83RDRACR

Hey guys my build thread and these pics are in the fabrication forum "home brew road racer" but I thought I would post some here just to try and get more eyes on it and get a little more feedback.

I got a complete 4th gen k-member with rack, brakes, upper and lower arms and shocks/springs. I modified the k-member to lower the front 3 inches and made it bolt to the factory 3rd gen frame rails. The stock 4th gen lower a-arms mount in there factory positions. The spindle center line is now 5" forward from stock. This should really help with weight distribution.

The car has a 12 pt cage so the upper front rails mount modified G body stock car upper arms. Double adjustable coil overs replace the gigantic 4th gen pieces. A heavy wall, tubular, lateral brace ties the two sides together and I added some diagonal braces back to the corners of the reinforced firewall to further eliminate flex.

Take a look and let me know what you think. The car is still welded to the steel ramps so I can make changes if needed.

SlickTrackGod

I guess I'll give some imput since no one else has responded.

What I see in initial opinion is a car that was butchered. As I COMMEND your effort, AND UNDERSTAND YOU'VE PUT A LOT OF TIME AND EFFORT into it- I ask myself what is your sole intention? THe car is not legal for any kind of class, the wheel base is extended 5" forwards making it harder to turn the car in rotation, the fenders will not align now so the value of the car went into the toilet unless you pull a rabbiit out of... (well you know) and win an unlimited class- but with all that weight addition I can not see that happining. 3rd gens have proven to handle better then 4th gens. I personally don't get it.

Now before you respond angrily towards my comment, YOU ASKED FOR FEEDBACK.

Dean

SlickTrackGod

I think the knowledge people lack when wanting to improve on handling it the two main essentials.
#1 weight reduction
#2 ..Most importantly is unsprung weight reduction ratio. While you are removing 4 lbs up top, you'd better be removing 1lb minium on the unsprung side to drop the unsprung weight faster then the needed sprung weight drop. Lighter is faster/quicker, not heavier.

I have started work on something of this sorts with another type of vehicle. My goal is to set track records everywhere I go. My entire car will not weight more that 1500 lbs.I am building the entire car underneath pretty much from scratch and putting my 67 Austin Mini Cooper body onto it with a 4" chop top. If you plan to run an unlimited class then narrow, short wheelbase, and low center of gravity with wide *** tires is essential.

83RDRACR

Dean, just the guy I was hoping to hear from as I respect you knowledge and experience. I have read many of your post and stickies so I was expecting one of your "frank" responses.

I probably should have described the purpose of the car better. It is a track day/auto cross car that will still be street legal with lights, wipers, defrost, aand doors and windows that open. It is not built to any rule book but was a project I always wanted to try. The car is being built and driven as a hobby and not an investment so not worried about resale value. Either it will work well or it won't.

My whole reason for this post was to get some critical feedback on the design and construction of the modifications. Does the bracing look sufficient to control chassis flex? Should I add an x brace under the engine bay?

The car has been cut up a lot, but not butchered. I didn't cut the wheels wells out until I had the k-member, lower control arms and spindles welded up and in place. Even the upper control arm mounts were designed to allow me to change roll center height from 0 to 4 inches.

In your second post you talk about weight reduction and I couldn't agree more. The 3rd gens are a heavy beast and very nose heavy. This car was 3208lbs without driver before I started the project. It had a perfect 60/40 split, 1900lbs frt and 1308lbs rear. Now 3200lbs is not a bad weight for a full dress street car and it is not a bad weight for a steel body race car with a full cage either. Our street stock stock cars had a 3200lb minimum and that included about 100lbs of added ballast.

The problem is all the weight on the front end. Since I can't make this a 2800lb 50/50 race car I had to find another way to tip the scales. Moving the wheels forward seemed like the best solution. The 3rd gen has a 101" wheelbase but the car is 192" long, meaning half of the car is hanging out past the wheel center lines. This sounds like a polar moment nightmare.

When I was doing research for the car I came across an in depth article about Billy Hagan's 1982 24hr Daytona car. The specs list the wheelbase at 108 inches and given that the engine sits behind the front spindle center line you have to figure they moved the front end forward quite a bit. Moving my wheels forward 5" should give me about a 5% change in weight distribution to 55/45. Removing the wheel wells, a/c, core support, battery, etc. from the front end should at least offset the weight added by the extra frame work, plus it is way more rigid. With most of the extra framing and rollcage sitting behind the firewall I am hoping to gain another 2% or so weight shift and end up at 53 or 52% front weight.

