CategoryLocost

Locost: Airfield Testing

I get super nervous when it comes to things like this, logistics and towing always freaks me out. Getting the car to and from an airfield… on time… on a trailer… with all my tools and spares… there is plenty that can go wrong. Fortunately barely anything went wrong!

Setup

Prior to IVA I need a reasonable fuel map in the car so it can be driven around, undertake the emissions tested, test the speedo etc. I have changed so much in and around the engine that I needed to start from scratch this time around. Following lessons I had learnt running DIY fuel injection in my daily Sierra, I knew the benefits of using throttle position as the ECU load input, this is known as alpha-n tuning and is what I will be running in the Locost from now onwards as opposed to the blended tps/map setup I had been using before.

In short, I needed somewhere to drive and map the car. It had to be private land and with plenty of space to be able to drive at wide open throttle for long periods of time. After a visit to my local airfield, and a phone call with the very generous land owner, I was ready to go.

I made a big push to get the car into a ready state for the day, finishing with a pre-IVA job list of about six items. If all went well, I would be in a comfortable place to put in my paper work afterwards. Spoiler: my job list is now much bigger!

Journey

I barely slept the Sunday night before Mondays testing and after making sure everything was loaded correctly I arrived 15 minutes early at 9:45am.

Fortunately, my nerves amounted to nothing. The drive was a cool 1 hour 15 minutes with no hassles and very little traffic. Within half an hour of getting there my brothers Alex and Neil arrived to help me out, having driven for hours to get to the airfield. I love it when a plan comes together.

Initial Running

The first job of the day was to build confidence in the engine, shake down all of the many new components on the car and get some of the cruising fuel table positions filled in. Alex took to the drivers seat while I plugged in the laptop and watched the ECU do its thing and auto-tune the low speed elements of the table.

I did scoot the car around a little bit before everyone arrived and I could already tell it was driving better than it ever has, at least from a handling perspective. Over the winter I was very specific about the alignment I applied and made sure it was dead straight. The limited slip differential has also completely changed the feel of the car.

More RPM

After an hour or so of driving, and lots of stopping and checking for leaks, we started to build up the engine speed and mapping the wide open throttle (WOT) parts of the fuel table.

First 3000rpm, then 4000rpm, then 5000rpm and soon 6000rpm. The engine sounded loose and happy, free revving to whatever we threw at it. The auto-tune feature of Tuner Studio was pulling fuel out every thousand RPM we went up, suggesting my initial guess was too rich, exactly as I had planned.

Things weren’t entirely without incident and a number of issues became apparent at this point:

  • The front wing stays, on the rough surface of the World War 2 airfield, were far too soft. The wings themselves were bouncing around all over the place.
  • The clutch was progressively falling down the pedal. You could put this down to temperature but I was pretty sure the slave cylinder was leaking into its rubber boot. We removed the pedal stop to allow us to keep going.
  • The fuel filler tray gasket wasn’t doing its job and fuel was weeping out of the top of the tank. Eventually this went away as we burnt through fuel but would need to be fixed as soon as possible.
  • The fuel injectors were leaking at the manifold side, just a little, and the seals clearly weren’t sealing correctly.
  • Worst of all, the engine was burning oil badly on over-run. Sometimes clouds of it, sometimes not.

We decided to take note of the issues but simply crack on. Its not often you get access to an airfield for the day and we wanted to get the most out of it.

Calibrating the Speedo

I had a three point job list that I had to get done at the airfield:

  • Map the engine enough to get the car driving reasonably
  • Confirm the brake balance locked the front wheels before the rears
  • Calibrate the speedo

The first two were not a problem at all, but the third required a bit of thought. The speedo appeared to not be working at all, at least with the calibration I had put in at the beginning of the day. Based on my early maths, with a 4.3 ratio differential, and four bolts on the prop-shaft flange to read from, the gauge should have been seeing approximately 15000 pulses in a mile and that’s a what I set it to.

