categoryEngines

ManDoCar: Episode #3, Painting Dinghy’s, Man Do Compressor, Nissan Leaf Smugness

It happened again. Alex and I got behind our microphones and discussed the state of our hobby projects and many other random pieces of Engineering.

Dinghy updates, paint types, the magic of radio 4, man do compressors, compressed air cars, the Nissan leaf, electric car ownership, tesla’s, drag simulation, smugly pre-heating your car, the Locost’s shiny bodywork and the label “sports car”

Follow us on Twitter @ManDoCarPod

Holiday Drag Racing, Part 1/2

COVID19, and the isolation associated with it, has made us all go a little mad. Personally, I am in need of some Automotive escapism, and my choice of holiday TV has been Street Outlaws No Prep Kings (Season #3, you can find it on MotorTrend).

While drag racing is considered very niche in the UK, it’s huge over the pond and there are loads of online shows covering it. No Prep Kings pits big high powered American cars against each other in eighth mile drag races. Each round the losers are knocked out until there is only one winner left. With approximately 32 cars competing in each event, and with some serious personalities knocking around the pits, it’s properly entertaining.

I’ll be honest with you, I often skip the preamble and go straight to the racing, so lets do that right now!

Straight-line Simulation

To my British audience: Don’t write-off Drag Racing just yet. Yes they only go in a straight-line, but there is a lot more involved in proper drag racing than it may first appear and the cars are not trivial to build or tune. That said, I don’t own a drag car. I own a British Sports Car, and that is going to be our reference point.

I have thrown together a very quick and dirty simulation to get things going; the code is attached at the end of the article. It’s rough. Really rough, so to all the Engineers out there: this is a tool to show how interesting drag racing is, not a Curriculum Vitae. The results also yield insights into how to go fast in a straight-line, which I think is worthwhile.

A simulation isn’t worth much without some input data, so to begin with we I used some rough estimates of the key variables of my little Locost.

Chassis

VariableValueUnitNote
Total Mass600kgAbout right. It was measured at 490kg back in 2014 before receiving its road gear and dry sump. Then add my weight and some fuel…
Weight Distribution Forward43%Again, measured back in 2014 and I doubt it has changed much since.
Height of the Centre of Gravity0.4mI have guesstimated a number well above the crank centre line of the engine and slightly above the top of the chassis. If anything, it’s probably lower in reality
Wheelbase2.35mMeasured in CAD and confirmed with a tape measure
Drag Coefficient (pCdA)0.9I had to get a reference for this from an American Locost forum, but I do know this number is “high” which is correct for a Seven; they are very high drag cars. Note that this number includes air density, which simplifies the drag equation
Rear Axle Grip1.2N/NOkay, stick with me here. I reckon this is the grip level of a decent touring car tyre at a reasonable weight and pressure. But we’ll soon find it doesn’t matter that much to begin with.

Engine

I had to have a guess at an engine torque curve given that I am yet to have a successful dyno run. The stock G13B is said to make 110Nm at 5500rpm and 100hp at 6500rpm. My quick maths suggests a torque of 109.5Nm at 6500rpm (torque=power/speed). That’s only two data points! To round things off I set the zero speed torque as 90Nm and the roll off torque at 8000rpm to 80Nm; this is probably optimistic but it will do for now. The curve was as follows:

To begin with the engine shifts at 6500rpm (peak power).

Drivetrain

The following gear ratios are from the early model Suzuki Samurai gearbox that is in the Locost. I confirmed these ratios to be correct using engine speed and wheel speed calculations (they can also be found here).

VariableValueUnitNote
1st Gear Ratio3.652:1Terribly short ratio
2nd Gear Ratio1.947:1
3rd Gear Ratio1.423:1
4th Gear Ratio1:1Not unusual
5th Gear Ratio0.795:1This is the early Suzuki Samurai gearbox. A slightly shorter ratio is available in the later boxes
Final Drive Ratio4.3:1MX5 Mk1 Differential. The only ratio available I believe.
Wheel Diameter0.5522mBased on a 185mm wide 60 profile tyre on a 13inch rim
Wheel Circumference1.7348mThe diameter multiplied by pi

Anyone that knows anything about gearboxes can spot that these ratios aren’t great. The first is way too short and the fifth is way too long. But, I am hoping through a little simulation, we can work out some strategies to live with what we have.

