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"Hit" is how much weight is applied to the tires. If the tires can't stay hooked(traction) they spin. A little like pre load. Harder the hit the better the traction. Carrying the wheel(wheelies) is a product of hp/trq but suspension,weight, and transfer can control it. You will see I have 2 leafs only and lowered and air bags(can't see). Some people run one or a single slip leaf, again faster transfer. I want as much transfer and weight applied to the rear wheels as tires can handle. Moving the IC farther forward is how we do that. To soften the launch I can raise the front mount moving the IC to the rear.
Rear bracket holes allow me to add even more IC as the front point is lowest then I raise the rear the IC in in front of the engine. this goes back to the ideal position is said to be horizontal or parallel. You see this in 4 link and f-body(lower arms/relocation brackets).
I think you are miss thinking the role of leaf springs. it is a suspension part but in a launch all it does is affect how fast the truck squats. Also the leaf stays some what straight and with the traction bar it acts more like a 4 link and all points are fixed. the axles doesn't move at all other than pinon angle do to the suspension travel under load. As long as this is in spec and there is no axle wrap, we never look at it again.
All of this doesn't matter as you only have two options on yours and I would guess you will not get to the point of seeing the difference in the two.
The bottom plate is removed on a flip kit rear and the stock u bolts bolt to the new bottom bracket same as caltrac. Not sure where you thought there are no u bolts?
Oh yes people have posted pics of broken and en-longed bracket, but in truth huge HP cars.
Much of what you say is not intuitive to me and, being an Aggie mechanical engineer and plagued with the unsatiable desire to figure out how things work, I’m struggling. I know rules of thumb can be dangerous unless you really know where they come from. Sounds like you have a lot of experience with it. I really just want to reconcile experience with Mother Nature so I can understand.
What I do know to be true. Not trying to be argumentative just getting it right.
*Moving the rear connecting rod attachment location does not affect the location of the instant center. At least from a static standpoint. If it causes the truck to squat differently that would make a difference.
*The torsional stiffness of the system ( resistance to axle housing rotation) is not infinite so there is still some axle rotation. It’s not zero. The location of the attachment of the connecting rod will affect the stiffness and therefore the axle windup. How much? No idea.
* Changing the attachment point at the rear changes the load on the rod and the direction of the forces on the front and rear attachment points. The load in the rod can only be in the direction of the rod as the Hemi joints can transmit no moment. Depending on the direction this could lift or lower the rear end. Won’t be happening with the Caltracs. Score Assassin.
I understand what is meant by squat and suppose it has to do with weight transfer. Doesn’t sound like it matters as much on a 4wd truck.
The comment about no u-bolts comes from Assassin advertising. Must be for a different vehicle.
Regards
Last edited by Littlefield; 11-12-2018 at 06:56 AM.
Ok so here we go.
1- is false as even you stated an imaginary line is drawn of the bar and that is the IC so if we agree the front point moving up and down moves IC why wouldn't moving the rear change IC also. It is like a laser light pointer end or back end changes the light moves. all angles are affected in IC.
2-Some what true there is some axle(pinon) change. Only because of the movement in the leafs. Another reason 4 link is better. And as stated there will still be some in 4 link only because the differential moves up and down.
3- Don't believe true once the "load" is applied it pushes on the bracket and being solid that force is over with other than the affect it has on the "lift" of the front and squat of the rear. The hemi joints are just a flexible mount. I understand there is a point that is impossible but lets take about it, where if the bar was like a floor jack and straight under the truck there is lift. Now if same force was straight into the rear bumper the truck would slide forward. If I wheeled my truck the slicks would wrinkle up and hook hard as 5000lb+ would jam those tires into the road. Also weight transfer on a 4wd and awd matters just as much on as a rwd. watch some videos of the Skylines launching. Difference is they a super low to reduce the amount of max squat to not unload the front tires. But believe me the rears are working the hardest.
Oh the comment on the single spring was to make the point that the faster the weight transfer takes place the better the reaction time and over all time. the suspension movement takes time. Back to the lower softer and more transfer. AKA more adjustment and importance of IC. this is the point other than Axle wrap.
As I have told others you should throw a go pro under there at the track and watch the pinon angle.
