OK Ima working on the suspension for our Q45 project and would like some feedback on our thoughts and calculations. The basics are we are swapping an 87 C4 front cross member into the Q45 frame. I have some QA1 coil overs I would like to use as they are challenge priced and rebuild able and revalvable, we have not chosen any spring rates yet as I want to get the car closer to finished so we can get accurate corner weights.
There are two ways we are considering doing this, direct connection of the coil over to the a arm at the same location that the original spring as connected. I ahe done this before on a 57 Chevy conversion, but that used specific shocks to fit in that location and had the correct travel requirements. I could make a taller upper shock mount and use the shocks I have but I think there is a disadvantage here because of the motion ratio between the wheel and the shock.
The other thing we are considering is making a push rod suspension with a rocker mounted over teh frame and the shocks mounted inboard. This would give us about a 1:1 wheel to shock motion ratio and move the shocks inboard. Below is a chart I made of measured movments and spring cacluations based on a 300lb/in spring.
To me this looks like the push rod suspension offers a much better option but I am open to other opinions.
Sample layout
In reply to Fladiver64 :
Realistically, for the Challenge autox site you don't need more than 2" of travel in either bump or droop. So if you can plan & build your suspension around that you'll likely be closer to ideal.
Keep in mind these 2 points though: 1.) whichever mounting method you choose, ensure that your suspension never gets into the range of "falling-rate" - where the geometry effectively causes you to lose spring rate as the suspension moves in bump. 2.) If you can build it to use most of the available travel of the shocks(and presuming they're calves correctly for whatever spring rates you need), you'll get better responsiveness & control from them.
I would agree that the pushrod setup is the better choice, but it will likely cost more in both time & materials. Are those resources better spent elsewhere on the car? Also, are you sure the extra space required for the pushrod setup won't be needed(or better served) by locating something else there?
Plus, with a pushrod setup you can effectively change spring rate through rocker motion. That could make testing/tuning easier, and maybe there's some potential for the drags to emulate the lower spring rates & damping of drag shocks through rocker ratio changes?
Just some more things to think about.
In reply to Pete Gossett :
Thanks Pete, those were my thoughts so nice to hear someone else agree. The cost is about $20 a corner for steel and bearings so I think it is worth the effort.
I set my shock angles up to that fully compressed is 90 degrees just to avoid the regressive spring rate issue.
I need to think some more about the change for the drag strip as that is an interesting idea.