Our First Pass

With all that committed to code and the use of a really simple linear integrator we get a quarter mile pass that looks something like this:

A 13.463s quarter mile, going from 0-60mph in 4.495s? Not bad for a little 1.3 litre sportscar. Sadly though, there are a number of assumptions in this simulation that may make this massively unrealistic:

  • Instant weight transfer. There are no real chassis dynamics in this simulation.
  • A completely locked rear differential. Okay this is not as weird an assumption as you might think. I now run a locking differential which should hopefully, under hard launch conditions, be locked.
  • The grip is relatively high. The throttle is pegged at 100% the whole time. But I’ll be honest with you, this is the case for the Locost on warm tyres and a good surface. Its not got acres of power so you don’t need to pedal it.
  • A perfect launch. There is no holding the revs and trimming the clutch here.
  • No gearshift times. This is one thing I just can’t stand for. In the above pass there are four gearshifts that all take place instantaneously. The time these actually take could have had potentially a huge effect on the outcome of the simulation time.

Adding a Gearshift Delay

With a manual synchronised transmission you waste time clutching the engine/gearbox when selecting a new gear. During this time period you are not accelerating forward; in fact you are slowing down due to drag.

From my own data I know that a gearshift can take anything between 0.5s to 1.0s to complete, depending on how aggressive I am being on the gearbox. I added this into the simulation as a time period after any shift where no engine power is used.

The updated simulation looked like this:

Well. That’s sucks.

Adding a gearshift delay into the simulation of 1.0s cost a total of 1.664s in the quarter mile and 2.125s in 0-60mph time. I’d rather have that performance back thankyou! Here is a table giving a sweep of the results:

Run [#]Gearshift Delay [s]Quarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
10.013.463-98.58-4.495-
20.514.3050.84296.37-2.215.5581.063
31.015.1271.66493.35-5.236.6202.125

So what options do we have to get this performance back? We could simply reduce the shift time (automated paddleshift anyone?) but that isn’t a realistic option for the time being.

How about making better use of the torque that we already have? If you look at the acceleration plot its clear that the car is still accelerating at 6500rpm. While it continues to accelerate hard, and the engine can take the extra rpm reliably, its worth delaying the gearshift.

Lets sweep the shift rpm and see what difference it makes, keeping the 1.0s shift delay in the simulation for realism.

Engine Speed

The results of the simulations were as follows:

Run [#]Engine Shift Speed [rpm]Quarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
1650015.127-93.35-6.620-
2700014.795-0.33294.040.696.425-0.195
3750014.529-0.59894.401.056.287-0.333
4800014.327-0.894.190.845.068-1.552

Well that’s mighty interesting! Shifting at a later RPM yielded a benefit in every case, and in the final simulation saw a full 1.219s improvement in 0-60mph time. But why might this be? Plotting each run against each other makes the differences quite clear.

Note that the following plot uses distance as the x-axis, as opposed to time. I find this makes comparison much easier.

Well there you have it, shifting at 8000rpm means you are only changing gears only once before 60mph; hence the big improvement in this metric. This kind of suggests that 0-60 times are a little redundant and are very dependant on gear ratios and shift points. That said, it did go faster!

Also note that even though peak horsepower was at 6500rpm, shifting at 8000rpm was faster in a straight-line. This means that the shape of the torque curve beyond peak power is important, and dictates the most efficient shift point. Keep that in mind when mapping an engine.

Obviously my current torque curve is a complete guess so it may not actually be beneficial to shift at this rpm in the Locost, but its worth considering.

Power and Gear Ratios

Up to this point the very short first gear ratio hadn’t caused any problems. The throttle is always pegged at 100% throughout the whole run when not shifting gears. However, what if we add more power?

The Cultus Spec G13B

In my recent engine rebuild I used Suzuki Cultus Cams and Pistons. This raised the cam lift from 7.5mm to 8mm and the compression from 10:1 to 11.5:1. These parts were only available in Japan and are relatively rare, but raise the peak horsepower from 100hp to 114hp. I believe peak horsepower is moved from 6500rpm to 7250rpm, but I can’t remember where I read this; details on these engines are hard to find in anything but Japanese.