Given that this number was clearly wrong I adjusted the pulses per mile to 1000 and took the car out for a short drive, while referencing the GPS speed on my phone.

32 mph on the GPS, was 20mph on the gauge, at 1000 pulses per mile

My initial guess was super far off! How did I mess that up? Anyway, it was reading low, so by reducing the number of pulses per mile we could increase the speed seen on the gauge.

Doing a little bit of quick-maths suggested the actual calibration should have been 625 pulses per mile. Given that for the IVA the gauge has to read between the actual speed and 5% over we opted for 600 pulses per mile.

I did however want to back calculate my maths, which I will do here:

1 mile is 1609.34 meters
625 pulses per mile is 1609.34/625 = 2.574 meters per pulse

a 185/60 r13 ns2r tyre has a diameter of 552mm
this gives an circumference of 552*3.142/1000 = 1.734 meters

therefore 2.574 / 1.734 = 1.4844 full wheel turns per pulse

with a 4.3 differential ratio that is
4.3*1.4844 = 6.38292 propshaft turns per pulse...

that makes no sense

So yeah, the maths doesn’t add up and I don’t trust the gauge manufacturers instructions… but it works!

In fact, lets do some maths in the other direction…

4 pulses per propshaft rotation
4.3 propshaft turns per axle rotation
4*4.3 = 17.2 pulses per axle rotation

1.734m circumference gives 17.2/1.734 = 9.919 pulses/m

1 mile is 1609.34 meters
1609.34 * 9.919 = 15963.04346 pulses per mile

Now this kind of looks like the number we came up with in the end… can you see it?

15963.04346 * 4 / 100 = 638.5217384 ~= 638 somethings

Now the gauge manufacturers documentation describes this number as the “frequency”, so the factor of four kind of makes sense, maybe, and the factor of 100 could just be for the sake of storage or to give resolution for certain gearboxes.

Either way, done.

Driving on my own

Even though the engine was blowing a fair bit of smoke on up shifts we decided to get some miles on the piston rings and shake the car down further. Issues aside, it felt fantastic. Getting from a stand still to 70mph happens pretty damn quickly and the steering feel was better than it ever had been.

At the far end of the air strip was a number of coned gates setup for truck driving tests and I couldn’t help but have a little play in-between them. No complaints regarding the chassis.

Evolution of the Fuel Table

Below is the Volumetric Efficiency (VE) table we started the day with, the table we ended the day with and the difference table showing the changes made. The VE is simply a measure of how much fuel flow the ECU is demanding relative to the amount required to achieve stochiometric mixture at wide open throttle. Technically, if the engine is 100% efficient as an air pump, it would achieve 100% VE across the top of the table.

As you can see, the fuel table isn’t perfect, especially at high rpm and part throttle where it was barely touched. Its quite difficult to consistently drive this area of the table! I also did a substantial amount of manual adjustment based on what the wide open throttle numbers suggested. I could smooth it over more but I am going to leave it for now.

Notice that at low RPM the engine needs more fuel for lower throttle angles. This makes a lot of sense, as the throttle plates don’t act as much of a restriction at low flow rates, but as the flow increases at higher RPM’s they do a better job of restricting flow into the engine.

This map will do for the IVA, then I will take the little red car to the dyno.

Final Thoughts

I am really glad we got this day to shakedown the car. Its highlighted a few jobs that really need to be done before submitting my paperwork and its better to get them done now rather than later.

The engine is still a bit of a worry but my gut feeling is the valve guides have worn out. Prior to rebuilding the engine it had started doing the same thing and I had assumed it was the piston rings. The engine has fresh stem seals, so it points to the guides themselves. I have a spare cylinder head in great condition that I am going to drop in.

The chassis feels great and it was nice to have someone else drive it for a change. I’m looking forward to getting on the road later this year.

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!

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.

 

 

 

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