Fox Let's Plot My Rear Suspension...with Track Results!
- Thread starter RangerJoe
- Start date
measure to the center of the crankshaft and add the dimension from the cam to the crank centerline, when i was plotting my car i found it via google.
Also, the numbers you are using for the control arms is the hypotenuse dimension(center to center), since it is angled, as far as i know, you need to use a straight dimension for that calculator, so you need to find the angle of the control arms and do some quick trig to get the number correct. At the time i found this out i said screw it, ill spend some time messing with the shocks cause these numbers arent going to get me a faster timeslip.
Also, the numbers you are using for the control arms is the hypotenuse dimension(center to center), since it is angled, as far as i know, you need to use a straight dimension for that calculator, so you need to find the angle of the control arms and do some quick trig to get the number correct. At the time i found this out i said screw it, ill spend some time messing with the shocks cause these numbers arent going to get me a faster timeslip.
you would need to use the Pythagorean theorem to get the straight length for accurate numbers, a^2+b^2=c^2.
http://www.yellowbullet.com/forum/showpost.php?p=2949358&postcount=73
http://www.yellowbullet.com/forum/showpost.php?p=2949358&postcount=73
Using the cam as your center of gravity is an estimate for the center of gravity, it's not exact. Knowing that, I looked at a bare block and saw that the drivers side, lower water pump bolt is pretty dang close to the same height as the center of the cam, so, i measured off that bolt.
Yes, you are not measuring the actually length of the arm, but the distance between the mounting points along a parallel line to the car (if this makes sense).
I dropped plumb bobs off the arm bolts and used framing squares to work out my measurements. There are several methods for finding these measurements. Seeing that the calculations are subjective to the measurements, Kevin suggested that I use MY numbers as a baseline and go from there. For example, you and I could put the exact same arms on, adjusted the exact same way; however, we may take our measurements different and get different calculations. It doesn't really matter, because the number is just that, a number. We will adjust from that point and move on. I just needed to get in the ballpark.
Joe
Just read a few pages of that thread. Very good info in there. It's a long thread...tells me more than a few know/and others want to "know". Lol I'm going to watch/read this thread and The YB one.
I agree with everything here with exception to the slicks. I'm a radial fan, but we all knew that lol
@84Ttop @90lxcoupe @A5literMan @Sharad and any others....
I finally got to the track for some test n tune.
2nd pass, suspension setup as last plotted. 16.5lbs in rear tires. Rear shocks at 3 clicks from full stiff, fronts 1 click past middle (front likes to rise and fall fast). Launching at 3900 off 2 step resulted in lots of spin but a new best of 1.709 60ft and 7.58 @ 91.66 ( old best was 7.86 with 1.83 60ft).
View: https://m.youtube.com/watch?v=s8EwU-l0KDw
Following the suggestion of my local former racer buddy, I decided to start adjusting ride height in the rear by 1/4" at a time, in the lowering fashion, so I went 1/4" lower, no other changes. Car responded with very small spin then bog and the 60ft slowed down.
View: https://m.youtube.com/watch?v=-tVhHbeBnCQ
We decided that was a good thing and went from a 3900 to a 4300 launch. Car spun bad and 60ft worsened.
View: https://m.youtube.com/watch?v=7wJlacTAjtk
By now it was getting late and the lines were getting long. I got a little hasty and decided to make a couple of changes that were probably not the best choice. Tire pressure went to 15, front shocks to 3 and launch back to 3900. Car bogged again but 60ft went back into the high 1.7x's.
View: https://m.youtube.com/watch?v=Qqbt1y11uSg
Overall, I am happy. I will have Friday at NMRA to play around a little more with it. Definetly don't have it figured out, but plotting definetly helped out. Went from a best of 1.83 to a 1.709. Went from spinning the tires at a 3500 launch to bogging at a 3900 launch.
Please, look at the videos and comment on what you think the car needs adjustment wise.
Joe
I finally got to the track for some test n tune.
2nd pass, suspension setup as last plotted. 16.5lbs in rear tires. Rear shocks at 3 clicks from full stiff, fronts 1 click past middle (front likes to rise and fall fast). Launching at 3900 off 2 step resulted in lots of spin but a new best of 1.709 60ft and 7.58 @ 91.66 ( old best was 7.86 with 1.83 60ft).
