BUILD THREAD 86 GP 2+2~Blown 6.0
- Thread starter 81cutlass
- Start date
Pretty much.
I took a mechanisms design class last year where we learned all of the math behind (any beyond) linkages so I am oddly informed on this topic...
Instant center is a generic term for the axis of pivot of a multi-bar mechanism at any specific point. Basically a 4 link G body rear end and almost any double wishbone front suspension is a 4-bar mechanism. Instant center turns 4-bar mechanisms into single-bar mechanisms. Visually it's a simplification to more easily study a suspension's movement. Think turning a G body front suspension into 60's-90's truck Ford twin-I beam front suspension. A Ford I beam always has the same instant center (think axis of rotation) because it's one bar. A 4 bar, double wishbone or 4 link rear has a complex curve for it's instant center, roll center, ect. as it moves through it's range of motion (suspension travel)
So short version is yes, the instant center of a rear is the same thing as the roll-center for your front suspension.
Honestly the baseline suspensions calculator is almost too basic and I wish it simulated suspension travel so you could see how the instant center changes as you go through suspension travel. I have a program we used in class that I could set up to do that so I am thinking of using it.
That would have helped significantly!
The inclination of that axis against the CG axis will tell you a lot about how the car will handle, but as you pointed out it changes as the suspension does its thing.
I can't imagine doing the job without that tool. You've got a lot of ingenuity.
Ingenuity is just another way to say too poor of a planner to order the tool, too impatient to wait, and too stubborn to buy it in the first place
I was away for Easter so I spent some time sitting on the couch with my laptop looking up tune things. I have 3 main problems I wanted to solve
1. My cruise doesn't work. It used to! When I had my 01 PCM I found an operating system on a Firebird with a t56 that I could swap all the t56 related info into the 4l60e sierra tune. My issue is when I went with my 02 Tahoe flex fuel enabled PCM I lost cruise. I found the PCM does an internal check where it looks at the engine RPM vs the VSS and if it's OK it allows cruise. I assume that's in case the vehicle is on ice, the trans is going out, or some safety related thing. I found out some people have the issue when they try swap the 1st gear planetary with a lower numerical ratio and their cruise won't work in 1st gear anymore.
The solution is either find a t56 tune with an OS# that can plug into the 02 Tahoe PCM (which doesn't exist, there is no t56 data that you can stick into a P01 flex PCM at this juncture) or change the gear ratios in a 60e tune to make it THINK it is a t56. Thats what I want to do. I would basically take 1-4th on the 60e tune and make it 3-6 t56 ratios.
The table convenient exists in this random F body tune
But my luck, look at my tune, the damn thing doesn't exist!!!
I at least found my issue. I have a request out to HPtuners. They replied back with the basic tech support stuff and said make sure you have it in advanced view (which it is), make sure you have the most up to date version (it is) and to do a debug scan and send it to them. I know they are doing their diligence for people that have simple issues, but I can see the damn table, they just don't have it enabled on the flex tune to change.
I have somewhat low hopes they will add the table to my flex OS but here's hoping.
2. The DBW issues strike randomly and I hit limp mode. I stumbled on a solution (some tables to max out) and I did that so hopefully I can rap the thing out in 1st and 2nd gear and it wont cut out on my now. It's fine WOT but high RPM runs (like autocross) it hit limp mode often when it's partial throttle little boost and high RPM.
3. The car always wants to die when I am coasting with the clutch in or coasting in nuetral. I found out the decel commanded RPM table was never setup (big dummy me) and it was commanding 0 RPM in coast and instead entering stall saver mode which went lumpy-lumpy and wanted to die. It was really bad when the AC was on and I mostly ignored it before then but now its actually annoying.
In other news I also ordered up some clone ZQ8 bumpstops. With the rideheight set more or less I only had 1" of travel in the front before I hit the bump stop. The factory bumpstops are like puncing a carpeted concrete floor so when I hit a pothole I feel it. The word on the street is zq8 foam bumpstops but they are discontinued and kinda hard to find in OEM GM part numbers without paying $55. I found these ones on ebay and they are the same color as factory so I will see if they hold up. They are softer than I would expect, maybe pool noodle durometer for the first 1/4" that I can press and then I run out of hand strength. These were like $18 shipped on fleabay.
New foam bumpstops are 1/4" taller than the old hard rubber ones.
Hard to tell but there is like 3/4" of gap between the top of the bump stop and the frame at normal ride height.
Control arms on the bottom are damn near flat to the ground.
Ingenuity is just another way to say too poor of a planner to order the tool, too impatient to wait, and too stubborn to buy it in the first place
I was away for Easter so I spent some time sitting on the couch with my laptop looking up tune things. I have 3 main problems I wanted to solve
1. My cruise doesn't work. It used to! When I had my 01 PCM I found an operating system on a Firebird with a t56 that I could swap all the t56 related info into the 4l60e sierra tune. My issue is when I went with my 02 Tahoe flex fuel enabled PCM I lost cruise. I found the PCM does an internal check where it looks at the engine RPM vs the VSS and if it's OK it allows cruise. I assume that's in case the vehicle is on ice, the trans is going out, or some safety related thing. I found out some people have the issue when they try swap the 1st gear planetary with a lower numerical ratio and their cruise won't work in 1st gear anymore.
The solution is either find a t56 tune with an OS# that can plug into the 02 Tahoe PCM (which doesn't exist, there is no t56 data that you can stick into a P01 flex PCM at this juncture) or change the gear ratios in a 60e tune to make it THINK it is a t56. Thats what I want to do. I would basically take 1-4th on the 60e tune and make it 3-6 t56 ratios.
The table convenient exists in this random F body tune
View attachment 172398
But my luck, look at my tune, the damn thing doesn't exist!!!
View attachment 172399
I at least found my issue. I have a request out to HPtuners. They replied back with the basic tech support stuff and said make sure you have it in advanced view (which it is), make sure you have the most up to date version (it is) and to do a debug scan and send it to them. I know they are doing their diligence for people that have simple issues, but I can see the damn table, they just don't have it enabled on the flex tune to change.
I have somewhat low hopes they will add the table to my flex OS but here's hoping.
So a segment swap is out of the question?
Yup. I asked HPtuners a few months back if they are aware of an OS that allows flex and t56 segment swap and they said no.
I took the car for a cruise tonight and besides blowing both fan fuses (apparently 20 amps isn't enough for low or high on an intrepid fan) everything is still good. I just needed to get over 30mph and it got enough air flow that it self cooled. I threw a 25 and 30 amp in the low and high to see if either helps. I think those little fuses just don't have the amp rating for quick high amp draws when they turn on.
Maybe it's just confirmation bias but the front end actually rides better with these foam bump stops. Before I bottomed the suspension out relatively easy and I knew when I got a big bump. I don't feel that harsh hit anymore which is a win. Honestly I think I'm putting those foam ones on my Cutlass this winter as long as these hold up on this car for the summer.
So what's the endgame here? Do you want cruise and E85? I feel like I glossed over a detail here.
Yeah, the Intrepid fans need 30A fuses. I went through that with my Buick years ago. Racetronix sent their PnP harness kit with 20As loaded and 30As in the bag. I thought they were spares. Nope.