I assumed the details above were correct and made a modified torque curve to suit:

To create the above I shifted all of the data points by 725rpm and then multiplied the entire torque curve by 104%. This gives the desired 114hp at 7250rpm.

Engine Comparison

Using the same simulation as before, with 8000rpm shift points for the original engine and 8725rpm shift points for the new engine, I could make a comparison. The results were as follows:

Run [#]EngineQuarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
1Stock G13B14.327-94.19-5.068-
2JDM Cultus Cams and Pistons13.74-0.58796.942.754.712-0.356

Well that’s a bit more like it. Much closer to the original numbers without gearshift delays and considerably quicker in a straight-line.

Note however that the car is still not traction limited. If this is truly the case in real life than this first gear ratio is not the end of world at this power level. That said, I was still interested in what changes in first gear ratio would make.

Different First Gear Ratios

A scan of first gear ratios yielded the following comparison. I made use of the new engine data above as a baseline setup.

Run [#]1st Gear RatioQuarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
1Original 3.652:113.740-96.94-4.712-
23.000:113.8420.10296.7-0.244.8840.172
32.500:114.0910.35196.13-0.815.2940.582

And… it went slower. My thought is a longer first gear is only needed if you are traction limited in 1st gear. That means if you have more power or lower grip, its worth changing. Other than that, short is fast… as long as you have a relatively flat torque curve and the drop off in torque on the upshift isn’t bad.

Plenty to discuss, but this is not the space to go in depth.

Drag Sensitivity

I was interest in what effect decreasing drag would have on quarter mile time. My little Lotus 7 is pretty quick from 0-60mph but runs out of steam somewhere beyond that point due to the large drag coefficient is has.

I can vouch that the original Suzuki Swift GTi that its G13B engine came out of could do 125mph in a straight-line, but the Locost tops out at just over 100mph. That’s a huge difference in drag.

The results from the drag scan were as follows:

Run [#]Drag [-]Quarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
1Original13.740-96.94-4.712-
2-5%13.712-0.02897.610.674.703-0.009
3-10%13.684-0.05698.291.354.694-0.018

The results were quite interesting as I expected the drag to have a far greater effect than it did. There appears to be a clear change in the shift point between third and fourth gears, but this is almost 75% of the way down the track, so the overall difference in quarter mile time is minor.

Interestingly, when I was driving around Snetterton I spent most of my time in 3rd and 4th gears, where the data above suggests drag has a notable effect.

Grip Sensitivity

Lastly, before I venture into the world of 1/8th mile monsters, I wanted to simulate the Locost on a less than perfect surface or tyres.

Autosolo events have to start with dead cold tyres, no warming is allowed, and the surface often starts the day covered in stones and debris. This means the first few starts are always worse than those later in the day; this is due to low grip.

The results from the grip scan were as follows:

(Appologese for the lack of legend, I have been fighting Octave on this front! Baseline is Black, -15% Grip is Blue, -30% Grip is Red)
Run [#]Grip [%]Quarter Mile [s]Delta [s]Speed [mph]Delta [mph]0-60mph [s]Delta [s]
1Original13.740-96.94-4.712-
2-15%13.7670.02796.91-0.034.7490.037
3-30%13.9970.25796.72-0.225.0330.321

Lower grip, slower car; not a surprise. That said, such a little lightweight car with low power wasn’t as much effected by lower grip than I expected.

Summary

On a good day with warm tyres the Locost in its current trim can potentially do a 13.74s Quarter Mile @ 96.94mph, with a 0-60mph of 4.712s. One of the lowest hanging fruits is shift times (I knew this!) to make the car quicker in a straight-line.

What I didn’t tell you is that this is equivalent to an Eighth Mile time of 8.772s @ 82.43mph. No Prep Drag Cars can do this in as little 3.900s!

In the second part I will play with the numbers and see what is required to a get a car to travel this distance in a much shorter time.

