Back Again Guys With My Cobra

Hey guys,

I have had so much going on at home. The wife is ill and other projects have taken my time. However I have still been searching for ideas for my Cobra Kit with a C3 Rear. I have come up with two ideas. One is to build a Lower Control Arm with a watts. Some of the Cobra guys have gone this way with there Jag setups. Then idea two borrows from Guldstrand, I can lengthen my lower forward link app. to 22" however the upper forward is tight maybe 12". The idea with this setup I think is to have parallel equal length forward links. So what if I built a watts link for the upper then moving the hole in the carrier mount off center would give me the same arc as the 22" lower link. My thinking is that longer is better and that a 22" gives much less forward and rearward movement. I triged it out and jounce equals .025 movement and rebound equals .220.

Hope all is well guys!


Two setups below, excuse the crappy sketch please.

Do both of the setups you are thinking about use the halfshaft as the upper link?

Yes they do. Jag is the same as a Corvette in that regard. The Jag also has an upper watts if you look close.

The two ready to go rear ends that have my attention is the 03-04 cobra IRS and the Pontiac GTO IRS that is all over Ebay for cheap.

Well I own a C3 unit now and looking to modify. If I had the cash I would be looking at the RCC SPECIALTY PRODUCTS 9 INCH UNIT.

http://www.kitcarmag.com/howto/rcc_specialty_products_ford_9inch_irs_cobra_replica/index.html

A question I have involves moving the center hole on the watts. I would like to get some feedback as far is if it seems mechanically (geometrically) sound?

Moving the center pivot looks like it will work. As, you stated. you should be able to get (the equivalent of) a 22 inch arm for the upper link and 24 for the lower. However, you stated that you wanted these arms parallel. I think that you want the instant center of these two arms to intersect the CG at ride height. This is a C4 layout:

BBShark,
That is something I also wonder about. The C4 does intersect, however Guldstrands set up is a equal length parallel set of links. So do they have to intersect? I also think the longer the link and less of an angle, will reward less anti squat.

I'm not familiar with the Guldstrand suspension. As far as the C4 suspension goes, I know there were changes made that (may have) included changing the camber mount position and perhaps the front bracket that the control arms mount to.

Your watts link setup is interesting. I assume your diff is rigid mounted to the frame. That means acceleration and braking torque is introduced into the watts link. Have not really thought that through, but those forces might jack or squat the suspension?

Yes the third member is rigid. On the watts the forward link points up and the rear is reversed. So one would force the chassis up and the other down. But also the center hole on the watts would favor the forward link which I have termed the primary link. The reason I say primary is that the motion and the forces would favor the link most close to. So the watts I believe would have some anti squat effects under acceleration. But also because of the forward links increased length and lower angle compared to the C4. This upward force would be minimal in my opinion. Or I'm full of crap, which happens often!

What I like about parallel equal length forward links, is that I would think there should be little to no rotation of the bearing carriers. Which would reduce any sort of toe condition.

Ralphy

BBShark said:

Moving the center pivot looks like it will work. As, you stated. you should be able to get (the equivalent of) a 22 inch arm for the upper link and 24 for the lower. However, you stated that you wanted these arms parallel. I think that you want the instant center of these two arms to intersect the CG at ride height. This is a C4 layout:

Click to expand...

I think I have learned a little now. In this picture the forward links are set at specific angles to do specific jobs. The more you angle either of the two forward links upward the more anti squat you will achieve, the red lines show nothing more then where they intersect. If the upper link were parallel to the lower you would have even more anti squat. The lower link is the one that does this work (anti squat) primarily due to the higher angle. Then also because of this angle when you hit a bump in the road this angle also causes the rear wheel to decelerate elongating the wheel base, smoothing the ride. However I think if a wheel falls into a hole the opposite happens and the bump increases. A parallel forward link performance wise is better then the C4 design. The C4 is a compromise on performance vs. ride. The lower also helps to increase wheel base under jounce and the upper tends to basically stabilize motion in a flatter angle. However this setup causes the carriers to rotate which can cause some toe issues. I'm sure the engineers know if and how much.

Just my opinion!