Revised June 6 1996

Revised Sept 22 2001

This tip applies to mostly racing cars although some street cars do have fancy exhaust piping. Racing cars usually have individual piping from each cylinder while most road cars have a single piece simple exhaust system.

For cost reasons and molding limitations the model manufactures provide one piece exhaust systems that are blobs of plastic with sink marks and ejection pin marks everywhere. Some of them can be cleaned up and puttied to look good but others should be tossed and new ones made. The sections I will be describing are;
1. The exhaust pipe
2. The connection piping
3. The bent piping (header)

1. The Exhaust Pipe
This part of the exhaust system is where the exhaust exits. This is probably the easiest part of modifying the system. Most of the time the kit part can be used. All the modeller has to do is drill out the end. once this is done the wall should also be thinned with an exacto knife to get the correct look. This shaving motion has to be done smoothly or the blade will catch and create jagged edges. Paint the inside black to give it an even deeper look.

Sometimes the kit part is so badly made that it should be replaced with a brass or aluminum tubing. The aluminum and brass tubing usually has to have its walls thinned also. Paint the inside black as well.

Chromed Exhaust Pipe
If the exhaust pipe is supposed to be chrome you can replace the plastic part with aluminum tubing. To polish the pipe up, place the tubing in a Dremel tool (or equivalent). Use a longer piece of tubing than what you need. Polish the tubing by starting with a fine grit sandpaper (600 or higher). After this use the edge of a piece of paper to give it the final polish. If left by itself the tubing will turn dull again from oxidation. To keep the chrome look, a clear coat should be applied. I usually just dip this in some future floor wax and let it dry for several days. Note that the walls of the tube should be thinned before polishing. Also when left out to dry the clear coat, point the exhaust end up. This way the clear will not collect on the part of the exhaust pipe that will be seen. When dry cut to desired length

Some cars have instead of a muffler a baffle system(I can't remember the common name for this part). These are disks and look like they are blocking off the exhaust pipe. These can be made by fairly easily. White glue 4 or 5 small sheets of plastic together. File into a circular shape 2 different sizes. Take apart circles and clean up. Laminate circles then glue to end of exhaust. If you have a punch set (expensive) this would be very simple.

Some exhausts are flat (Oblong). To replicate this with tubing, it has to be bent carefully so that the middle section does not collapse into itself. Use small needlenose pliers on the tubing and carefully flatten one inside wall then the other. Go slowly until the desired shape is achieved.

2. Connection Piping
This is usually the only part of the kit that will be used on the scratch built exhaust system. Cut the exhaust pipe and the headers from the connecting pipe and clean up. To connect the new bent piping and exhaust tube usually pins have to be drilled into the kit part and brass rods placed in. Due to the different objects being glued together (plastic, aluminum etc.) CA(super glues) or epoxy glues have to be used.

3.Bent Piping
This is the hardest section of the scratch built exhaust system. The easiest method would be to work with the kit part to make it look good. This is sometimes hard since the exhaust tubing is round and this is hard to keep the shape with filing sanding etc.

The sample we are doing here is a V12 engine. This system has four sets of three (3) pipes converging to one. Other engines may have four (4) converging to one (V8). The diagram (figure 1) shows only one of the 3 pipe sections attached to the

Figure 1

STEP 1 - Hole Spacing Template
Using sheet styrene mark and drill the hole spacing for the exhaust system (figure 1 bottom). Use the kit engine block for reference. Make sure the diamters of the hole are the correct size. Test the kit exhaust pipes on your template to make sure it will go in snugly. There should be no play at all.

Figure 2

Step 2 - Bending the pipes
After getting the correct diameter solder find a short length of aluminum tubing that the solder will slide into. Slightly flare out the end of the tubing. This will be used to bend the solder. We need the slight flare and the aluminum tubing (as opposed to brass) to prevent kinking and nicking of the solder as we bend it. Using the kit part as reference bend each individual pipe to the approximate shape. Do each one from the end of the roll of solder. This will make it easier to handle. Once you are sattisfied with the shape cut the formed part off of the roll of solder. Leave extra length at the ends. These will be cut to size later. Repeat for the other pipes.

Figure 3

Step 3 - Assembly
Dry fit the bent solder to get a general idea of how good the fit should be when they are glued together. Place the first and second bent solder into your template that was made earlier. Don't worry if they do not line up perfectly or if one is longer then the other.
If the two are slightly out of line bend them so they line up together. Add CA glue on the inside length where the two pipes meet (along length "L"). This will hide the glue marks in the final assembly. I prefer CA glue because of the faster drying time but another glue choice would be 5 minute Epoxy.
Make sure the CA glue is dry before adding the third pipe. When adding the third pipe you may find it needs a lot more massaging to get it to fit the first two pipes. Sometimes it may be necessary to make up a new piece. Once the third piece is in place make sure the application of glue is done carefully.

I prefer CA glue with the long tubing since I can apply it without making too much of a mess. If CA glue does get all over the place try and wipe as much of it up as soon as possible. If there is still some left, let it dry before trying to get it off. When dry use your fingernail or toothpick to get the errors off. Do not use an X-acto knife or any other metal object since this can scratch the solder. It is actaully pretty easy to get the CA glue off the solder. With this you may think that the CA glue doesn't hold the solder very well and your assembly is going to be fragile. It turns out that the final assembly is actually pretty sturdy.