Code (Octave GNU or Matlab)

clear all; close all; clc;

# Vehicle Definition
mass = 600;       # [kg], Total Vehicle Mass
wd = 0.43;        # [-], Forward Weight Distribution
h_cog = 0.4;      # [m], Height of COG
wheelbase = 2.35;  # [m], Wheelbase, A guesstimate from the CAD, it changes with castor
drag_pCdA = 0.9;   # [], Drag Coefficient * Area * Air Density
# Taken From: http://www.usa7s.net/vb/showthread.php?9876-Caterham-Wind-Tunnel-Testing
# Approximately 1.5 * 0.66, which is inline with what others are quoting
# I trimmed this down by 15% inline with observations at Snetterton
grip = 1.2;       # [N/N], Rear Axle Peak Grip

engine_speed = [0,5500,6500,8000]; # [rpm]
engine_torque = [90,110,109.5,80]; # [Nm]

# Plot for Engine Power / Torque
if 0
  figure; hold on; grid on;
    plot( engine_speed, engine_torque, 'b' );
    plot( engine_speed, engine_torque .* (2*pi*engine_speed/60) * 0.001, 'r' ); # [kW]
    plot( engine_speed, engine_torque .* (2*pi*engine_speed/60) * 0.001 * (1/0.7457), 'r' ); # [hp], Metric
    h = legend( 'Engine Torque [Nm]', 'Engine Power [hp]' );
    legend (h, "location", "northeastoutside");
    xlabel( "Engine Speed [rpm]" );
endif

gear_ratios = [3.652, 1.947, 1.423, 1, 0.795];
# From: http://www.zukioffroad.com/tech/suzuki-samurai-specifications/
gear_ratios_max = 5;
gear_final_drive = 4.3;
gear_wheel_diameter = (185*0.60*2 + 13*25.4) * 0.001; # [m]
gear_wheel_circumference = gear_wheel_diameter * pi; # diameter * pi
gear_shift_rpm = [6500, 6500, 6500, 6500, 6500];
gear_shift_time = [0, 1, 1, 1, 1];

# Simulation Variables
g = 9.81;         # Gravity
t = 0;            # [s], Current Time
dt = 0.001;       # [ds], Delta Time
a = 0;            # [m/s^2], Instantaneous Acceleration
v = 0;            # [m/s], Instantaneous Velocity
s = 0;            # [m], Distance Travelled
gear = 1;
zero_to_sixty_time = 0;
gear_shift_timer = 0;

# Datalog
t_log = [];
a_log = [];
v_log = [];
s_log = [];
rpm_log = [];
throttle_log = [];

# 1/4 Mile = 402.336 meters
# 1/8 Mile = 201.168
while s <= 402.336
  
  axle_speed = v / gear_wheel_circumference;
  
  # Calculate engine rpm based on current speed
  rpm = gear_ratios(gear) * axle_speed * gear_final_drive * 60;
  
  # Should we up shift?
  if gear < gear_ratios_max
    if rpm > gear_shift_rpm(gear)
      gear = gear + 1;
      gear_shift_timer = gear_shift_time(gear);
    endif
  endif
  
  # Calculate the weight on the rear axle (including weight transfer)
  # and the maximum force the tyre can supply
  mass_rear = mass*(1-wd) + (mass * a * h_cog / wheelbase); # [kg]
  if mass_rear > mass
    mass_rear = mass;
  endif
  max_tyre_force_rear = mass_rear * grip * g; # [N]
  
  if rpm > gear_shift_rpm(gear)
    engine_torque_output = interp1 ( engine_speed, engine_torque, gear_shift_rpm(gear) );
  else
    engine_torque_output = interp1 ( engine_speed, engine_torque, rpm );
  endif

  engine_torque_at_axle = engine_torque_output * gear_ratios(gear) * gear_final_drive;
  engine_force = 2 * engine_torque_at_axle / gear_wheel_diameter;
  
  # Calculate drag
  drag_force = 0.5 * drag_pCdA * v * v; # [N]
  
  # Estimate throttle position
  throttle = 1;
  if engine_force > max_tyre_force_rear
    throttle = max_tyre_force_rear / engine_force;
  endif
  
  # Are we shifting gears?
  if gear_shift_timer > 0
    max_tyre_force_rear = 0;
    engine_force = 0;
    throttle = 0;
    gear_shift_timer -= dt;
  endif
  
