3D Printing: Improved Inlet Trumpets

Nothing quite gets the internet clickidy-clicks like a 3D printing article! In the following post I use 3D printing to fix something that wasn’t really broken.

The OLD Design

I have never been happy with the original mountings for the inlet trumpets on the Locost. Its quite common to use silicone hose to align everything within a retro-fit throttle body system and sadly mine was no different. This design can lead to miss-alignment between the trumpets and the throttles, potential shrouding of the inlet path and variations in inlet length; cylinder to cylinder.

This is the kind of stuff that keeps me up at night and it needed to be improved.

The original setup used a nice carbon fiber backing  plate to mount the airfilter too. This was as soft as a chocolate tea pot, and four aluminum trumpets were glued-in with black polyurethane sealant. It never failed, it was light and did its job okay; but it wasn’t perfect.

I wanted a new design that would allow me to interchange different length trumpets, for testing on the dyno, and ensure the trumpets would inline with the inlet tract. So I turned to CAD to see what I could conjure up…

The NEW Design

Engine tuning is highly sensitive to inlet path length (read one of the best articles in the world if you want to know more), and I wanted to ensure that this variable remained static/constant. This being the case, It was important that the aluminium inlet trumpets were held up tight to the throttle bodies and positioned concentrically.

I started by measuring the GSXR throttle bodies that currently sit on the engine and then 3D printed some prototypes. The first design to nail down was the backing plate mounts. These would make the transition from the round throttle bodied to the flat air filter backing plate and essentially hold the whole lot to the engine.

I settled on a design that pushed onto the throttle bodies and over a useful cast-in ridge. This then clamped down with a jubilee clip. As a rule of thumb, jubilee clips aren’t super sexy, but when combined with dark grey plastic parts they can look utilitarian and purposeful.

I did try a version that held on using the friction supplied by an M4 bolts. This was a terrible idea. Plastic parts are not strong in tension and it would simply bend the mount when being tightened down.

The final design looked like this.

From here I had a nice flat surface to work. I carried across the jubilee clip compression-based design over to the trumpet side, as it worked so well on the throttle body side. This also allows quick release of the trumpets for switching to different lengths.

Its hard to see in the following CAD drawing, but the whole lot is sealed together with rubber nitrile o-rings. There is an o-ring between the backing plate and the throttle body mount, and an o-ring between the throttle body mount and the throttle body itself. These are super easy to design in, reusable and reliable.

 

Then is was simply a case of printing out eight the separate parts and cutting out the backing plate. The inner prints took approximately 3hrs each to make and the outer 2hrs each.

As always, hit go and come back later. These were made is standard PLA and, as they are on the cold side of the engine, I have no qualms about it.

The whole lot was finished off with some pretty aluminium mounting bolts for the air filter.

This setup is definitely heavier than the previous, but its far more stout and should allow for some fun experimentation on the dyno.

 

 

 

Locost: Dry Sump, Part 1/2

I have been considering building a dry sump for a long time, in fact, ever since I started building the the car. However they are a fairly complicated piece of kit, and I have therefore shied away from them until now. Fortunately I changed my mind due to the data I collected at Snetterton and having access to a decent Turret Mill at my new job. Lets get into this.

What is a Dry Sump?

Up until now I have run a Wet Sump on the Locost. In a Wet Sump system oil passes down into the oil pan under gravity and is fed back into the oil pump via a static pickup. Under longitudinal and lateral acceleration this pickup can become uncovered, leading to oil starvation and heartbreak.

A Dry Sump deals with this problem by running an extra pump attached to the engine; a Vacuum Pump. This moves oil from the sump pan to an external tank, which is tall and thin, and much less susceptible to oil starvation. An external oil pump, or the original internal pump, is then fed from this tank; supplying oil to the engines bearings and moving parts.

Although I have built a complicated baffled and gated Wet Sump the car still experiences a slow drop off in oil pressure in long right hand corners. I felt it was finally time to take the leap and fix this once and for all with a Dry Sump System.