Figure 4

Step 4 - Cutting to length
Once the glue has had a long time to dry it is time to cut the assebly to the correct size. Using the kit part determine where the assembly has to be cut. The pipes have to be cut where they will meet the connector pipe. Be careful with the razor saw that you do not scratch the part of the solder that is going onto the model

Figure 5

Step 5 - Connector Pipe
Once the solder assembly has been cut and filed to the correct length you can cut the kit part for the connector section. To make a strong bond you should pin the assembly. This means you should drill a hole in the solder assembly and place a brass pin in there. In the connector kit part you should drill a matching hole for the brass pin. The solder assembly is chrome like you may be tempted to leave this as chrome because it looks so good (maybe not realistic). This decision is up to you, however the connector pipe from the kit will be made of plastic and this may not look good.

If you are able to scratch build a connector pipe out of other material then go ahead.

You may try;
1. soldering brass tubing together. You can cover the brass (tinning) with the solder to get the chrome look
2. carving something out of stock aluminum
3. try and melt some solder into a blob then carve to shape.
Not many easy choices. If you are good at soldering try choice 1 otherwise option 3 seems to be the easiest of the bunch.

Step 6 - Final Steps
Test fit the completed assembly to the engine block. Note that because you have scratch built the exhaust pipes the fit of this to the resat of the kit may be slightly out. Future assemblies may be affexted.
As a final detail you can replace (or cut off) the end of the kit exhaust and replace with aluminum or brass tubing.

If you know you are going to paint the exhaust pipes you should give them a light sanding (600 grit) to give the pain tsome tooth. Otherwise it might be easy for the pain tot chip off.

1. The exhaust headers have a flange that bolts to the engine block. There are aftermarket PE ones but I have never used them mainly because I haven't seen any that are the right size for my applications.
2. The individual bent pipes are attached to the connectors (3 into 1 etc). These are usually bolted together which means there are usually flanges for the bolts. Some systems also have some type of spring mechanism so that the vibrations from the engine don't go down the entire exhaust system
3. Weld lines

Be warned that this is not an easy task and the finished piping may not mate easily to the kit engine block.


Sept 22 2001


Here is some tips on how to paint existing kit parts to get a realistic looking exhaust system. This allies to the above exhaust system but also to the kit exhaust system that does not need modifying. Due to moulding limitations most kit exhaust systems are not completely round. If this is the case it is recommended that the excess plastic be carved away with files and hobby knives. Of course also fill in all ejection pin marks.

Here are two pictures of my Honda 273A 1:12 F1 car. The exhaust system was to be painted white. To give it a worn look I airbrushed light brown on the exhaust system where the pipes changed direction. Be very light on the airbrush. Too much and you can ruin your finish. It is the same with any weathering. Knowing when to stop. I guess I could have dry brushed the brown on butt my dry brushing technique isn't the best and I think the airbrush will give the better faded look. It is better to be light on your shading as opposed to being too heavy with the shading.

These are two pictures of my Tamiya 1:12 Ferrari 641/2. In this case the kit came with a chromed exhaust system. Unfortunately there were mould seam lines that had to be fixed. This ruined the chrome so I stripped it all off. Next my references showed weld lines. Go to my weld tips to see how I made these welds. After the welds were done I primed the parts with Plasticote sandable primer. Next came a coat of Testors Chrome from a spray can. This produces a very chrome look but if fairly fragile and dulls quickly when touched. For this reason I did as little handling of the part as I could. When I did handle the parts I used rubber gloves.

The next step was to airbrush Tamiya clear yellow onto the weld lines. Yellow was chosen because this is what was shown in my references. I thinned the Clear yellow so that when the paint hit the kit parts it was very faint. This process took several coats but allowed be the time to slowly build up the shading.


Here are three views of the exhaust pipes for the Tamiya 1:20 Ferrari F1-2000. This was painted with Alclad II Chrome. This stuff is amazing, looks great and is durable so it can take some ahndling. I have received quite a few good comments from fellow modellers in this state. It is amazing what is available to the modeller these days. Checking references we will now start the shading process. Another name for this is type of shading is calling it heat stressing.

I wish the picture was clearer but at the yellow arrows I have lightly brushed on some Tamiya acrylic clear blue. Notice that the arrows are pointed at bends and the end of the exhaust system. I tried dry brushing but the clear did not like to do this. Dry brushing appears to be one technique I can not get a hang of. To prepare the brushing process I wet my brush with thinner (rubbing alcohol) before touching the tip in the blue paint. I found that if I just dipped the tip into the paint without using thinner first the paint would quickly dry on the brush and if I tried to apply it the paint would gel on the part. Taking thinner to the kit part tended to take a bit of the chrome off. Again be very light with the blue. If you apply too much try and quickly take it off with the brush and hopefully the chrome finish will be ok.

here is the reverse angle showing the blue applied to the end of the pipe and also the inside. Don't forget this area. They look great and I considered stopping here. The other option was to add a different colour as seen in references and ruining the work I have done already.

I decided to go for it and applied Tamiya clear red to the parts just beside the blue portions. The red was applied very sparingly and blended with the blue slightly. This was done to try and make the colour change gradual. I was also fairly random in painting the blue and red. Making similar concentric rings would look too fake. Having the random element is more realistic. The picture above is a bit dark and the slight differences in real life look great. Blue lines showed where I painted blue and the same for the red lines

The reverse angle that shows the colour change nicely at the tip

I was working on 3 kits at the same time so I could take this picture of the different steps.

1. Chrome by itself looks great and fooled quite a few fellow modellers

2. Add some blue and the exhaust system looks 100% better. Now do you leave it as is or risk ruining it

3. WOW the red has made the exhaust system look another 100% better. I have chickened out and decided to leave it as is. I don't think I can get it any better but then again I thought the same thing after applying only the blue. Part of modelling is know when to stop

Reverse angle. Not as obvious but the one on the bottom looks amazing.






Return to Home Page http://www.interlog.com/~ask

Send comments, suggestions etc. to ask@interlog.com