AuthorJosh

Locost: Fixing the handling

I have been really looking forward to this phase of Locost ownership: the development! With the car on the road I can now make changes and feel the difference in the engine and the handling almost straightaway. Back in my previous job I used to do this in a high tech racecar simulator, but I felt the real learning would always be on the road in my own car. Here goes!

Super scary to drive

I have put approximately 100 miles on the Locost since it first hit the road. These have been spirited drives to get to know the handling and deal with any reliability issues, as well as a few commutes to work. In short: I have been dodging winter showers.

The car has been really struggling with poor straight-line stability. Once its in a corner it feel “okay” but in a straight-line it would dart in and out of bumps, and generally wonder across the road, even though I was holding the steering dead straight. This has been really hindering my enjoyment and generally slowing me down. I can’t push the car without holding on to the steering wheel for dear life, which doesn’t seem entirely right!

With this in mind I put the car up on axle stands and reviewed the setup.

Setup “A”

For the first time in pretty much ever I am going to put my cards on the table and show you my setup. If for any reason you decide to use these numbers, you can do so at your own risk.

I’m not racing anyone other than myself, so there is very little value in these numbers other than in comparison to other setups that I might choose to run on the car, or you might choose to run on your car, so enjoy!

VariableFrontRearUnitNotes
Camber-1.1 / -1.1-1.0 / -1.0degAt design ride height with setup pins in place
Spring Pre-load-3.0 / -6.04.0 / 4.0 mmAt the damper, full droop
Castor4.6n/adeg
Toe In-22mmDelta front to back across the axle over 300mm
Tyre Pressures1818psiCold
Spring Rate200120lbs/in
35.0321.02N/mm
Motion Ratio1.6701.128Wheel / Damper
Spring Rate @ Ground71.7194.3 lbs/in K/MR^2
12.5616.51 N/mm
Track Width14401390mm
Roll Stiffness227.30278.40Nm/deg0.5*K*w^2
* (pi/180)
% Roll Stiffness Forward44.95%
Weight245295kgExc. Driver, Full tank, Wet
% Weight Forward45.37%

So there you have it, all my numbers for the world to see. But which of these could be causing my instability issues? Well three of them stood out to me as potential causes for concern: the front castor, the front toe-in and the roll stiffness distribution.

Front Castor

So what does Castor do and why should we care? Here is a picture I stole from suspensionsecrets.co.uk. Some of their written text is a bit dodgy but their pictures are great!

That looks about right!

Increasing Front Castor:

Castor is the angle from vertical made by your upper and lower ball joints, as viewed from the side of the car. Increasing this angle moves the steered axis further forward of the centre of the tyre contact patch on the road, which is approximately where the lateral and longitudinal force is applied; this measurement is known as the “trail”. This causes the steering effort to increase for a given amount of load on the tyre, and the self centring moment to increase.

Why would that help my issue? Well I have straight-line stability problems and increasing the self centring moment means the whole upright assembly, and steering is less prone to wander in response to external steering inputs, like pot holes and bumps. It wants to go in a straight line.

From my experience working with small lightweight single seaters, albeit virtual ones, I know that 4.6deg front castor is very low for this weight of car. I remember Formula 4 cars running in the region of 7 to 10 degrees. In fact the weight on the front axle is very important when picking a castor angle, the lighter the car the more castor you have to run for a comfortable steering load.

The Downside:

I actually reduced the castor down to 4.6deg back in the summer of 2020, and for good reason. I have been running in the region of 7deg for a long time and was happy with the steering feel but I was really concerned about the additional negative and positive camber it induced at high steering angles.

If you look at the following pictures you can see the masses of inside wheel positive camber at medium to high steering angles. With the amount of camber gain that my suspension has its actually quite difficult to control camber, especially when the car pitch’s forward and backward.

But as you might have guessed, I have reluctantly put the castor back into the car as the steering lacks self centring and ultimately stability; its all a balancing act.