If you still have no idea what I am on about, my previous post covering the build of my Wet Sump is a good place to start  (link).

What are the Benefits?

  • Depending on the oil tank used, it allows constant cornering at a lateral acceleration of up to 5g.
  • Instead of the crank case being under positive pressure, due to combustion blow by, it can be designed to be under constant vacuum. This helps to…
    • Reduce Windage, increasing engine efficiency at high speeds.
    • Improve the in-cylinder octane level, as less oil passes by the rings into the combustion chamber.

The Build

As a Design Engineer I’m trying to do more… Design, when it comes to the Locost. So instead of jumping straight in and cutting metal on day #1, I drew up what the system was going to look like and got an idea of the layout. Packaging in the Locost is TIGHT, so this wasn’t ever going to be easy.

This is the space I had to work with. The ignition trigger wheel was already there and potentially in the way, and there wasn’t enough room to fit a pump on the passenger side of the bay (the alternator was in the way!) and the pump needed to be positioned to avoid the chassis rail and steering column. Oh, and retain a place for the ignition trigger sensor…
This was my initial design. I already had a Pace CD2000 Pump that I had bought many moons ago for such an occasion and I modified it into a two-stage vacuum pump, with no pressure stage. I then used some calipers to measure and get it into cad. This allowed me put a drive gear on the front of the “engine” (well sump flange and front pulley) and work out the beginnings of the new oil pan.

After many evenings and iterations it looked something like above. I had decided to use silicone hose for the oil routing between the sump and pump, as it gave many more options in terms of packaging. This mean’t I had to run steel tubing out of the pan.

I then finalised the design of the drive-hub and gear. It indexes onto the lower cam-drive and is driven through the five M6 bolts that hold onto the front pulley.

With the component designs sorted I could finally start cutting steel. I had a spare standard sump on one of my engines, so I used that as a donor flange. When I built the baffled sump I made my own flange and… it wasn’t as good as the pressed Suzuki item. All the small details really help to seal the gasket to the block and I was happy to carry them over. I marked the sump 25mm down from the flange and attacked it with the grinder.

At this point I got my own lathe to help move the project along; achieving a massive life goal in the process! Its only a little Sieg SC3, but it is super useful for making little top hats and smallish components. The drive hub for example.

I was able to go from bar-stock to component in one afternoon. I had made my own digital read out for the top slide which made boring accurate depths super easy.

The final features were then machined on the mill. A slot to clear the crank keyway, the five M6 bolt holes and the five M4 gear mounting threads.

This was what I thought would be the hardest part of the project, but once I used the right equipment to make the components it was actually really straightforward.

At this point I could properly place the vacuum pump in the real world, choose a belt length, and finish the oil-pan.

What I don’t have is pictures of the countless hours I spent trying to seal the sump for leaks. I used water and air to find pin-holes and just kept welding, grinding, checking and repeating.  Side note: I need to get a TIG welder…

I also added some bolt-in mesh within the sump to protect the outlets. You’ll noticed that I ended up moving one of the oil outlets relative to the CAD. It actually ended up far tighter and better packaged in real life.

Having made the oil-pan, pump-mount and drive, there were a few small components that needed to be made before I could install the pan. One of these was a bung for the original oil pickup in the engine. This was essentially a large top hat, bolted in place, allowing the use of the original pickup seal.

Following this I could finally install the whole lot in the car.

In the final part I will cover the installation of the oil tank and oil lines, and then find out if it actually works!

Fabrication: From CAD, to 3D Print, to Fibreglass

To trackday a car it needs a reasonable level of illumination, to communicate your intensions and make yourself more visible in low light conditions. Indicating left, pass me on the right. Hazards flashing, I’ve had a bad day. This is something the Locost has not needed until now, as it has only ever been driven on closed courses with only one car competing at a time.

I already own a set of rear light clusters that I bought almost six years ago when I was initially stockpiling parts. I decided to go with these “hamburger” style rear lights as they mirror the round headlights at the front of the car, that I am also yet to install, and also I could get them with clear LED’s which would keep the car aesthetically pleasing. It also helps that they weren’t cut-off-your-left-leg-and-right-arm expensive.