  # Calculate Acceleration
  a = ( min(max_tyre_force_rear, engine_force) - drag_force) / mass;
  
  # Rough Integration
  v = v + a*dt;
  s = s + v*dt;
  t = t + dt;
  
  # Add to the Datalog
  t_log = [t_log; t];
  a_log = [a_log; a];
  v_log = [v_log; v];
  s_log = [s_log; s];
  rpm_log = [rpm_log; rpm];
  throttle_log = [throttle_log; throttle];
  
  # Grab 0-60 time
  if zero_to_sixty_time == 0
    if v .* 2.23694 >= 60
      zero_to_sixty_time = t;
    endif
  endif
  
endwhile

figure;
subplot(5,1,[1 2]); hold on; grid on;
  plot( t_log, v_log .* 2.23694, 'b' ); # [mph]
  ylabel( "Speed [mph]" );
  title( [num2str(t) "s Quarter Mile @ " num2str(v .* 2.23694, 4) "mph, 0-60mph in " num2str(zero_to_sixty_time) "s"] );
subplot(5,1,3); hold on; grid on;
  plot( t_log, a_log ./ g, 'r' ); # [g]
  ylabel( "Acceleration [g]" );
subplot(5,1,4); hold on; grid on;
  plot( t_log, rpm_log, 'k' );
  ylabel( "Engine Speed [rpm]" );
subplot(5,1,5); hold on; grid on;
  plot( t_log, throttle_log  .* 100, 'k' );
  xlabel( "Time [s]" );
  ylabel( "Throttle [%]" );
  ylim( [0 100] );
set( gcf, 'position', [300, 202, 560, 755] );

ManDoCar: Episode #1

I couldn’t bring myself to write a full article on how the car is getting on, so I decided to do something a little different: a podcast! Enjoy. All the relevant pictures are below as well as dingy chat!

We discuss painting, IVA preparation, driving at Snetterton, engineering learning, SpaceX hydraulic systems, faulty brake callipers, peak performance, why limited slip differentials rock, the Hoonigan donk, exhaust wrap, and lastly, engineering in a pandemic.

Dingy Chat

Pantone 333c Colour Chip

The Locost

New steering rack mount. Major surgery!
The chassis finally in a state to clean and paint. Spring 2020
Chassis all cleaned up and steering rack back in
Steering joint over the 10 degrees required for IVA
A very clean and red engine block
ARP Main Studs. Lovely.
Plastigauging a main cap
One of the old big end bearings. Not nice at all. These were new not long ago.
Inside of the drp sump pan.
New seat padding by JK Composites.
Bottom end back in the car.
The entirely wrong brake calliper slides …
… this is what they should look like
A freshly rebuilt and cleaned diff. Kaaz Limited Slip inside!
Auxiliary belt idler. Makes the engine much quieter.
Front lights! Looking great
Oil on plug #1. Not fouling, but not great. Need to do a proper break-in before any concern.
Hello!

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!

Locost: Snetterton Damage Report

We made it to Snetterton; its official. I’m going to leave it until later to give you a run down of what it took to make my little red car trackday-ready. However, its fair to say the six weeks leading up to Snetterton left me feeling both physically and mentally achy.

Having just performed a two day fabrication marathon on Saturday and Sunday (Feburary the 11th/12th; for posterity), the car was sat on the trailer ready to go at 7pm. After a quick batch of takeaway pizza and beer we were ready for bed; we had a 5am start the next day to get to the track. “We” was myself and my younger brother Alex, who is now the official truckie for OgilvieRacingTM and second mechanic (he fit the passenger seat in the car the day before).

The two hour drive to Snetterton went without a hitch and we rolled in at about 7:40am, giving us 50 minutes to unload and sound check the car.

Sound Check

Every circuit has a different static noise level which your car must pass to be allowed on track. Snetterton’s static noise level sits at a deafening 105dB, which mean’t I was quietly confident the car would sneak in under the volume radar. While sitting in the cue waiting to be tested we both got quite giddy, as it dawned on us we were actually at a race track track and it was really happening. Hence the following terrifying selfie.

We were surrounded by Sevens of many shapes and sizes, Subarus, RGBs, Hatchbacks and a multitude of MX5s. The atmosphere was quietly buzzing as everyone was excited to be there and not taking themselves too seriously.