“How do you adjust the castor on your car?” I hear you ask? Well its really easy. The upper wishbone can slide backwards and is held in place by shims. This moves the upper balljoint backwards and increases the castor. It should be clear in the picture below:

Front Suspension with toe/camber plate and damper pins attached

Eventually I plan on changing the front suspension geometry to be a bit more of a compromise between pitch and roll, taking into account additional camber induced by castor.

Bonus Round: Bump Steer

Having increased the castor back up to 7deg I rechecked the bump steer and it was very very high; my notebook says +3mm toe out over 64mm of axle bump. I had to shim the outer tie-rods downward by about 10mm to remove any bump steer.

This was likely the source of a major handling issues I had back in the day while doing autosolo. In fact, the car was very unstable over bumps and would wiggle around when rolling into a corner; the following video kind of shows that.

I’m glad to have dialled this out. I have learnt an important lesson over the years: You can build a beautiful looking well engineered car but if it isn’t setup properly it’ll be dead slow.

Front Toe-In

With the virtual “Formula” cars they always tended to run some amount of front toe-out and rear toe-in. This made them very nimble and they would turn-in to corners easily. If you visualise it from above, it can be seen as the front inside wheel already turning into the corner.

Here is another picture stolen from the internet to help you:

Toe-in and Toe-out

In terms of stability I was always taught to visualise the car in a strong side wind. With toe-out when the car transfers weight onto the outside wheels it will want to turn away from the direction of the wind, this is unstable. With toe-in the car will want to turn into the wind, this is stable. Like a wind sock.

I decided to give toe-out a go back in the summer of 2020, mostly in response to the weird handling I had on turn-in, which was most likely due to excessive bump steer!

Given my stability problems, nimbleness was the last thing I needed, so I reverted back to a small amount of toe-in. I went from 2mm of toe-out, 1mm a wheel, over 300mm width, to 1mm of toe-in, 0.5mm a wheel. With the Ackerman steering geometry in the car this toe-in will quickly disappear with additional steering angle, but in a straight-line it just numbs the steering inputs.

“But how do you measure toe-in Josh?”, I’m glad you asked. With the car on axle stands, and pins in place of the dampers (putting the car in its “design condition”) I take the boots off of the steering rack and place 3d printed shims to lock the rack central; see the pictures below. I then attach “toe plates”, something of my own creation, onto the wheels and use a tape measure to measure across the axle. Adjustments to the wheel angle are made via the track rods. I also ensure the wheels are both running straight relative to the chassis and generally square everything up.

Steering rack with the boots pulled back (lock stops are in black)
White steering locks in place holding the rack central
You’ve seen this picture before- see the toe plate on the right hand side

The same method works for the rear.

Roll Stiffness Distribution

Roll Stiffness Distribution is something that is often ignored or poorly understood by weekend warriors such as myself but it is a core handling characteristic of a car, or should I say balance characteristic. In fact in F1 it was generally known as the “mechanical balance”, as opposed to “aero balance” or “weight distribution”. Its mechanically controlled.

My little Locost has no anti-roll bars so this is purely governed by spring stiffnesses and geometry; we’ll ignore roll centers for now, my front and rear roll centers are at approximately the same height.

Another stolen picture. I just liked this one and its semi in context.

I’m not going to dig deep into the whys and wherefores of how weight transfer works, that is not what this blog is about, but it would help if you agreed with the following things:

  • Increased roll stiffness on an axle, relative to the other, increases the given amount of weight transfer that axle experiences while cornering relative to the other. If the front axle is stiffer than rear axle, then more weight is transferred between the tyres of the front axle than the rear axle (sort of, this is a simplification, lets go with this for now).
  • Weight transfer on an axle reduces its potential peak grip and cornering stiffness, because this is how tyres react to vertical loads, and an axle is just two tyres. I’m not going to dig any deeper for this article.

All make sense? Great! If not, I strongly suggest reading a book like Tune to Win by Carrol Smith. There are loads of really readable references out there.

The final statement I am going to introduce covers an element of the system that I think is generally missed by most. It was somewhat of a “eureka!” moment for me when it was first introduced:

  • The further an axle is from the center of mass the greater the turning, or stabilising, moment it creates around the center of mass.

