Powerspeed Exhaust Fitting Experience and how to avoid sideskin vibration question

[Alastair B]

I have just finished installing a Powerspeed 4-2-1 exhaust on to my 1.6K which already had a DVA K13a head upgrade package with verniers.

In the interest of sharing knowledge I wanted to post my findings from doing the installation myself and make some observations that other members might find useful.

The installation of the exhaust was well within the capabilities of a reasonable confident home DIY’er with straightforward removal of battery, diagonal cross-brace, primary collector and exhaust. I was fortunate and Dave Andrews had already ground off the excess head stud length when the K13a package was installed so to facilitate easy existing collector removal. As such the engine mounts and canting the engine over was not required.

My installation has at cylinder #4 not a stud/nut for the final fastener but a cap headed screw as the water rail was very tight ot the head at this position. As such I had to dremel grind some small chamfers to the header flange to fit the #4 pipe to the head. The header flanges are about 2mm thicker than the standard Caterham short primaries and this is the reason for the increased interference at this location. I informed Powerspeed of this and they had not experienced this before. So if you have a circa. '99 vintage car, check your #4 cylinder securing mechanism if you are to install yourself and have the ability to grind stainless steel.

The challenging part was taking the ‘brave pill’ and setting about the cutting of the side skin. Powerspeed provide simple but effective instructions, follow-them and you will be fine. I used a drill powered nibbler that I bought from ebay for ~£20, did the job fine. Cut slowly and keep checking with installing the primaries one-by-one and securing tightly to the head to establish the final resting position.

Finishing of the cutting was done with ‘joining up’ some curve cuts with straight line achieved with a dremel grinding disc and a fashioned straight line ‘guide’ which was a steel  hack saw blade smooth side g-cramped to the skin. Then a round-edge file was used in ‘pushing’ mode to avoid smearing the Aluminum onto the outside of the side skin. Finally some fine emery paper used to smooth the final for. You will be amazed at how quickly even the emery cloth shapes the hole with Aluminum being so relatively soft.

Then silencer installation to the 4 loose fitted primaries. I did not have available help at the time to support the collector, but I did have loads of bubble wrap from the Powerspeed packaging….and I mean loads! I used this as a convenient ‘pair of hands’ by resting the collector on a pile of it at just the right height. Then you set about ‘bashing’ in the can to the primaries with a rubber mallet. It is a tight fit, so you have to give it plenty of bashing, but it does progressively move as the interference on the primary to collector pipes takes-up until the middle and rear mounts line-up.

So the result, took it out today and it is fantastic. The sound is deeper and much quieter than my ‘tired’ standard can, it could be driven without earplugs which is a novelty for me. The mid-range torque is the performance reason for such an exhaust and whilst not scientific I felt with my 5-speed box more rapid progress from say 4k rpm in a gear than before. When pulling higher revs the exhaust adds to the previous upgrades and seems more lively and urgent. Plus of course it looks the business!

So to an observation and question;

Q. The side skin panel above the primaries when at idle now vibrates with some stiffness being removed with the larger hole created and my rather lumpy idle, I was thinking about stiffness/change of natural resonance by adding with some ‘sticky lead tape’ or some such, thoughts on this or alternatives welcome.

[Jonathan Kay]

I was thinking about stiffness/change of natural resonance by adding with some ‘sticky lead tape’ or some such, thoughts on this or alternatives welcome.

A related question came up a few months ago about possible ways of stiffening a bonnet.

If sticky lead tape exists it sounds worth trying. Gluing some aluminium strip or channel would be another possibility. Can you identify the mode of vibration to work out which axis should be stiffened? Might be worth filming it and watching in slow motion. 

Jonathan

[SM25T]

The 4-2-1 collector does give some nice mid range torque doesn't it.

[SM25T]

Assume the primaries are not touching the sideskin in the cut out ?

[Alastair B]

Will check for touching of pipe to side skin. I do think I might have to do a little more fine tuning to the opening.

Vibration seemed to be a simple harmonic with the side skin being pushed in and out transversely across the width of the car. Some channel or such in the direction of front to back bonded across that part of the skin for say 20cm would probably add a lot of skin stiffness

I will see what I can get my hands on and update when completed.

[Alastair B]

Took another look and followed up on John's advice.....#3 pipe ws touching the side skin. It is quite feasible this was putting in all that nasty vibration energy into the skin. The pipes weren't touching before the collector went on, so this part of the final assembly changed the position slightly. So all off and back to fettling the hole.

[SM25T]

Glad it was something simple. Albeit a nuisance. Ian

[Smithy77]

Did you use cooper RTV silicone to seal the joints? When I use this stuff the exhaust slips together like a slippery salmon (and comes apart just as easy). No bashing of the exhaust with a hammer required! Just some twisting and wiggling

[Alastair B]

"Did you use copper RTV silicone to seal the joints?"

No I didn't just brute force and clearly ignorance. I will look to get some, thanks