Mid- Engine Modified Sports

[manta22]

I believe it Chris!

Regards, Neil  Tucson, AZ

[manta22]

I re-located the pickup point for the front anti-roll bar downlink to the lower a-arm. Now there is no problem, even with the steering lock-to-lock. I should have done it that way from the beginning!

After installing the front anti-roll bar I discovered that it interfered with the fluid (brake & clutch) reservoirs so it was necessary to make a new mounting bracket. I wasn't satisfied with that first one anyway so I rummaged through a box of surplus aluminum extrusions that had I bought from a guy on eBay. There was quite an assortment of sizes & shapes, mostly 7075-T351 from Boeing! I used two L-sections fastened together with 3/16" Huck Lockbolts. Pulling these were beyond the capability of most of my rivet guns as the have 114ksi stems, but a hand-operated hydraulic puller and all my hand strength finally managed to pop the stems.These are NEVER coming apart!

This was an exercise in overkill but it was partly an experiment to see how some of this stuff worked. Drilling 7075 with a new, sharp drill is an experience in itself.

Regards, Neil  Tucson, AZ

[manta22]

Despite the lack of any postings in the build diary lately, I've actually been working hard on the car. Unfortunately, the majority of my effort has been on re-doing the rear chassis so the suspension pick-up points are better located in the structure. This involved cutting out a part of the chassis tube structure and building it up again.
 
I found that the original Porsche geometry they used on their 996 was not very good in my application-- too much bump steer. I bought a program-- Suspension Analyzer v2.4-- and designed a 5-link suspension using the same Porsche 996 rear uprights but optimized its geometry. The new pick-up points on the chassis were not in the same place as I had originally put them, so things needed to be changed.
 
Why the 996 geometry wasn't as good as I would have liked might have been something to do with their use of compliant rubber bushings or maybe they were compensating for some other behavior-- who knows. Anyway, three steps forward and two steps back-- so it goes.

One minor detail was making a new mounts for the top attachment point for the rear coil-overs. I used surplus 1/2" titanium bolts and ground two flats on the round floating bushing so I could get a wrench on it to tighten the assembly.

[Glen]

Looking good Neil, send more pictures of the rear end mods etc.

[manta22]

Thanks, Glen; I'll take more pictures when I get the new chassis sub-frame tacked in place.

[Milwaukee Midget]

three steps forward and two steps back-- so it goes.

Still puts you one step up, and let's you see where you're headed.  Looking forward to more pics - keep at it, Neil.

Chris

[DND]

Hi Neil

The Carl Haas Can-Am team was next to our shop and i would stop and watch Colin & Gil set the bump steer, what a job to make all those adjustments and get it dialed in.

They would set the tub on 4 by 4's as the ride hight was 3 1/2" then hook up the music wire streched very tight and measure over to the rotor etc, wow that was 44 yrs ago in 68' and sad to say they are both gone now R.I.P. Cool Guys

Don

[manta22]

Don;

We raced against that Carl Haas team back in '72 & '73-- thrilling times indeed.

It's easier these days to set up bump steer-- we have tools that didn't exist back then.

Regards, Neil  Tucson, AZ

[manta22]

Since I had to move a few bushings to accommodate my revised rear chassis design, I decided to max out the linkage by using Thomson Super-12 (3/4" ID) linear ball bushings and mil-spec Apex u-joints. The u-joints are bolted rather than welded to 3/4" OD stainless tubing so that the linkage can be disassembled easily and so the u-joints are not ruined by welding heat. If the holes are very carefully drilled there will be no problems with play at the tube/u-joint connection. I used thin wall chrome moly tubing for the bushing housing simply because thin-wall seamless mild steel is hard to find and used 1 1/4" snap rings to retain it within the housing. Getting the bushings to align with each other was a chore and after welding a support structure on, some shimming was required.
 
Notice that since I ran the shift tube along the right side of the engine & transaxle, I had to reverse the rotation of the tube to get the proper shift pattern for the G50. You can see how I did that in one of the pictures below.
 
This is my "swinging link" solution to the lower pivot problem of the original design. The link is threaded so it can be adjusted fore and aft. I mounted the bushing to the read so it would have clearance for the 2nd & 4th gear position. Lots of chips on the floor from drilling holes for the Nutsert threaded inserts for 1/4-28 bolts:

[manta22]

Well, the revised 5-link rear suspension is finally together-- at least until it is time to pull everything apart for final welding, blasting, painting and riveting panels on. Whew!
 
The rear suspension was based on Porsche 996 geometry but modified by a computer analysis which showed that an improved geometry could be achieved by moving the inner arm pick-up points on the chassis. That made it necessary to extensively modify the existing chassis tube structure. There is more cut-up tubing in the scrap pile now.

The right side headers are not installed yet on the right side. Spring rate is 400 lbs/inch, free length is 10".

Rear view. The paper taped to the floor was graph paper that I used to plot the X-Y locations of the pick-up points on the chassis. The parachute attachment swivel is visible on top of the G50.

[Glen]

Looks great nice work

[Jonny Hotnuts]

Neil,

Just wondering if you have thoughts of doing some SCCA road course running with this car also?
Also.....its looking like it getting really close.....any planned event debut???

~JH

[manta22]

JH;

Actually, it probably could run in road racing events but with all the SCTA required stuff-- heavy duty roll cage, etc-- it would probably be too heavy to be very competitive in SCCA class racing. It might be fun to use it as a "track day" ride, though. There are still lots of things to get done so I'll make no predictions. I'd just like to get it finished before I'm too old to drive it!
See you at Speed Week this year?

Regards, Neil  Tucson, AZ

[manta22]

Well, I may have changed my mind about painting the chassis. On the way home from lunch today with the "Car Guyz", I swung by a surplus place that I had not been in for a couple of years. There was mostly stuff that I wouldn't have carried home if it was free, but I spotted some cans of paint on a shelf and asked the guy what he wanted for the stuff.
 
"Hmmm... what'll you give me?"
"A couple of bucks a can"
"How many do you want?"
"I'll give you a 20 dollar bill for 10 cans"
"Uh. OK"
 
Thus I now have 10 cans (that was all he had) of Aliphatic Isocyanate Resin MIL-PRF-85258D, Type 1, Class H, Color 33538 Yellow. It’s a 2-part military/aerospace paint that is really tough and resistant to weathering.
 
Here is the Federal Standard Color: http://www.colorserver.net/showcolor.asp?fs=33538&size=s  Not exciting but OK. Each can when mixed with its hardener makes 1 quart so I should have enough to paint my chassis.
 
The hard, tough polyurethane coating has the same drawback as powder coating-- it is hard to repair or modify-- but since the paint is a much thinner coating than powder coating, it should be easier to sand off. This paint should give good protection against salt corrosion-- better than spray-can enamel. Has anyone tried this type of coating?
 
Regards, Neil  Tucson, AZ

[maguromic]

Neil, Nice find, and I wouldn't say it was an exiting find.  Thanks for the updates on the build I really enjoy reading it.  Tony