Basic physics right?

Given all of the above it would make sense that the further an axle is from the center of mass the less force it should produce, or grip, to keep the car in balance. This is the balancing of the front and rear turning moments.

Its not too big of a leap in logic to realise that if your weight distribution is towards the rear (say ~45% of the weight on the front axle) then your front roll stiffness should be higher than your rear and not ~45% of the total like my little Locost.

Some Basic Maths:

We’ll need to do some very basic maths to work out the roll stiffness of each axle and then adjust the front springs to change the distribution. Ignoring the contribution of roll centers and such, the roll stiffness of an axle can be calculated as follows:

I stole this from another website, and they ripped it out of a book, will we ever learn?

Well, that is kind of useless as we don’t have a solid axle with perfectly vertical springs attached to it, but we can turn the Locosts suspension into an equivalent axle by calculating the spring equivalent stiffness’s at the ground. We do this by using the motion ratio between the damper and the contact patch of the tyre. The maths is as follows:

I made this using math.tools/equation/image and paint

Where:

  • K is the stiffness of a spring, in Newtons per Meter, [N/m]
  • x is the displacement of a spring, in Meters, [m]
  • MR is the motion ratio between the wheel and damper, in Meters divided by Meters, its non-dimensional

Given the above equation we can calculate the spring equivalent stiffness’s at the ground and then use the track width (tyre center to tyre center) to calculate the overall roll stiffness for each axle. The distribution is then the front roll stiffness divided by the total roll stiffness (front plus rear, two springs in series).

The End Result:

I’ll reiterate the numbers from the table above:

VariableFrontRearUnitNotes
Spring Rate200120lbs/in
35.0321.02N/mm
Motion Ratio1.6701.128Wheel / Damper
Spring Rate @ Ground71.7194.3 lbs/in K/MR^2
12.5616.51 N/mm
Track Width14401390mm
Roll Stiffness227.30278.40Nm/deg0.5*K*w^2
* (pi/180)
% Roll Stiffness Forward44.95%

As explained, the front is softer in roll than the rear. How did I solve this? I increased the front spring rate from 200 lbs/in to 275 lbs/in, giving the following:

Variable Front Change Unit Notes
Spring Rate275+75lbs/in
48.16+13.13N/mm
Motion Ratio1.670Wheel / Damper
Spring Rate @ Ground98.61+26.9 lbs/in K/MR^2
17.27+4.71 N/mm
Track Width1440mm
Roll Stiffness312.55+85.25Nm/deg0.5*K*w^2
* (pi/180)
% Roll Stiffness Forward52.89%+7.52%

That is a whooping big change in Roll Stiffness Distribution, 7.52%! In the simulator I would usually aim for steps of 4% as these were usually noticeable, but I’m not messing about with the Locost. It was hideous to drive at speed and I wanted to feel confident in the car and enjoy it.

Setup “B”

The changes listed above amount to following setup differences:

VariableFrontChangeUnitNotes
Spring Pre-load-6.0 / -6.0mmAt the damper, full droop
Castor7.0+2.4deg
Toe In1+3mmDelta front to back across the axle over 300mm
Spring Rate275+75lbs/in
48.16+13.13N/mm
Motion Ratio1.670Wheel / Damper
Spring Rate @ Ground98.61+26.9 lbs/in K/MR^2
17.27+4.71 N/mm
Track Width1440mm
Roll Stiffness312.55+85.25Nm/deg0.5*K*w^2
* (pi/180)
% Roll Stiffness Forward52.89%+7.52%

The Result

After all of the above it was time for the fun bit: driving! So how does it feel?

  • The steering weight greatly increased. I can now feel the lateral acceleration build up and fall off with steering input. Its not uncomfortable but it is readable.
  • The car now tracks straight and doesn’t wander over bumps and dips in the road.
  • It still feels nimble and will quickly “take a set” in a corner; its not unpredictable.
  • Its not understeery or too stable, the balance of the car can be changed with the brake on entry and the throttle on exit.