If you or anyone else would care to comment on the structural integrity, the placement of the various components, steering geometry or the like, please jump in. i built the car for me, not a rule book and not for resale. I plan to beat on it pretty hard and the last part I want to test is the halo bar and roof supports.

Thanks for looking in.

Dave

SlickTrackGod

Keep in mind the use of the car you quoted. That Hagan/Felton car was designed to run Le Mans at speeds nearing 200mph. You need wheelbase of stabilty. it is also the reason why NASCAR limits wheelbase to 105- a lot of grassroots is 108" to keep the cars more stable at higher speeds. Corner speed in all the cars I just mentioned hardly get lower than 65mph with lap average sppeds of about 95mph up to high 3 digit speeds.

Autox you may average around 50mph at best, coming off a lot of 15 mph tight corners and hairpins. You need a car with much shorter wheelbase to rotate competitively. Stability is not an issue. Case in point- My old Vette has a 98" wheelbase along with the current Dodge Vipers. New Vettes keep creeping up and are in the 106" range now because the cars are getting too fast for the general public to handle in a short wheelbase- especially when average Joe turns off the "nannies".

I took a glance at the Hagan car to confirm first before I wrote this, but I already speculated that car was a tube chassis built from ground up. It was not a street car converted. The engine sits rearward- they did not lengthen wheelbase forward. Pretty much the same I guess, but their reason was, as already stated, to improve high speed stability. ***I would highly recommend you move t wheelbase back where it was, and then move the engine back and shorten the driveshaft.- a far better result when running the speeds you seek which will probably never breach 140mph at best and mostly under 60 in the fastest corners. I use to run my Camaro on California Speedway on occation on the 2.8mile roadcourse. I would do about 120 around the high bank 1-2, but then when I dropped down into the infield I would crest one high speed sweeper at about 60-65 range where as all others were under 50mph. At 100 wheelbase I was perfectly fine (yes 100 ) I would do 165 down the front straight in my Vette (the same track) with a little aero wobble, but nothing too scary since I was up and back down fairly quickly settling into about 130 through the bank 1-2 oval (that is a 540 hp (rear wheel) car that ran a 10.89sec 1/4 on a road race setup once) I am also a very skilled driver over most- but mute point. I could see getting into trouble in that car in traffic and bad air at those speeds if sustained longer.

What I would do? Like state- Move the Kmember back into the 101 position. Push the motor back about 4-5 ", and move the rear wheels forward 1". Remove polar weight (ie- heavy exhaust routing behind wheels, etc) and call it a day.

SlickTrackGod

Might want to also push the motor a little to the right side while you are at it to get left/right balance of drivers weight.

83RDRACR

Dean, you are right about the Hagan Camaro being a purpose built race car, full tube chassis, extended wheel base, and both the engine and driver are set back several inches. Two other notable changes from a stock 3rd gen are the SLA front suspension and 3 link rear suspension. I have tried to incorporate many of these same things into my build, not just based on the Hagan car but other third gen road race cars running in various SCCA and NASA classes posted on the internet as well. I wanted to make the car as balanced as possible, not just wheel weights, but braking and steering as well.

I have tried to build adjustability into all of the major suspension pieces so the car could be tuned to the driver and the track. With just a few wrenches I can change the roll axis, bump steer, roll steer, anti dive and anti squat, ride height, shock valving, and sway bar arm length. Add in a brake bias adjuster and a power steering pressure regulator and I should be able to tune the car to get its maximum performance. Or I could get totally lost and make the car steer like an old farm truck!!!!!!!

About the engine offset, from the factory the engine is already about 1 1/4" to the right. Tp move it over more would require notching the frame rails for header clearance and probably a custom rear axle to keep the driveshaft in alignment.



The car will see more street time than track time and more open track events than autox, so the longer wheel base shouldn't hurt too bad and I will take the better weight distribution as the trade off. I am a road race want-a-be and will be getting my SCCA license in August. The car should be road worthy by next summer