I have a stock suspension 1600hp car now being changed over to 25.2 with much more power. Me and the Fab shop have gone over this for months. Now it will be 4 link per class rules. My other car was a stock suspension torque arm. And we broke most of it getting it to have track manors. This is back in the day when the big companies where still working on r&d and fast was high 9's.
in this picture you see that on a lifted truck the IC moves so far back they need longer bars. Back to the idea of the rear mount and the bar angle affecting IC. If this truck had caltracs the ic would be the back seat.
Makes sense with that lift. The point being that Caltracs forces attachment at the front of the leaf spring? Ok. I assume it’s well known that with a lifted truck you can’t just connect up to the spring. I bet even Caltrac knows that. These things are complicated. I need to understand my application, i.e. 4wd. I want to minimize weight transfer to the back so the front doesn’t start spinning. Or maybe because the rear locks and the front doesn’t I want to transfer no more than 1/6 the weight so I have 1/3 and 2/3. Think I’ll start drawing free body diagrams, understand as much as I can and jump over to dragstuff with this topic.
Last edited by Littlefield; 11-12-2018 at 06:03 PM.
Makes sense with that lift. The point being that Caltracs forces attachment at the front of the leaf spring? Ok. I assume it’s well known that with a lifted truck you can’t just connect up to the spring. I bet even Caltrac knows that. These things are complicated. I need to understand my application, i.e. 4wd. I want to minimize weight transfer to the back so the front doesn’t start spinning. Or maybe because the rear locks and the front doesn’t I want to transfer no more than 1/6 the weight so I have 1/3 and 2/3. Think I’ll start drawing free body diagrams, understand as much as I can and jump over to dragstuff with this topic.
Some of the big power truck guys launch in 2wd and switch out to 4wd later. Big power 4wd have track steer. It is crazy you drive with the wheel to the left to go straight. we saw this in the 9's on awd trucks/cars.I would just stay in 2wd and max the weight transfer as you have so much suspension travel to go through. Also less drive train loss in 2wd. The rear tires are the most important at the strip. you don't make enough power to worry about the front till to get slicks and start lifting the front tires. If your drive train can handle it launch control the truck, I use the TC but change the settings. I would log the trans pids. Check for slip. I see the stock stall I would change that make a world of difference. Once you see under a good hit and full traction what the stall flashes to and what the dyno curve looks like order a stall to match. I could use one also but with the turbo It likes it lose up to 2500 but can easy jump to 3000. So really that is good for me other then slipping.
You may like forums like Yellowbullet to read up on real drag racer input. They are hard hitting jerk ******* types but most all know there **** better than any forum I know.
Finally made it back to the track. Good news - dropped .1 off 60 ft times, best of 1.89, several 1.99. Driver proved capable of 0.05 reaction time.
Bad news - WOT 2-3 shift mostly nonexistent, super erratic with a couple different tunes that I had adjusted the shift points on. Driver typical reaction times not close to 0.05.
More good news - there’s a super slick user developed spreadsheet called Bluecat that calculates shift points based on a bunch of vehicle specific stuff. Will give it a shot and report back. There’s a TNT Friday if I can make it.
Thanks for that. I tried to get to it unsuccessfully through that link. Found it on HPtuners/transmissions in a 06/18 version. I may have messed up the driver demand table previously as I made adjustments up into the 86% throttle range were the computer oddly thinks WOT is. Anyway, went through the Bluecat, super nice. Generated a couple new tunes to try, one with the torque convertor locked up in 3rd to see any mph difference. Unfortunately my Hptuners data logger is not recording transmission pid's so may have to fake slip from something else. I run with traction control off and noticed the TCS demanded torque stays flatlined at 266 while actual engine torque is higher. Must think it's slipping even in 4wd. Not sure how it would measure tire slippage with all 4 driving.
PS this 1.37 version of Bluecat has a more in depth method to calculate desired lead, if you want to use it. Wasn't sure what to use so I matched shift mphs for same desired shift point as on a previously successful tune. Then adjusted the shift point up. It calculated reduced shift point vs desired. When I did it by hand I had all the same actual vs desired shift points.
11-11-2018, 04:55 PM