The easiest and quickest place to mount rear lights on a seven is directly to the rear bodywork. While this could have been done on a Saturday afternoon, with time for a few cups of tea in-between, it would have been almost irreversible and completely illegal for road use if I ever felt like going that way (lights must be a maximum of 100mm from the outer most bodywork). So this left me with only one option which was to mount them on the rear wings. Never one to turn away the opportunity to do something the hardway I decided this would be a great opportunity to make my own light pods, in my own asthetic style- fire up the 3d printer!

CAD

First of all, my printers build volume is a measly 150*150*150mm, and would have never been able to print an entire light pod in one go. Also, PLA plastic would have never been a good choice for components like this, given that they will sit in the sun for extended periods of time (damn you 60degC glass transition temperature). These would have had to have been printed in ABS. Printing thin walled ABS shapes is pretty much a no-go without some major warping, so this left me with only one option… a 3d printed mould.

I grew up around fibreglass in all its forms. Quick shabby make-a-mould-out-of-Tupperware fibreglass, and top quality a-thousand-layers-of-wax-and-lots-of-polish fibreglass; this was going to be something in the middle. Because of my limited build volume I opted to design the mould to split into four separate parts. This also meant that releasing the strangely shaped light pod would be relatively straightforward as long as everything was unbolted and persuaded a little; so it was win/win.

After measuring the curvature of the rear arches and the geometry of the lights I frew the mould itself and split it in the X and Y axis. This is a female representation of the lightpod, with the reverse being the actual “male” final piece. Getting a clean striation-free mould surfce was going to be unlikely, and comes with the territory when 3d printing, so I knew I was going to have to sand and polish the final mouldings after they were produced.

Light Pod Mould

3D Print

I believe these components took between 16 and 19 hours each to print in PLA, which goes to show how awesome my Printrbot Simple Metal is. I’m very happy with my printer setup at the moment, as it’s hugely reliable over a long period of time. Hold on, where’s your RepRap gone Josh? That’s a story for enough time…

Light Pod Complete Mould

The mould was sanded with 200 grit sand paper and given 5 layers of wax. The wax helped to fill in the crevasses between the separate mould pieces and massively helped the release after moulding. In short, this stuff rocks.

simonizwax

Fibreglass Mouldings

Once the mould itself was ready to use the mouldings were made in a fairly simple way. Firstly a layer of White Gel Coat was applied to the mould with a brush. Gel Coat is essentially resin with pigment in, which gives the moulding an outer layer which can be sanded and painted to achieve a nice finish. If the mould is of a high quality the Gel Coat can simply be left as is. I would eventually be painting these moulds so I wasn’t too bothered about the initial surface finish.

Light Pod Gel Coat

Once this had adequately hardened polyester resin was brushed into the back of the Gel Coat and 450gram fibreglass rolled into that (I gave it approximately 4 hours at 10degC, with a 3% mass fraction of catalyst to kick things into gear). The rolling process is important as it helps to remove air bubbles from the structural fibreglass and improves the strength of the composite. It also helps reduce the amount of resin you have to use, as the fibres are pushed tight against the Gel Coat and the resin soaked through. If the whole lot was just brushed on then it would have likely had a higher resin content and been heavier.

Light Pod Laid Up

This was left for two days to harden and then extracted from the mould. I’m very happy with the final product and its far lighter than I expected it to be. The ‘pods will be glued into the back of the arches and then faired in with filler. The whole lot will then be smoothed and painted; probably glossy battleship grey.

Light Pod A

Light Pod B

Light Pod C

Have you ever tried any Fibreglass work? If not, give it a go! Its actually ver y rewarding and if you take your time with each step you can achieve great results.

Locost: Baffled and Gated Sump

This is the first part in a series I like to call “What’s wrong with the Locost?” or WWWTL for short. I promised myself I would do a Trackday this year and as things are starting to slow down for the summer I now have time to prepare the car.