But what does all of the above actually mean? It means the car is finally fun to drive! I went out for a good long session on a sunny sunday afternoon and people were waving me by and giving me the thumbs up. I managed to catch up with a group of Porsche owners out for a pleasant drive and give them a bit of a wake up with my bright red loud viper of a car. It was awesome.

Now I spend my days looking out the window waiting for the sun to shine… keys in hand… just waiting…

Locost: IVA Test and Finish Line

Its been about six months since I last posted and as always I have been squirrelling away in that time. My last article, posted back in May, covered airfield testing of the car and the uncovering of a few gremlins. Lets start there.

Post-Airfield Fixes

Remember I said the engine was smoking on over-run and I was pretty sure it was the valve guides? Well I’m not always right about these things.

I wasn’t confident I could get the valve guides replaced in a short period of time so I decided to strip the cylinder head off one of my spare engines, given that’s what they are there for, and check the valve guides. If they were good and within tolerance I would give the head a quick rebuild and swap it with the one in the car.

The donor engine was out of my old daily Swift Gti and as such I knew it was in “okay” condition. It had started running a bit weird before it was pulled out of the car, but years later I would diagnosed it as either a faulty fuel pump or a jammed up fuel filter. It had started to loose power over 3500rpm and the plugs showed all the signs of being a bit lean, but generally healthy. This engine had sat in storage for about five years but actually looked pretty good on the inside. Just a bit carbon’y.

Replacement cylinder head. Dirty on the outside, clean on the inside; perfect.
Under the carbon build up this engine was as clean as you like.
That is a tea spoon of oil in each bore. Nice.

I leak tested the chambers, which were fine, and stripped apart the cylinder head . Suzuki gave a tolerance in the workshop manual for the valve guides and I had a drill-bit that was exactly the low end of their tolerance. If the drill shank fit within the guides and was tight, then they were good. Every single one of the 16 guides was a tight fit; which was fantastic.

I gave the cylinder head a good clean, re-seated the valves with course and fine cutting paste, and replaced all of the stem seals. At this point it was ready to go into the car. So I pulled the old cylinder head off the engine in the car and…

Well the picture above shows you the horror. A tea spoon oil in each cylinder. No wonder the plugs were wet! This certainly accounted for the smoke I had been seeing and meant my fix would need to be a lot more drastic. This was a huge gut punch given the amount of work I had put into rebuilding the engine, but I was done messing around and if I was going to drive the car on the road before the end of year the engine would have to get replaced.

Over a number of weekends I cleaned the donor engine and swapped over all of the important parts. The ARP head studs, dry sump system, uprated clutch etc. The old short block was out and the replacement cleaned-up version was in the car after three afternoons; I was pretty happy with this.

Cleaned up cylinder head
Replacement short block in place
Cylinder head all bolted down

With the new engine in and running it was a night and day change. A completely clean exhaust, even during warmup, and lovely clean plugs. For the first time since before 2018 I had a happy running car. This was a huge step forward and I knew that IVA was going to be possible!

Up and running!

We had a leaky clutch slave, leaky fuel tank filler, damaged rear cover and broken wheel arch bracket after airfield testing, and all of these were amended before August 2021, at which point I put the car away to sleep for a while as I was about to get married!

Pre-IVA Work

After my wedding and honeymoon I put the paperwork in for the cars IVA test (Individual Vehicle Approval) and got to my very last concerns.

My wife asked me what the car might fail on so I could prioritise and focus on a first time pass. The first thing that came to mind was noise. Back in 2017 at Snetterton the car managed 100dB at 5000rpm which was 1dB over the legal limit for IVA (99dB). I wanted to make sure the car breezed through the noise test with no issues so I decided to perform my own, as well as rebuild the exhaust back box.

The back box was some unknown carbon fibre unit I bought off of ebay many moons ago. I knew it was a from a Yamaha sports bike and appeared to be rebuildable but that was about it. I tried to remove the carbon fibre outer body and weirdly enough there was some 3mm thick aluminium underneath it! So the carbon fibre was just for looks; not my kind of think.

