar times and both have great 60 ft. times most of the time, i use those particular cars since they have the same engines and cars for the most part and they are team mates, obviously 2 ways to the same goal (except line is off on the tree this year and when the ield is within hundreths most of the time there isnt room for that)
also found this, i know everybody put their vid on your thread, but its to show mine going down track, and i might add that this isnt a dragstrip and its pretty slick http://www.youtube.com/watch?v=mrSKxuE-GO4
Last edited by car_fixer; 10-11-2007 at 12:01 AM.
Reason: vid
The second time the back comes up is when the tires unload. It takes a bit to see it happen. Once it comes back down, it stays down. It's like once the tires get their initial hit, they jump up before planting.
As much as I'd like to launch like a Super Stock car, it isn't necessary. With the times I'm running however, my 60' times don't reflect it. They should be in the 1.3x range but I'm losing it on the launch. It's not that the front end isn't coming up for weight transfer. It's the rear suspension unloading the tires making for a bad 60' time and causing the front to come back down too quickly.
Oh, and it's not so much that I should get double adjustable shocks but better single adjustable ones. Strange, Koni, QA1 all make a better multi position single action shock that's better than the Competition Engineering 3 way adjustable ones and don't need to be removed to be adjusted.
OK, going over the 4-link software looking for suggestions has come up with a different way of thinking.
The car is launching like it supposed to. Front end is coming up due to the initial force of launch which all cars will do however the back end is dropping. Why? My current IC is roughly directly below the CG. It should be lifting the whole car equally which it may just be doing however the front of the car is also coming up by itself without the extra lift. This is changing the weight balance and forces the back to drop.
The 4-link software suggests an IC point from 42-44" out. From previous reading and my CG being around 61" out, you would want the IC out more to lift the front more but that's wrong. Lifting the front more puts even more downforce on the back and it's already squatting too much. The only way you could do this would be to use dump truck springs and very stiff shocks so they wouldn't compress from all that downward force.
With the suggested 42-44" IC point, it forces the IC to lift the back of the car. Since the front end is already coming up on it's own, the IC point behind the CG will lift the back preventing all the front upward movement from slamming the back of the car down. The software offers no suggestions on IC height but low means it hits the tires softer. Usually a good suggestion for a transbrake or stick car.
Along with this IC setting, a soft setting on the shock extension will allow the rear to separate easier.
I wonder if I'll be able to get some track time this Friday night to check some different settings?
uh, have you checked your pinion angle? not that it is relative to this discussion but, every time you change things in the 4 link it will change, its not supposed to, but with the front bracket low the arc's no longer line up.
and the rear squats due to the angle at witch your lower bars are at, and so far this has gone full circle, and now you are disagreeing with yourself about what the software is saying, now slow down a bit, how did the 4 link instructions say to set it up originally? comp engineering is a little diffrent than most, they say higher in the front (slightly) most say lower bars parralel to the rocker panel when level, this will now be hard to do. you have alot of adjustment in the front to control it from going too high so stop worrying about that, with trick springs and spa1's a mild small block will leave with the front as high as yours , and you can put limiters on it to stop the front from extending, on a 4 link with level bars on bottom, the lowest one would be for low horsepower, and the more power th higher hole you would use, and then you could change the ic all you want and never have the pinion angle move, so now you will need to crutch that bracket being too low, you will find a place it works ok and probably never move it again, unless you change engines or horsepower dramatically, also too short of an ic will unload the rears quicker and too much anti squat will raise the back of the car down track and that usually makes the tires spin, so bring wrenches and try every thing you got if you lengthen the ic out slow the shocks down, mine do no not change much for the first 2 turns of the handle, on straight engine with a 355 i ran them at 2 1/4 with the 383 2 1/2 with nitrous, i had them on full stiff, and went too high, but i also have a fixed ic (way out there 65 inches) and a small block, a 55 to 60 inch ic should not be a problem if you make complimentry adjustments. ( slow the front down) mesure the ride hight from the rim to the fender in the back, raise the car up on stands with the rocker panel level, jack the rear up to ride hight (might need to weight rear of car, or lower spring preload) and look at the 4 link imagine lines extending from the bars where do they meet? if you want to use the program on the computer does it seem to match? if it doesnt why? if the car isnt doing what the computer says then following the computers advice might not work. if your ic is 18 inches under ground what does it do? the way your lower arms are there is no way the ic is up 4 inches just a straight line from the piviot points of the lower bar is under ground like 48 inches out so 61 its below ground not 4 inches up from anything straighten the lower bar so that the rear is only slightly higher than the front and then maybe its 4 inches up, i think the problem all along has been the location of the front bracket and the computer not knowing that computes it like is was correct, raise the rear ride hight 1 and 7/8 inches and then maybe it will work diffrently with the same bar settings, and throw those shocks out, get some konis or something better , double adjustable will come into play down track, now go to the garage and get busy , that way you can get some track time and see what happens, if you can raise the ride hight do that before anything else the shock brackets should allow you to do that without changeing preload
Watching a lighter version over and over, I can really see the rear suspension unloading. When the transbrake releases, I can see the rims being driven into the ground. As everything starts to lift, it looks like the back wheels are trying to jump off the ground (wheel hop).
There's 3 things I need to adjust. Adjust the shocks to make sure the rebound is on the softest setting, More tire pressure. Move the IC back about 10" and up slightly.
I thought about mounting the camera under the car but I'm borrowing this one. Once I get my own, I'll try different shots. I'd like to mount it of the outside also somehow.
Sounds like the tire may be rolling over itself, I have a pretty good pic of my TA doing that caought at just the right time when the M/T's were old.. Also let me know it was time for a stiff sidewall.. That was running 13 psi..
That jester TQ arm just hammers the tires though, just as IHI noticed with his.
Steven , I watched your last vidieo several times. The car is deffinately unloading the tires. What do you have your pinion angle set at? The bottom bars should not be lower in the front. I would either raise the front of the car or lower the rear for starters. You would probably benefit from a stiff sidewall tire too. I was very lucky on the setup of my Grand Am. It weighs 2840 lbs with my fat butt in it. I cut 1.39 1.40 60s and run 6.70s with it. I run a 14.5 32 Hoosier stiff wall tire. I also believe you are hitting the tire too hard, smashing it. More tire pressure with cause it to unload the tire quicker in my opinion. There is a very good book on the market called door slammers. I don't remember the author right now, but he goes through everything in it. I studdy it in the off season. My son did some vidieo of my car last weekend, I was fighting tire spin for the last few weeks. Lack of track prep and very old tires were the cause. Also built my son a 4th gen bird with a 406 Pontiac over the summer. Only got to make 1 pass in it, but it left real good. Had so much bump steer in it, was dangerious to drive. I'd try and find the book. Good luck this winter.
I just watched your clip about 20 more times. I believe you either have too much antisquat or leaving too far from the converter flash point. If you are leaving more than about 500 rpm from the flash point , it could cause that. I would move the ic closer to the front and , go as close to the flash point as possible on the launch. I fought the same problem a few years ago on a 2nd gen bird. But the car wasn't mine and I couldn't cut it to make work. Too much rear seperation will cause tire spin in the first 10 ft after launch.
Just a simple night run at the track going against the car I worked on all week and kept me from working on mine. Friend doing the filming missed the burnout grrr 
