mdb4879

Hey everyone, so I have an interesting/crazy project in my head and would like some suggestions for it. Long story short, YouTube has me wanting to see how cheap I can build a 10 second Civic. It's not a pure challenge as once I mentioned I was scouring Craigslist to find a car to build my friend donated his Civic for the cause (an EG hatch with a supposedly built LSVTEC that once made 500+whp which we were going to repurpose for rallycross with a small turbo setup, but now will find its way back to 500whp). So we pretty much already have everything to make the power short of enough fuel and a turbo and manifold capable of that power. There aren't any 1/4 mile track close to us so for now we'll just be setting an 1/8th mile goal. I'm thinking 7.0 or high 6's should be a good mark. I know that kind of power should make a "10 second pass" possible with the right setup, so in my mind I've turned this into how fast can we go with 500whp or how little power can we meet our goals with, via weight reduction. This is where it gets fun. I want to build a car like this:


Basically a cage with the body skins attached and all the inner structure removed. That may be a bit wild for 500whp, but it'll be fun to see what it's like. So thinking about this build has me wondering what I should do about rear suspension. I've heard way back in the day some people would use solid rear shocks or something of the sort to lower 60ft times and make better launches on FWD cars. I'm sure that's not the best way otherwise the big teams would be doing it, but it seems like it didn't do a horrible job. So my question now is should I build a solid rear axle tied into the cage/frame as seen in the video above to be able to cut more weight out of the car, or would I benefit more from having a functional rear suspension? I'm leaning towards the solid axle because I'm sure it would be easy to get the car down under 1500lbs and I'm expecting it to be closer to 1200lbs (maybe less, who knows how much weight can actually be cut from the car), so that extra 100lbs of weight or more seems like a lot when the car is that light. Plus not having any dynamic toe change as the rear end squats or lifts sounds like a nice added benefit. I'm also not going to spend $6000 on shocks. If the car gets anything it'll get my Koni race shocks and different springs from my old SMF autocross car until I build another at which point it'll probably get cheaper coilovers than that. So what are the recommendations and why?

sneakysneaky

Solid rears are somewhat sketchy and are not legal to run in any motorsports that I can think of. You can cantilever the shocks to drop some unsprung weight and make some tubular A arms.
If you are hooking in the 1200 LB weight range, you would only need like 200 hp to run in the mid 10s. Better off building a 4 cyl dragster if you ask me...

Full_Tilt

^What he said.
You dont need that kind of weight reduction to run 10s. People were running 10 flat with ~500hp D series almost 10 years ago and didnt need abnormal weight reduction to do it.

mdb4879

I've seen (well, read about) people run 10's in 500whp 2400lbs turbo cars and in 300whp 1500-1800lbs cars. I know this is overkill, which is why I don't have a clear goal set. It's more of a "for fun" thing I've been wanting to do to a car and why not make a lot of power while I'm at it? I'm not worried about any sort of competitive drag racing as long as my local track will let me run TnT. No street driving, obviously. So this is really more of a how fast can it go with that power and as little weight as possible, or how little power can we reach a certain with weighing as little as possible? I won't build anything structurally unsound, but if it comes down to the car being sketchy (and dangerous) to drive because having the rear suspension do nothing while the front does then I won't go to that extreme. If it's just different and driving adjustments need to be made then I can do that. I also don't want to sound like I'll be sending an untested car with that much done to it down the track all out. It'll likely make the power first in what I'm guessing is about a 1900lbs car right now, do some testing, then start removing weight and adjusting power accordingly.

So how do FWD cars with a solid rear axle with suspension do? Would it be worth going that route with a triangulated 4 link?

bauergold

I'd just run the stock style suspension. It works well. You can get well under 1900lbs with driver with enough cutting.

There's also a much much higher chance of this car actually getting built.

mdb4879

Looks like I'll just be putting it together as it is, sorting it out, and going from there once we see how the car does and know what we want to do at that point.

sneakysneaky

f@sth@tch89

iTrader: (3)

mdb4879

What do you mean by pushing weight down on the front? Does weight not transfer regardless of suspension firmness (just happens faster the stiffer it is)? Or are you simply referring to the effects of suspension geometry and anti-squat in the rear? How do you feel about a standard 4-link with a panhard bar vs a triangulated or double triangulated 4-link? the rear end shifting sideways under load with a panhard bar has never sat too well with me, but that's just in my mind and not through experience.

What am I looking at in that picture? Equal length and angle upper and lower control arms, custom spindle, trailing arm, and shock mounts? That sounds like it would work great while keeping weight down. How much toe change do you get through the travel of weight transfer and how does that affect the car?

(I'm pretty sure I'm thinking too deep into this for all I'm going to do. Not the worst habit to have, but it's what I do)

sneakysneaky

The picture looks to be a ladder bar setup.
If anything read up on instant center and anti squat..
all of the systems work, its just how you them.
a standard 4 link with a track bar when using a straight rear axle is the easiest to buy parts for imho.
Haven't looked in years for kits but if your doing something more complicated you will likely need to fab some if not most of it.

front suspension matters too.
suspension is pretty complicated and simple at the same time.
there are tons of videos on youtube that show how it works.
the front suspension you want to squat to push the front wheels down, but the more power you have the less squat you want.
Adjustability is nice unless you do the math and are dead set on it. Lots of People run decent times with stock suspension though.

SPOOLINmatt

Well in the interest of fairness, the fastest drag cars on the planet aka the fastest accelerating cars on the planet have solid rear suspension.

sneakysneaky

mdb4879

Sorry for the delayed response. In the case of top fuel dragsters, is the front suspensions solid as well? If so then I would say it makes sense that the rear is solid. I've heard having that much difference in articulation (solid at one end and not at the other) causes dynamic problems. Probably what makes a solid rear Civic sketchy? Kind of like how when it comes to cornering a proportionately stiff rear will likely induce oversteer and a stiff front will make understeer. I see this being more of an issue with RWD cars because the torque of the motor twist the chassis longitudinally and can load one side of the suspension where front and rear are different whereas in a FWD car the motor twists to the back so my theory would be that it's more stable. Until somethings goes a little awry and you have to make a significant steering correction. Also, those dragsters have enormous tires which could, in a sense, act as suspension.

I agree, getting it right the first time is what's important and also deterring when it comes to making the rear solid. However, I thought it might not be too bad since it won't articulate I could set it up at zero toe and zero camber. Having those be dynamic through suspension travel is when having adjustability is most important to find the best compromise between those static and dynamic specs. I come from autocross, so I'm not sure how much difference various pavements make to the ideal setup for a given car. I imagine it's just as much as it is with autocross. I guess I could always 4-link the rear and do some testing with solid struts in place of the coilovers and if it seems worthwhile just weld it up solid.

Funny you mention putting the motor in the back. I was joking with my friend saying the final stage for the car would be to cut off the firewall and everything behind it, then build forward. Even make a road race worthy front suspension (probably copy the front suspension geometry of a Civic). Then we'll have a Honda based formula style car. I'm sure there are much easier, effective, and proven designs already out there than trying to work around the factory Honda stuff. Particularly the height and shape of the steering knuckles limiting how inboard the wheels can set. I've got to run a 15mm spacer just to get my 15x11 6ULs to clear the knuckle. The Civic doesn't offer much room for backspacing.

sneakysneaky