So, not carbon fibre than?
It had maybe 5mm of very burnt old padding inside it
Err.. no thankyou

I had to cut and peel the outer shell off to get at the internals and by this point I had already committed to completely rebuilding the whole box. Inside appeared to be a small gap for fibreglass padding, 5mm-ish all the way around, and then a series of weirdly routed baffles. The outlet didn’t even fully align with the internal piping which was quite disappointing.

I jumped on the internet and ordered a 5inch diameter piece of stainless exhaust tube, which is flared both ends to allow the old end caps to be used. I also ordered some 2inch diameter perforated stainless tube to run down the middle of the box. This was wrapped with 1.5meters of Acousta-fil exhaust material.

After a bit of welding, drilling and riveting I had a fully rebuilt back-box.

Pretty much a build your own back-box kit
Much better
Fully modified and back on the car

Using the noise meter from work we could do our own mock noise test. With the new back box installed the car managed a whisper quiet 105dB! Oops. I knew the Acousta-fil needed some time to expand and do its job, but either way I had made exhaust noise worse. That said, it sounded fantastic 🙂

How did I resolve the noise issue? I went the tried and tested route and installed a dB Killer. Not my proudest moment but they really do work. Having modified and installed this in the back-box inlet we managed 95db at 5500rpm, a full 10db reduction! That is huge. Its great to have the option to make the car more friendly if needs be.

A dB Killer baffle, with the internals switched around
Installed. I am happy that baffling is in the correct direction

Other than the odd bit of trim here and there, that was it, the car was ready for IVA.

IVA Test

Early Start and Arrival

To get to the test centre with time to spare I reckoned I needed to leave at 5am in the morning. You have to be there by 8am, with the car unloaded and ready to go, and it was an hour and half drive away from me. I understand that my maths doesn’t entirely make sense, but there was absolutely no way I was going to be late! Subsequently the traffic was amazing and I ended up sitting in the services next door beforehand, but it never hurts to be prepared!

Needless to say I got to Bristol test centre with plenty of time to spare. Although it was cold and autumnal it was quite a beautiful day, and very quiet down on the docklands.

A beautiful sky over Bristol at 7:30am
Waiting to be probed and proded

Weigh bridge

After introductions and a quick look over of the car it was straight onto the weigh bridge. The car came in at 540kg (245kg+295kg) with a full tank of fuel. This was a little disappointing as this was the heaviest I have ever seen it on the scales, although maybe this is simply the real road going weight?

It was weighed many years back in racing trim at 475kg; completely dry. Since then it has gained two full size seats with padding, a properly working water system with header and spill tank, a dry sump system with a 5 litre oil tank, a full full size fuel tank, mirrors, IVA trim, padded interior, lights, full size arches etc etc. So 540kg sounds about right! That’s the price you pay to have a proper road going car with a roll cage; I’m not going to complain.

For comparison a Mk1 MX5 weights 960kg and a Mk3 weighs 1122kg…

General build standards

The two testers had a good poke around the car before going much further just to make sure there weren’t any glaring failures or safety issues right off the bat. So far so good. They were very complimentary on the construction and there was definitely a good vibe. I felt I had presented a clean car.

While the car was on the trailer the day before I had taken the fuel cap assembly out and loctited the bolts, but I had forgotten to reattach the fuel filler cap tether! They were very forgiving and let me use my spanners to fix that issue right there and then.

Emissions

Not much to say, the 30 year old 100k+ engine flew threw with almost comically good emissions. I am glad I swapped them out!

Exterior and Interior Radii

This was the one thing that worried me the most. The radii rules are absolutely brutal. The car is tested with a fake 100mm “knee” and anything that contacts it, which is less than 5mm above a surface, must be radiused to 2.5mm. Fortunately all of my hard work, rubber trim and 3d prints really paid off! It flew through on both Exterior and Interior Radii.

There were a few questions over components I had used and we discussed what constituted a pass or a failure. It was pretty informative.

Underbody construction and alignment

After that the car went up on a hoist and was checked from underneath. It was quite cool to have someone different actually look at all the work under there. Very few, if any, people have looked at the car from that angle.

