I'm not picking on you, I was asking questions about what was added to reinforce the car.

It is important that you post up results of this mod after your done and after you've done quite a few drag lauches to show us how it is holding up.

 

Keep in mind I am no drag race or four link guru, but isn't the geometry with that four link going to have a whole lot of wind in the axle whenever the car squats at launch? The driveshaft angle at the diff is going to be all over the place.

Is this normal?

 

Obviously

 

...but I do understand geometry and hoped for some enlightenment since you said you guys had worked out all the angles. Not trying to flame you, just wanted to hear a real answer for my own knowledge from the guys who designed it.

 

The main thing I noticed that I don't see that is the main benifit of a 4link is adjustment points. It looks as though they are fixed in one position.

 

They're adjustable from the two lowers,two uppers and panhard bar.

 

Pinion angle is critical under hard launching conditions. The action/reaction tendencies of the pseudo four-link suspension creates a pretty significant amount of axle rotation under hard launches. As the tires bite, the pinion's reaction is to rotate upwards towards the pinion snubber. This tends to unload the tires and create wheel hop. The optimum power transfer would be if you could get your transmission, driveshaft and pinion to form a perfectly straight line as shown in the top figure. Unfortunately, with articulating suspension, varying ride heights and other geometric considerations its highly unlikely that you'll ever wind up with that perfect alignment.Under hard launches, the pinion will have a tendency to rotate 3 to 4 degrees upwards which was leaving my pinion pointing to the sky (well almost). This is where the adjustability comes in with the 4 link. The adjustable uppers allow you to shorten (or lengthen) the upper control arm, which changes the initial pinion angle. By shortening the UCA length, I was able to get the pinion pointing about 6.0 degrees downward with the driveshaft following it to about 2.0 upward. This provides a total difference between the two of about 4.0 degrees downward (negative) pinion angle. Under hard launches, if the pinion rotates 3 to 4 degrees upward, it should just about straighten the driveline for maximum bite and power transfer.

 

I get it; you set the pinion angle so that under load at launch it is straight.

What about the chassis mounting location of the upper links? Varying the upper rod length will adjust pinion angle but you could vary the anti-squat of the suspension by moving the chassis pick up point up and down as well. Seems that would be very handy to tuning how much weight transfer the car gets coming off the line. Or did someone already figure this out for an FD? Seems tire size may dictate different optimal upper link angles (more or less anti-squat).

 

Wow Eric I've always admired your car ever since I seen it afew years ago.

Its coming along real nice. I remember you used to have a T88 right? Still have the T51R?

Also what kind of power will you be making?, it seems like your getting really serious and making a all out drag car

Anyways, good luck with your car. I can't wait to see it perform

 

Thanks, yeah this is a never ending project. Maybe one day I'll actually get to drive it for more than 2 weeks without breaking something

I had the apex turbo a long time ago then swithed to the greddy T88 two years ago and now I've got my HKS T51R KAI

 

I forgot, we also had to build a new transmision mount because we aren't using the stock power plant frame anymore. We also had to make a new drive shaft in house. I'll get better pictures of the final project today.

 

i am pretty impressed it looks good.......i think i've finally figured out how to stop blowing diffs..... so far so good this year lol

 

More pics.......

 

Pic

 

Pic

 

Pic

You can't see the upper arms in this pic

 

Ride Height

 

Brake pic

 

I took it out for a drive last night and everything seemed fine. It was just down the road to grab a cold one so I didn't get to get silly in it yet.

 

Well goddammit GET SILLY!! I wan't to see wheelies!

 

There seems to be a TON of lateral axle movement with the panhard bar at that angle. Or is it just deceptive from the pic?

 

The only axle movement is up and down.

 

But a panhard swings in an arc. Since one end of the panhard is fixed to the chassis, the end that locates the axle actually moves the axle laterally anytime the suspension moves. The higher the angle between the panhard and the axle the more lateral movement of the axle. This is the reason you want a long panhard bar and to keep it as parallel as possible to the axle; to minimize the lateral movement.

If the panhard is not nearly parallel with the axle housing you also get lots of jacking and binding whenever the car is cornering. Drag cars only go straight, but at launch when the car squats the axle is going to move sideways under the car and make the car wish to crab off the line since the drive is effectively no longer centered under the car.

I can't see the tab where the panhard attaches to your chassis, but if it were made longer than the panhard bar would be in a much more favorable position.

See pic below:


Here you see the panhard is absolutely as long as the chassis will allow, is nearly parallel with the axle and also has provisions to adjust the roll center.

 

That pic above has his suspension in full rebound, making the angle exaggerated, no? Still, looks like he attached to the center of the crossmember mounts or old diff mount, giving short arc radius and extra lateral movement like damon mentions. I asked this question wayyy in the beginning exactly because of Damons reasoning. That thing's gonna walk at squat and again at rebound. Still, neat to see a full drag race prep suspension on an FD. Keep it up...

 

regardless of how he sets it up, a panhard bar totally sucks for locating the rear end. that's why no one ever uses them for racing anymore. everyone either uses a diagonal link or a wishbone.