Lexan Rear Hatch for Porsche 944

Lexan Rear Hatch for Porsche 944


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




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

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.


DIY home piston notching

DIY home piston notching


A race engine was brought to our shop after a failure. Before reassembling the engine I decided to check the piston to valve clearance since this was a hybrid engine using an older head on a newer block.

We placed modeling clay on top of the piston, bolted the head in place and timed the cam.  Then we carefully rotated the engine two turns.  We took it all apart to measure the thickness of the clay to determine the clearance.  However, there was no need to measure as the clay had been cut by the valve indicating there was already some slight contact between the valve and piston.

We carefully examined the old pistons from the failed engine and sure enough when we knew what to look for, there were impact marks on the tops of the pistons.  We determined that notches were needed to be cut in the pistons to make the engine runnable.

We came up with the idea to use an old valve coated with abrasive grit to do the cutting.  After some internet research, this was found to be an acceptable practice.   We did some research to see what had worked and what had not.

I repaired the damaged head enough to use it as a guide for the notching procedure.  We used adhesive backed 40 grit sandpaper cut slightly larger than the valve and pressed in place.  In order to get the paper to stick, we had to wire brush the valve face, clean it with brake cleaner and then use a piece of duct tape to remove the last bits of dust off the face.   The sandpaper held pretty well when this process was followed.

We put the valve in the old head and use a drill to spin the valve stem. We gave up on the idea of using a collar to measure the depth cut and just made the cut in several small steps.  We did not bolt the head on just used the dowel pins to locate it on the block.  This allowed up to lift the head easily and check the progress of the cut.

To reduce the amount of metal shavings left in the engine, we used masking tape to seal off the top of the piston being cut.  When the head was lifted off, we used a shop vacuum  to clean up before removing the tape.  We simply cut through the tape rather than trying to predict where an opening was needed.

After we had determined the amount to cut by repeating the clay molding process, we moved to the next piston. We found that the best way to keep the clay from sticking was to have the piston top as clean and smooth as possible. Using oil or WD40 just made it stick worse.  We used a dremmel to smooth the cuts made by the sandpaper on the valves.

By using a valve to cut the notches we assured ourselves that the notch was in exactly the right place to clear the valve and at the correct angle.  Making these cuts on a milling machine would have involved tearing down our fresh short block and collecting data on the center of the desired cat as well as the angle.  Our DIY method eliminated al lot of these variables as well eliminating the expense of the machine work.  The results looked fantastic. Time will tell how well it performs but I expect it will work well.

Trailer Brake upgrade

After hauling our Chump Car racer to Charlotte, I felt he current brakes were inadequate.  They are over 20 years old but have new magnets and drums.  Still he same old shoes however.   When they were new, they would lock the wheels easily. Now even with full voltage applied, they will not quite lock even withe trailer empty.

My first upgrade was to install a new brake controller. I got one with a “boost” feature that really helped liven up the old brakes.  However, the instructions boldly said not to use the boost feature to compensate for weak brakes.

I was about to buy new brake shoes when I discovered that for just three dollars more, I could get a whole new backing plate with a new magnet and new shoes installed.  I then decided that since I was getting new plates, I could just put them on the other axle that does not have brakes. Then I would have four brakes instead of two.  I just needed to add new drums to the order.  I also discovered that the non braked axle did not have the mounting flange installed so I had to buy that as well.  So my brake relining job quickly escalated.

When the big box arrived, I began by pulling the rear wheels up on ramps allowing the front axle to hang free.  I removed the wheels and the hubs. I then pulled the rusty U bolts and removed the axle from the trailer.  This step allowed me to carry the axle to the welding table instead of trying to bring the welder to the trailer.

I found the mounting tab fit nicely into a ridge on the spindle like it was mode for it.  I test fit he backing plate and drum to confirm that was the right place.  I had to clean some rust off the spindle surface to make it fit right and to get a good weld. I put a bead around the back on each flange. I made sure it was lined up square with the spring perch.  I used masking tape over ht bearing surface of the spindle to protect it while grinding and welding.

I then reinstalled the axle.  I bought new U bolts but they did not fit so I ended up reusing the old ones. I chased the threads with a die first.

My first glitch came when I discovered the brake plates did not come with nuts.  They were 7/16 – 20 so not something I had in stock.  I made it to Home Depot at 8:58pm to buy some.

The baking plates fit perfectly on the mountings flanges. I then greased and installed the new bearings that came with the new drums. I then discovered the new drums did not come withe a new castle nut washer or key. I reused the old nut and washer and used a new key from stock. I had trouble getting one of the new caps on so I reused one old cap.

Next came wiring.  I was not looking forward to crawling under  the trailer to run wires.  So I spent a few minutes figuring a way to put the trailer on my car lift.  It fits between the post with only an inch to spare.  The arms can’t swing under the frame because they hit the tires.  I ended up using some pipe to span the gap between arms and lifted the trailer that way.  I did not try to thread the wire inside the axle tube although there are holes for this purpose. I just taped it to the outside of the axle tube.

I ran new blue wire from the new magnets to the front of the trailer and used a sheet metal screw to secure the ground side to the trailer frame. I know the instructions say to run a separate ground wire; but the old brakes have been wired this way for over 20 years and they get plenty of current to the magnets.  I spliced into the other brake wire right at the connector.  I may add a switch here later as the front wheels often don’t touch when towing the trailer empty.

A quick test pull showed that the new brakes give me a lot of confidence when towing. It feels much safer now knowing I actually have reserve stopping power and am not using all the brakes just to make a normal stop.