Firstly, the Locost is not perfect; I can easily stand and point my finger at a million things “wrong” with it and there are a few things I can’t really live with that I feel I need to amend before it starts turning laps.

You see, as you fix the fundamental setup issues on your home built race car, and attach a set of half decent sticky tyres, you’ll start to go around corners much faster. This has a big effect on the longevity of the car, increasing the loads through the suspension and engine, and you will definitely find some design flaws if you are lucky enough to have any. If you applied good engineering when designing/building said race car you will hopefully have no issues. You would have considered all loading conditions, and you will suffer no tears/breakdowns/failures.

Something I feel I did not consider enough many moons ago, and potentially completely overlooked, was oil starvation.

 

The Oiling System

I’ll do a short run through of the oil system in a combustion engine to give you a basic idea of what we are dealing with.

Firstly, oil lives in the sump pan. This is essentially a bucket of oil at the bottom of the engine which stores a supply of oil for the engine; this is directly under the rotating crank. Oil is sucked out of the sump by a crack driven pump and forced through an oil filter, which removes all the small particulates which might potentially cause damage upstream.

From the oil filter it feeds the main oil gallery which gives oil to the main bearings and crank, ensuring there is adequate lubrication and load support for the connecting rods. The main gallery also has a vertical feed going vertically towards the head. This lubricates the cam bearing surfaces and pressurizes the hydraulic lifters.

Oil slowly leaks out of the bearing surfaces, and flows back to the sump thanks to gravity. The restriction between the pump and atmosphere (the effective hole size in which the oil leaks out of) leads to a pressure build up in the oiling system. Once a given oil pressure is reached a blow-off valve allows oil to flow straight back into the sump, restricting how much oil pressure will be achieved. Therefore the less wear on an engine, the greater the restriction and the greater the running oil pressure (until the blow-off valve pressure, which is usually 60-70psi).

As an aside, when an engine is cold the oil is thick and viscous, and therefore the oil pressure is higher.

G13B Oil System

So, if for some reason the engine is starved of oil it will pump air and the oil density will drop, flowing easily through the gap in the bearings and reducing the oil pressure. Air does not lubricate or bear load very well, leading to excess wear and potential engine failure.

In short, oil pressure is an effective measure of engine health.

 

The Sump

So how does oil starvation occur? Well usually its one of three things, a lack of oil in the sump (check your dip-stick!), aerated oil or oil slosh away from the pickup. Keeping the sump full is easy, and really there is no excuse for having a low oil level, however the other two are not so obvious.

Oil aeration occurs when the crank stirs up the oil in the pan and fully/partially turns it into foam. This can be designed out with use of a Windage Tray; more on that later.

Oil slosh occurs due to the accelerations that are applied to the oil volume. If you achieve a lateral acceleration of 1g (at the apex of a corner for example), there will be a force pushing the oil against the side of the sump equal to gravity and it will set in triangular shape; as illustrated below:

Oil Slosh

In this case the pick-up is partially open to the air and pumps that as opposed to oil. This leads to bearing on bearing interaction, friction, wear and potential engine failure. The secret to good sump design is to reduce the chance of the pick-up being exposed to free air.

You can do this by using a tall deep sump, or by baffling and gating the sump. As the Locost is a small tightly packaged race car its nearly impossible to package a tall sump without running an impractically high ride height, so the sump needed to be baffled and gated, with an inbuilt windage tray.

 

Old/Poor Sump Design

My old sump was built from the flange of a standard front wheel drive sump, with custom sheet metal work underneath. The pickup was at the front and approximately central. It had longitudinal and lateral baffles with liberal drainage holes between each (making them almost useless) and a bolt in windage tray. It looked a whole lot like this:

Old Sump with Windage Tray

With the windage tray removed the baffles were accessible:

Old Sump Baffles

In hard right hand corners I think it was possible for the oil to slosh to the left hand side of the sump and expose the pick-up; as you can see there is no baffle in the central section where the pickup was located. The only saving grace of this design was its large capacity, giving minimal oil depth change when oil is trapped in the top end of the engine. Fortunately when I put slicks on the car it had terminal understeer and I don’t think I did any serious damage.