Again, they were very complimentary on the quality of the build.

Light Alignment

I had setup the light alignment using the numbers in the IVA manual and sticky tape on my garage door. My drive is not flat. That said, one of the lights was bang on and the other required a minor adjustment to pass. I was happy with that.

The equipment they use at the test centre actually shows the light pattern on the same piece of paper displayed in the IVA manual. Its pretty impressive.

Brakes and Brake Dyno

This was the first of two rolling roads that the car would go on during the day. The front and rear axles were tested separately, measuring the peak longitudinal loads they could achieve before locking, and the relevant pedal effort required to achieve those loads. This was also done at a number of increasing pedal loads to give the characteristic of the braking axles. Again, all very impressive and fun to watch.

On the rollers for the brake test

Speedo Calibration

Given you have probably already read my article covering airfield testing you know all about my method of calibrating the speedo. Guess what? It bloody worked. The car flew through the speedo test.

This is actually a really cool test as the car is put on a rolling dyno and run up to 70mph. The tester waded through the gears and the car sound great as usually. I was darn proud at this point.

Noise

Next up was the noise test. Given the dB Killer and measurements I had done beforehand I was pretty comfortable it would pass the test. It easily flew under the radar at 93ish dB. No worries there then!

One issue that did raise its ugly head is hot starts of the engine. I have been playing with the settings in Megasquirt to reduce the amount of start-up fuel put into the engine when the engine is warm but I think the firmware has a bug in it, and the temperature sensitivity doesn’t work. So it bellowed black smoke on restart for about five seconds before doing the test. Great.

Mirrors

Not much to comment on. It flew through.

Dynamic Brake Test

I have no idea what went on during this test but it sounded like the tester was enjoying himself. The intake noise was glorious.

Debrief

And that was that. Almost three years of hard work to take my little red race car from track toy to road legal car. I can’t say it didn’t have its ups and downs, especially with COVID hassling me and having a somewhat broken engine, but I am really happy with the end result.

The Locost is a weird thing. I have put so many hours into it that it kind of scares the crap out of me even when its stood still. A new phase of our relationship has begun which will hopefully be a little bit more give/take!

The final picture says it all really.

Pass! One very tired owner and one very happy car

Bonus Round: First Drive

It has taken me some time to write this article as life as been relatively busy.

All in all it took about four weeks from the IVA test to receiving my registration number. Considering the amount of flak the DVLA get they actually seemed to do everything in their power to get my registration turned around and they were really helpful on the phone.

I received my Q plate on a Friday afternoon and I had it insured and number plates the same day. This lead to me to waking up at 6:30am on the Saturday like a giddy child for my first ever drive on the road….

The early hours

What can I say? Its awesome. All of the performance numbers and pub chat aside, driving one of these cars is an experience. I imagine its much closer to riding a motorbike than it is to driving a modern hatchback. Its interactive, you feel everything. Not only that you feel like you are going warp speed when you are cruising along at 60mph. The exhaust note, the direct steering, the throttle response. Its unique.

There are certainly quicker cars. There are certainly “better” cars. But there are none like mine.

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 #5: SN15, Motorbikes, Bows, Boats and Completing a Hobby Project (Guest: Neil)

This time its not just two but three brothers having a natter.

We discuss SpaceX’s Starship SN15, running a canteen on the moon, Motorbikes, Bow making, carpentry, fixing dinghy’s and living life once a major hobby is complete. Neil is guest: he is a civil engineer, biker, archer and father of two.

ManDoCar: Episode #4: SN9 Landing Sploshion, The Cost Of Hobby Cars, Alex Buys Another Boat

A new episode of Man Do Car! Two brothers just having a natter.

We discuss the Mars Rover Landing, SpaceX Starship SN9 Landing Sploshion / SN10 Non-Sploshion, the cost of Volvo 240’s, Alex Buys Another Boat, Weird Sailing Events, the cost of Hobby Cars, Expert Rigging, Twitter Bots, curbing your enthusiasm and Electric Car Chargers.

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