8 second OEM 4 link drag race chassis setup
- Thread starter Alky V6
- Start date
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An interesting thing to note.
I came to the track with feathering of the tread on the slicks. The typical trick is to rotate the slicks side to side to remove the feathering, if the slicks are the type that can be rotated side to side. I was lazy and didn't do that this time around. Typically, I don't bother with it. Well, on one of the runs where the launch was more tamed down (13 psi launch boost control pressure) the tread ended up looking as it should. A fine grainy appearance. On the next run, I increased the launch boost control pressure 1/2 psi. When I returned to the pits, the feathering was back. I had read at some point that the feathering is caused by too hard of a launch. I was surprised that 1/2 psi difference was all it took to have the feathering reappear. I may go back down with the launch boost control pressure to see if the feathering goes away. I thought that was interesting.
I came to the track with feathering of the tread on the slicks. The typical trick is to rotate the slicks side to side to remove the feathering, if the slicks are the type that can be rotated side to side. I was lazy and didn't do that this time around. Typically, I don't bother with it. Well, on one of the runs where the launch was more tamed down (13 psi launch boost control pressure) the tread ended up looking as it should. A fine grainy appearance. On the next run, I increased the launch boost control pressure 1/2 psi. When I returned to the pits, the feathering was back. I had read at some point that the feathering is caused by too hard of a launch. I was surprised that 1/2 psi difference was all it took to have the feathering reappear. I may go back down with the launch boost control pressure to see if the feathering goes away. I thought that was interesting.
Here is a datalog of the best run of the weekend. Still a little rough here and there, but she's coming around. Notice how much boost is held back at the start of the run to maintain traction. The next run, I increased boost at the launch and through the 1-2 shift 1/2 psi and was rewarded with too much tire slippage.
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An interesting thing to note in the datalog above. If you remember some of the more recent datalogs, there was a blip of tire speed at the beginning of the launch. I think I asked Kevin at one point what he thought of it. He wasn't sure without having a video along side the datalog to study. Anyway,... that blip is gone with the latest suspension changes.
I've come to the conclusion that the spike in tire speed that I was getting at the launch prior to the latest major chassis changes was due to the amount of front suspension travel limit I was using. The front end rebound travel was limited to a small distance and as the car began to pitch rotate on the launch the front suspension topped out too soon and was upsetting the rear tire plant.
If you study the datalog, you will notice that there is a small glitch in the tire speed at the launch. That corresponds to a quick leaning condition of the a/f mixture. You can see the quick lean spike above 12.0:1 in the a/f ratio trace, just before the aux fueling is activated and the a/f ratio drops to a steady level for the remainer of the run. That will be fixed soon. That point is just before where the aux fueling system is activated. The activation of the aux fueling will be moved to a lower boost level to cover that leaning condition. It's mainly brought about by a limiting factor that I have with the EMS involving my aux fueling strategy.
At that particular map level, the fueling requirement of the engine spikes for a very short range. In the past fuel maps I used a 'wall' of fuel to cover that need.
I've also found that the fueling needs aren't dropping as quickly as I had thought after the 300kPa boost level. I've ramped in more fuel in that range for next time out with the car.
At that particular map level, the fueling requirement of the engine spikes for a very short range. In the past fuel maps I used a 'wall' of fuel to cover that need.
I've also found that the fueling needs aren't dropping as quickly as I had thought after the 300kPa boost level. I've ramped in more fuel in that range for next time out with the car.
I made one last small change to the corner preloads.
w/o driver and w/o ARB preload.
LF 27, RF 26.5
LR 29, RR 28.5
LRSH 9 15/16", RRSH 9 13/16"
w/driver, w/o ARB preload.
LF 26 1/2", RF 26 1/4"
LR 28 1/2", RR 28 1/2"
LRSH 9 11/16", RRSH 9 3/4"
1/16" (8 lbs) of spring preload on the LR corner. Zero ARB preload w/driver.
w/o driver and w/o ARB preload.
LF 27, RF 26.5
LR 29, RR 28.5
LRSH 9 15/16", RRSH 9 13/16"
w/driver, w/o ARB preload.
LF 26 1/2", RF 26 1/4"
LR 28 1/2", RR 28 1/2"
LRSH 9 11/16", RRSH 9 3/4"
1/16" (8 lbs) of spring preload on the LR corner. Zero ARB preload w/driver.
Squid4life
Well-Known Member
- Joined
- Jul 5, 2004
- Messages
- 6,275
That is exciting! You running it this weekend or next?
Next weekend.
I wasn't happy with the spring preload being on the LR. I lightened the LF corner a little (under 1/2 turn of the spring seat) and put a .150" shim under the RR spring.
New measurements w/driver.