View: https://m.youtube.com/watch?v=s8EwU-l0KDw
Following the suggestion of my local former racer buddy, I decided to start adjusting ride height in the rear by 1/4" at a time, in the lowering fashion, so I went 1/4" lower, no other changes. Car responded with very small spin then bog and the 60ft slowed down.
View: https://m.youtube.com/watch?v=-tVhHbeBnCQ
We decided that was a good thing and went from a 3900 to a 4300 launch. Car spun bad and 60ft worsened.
View: https://m.youtube.com/watch?v=7wJlacTAjtk
By now it was getting late and the lines were getting long. I got a little hasty and decided to make a couple of changes that were probably not the best choice. Tire pressure went to 15, front shocks to 3 and launch back to 3900. Car bogged again but 60ft went back into the high 1.7x's.
View: https://m.youtube.com/watch?v=Qqbt1y11uSg
Overall, I am happy. I will have Friday at NMRA to play around a little more with it. Definetly don't have it figured out, but plotting definetly helped out. Went from a best of 1.83 to a 1.709. Went from spinning the tires at a 3500 launch to bogging at a 3900 launch.
Please, look at the videos and comment on what you think the car needs adjustment wise.
Joe
Good job! Car sounds awesome btw! I would try losen the front struts to full soft,with 15# pressure in tires,and use 4K rpm as start point. I wouldn't make full runs either at first. Just get through 330' mark. Make 2 hits like that. See if there is a difference between them. Your frontend action looks pretty quick/short to me.
I would then stiffen the fronts a click. Keep everything else the same. Make 2 hits and check results if it doesn't change much I would then look at increasing launch rpms. All you want to really do is check your 60ft times/330 splits at this point. If you start seeing a big change(+/-) you can adjust from there and look at other areas(like rear shock settings).
Just try to get a baseline and make small changes and work methodically (keep good records of everything you can). You want a slight wheel spin at hit and a linear "hook" factor. A bog/straight hook is the hardest thing on parts. Your first run(with slight spin and fastest 60ft) is the closest to a great run. I always hear of guys 60ing in the 1.3-1.4 range with our cars. I never got there. Best I did was 1.60's and it was with a slight spin/hook. I could hear the tire squeak slightly. I also broke an axle once(stock) with a 5-5200 rpm launch. Dead hook and boom! Buddy said I got a tiny amount of air under front tire lol before it broke.
Hopefully the other guys will chime in they have a lot of track/suspension experience. Also did you install that ARB yet?
I would then stiffen the fronts a click. Keep everything else the same. Make 2 hits and check results if it doesn't change much I would then look at increasing launch rpms. All you want to really do is check your 60ft times/330 splits at this point. If you start seeing a big change(+/-) you can adjust from there and look at other areas(like rear shock settings).
Just try to get a baseline and make small changes and work methodically (keep good records of everything you can). You want a slight wheel spin at hit and a linear "hook" factor. A bog/straight hook is the hardest thing on parts. Your first run(with slight spin and fastest 60ft) is the closest to a great run. I always hear of guys 60ing in the 1.3-1.4 range with our cars. I never got there. Best I did was 1.60's and it was with a slight spin/hook. I could hear the tire squeak slightly. I also broke an axle once(stock) with a 5-5200 rpm launch. Dead hook and boom! Buddy said I got a tiny amount of air under front tire lol before it broke.
Hopefully the other guys will chime in they have a lot of track/suspension experience. Also did you install that ARB yet?
Thanks for the advice. I think Friday I will hit it like it sits and see what it does on a different track. Then I will start adjusting front end travel like you said.
I haven't done the arb yet. My former racer buddy suggested waiting until I had the ride height determined before welding it in. That way I was sure not to run out of adjustment in the down links.
Joe
How much adjustment in the front shocks?
Same for rear shocks?
What tire are you using again?
If the car is bogging and not spinning you need to hit it harder. Any wheel spin at all will cost you time, the idea is to get it to dead hooks and keep enough power in it to move down the track!
Same for rear shocks?
What tire are you using again?
If the car is bogging and not spinning you need to hit it harder. Any wheel spin at all will cost you time, the idea is to get it to dead hooks and keep enough power in it to move down the track!
Strange 10 ways front and rear. The rears were pretty tight, on 7 (past wheel hop) and fronts were tight too at a 6 ( front end likes to jump and fall quickly). On the last run the fronts were lowered to 3 or 4, I believe 3, I will have to check again.
26X10.5 ET streets (really 8.5" tire).
Sounds like you may be thinking looser front end?