When our turn came around the operator asked us what type of engine we were running, I said “A 1300”, and he explained that we should bring the car up to 5000rpm and hold it there for the test. This was based on the car being at ~3/4 of its peak RPM, which was a fair guess as I was  planning to shift between 6500 and  7000rpm. Fortunately we breezed through with a reading of 100dB; even though I was running a weedy little motorbike exhaust can. This was our first achievement of the day.

Run 0 – Sighting Run
Data: None

Following the drivers briefing we were required to perform three sighting laps in a group of approximately 20 cars, to get a feel for the layout of circuit and any slippery bits. Given that it had snowed all weekend the track was very greasy and gave me a few surprises even at low speed. I was following a Porsche 911 , which was both gorgeous and  incredibly hard to keep up with at full chat! I took these laps to get used to the gearbox and pedal layout, having never driven the car for this period of time before. That said, it took to the track rather well and had a lot of front end grip.

Having completed my three laps I returned to the pits,.

Run 1 – A trip in the mud
Data: LOG022.TXT

Feeling confident, my brother and I jumped in and went for the first official
drive of the Locost at Snetterton; this didn’t last long. We did a slow out lap to
get a feel for the grip level and then started to push a little. The car felt good,
the gauges looked happy.

Coming into T6 (Oggies) on our first flying lap I over cooked it on the brakes, expecting
there to be a lot more grip than there was; doh! With a little steering angle the
rear would start to step out, and with less steering angle the front would plow on, giving me two options. Go off front-first, or off rear-first. I chose front.

Fortunately the car kept turning as it went into the mud and we were almost back on
track once we came to a stop. I slowly got the car back to the pits, thankfully without having to be rescued, and we were surprised to find that the car was not damaged at all. Just slightly sad looking. With an old towel in hand we were able to clean the car to an acceptable level and get ready for another crack at it.

About thirty seconds after we got into the garage my far-more-trackday-experienced-friend Dan rolled in covered in mud. He had also gone off at Oggies, which made me feel a lot better about my driving!

Run 2 – Before Lunch
Data: LOG023.TXT

Given how slippy the track was I made some setup adjustments before heading out again. I raised the Front Ride Height by 3mm at the front dampers (1.5 Turns, ~1.6 Wheel/Damper Motion Ratio giving +4.8mm Front Ride Height), which also happened to reduce the Front Static Camber (due to the camber change in bump) and raise the Front Roll Centre; each of these helping to stabilise the car. I also increased the front damping by two clicks to slow down the initial turn in response. The car was a little two reactive for me at this time of the day.

The car felt great following the changes I had made and gave just a touch of understeer, with on throttle rotation on exit thanks to the open differential.

I only managed four laps, including my in and out laps, as I could see a big drop in oil pressure on the gauge in T7 going onto the back straight and I wanted to make sure the car was okay. That said, I drove the car as fast as I could while I was on track; it appears all mechanical sympathy goes out of the window once your at speed!

Having checked the data over lunch it appeared that the engine temperatures were safe and the oil pressure never dropped below 20psi. That said the oil pressure was dropping off in right hand corners, from 40/50psi to 20psi, but never going to zero.

It was likely the engine was sucking some slightly thinner aerated oil in these corners. To be safe we topped up the sump to the maximum amount I’d designed for. In fast right hand corners the oil pressure stayed rock solid; Turn 3 (Palmer), Turn 4 (Hamilton) and Turn 8 (Brundle).

Run 3 – PM Brake Bias Forward
Data: LOG024.TXT

Before lunch I was struggling to trail braking into the T2 hairpin (Montreal) without some rear inside locking; especially as I released the clutch. I decided to move the brake bias 2% forward to help with this, which was ~2mm at the balance bar.

I went out again with Alex in the passenger seat, so setup wise it wasn’t going to be too representative, but it is plenty of fun with a passenger on board.

Unfortunately I had forgotten to put my helmet strap on! Being smart I did an Out/In lap and fixed my helmet in the pit-lane. This coincided with a red flag on track so we ended up sitting in the pit lane for a little while looking at a red flag (the data suggests almost 6 minutes). We noticed the engine getting properly hot at this point, and blowing a little steam, so we took it back into the garage to cool down.

I didn’t notice it at this point in the day, as I already had enough to think about , but the fan had failed; maybe even when we towed the car to the track on the trailer. The data showed very high pit lane engine temperatures all day, however the car had not sat still for long enough for this to be an issue; until this red flag.