LF 26 1/4", RF 26 1/4"
LR 28 1/2", RR 28 5/8"
LRSH 9 11/16", RRSH 9 5/8"
1/16" spring preload is now on the RR corner.
New measurements w/driver.
LF 26 1/4", RF 26 1/4"
LR 28 1/2", RR 28 5/8"
LRSH 9 11/16", RRSH 9 5/8"
1/16" spring preload is now on the RR corner.
It turns out I'm not the only person offsetting instant centers to control body roll and torque transfer to the rear tires. I was recently at another shop of a friend of mine and they had a PSCA Turbo Mustang on a rack, up in the air. Like any other motorhead I was curious of the machine and began poking around under the car looking for 'top secret' stuff. There was some interesting stuff, but guess what else I discovered? The car was using a stock angled four link rear suspension. Modified, of course. And, the instant centers were offset. The lower control arms, for one thing, were clearly not angled symmetrically. Amazing that this thread is probably the only place on the internet where you will find documentation of a practical application of this rear suspension technique.
Some interesting results yesterday.
First off, the wing. There was high wind at the track, so I'm not too sure how to judge the wing. The wind was a tail wind.
One run did give me the impression of being more stable, and I clocked a 124 mph. It's been awhile since I've clocked that level of mph. Especially with worn tires and a tired engine.
There is a point on the track where they stop spraying the track. It's just before the finish line. On the above run, the driveshaft rpm spiked pretty high at the tail end of the run. I assume it was when the car reached the end of the sprayed section of the track. I'll have to double check the datalog, but I believe the MAP had peaked to 305 kPa on that run. 305 kPa MAP never felt this stable in past runs at this track. I typically would have to limit myself to around 275-285 kPa MAP to keep the car from feeling like it was skating on ice.
First off, the wing. There was high wind at the track, so I'm not too sure how to judge the wing. The wind was a tail wind.
One run did give me the impression of being more stable, and I clocked a 124 mph. It's been awhile since I've clocked that level of mph. Especially with worn tires and a tired engine.
There is a point on the track where they stop spraying the track. It's just before the finish line. On the above run, the driveshaft rpm spiked pretty high at the tail end of the run. I assume it was when the car reached the end of the sprayed section of the track. I'll have to double check the datalog, but I believe the MAP had peaked to 305 kPa on that run. 305 kPa MAP never felt this stable in past runs at this track. I typically would have to limit myself to around 275-285 kPa MAP to keep the car from feeling like it was skating on ice.
The chassis setup.
There was a tendency to pull left. I'm going to pull the .150" shim from the RR and install a .100" shim. This will even out the left/right spring preload in the rear. I'll test this out before making any further changes.
If the car still wants to pull left, I'll reposition the right rear LCA axle mounting one position up. This will put it in the original mounting hole provided with the Moser axle housing. The left side will stay at one position up (very close to level) from the original mounting hole provided by Moser.
Changing the position of the right side LCA will tame down the static/dynamic anti-squat % on the right side, and will move the control arm closer to a level position.
There was a tendency to pull left. I'm going to pull the .150" shim from the RR and install a .100" shim. This will even out the left/right spring preload in the rear. I'll test this out before making any further changes.
If the car still wants to pull left, I'll reposition the right rear LCA axle mounting one position up. This will put it in the original mounting hole provided with the Moser axle housing. The left side will stay at one position up (very close to level) from the original mounting hole provided by Moser.
Changing the position of the right side LCA will tame down the static/dynamic anti-squat % on the right side, and will move the control arm closer to a level position.
On one of the runs, I had a brain fart and released on the 3rd amber (sportsman tree). Normally, that would be fine, but I had put in some delay into the delay box as part of the latest boost control strategy I've been playing with. I should have released on the first amber. Anyway, what that caused was a higher boost level for the launch. As soon as I released on the last amber, and the car didn't immediately launch, it struck me. "Ooops. The delay in the box. I should have released on the first amber. Oh well. This is going to be an interesting launch".
Bam. The car launched the front end, and it continued to climb. You know. One of those bumper scraper to be launches. I got out of it for a moment, the front end came down and bounced right back up. Got out of it again and right back in it.
The MAP was around 210 on that launch. In the past, that much MAP at the launch would just over power the tires and result in spinning and a flat launch. This time, the tires stuck! I like this instant center setting. :biggrin:
Bam. The car launched the front end, and it continued to climb. You know. One of those bumper scraper to be launches. I got out of it for a moment, the front end came down and bounced right back up. Got out of it again and right back in it.
The MAP was around 210 on that launch. In the past, that much MAP at the launch would just over power the tires and result in spinning and a flat launch. This time, the tires stuck! I like this instant center setting. :biggrin:
Squid4life
Well-Known Member
- Joined
- Jul 5, 2004
- Messages
- 6,275
Sounds like all good news to me! Anyone get video or pics of the launch? Feel free to hang on to the wing for some more testing, I am in no rush. I would love to see the run when you get it all ironed out launching straight and hard, holding a lot of boost, and being totally stable at the big end. Would make for a very fun ride, and a signature block change I am sure. 