Given that the sump was off the engine, it was a great opportunity to inspect the oil/sump for particulates. The oil was clear of shiny aluminium bearing material, but there were some small bits of the cork gasket in the bottom; nothing scary but also suboptimal.

Blergh

I was happy to move on from this design…

 

New Sump Design

The new design was going to be wider and shorter than the original, positioning the pickup in the middle of four separate oil chambers, each giving the pickup instantaneous oil in the case of hard cornering. Also, the windage tray would bias towards the pickups central volume, to flood it and reduce the chance of oil starvation.

New Sump Flange

Fabrication started by cutting out the main flange to mount to the block. This was bolted to an old junk fitment engine I had lying around (I use this for making engine mounts, brackets etc).

New Sump

New Sump

New Sump Windage Tray

New Sump Pickup

Then the windage tray was cut to match the sump and measurements taken from the chassis.

New Sump Central Chamber

The sides of the sump were then cut and tacked to the windage tray. The central chamber around the pickup was mocked in place.

New Sump Gates

Sump Baffles

Welded Baffles

Then the baffles were put in place to create the four separate chambers. Four gates were added to the central chamber to avoid oil moving away from the central chamber in hard cornering; these were made from steel door hinges! Note that they have limiting tabs to stop the gates going over-centre and killing the engine. The baffles were welded into the bottom plate to stiffen the sump and ensure oil does not escape the central chamber.

Sump Drain

I almost forgot to add a sump drain plug (uh oh!), so I welded in an M12 nut. It turns out M12 course thread is not a standard sump plug size (arg!) so I had to use an M12 bolt with a magnet epoxied too it; could be worse.

Oil Leak Down Test

Once the whole thing was welded together it was tested for leaks using some old oil and left to sit for a few evenings.

Painted Sump

After this it got a snazzy coat of Racing Red!

Closing Comments

The sump is now bolted onto the car and we will see if it causes me any issues. On paper it should be a great improvement over my previous sump and I’m hoping it will give the confidence and peace of mind its designed too.

Before Christmas I will have gathered some track data, covering a large span of lateral/longitudinal accelerations and engine oil pressures. In a perfect world there would be no drop off in pressure over the full span of achieved accelerations; but realistically I’ll  be happy with just very low drop off and a healthy engine.

There is still plenty to do before hitting the track- front wheel arches, rear lights, blah, blah blah… I will get there eventually!

 

Fabrication: That time I made an Exhaust Manifold

I’m going to try to document a few of my older projects that fell through the cracks and didn’t make it on to here. Hopefully you’ll find these little articles both interesting and informative… and there are pictures!

A couple of years ago I made an exhaust manifold for a friends Seven. Having seen the stainless manifold on my Locost he wanted one in the same “over the chassis” style. The manifold on my Seven was/is OK, it does the job, but its not my best piece of work; I was learning along the way. The Locost itself is a testament to my abilities at each stage of its build; some parts are better than others due to improving my fabrication skills as I went along.

Locost Exhaust Manifold

Locost Exhaust Manifold 2

Locost Exhaust Manifold 3

Locost Exhaust Manifold 4

 

 

 

 

 

 

 

 

This second exhaust manifold project benefited from everything I had learn’t and was properly jigged and built close enough to equal length. I built it from separate bends of 316 Stainless Steel with 3/4inch headers and a 2 a inch collector. The primary lengths were specified based on the expanded volume of a single cylinder cylinder, going from atmospheric temperature to an exhaust combustion temperature I found on the internet (I have never measured exhaust gas temperatures before, so I think I can be forgiven for consulting the web).

From what I heard it did well on the dyno, and in truth I was sad to see it go; it took a lot of time and effort to make. Eventually the Locost will get one of the same quality, if not better.

Exhaust Manifold 1

Exhaust Manifold 2

Exhaust Manifold 3

Exhaust Manifold 4