Run 4/5 – Overheating!
Data: LOG025.TXT / LOG026.TXT

We went out for two short runs (two timed laps, three timed laps) but clearly the car wasn’t running right. Once we brought it back in and it was finally clear to me that it was overheating.

Once it had cooled down I opened the water cap and topped up the system, a lot; too much . Following the pit-lane incident in Run 3 the engine had spilled a lot of its water onto the pavement (I have no expansion tank) and was now running sub-optimally. There was still water in the head but the top pipe and the top of the radiator were completely empty. Flow across the thermostat would have been very slow indeed.

Fortunately I had dodged a bullet. The water was running clean and the oil was also clean; so no blown head gasket.

These runs did show an improvement in oil pressure in right hand corners, which was a relief. Topping up the sump had at least made a measurable difference.

Run 6 – Short Lived Glory
Data: LOG027.TXT

With the track having fully dried out, and my car back in tip top health, I went out for what would be my final run of the day; riding solo and at race weight with a little less than half a tank of fuel.

This fifteen minutes was what the day was all about. The track had gripped up nicely and the car was running the best it had all day. I kept pushing the braking points until I was starting to under rotate the front inside wheel and felt I had quickly found my limit.

The Nankang NS2R’s actually came in quite quickly, which was a surprise for a Medium compound tyre, and gave really good feedback. My lines were pretty lame and I was only pushing the kerbs on corner exit, but I was having a lot of fun and going faster each time around.

Coming into T4 (Agostini) on my fifth lap I felt a large front end vibration which suddenly disappeared. This was accompanied by some mid-corner understeer/weirdness and a general feeling of confusion. Once I limped around to T10 (Bomb Hole) I was flagged by the marshals to return to the pits. Upon my arrival the man in orange explained to me that I had broken my front splitter and it was waggling all over the place; fair enough!

At this point I parked the car and basked in my own smugness. I had experienced a small glimpse of all the fun that could be had doing track days and was relieved that I had made it this far. Of all things to break the splitter was the easiest to fix, but it would have to wait until the car was at home. This felt like the right time to pack up and call it a victory.

Final Thoughts

On paper, we didn’t have a hugely successful day. The car didn’t turn that many laps and suffered a few engine teething problems along way. However, that was never what this was about. The Locost has been the accumulation of almost ten years work, and started life in my young teenage mind going on fifteen years ago.

On Monday the 13th of February 2017 I achieved a life goal: I built and trackdayed my own little racecar; and I’m still buzzing about it! I have definitely caught the trackday bug it. A car like this, driven in a track environment  is a massive endorphin hit.

What really surprised me was how well the chassis handled on track. In the tight car park events that I am used too, it lacks rotation at a high steering angles and tends to plow on if you push it too hard. On track it eats up kerbs, rotates on demand on corner entry and, if your willing enough to use it, has great peak grip in the mid-corner. The small adjustments I made at the beginning of the day gave me a measurable change in handling, and the engineering knowledge I had learn’t in motorsport was both applicable and effective.

The Locost has always held a special place in my heart. Uncountable hours have been poured into it, however it hasn’t always been that usable. Now that I can drive it on track, I think I have fallen in love with it all over again.

Time for more trackdays, lots of development, and endless fun. Success.

 

Engineering Notes

Just a few bullet points about the car, which I will likely elaborate on in the future:

  • The engine was definitely down on power compared to where it could have been and is in need of a dyno session in the very near future. This was also reflected in poor drivability out of corners.
  • I am getting spikes in RPM from the ECU which suggests the ignition system needs more filtering/shielding. This tended to happen at the same engine speed each time, supporting my electrical noise theory. These could be felt as flat spots while driving and were obvious in the data.
  • The fan is dead, long live the fan; replace the fan.
  • The splitter needs supports back to the chassis at the forward edge; clearly.
  • Having to add so much front ride height to balance the car suggests the mechanical balance is too far rearward, and I need to get softer rear springs, stiffer front springs OR add a front anti-roll bar.
  • The GPS was broken on my datalogger all day and it needs to be torn down and investigated. This was also the case when I drove the car in the week, but I didn’t have time to fix it. It has been tested and known to work, so it was rather odd.
  • The car needs a water expansion tank. Badly.

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