Thanks, James. I'd like to do that. Next testing is in 3 weeks.Sounds like all good news to me! Anyone get video or pics of the launch? Feel free to hang on to the wing for some more testing, I am in no rush. I would love to see the run when you get it all ironed out launching straight and hard, holding a lot of boost, and being totally stable at the big end. Would make for a very fun ride, and a signature block change I am sure.
The present ICs;
Left side. At rest // +.200" rise // +.400" rise. +/- rise to simulate normal body torque roll on take off.
51.3; 10.6; 103.1 // 57.3; 11.0; 96.00 // 64.8; 11.6; 89.2
Right side. At rest // -.200" rise // -.400" rise. +/- rise to simulate normal body torque roll on take off.
54.4; 12.5; 115.2 // 49.7; 11.8; 119.6 // 45.7; 11.2; 124.2
With the possible future change to the right side IC, the new IC configuration would be;
Left side. At rest // +.200" rise // +.400" rise. +/- rise to simulate normal body torque roll on take off.
51.3; 10.6; 103.1 // 57.3; 11.0; 96.00 // 64.8; 11.6; 89.2
Right side. At rest // -.200" rise // -.400" rise. +/- rise to simulate normal body torque roll on take off.
59.9; 11.8; 98.3 // 54.0; 11.1; 103.7 // 49.1; 10.6; 109.2
This IC arrangement would be a more typical symmetrical IC setup. Very little static IC offsetting.
Notice how closely the left and right side specs nearly match as the body roll becomes .200".
Left side. At rest // +.200" rise // +.400" rise. +/- rise to simulate normal body torque roll on take off.
51.3; 10.6; 103.1 // 57.3; 11.0; 96.00 // 64.8; 11.6; 89.2
Right side. At rest // -.200" rise // -.400" rise. +/- rise to simulate normal body torque roll on take off.
54.4; 12.5; 115.2 // 49.7; 11.8; 119.6 // 45.7; 11.2; 124.2
With the possible future change to the right side IC, the new IC configuration would be;
Left side. At rest // +.200" rise // +.400" rise. +/- rise to simulate normal body torque roll on take off.
51.3; 10.6; 103.1 // 57.3; 11.0; 96.00 // 64.8; 11.6; 89.2
Right side. At rest // -.200" rise // -.400" rise. +/- rise to simulate normal body torque roll on take off.
59.9; 11.8; 98.3 // 54.0; 11.1; 103.7 // 49.1; 10.6; 109.2
This IC arrangement would be a more typical symmetrical IC setup. Very little static IC offsetting.
Notice how closely the left and right side specs nearly match as the body roll becomes .200".
Heck. I'm going to change the RR LCA axle mounting location now. I have a feeling that is where things are going, anyway.
Anyone else noticing that I'm slowly working back to being real close to the IC settings that I originally started out with? Looks like Moser may have had it right to begin with.
Anyone else noticing that I'm slowly working back to being real close to the IC settings that I originally started out with? Looks like Moser may have had it right to begin with.
I decided to put my suspension specs into a suspension analyzer. This particular suspension analyzer gives a 3 dimensional perspective of the angled 4 link arrangement of our cars (G bodies). I wasn't completely comfortable relying on the simple 2 dimensional 4 link analyzer. It had no way to take into consideration the angled 4 link arrangement, and how far all the different control arm mountings were from the vehicle centerline. This would become important for determining the amount of gain in IC location when the car torque rolled on launch. For instance, the lower control arm frame mounts would see more height position change during body roll than the upper control arm frame mounts which are located closer to the vehicle centerline.
To say the least, I was very surprised with the results. It turns out that there is very little change in IC length, IC height, and AS% during body roll. There is change, but the amount is really not even worth mentioning. A far cry from what the 2 dimensional 4 link analyzer was showing me.
The IC specs that I came up with, and these are still rough, are;
Left side: 55" length; 10.85" ht; 98.9 AS%
Right side: 50.6" length; 11.8" ht; 116.8 AS%
Total AS offset 17.9% (about 1" ht difference)
WFO!
To say the least, I was very surprised with the results. It turns out that there is very little change in IC length, IC height, and AS% during body roll. There is change, but the amount is really not even worth mentioning. A far cry from what the 2 dimensional 4 link analyzer was showing me.
The IC specs that I came up with, and these are still rough, are;
Left side: 55" length; 10.85" ht; 98.9 AS%
Right side: 50.6" length; 11.8" ht; 116.8 AS%
Total AS offset 17.9% (about 1" ht difference)
WFO!
