Lexan Rear Hatch for Porsche 944

Lexan Rear Hatch for Porsche 944

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In order to improve the aerodynamics of our Porsche 944 ChumpCar racer, we decided to add a Lexan hatch. The ChumpCar rules require all glass other than the windshield to be removed. For our first race, we removed the glass and ran just the hatch frame. After looking at the other 944s racing against us we decided to add a Lexan hatch like they had.

We ordered the material from Five Star Race Car bodies on the advice of one of the other teams. This is the same material sold by Porsche specialty shops for about $100 less. The material surprisingly comes rolled up in a small box so shipping costs were reasonable.

Since we already had the glass out of the hatch we were able to start right away. Removing the glass from the hatch frame is challenging and requires a lot of patience. I have seen youtube videos of people breaking theirs out but they still had to deal with all the little pieces in the channels. I used an oscillating tool to cut the bonding material and carefully removed the glass. I had a heat gun for some places but mostly where the bonding material was cut, the glass lifted out.

We began by laying out the screw holes making sure there was no more than ten inches between holes. We paid extra to have the material cut to the size of the original rear glass. We may have been better off buying the oversized version as ours was just a little smaller than we would have liked.

We marked and drilled all the holes in the perimeter of the frame. Then we set the Leaxan in the upper groove and pressed it into place. We then carefully drilled through each hole into the Lexan. I found that if the bit ran too fast, the material would melt rather than drill and would refill the holes when the drill bit was removed. After a few holes I had the technique down. The biggest trouble we had was finding the right place to drill the holes. The best spacing away fort eh edge of the window put us in a ridge on the inside of the frame. This caused some of the holes to be angled which gave us trouble later.

We used a hand brace and a large drill bit to cut the counter sinks. We used the screws provided in the mounting kit from Five Star. The kit seemed a good value as it came with the right screws, locking nuts and a drill bit.

Due to the way the nuts hit the back of the frame, the ridge caused the nuts to not seat right. We ended up using a cutting tool to notch the frame at each of the screw holes so the nuts could sit flat. This also allowed us to use the shorter screws in the kit allowing the hatch to fit better when back on the car. Notching the frame took away some strength but once careful handling allowed us to get the Lexan mounted without it bending. Once the Lexan was in place the rigidity returned.

We added the two required one inch wide aluminum strips over the hatch and bolted them top and bottom. We then put all the rubber trim pieces back on the hatch to cover the holes and retain the look and function of the original spoiler.

The new hatch is very light weight and looks nice. We hope the performance improvement will be worth the cost and two weekends of work required to make the swap.

DIY Cool Suit

It gets very hot in the race car wearing three layers of nomex and a helmet and gloves. Some smart guy several years ago invented a system that pumps cool water through a shirt to keep a driver cool. Unfortunately they still charge a lot of money for their nice system.

Being cheap – I decided to build my own. As a chemical engineer, I figured I could build a simple heat exchanger.

For the cooler pump, I used a cooler I got at Goodwill. I installed a boat bilge pump form Walmart. I drilled holes in the cooler for the wires to exit and one for the line off the pump. I got clear vinyl tubing from ace hardware and some fittings to reduce to 1/4″ tubing.

Next came the heat exchanger itself. I added a piece of cloth to a t shirt that had passages sewed vertically in it. Then I looped the tubing through. There is about 20 feet of tubing in the shirt.

I added dry breaks from McMaster Carr to the ends of the tubing to reduce the water splashed in the car. #5012K115

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coolsuitcoolerinside

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It seems to work in the garage. We will see how it works at Barber this weekend.

944 rear shocks

Koin Shock

Our Porsche 944 is intended to be a ChumpCar racer. So it has to meet certain rules. One of the controversial rules states that it can’t have adjustable shocks even if it came with them from the factory. We have elected to remove our very nice and expensive Koni racing shocks and swap in some KYB replacements.

The upper mount uses the stock bolt so we will reuse that. It can be accessed by dropping the suspension fully (removing the bottom shock bolt helps) and turning the head of the bolt from inside the wheel well. You will have to hold the nut with an open end wrench while turning the bolt from the wheel well.

The bottom of our Race Konis were mounted on very nice adapters that allowed the use of the spherical rod ends. To remove the adapters, we first had to support the wheel at just the right height to remove pressure from the bolt. Then the mounting bolt could be unscrewed from the adapter. The adapter was them removed from the control arm.

Since we did not have the original bolts to put the bottom of the shock back we started a quest. We measured the threads on the adapter and found they were M14 1.5. We estimated we needed 80mm of bolt. We set off to ACE hardware. They had one. But only in standard grade. I wanted a 10.9. Lowe’s and Home Depot were less helpful.

After some research on the internet we found that the factory bolt is actually 85mm. Porsche no longer sells it but BMW does. We have ordered a pair of part number 07-11-9-914-829 and will try again next weekend to get the bottom of the shock bolted in place. It is a shame to do so much work to make the car handle worse. But that is racing when you try to follow the rules.

Update: got the bolts from the BMW dealer. Also picked up several at pull a part as spares. Drilling the heads for safety wires was easier than I expected.

New race tires

We have heard a lot of good things about the BFG Rival race tires. They have the 200 tread wear required by Chumpcar and seems very sticky. However the set that came with our car were very worn. In fact a couple of tires had blisters after the hill climb. I ordered a new set from Tire Rack.

They arrived in a couple of days and I mounted them up last night. I am not sure if it is because they are so wide – 225/45-15 – or if it how they are made but even after breaking the bead they wanted to reseat on their own. I thought for a while I was gong to need an assistant but I eventually found a way to hold two tire spoons and the breaker bar to get the tires on and off the rims.

I stopped by NAPA and got some of their tire lubricant instead of using my normal home brew solution. I was pleased with the NAPA juice and will have to do a side by side comparison with my home made solution sometime. It was too hot last night. I look forward to running the new tires at Barber in August.

BFGTires

Safety wire

I have never given much thought to safety wire. We used it on several critical fasteners on the printing press I used to maintain, but I did not even keep the pliers when I left there.

However on our new to us Porsche Race car, the shift linkage was supposed to be safety wired and was not. This caused the shift linkage to fail on one of my starts up the hill at the Dragon Hill Climb. Not being familiar withe way the shift linkage operated, I first loaded it up and headed back how to the shop. However after consulting a mechanic friend, I decided to stop and take another look.

I set the trailer ramps on jack stands and backed the car out to make a mini work pit. With better visibility I was able to see that the set screw had backed out.

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I put it back and we went back racing. But it came out again. I was much faster at putting it back but I knew I had to do something different. The folks on the FL/GA 944 owners group suggested safety wiring.

I ordered a set of pliers. I also noticed that there was already a hole in the bolt head so it was intended to be safety wired.

Here is the result:

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I also decided that the cheap pliers I ordered from Amazon are nothing like the ones I used to use. I will be searching for a set of Milbar pliers in the near future.