Joe
I would like to see you in the middle with the rear shocks and 2 clicks from full loose in the front as a starting point. I don't have a ton of input as far as air pressure with that particular tire. @srtthis may be best for the tire help?
Just to add some data to this thread, here's where I was at the end of last summer (and I had to go back through my logs and was surprised how consistent this was). My setup was:
Stock uppers
MM XD non-adjustable lowers
Stock K and arms
FRPP B-srpings
Strange singles
Stock rear sway bar, removed front
26x11.5 ET Street bias-plys (no tube) on a 15x8 prostar (normally at 15psi hot)
15x3 skinnys
McLeod super street pro clutch (dual friction)
powertrain should still be in my sig (haven't paid much attention to that in a while)- dyno'd 330hp/338tq
I finally settled on a shock setting of 7 rear, 3 front and was consistent 1.68 give or take a few .001's dumping the clutch at 6k with a best of 1.674. Settings at 5/5 gave 1.7, and full loose (which i only tried a couple times with lower rpm) was 1.72. The looser the settings, the more the car wanted to "pop" the front and fall right back down again, not the smooth weight transfer you want (a lot like your vids, but more violent with the higher launch rpm).
That combo was probably both over-tired and over-clutched, even with the 6k clutch dump it bogged real bad, but again was better with the shocks set tighter. If I hadn't blown it up on a missed 3rd-gear shift it would have gotten teamz uppers and springs and hunting for 1.5's with a softer front-end rise.
Remember, the more energy the car puts into squatting or fighting the suspension, the less it can put into actually moving forward. This is where either a re-located upper or lower come in, as they can change how much the rear wants to pivot and crush/collapse by geometry/leverage instead of relying on the shocks and springs to overpower the tendency of the stock locations to collapse the rear. IMO, this is even MORE important on a low-powered car that doesn't have the extra umph after the hit to keep it going.
Stock uppers
MM XD non-adjustable lowers
Stock K and arms
FRPP B-srpings
Strange singles
Stock rear sway bar, removed front
26x11.5 ET Street bias-plys (no tube) on a 15x8 prostar (normally at 15psi hot)
15x3 skinnys
McLeod super street pro clutch (dual friction)
powertrain should still be in my sig (haven't paid much attention to that in a while)- dyno'd 330hp/338tq
I finally settled on a shock setting of 7 rear, 3 front and was consistent 1.68 give or take a few .001's dumping the clutch at 6k with a best of 1.674. Settings at 5/5 gave 1.7, and full loose (which i only tried a couple times with lower rpm) was 1.72. The looser the settings, the more the car wanted to "pop" the front and fall right back down again, not the smooth weight transfer you want (a lot like your vids, but more violent with the higher launch rpm).
That combo was probably both over-tired and over-clutched, even with the 6k clutch dump it bogged real bad, but again was better with the shocks set tighter. If I hadn't blown it up on a missed 3rd-gear shift it would have gotten teamz uppers and springs and hunting for 1.5's with a softer front-end rise.
Remember, the more energy the car puts into squatting or fighting the suspension, the less it can put into actually moving forward. This is where either a re-located upper or lower come in, as they can change how much the rear wants to pivot and crush/collapse by geometry/leverage instead of relying on the shocks and springs to overpower the tendency of the stock locations to collapse the rear. IMO, this is even MORE important on a low-powered car that doesn't have the extra umph after the hit to keep it going.
I ended the night with the same shock settings. 7 rear and 3 front. This got the bog and 1.79 60ft. I left the car here and it went on the trailer. I think I will try it again, maybe with a 4100 pill and see where it is Friday.
The car 60ft'ed the best while slightly spinning the tires. Not an initial spin then a hook, but a constant slight spin, eventually hooking up several car lengths out.
It looks like the rear end bounces a little at the hit. Not sure why it's doing that. My thought is that the spin then bog is causing the car to nose over a bit. Not sure if that is a valid evaluation of what's occurring.
Joe
bentley429isBAC
10 Year Member
Not a 4 corner deal. I did weigh it, and weighed front to rear distribution. Weighed 3360 with me in it, i'm 260. I will have to look in my log and see distribution.
Joe
You are going to definitely want some wheel spin with a bias ply, if it dead hooks it is going to slow down. Wheelspeed will be your friend. If it were my car i would bump the 2 step to 5500, set the struts to full loose, shocks in the middle of the adjustment, and the tires at 16psi and see what it does. It seems like there is a consistency issue with the launch, what are you using to release the 2 step?
