Hyperblade's KP61R - Toyota Starlet with Honda K20a

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So clutch and flywheel got balanced. and we still had the issue.

Eventually tracked it down to the rear coil...

Annoying that it was that simple, but it really didn't feel like a coil at the time and naturally only did it under load and high rpm.

So out for Club Day 1 with a spare coil

We had a great turnout of 25 cars, most in higher classes then me (meaning bigger engines).

Race 1 went ok.

 

Handicap for race 2, so really stoked to finish 3rd.

 

Came 6th for race 3 which I was really happy with too.

 

But as you can see from the videos I have a massive vibration again, both front and rear.

It was incredibly tiring just holding onto the steering wheel, and I probably should have pulled the car off the track, but i really wanted to race.

Damage total so far from either this new vibration or the coil vibration

• Radiator has started leaking
• Aluminum Intake brace broke
• Fuel regulator mount broke
• Multiple bolts lost.

Now have more things to fix and not much time to do so before next meeting.

Best guess at present for the vibration is wheel balance.

Have put a full set of NGK coils in at $55 each vs $200 each for genuine, so hoping those are slightly better quality then all the Chinese versions at a much more affordable price.

Have made one performance change, rears were continually locking up under braking, so after talking with AP and going through the system we have changed the rear master cylinder, which matches the rear calipers better. Fingers crossed that helps sort the braking out as I should be able to brake much later (was having to go early and gentle the whole day)

On the positive side, brake cooling is definitely working well, hit 400c but not 500c during the entire day. So will try and get those temps up a little bit by blocking the intakes with some tape and see if we can get the 500c paint to start flashing off.

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Forgot to add vibration also killed my External GPS unit I use for laptiming.

So while I was looking at logs for brake pressures I noticed the following

This is Race 2, off the line.

So few issues you may spot.

• TPS only hitting 87.7% (not a big deal as 74mm throttle so has heaps of air)
• Wheel speed dropping to nothing around 120kph, known issue which I've been working through with @h4nd and just need some free time to finally sort it properly.
• Bigger one is obviously the oil pressure instantly dropping to 0 multiple times under acceleration some times at over 8000rpm.

Looking at the logs it was happening throughout the race, but no consistency in when it was occurring e.g. race 3 had no issues off the line.

Looking at it, it will lose 100 psi of pressure and then back up to 100 psi in 250ms. Which we don't think is physically possible.

So best guess is vibrations affecting the sensor, and I'm going to remote mount it for the next event.

 

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So been a bit of a rush to try and sort things before the next race event as fairly busy with life.

Had to change the left bottom arm as ball joint decided to go after 40 years of hard use.

Replaced with one done by HBI Engineering (https://www.hbiengineering.com/) they now have a starlet bottom arm to AE86 ball joint on file if anyone needs one (stronger then standard starlet with the old T3 bushes).

Since the car need to be realigned decided it was time to get a laser alignment and get all my rims + tyres balanced and checked over

So down to Jason @ Matipo Garage to sort me out.

 

Here's the initial alignment, toe was different as had just changed the bottom arm.

The thing standing out there is that the REAR has -10mm toe OUT on the solid axle (with -9.5mm on the right side)

Now an interesting thing occurred a few years back where I won a simulator training session (on a high end simulator), the instructor noted that just as I braked I turned the wheel right.

With that much toe out when braking the rear of the car will instantly want to exit stage right, not to mention it explains why the rear wants to step out in left hand turns so easily.

So we evened it up to have -5mm on each side to get me through the next event and afterwards I will get it straightened, and may as well get a little bit of camber added at the same time...

 

Wheels

So onto the balancing, all the wheels needed balancing, some by a lot more then others. But it was interesting to find that 2 wheels on the car where bent (badly), and 2 wheels from my spare set were also bent. So there's a high chance at the last event when we tried changing the front wheels to see if it made any difference, we swapped one set of bent rims for another set of bent rims 🤦‍♂️

And to be clear, they all look straight, there is nothing obviously wrong with them, just a lot more noticeable rotating on a balancer.

So I had them off to Elite Wheels (https://www.elitewheels.co.nz/wheel-repairs/) (I can highly recommend them) it turns out all 4 wheels have twisted centers, so they machined the mounting face to get them right.

I run the Revolution 4 Spoke Race Wheels which weigh 4.5kg each so very light.

I have hit a few kerbs at high speed, and I'm probably on the upper end of the weight limit for them, so I probably need to be a bit more careful avoiding kerbs in the future.

So pretty much all set for Speed Festival 6th/7th September (free spectating) at Ruapuna

 

 

 

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Out for testing at Speed Festival

Finally some good news with the main vibrations sorted after balancing and straightening the wheels.

Used first test session to work on getting brake bias sorted after the master cylinder change and checking things over.

Then onto the second session, where I was still dialing in the rear brakes and end up having a big lockup and spin.

Yes that's a genuine LMP car going past (holy shit it's quick)

Unfortunately I managed to collect the kerb and broke my brake ducting.

The force to break that must have been fairly high, it was not a weak part. And shows how strong the brass inserts are, they haven't moved at all.

On the plus side, being the weak point means it looks like all the ducting around the rotor has survived untouched.

So currently attempting to print replacements on the new printer (first 5 versions did not go well) with not a lot of time left to go until qualifying tomorrow morning at 10am.

 

 

[Hyperblade]

So some background, when looking under the car before race day the underside has had a spray of oil cover it, we couldn't work out where it was from.

Best guess was at the time a leak from the valve cover (in the corner that is impossible to see or get at) and could just top up oil as required...

After qualifying there was a couple of drops of oil on the ground, not great, but could live with.

Then after Race 1 had more oil on the ground.

Hmm getting worse, and it looks pretty clean... better have a harder look.

Got it up on jack stands, and nothing standing out (like gearbox bung missing).

Hmm that doesn't look factory... nothing weeping out of it though.

So ran the car up in 6th gear and loaded it up on the brakes, started weeping instantly along entire crack.

For context, that's the rear case on the gearbox.

So decided not to try and bodge a repair and unfortunately missed the final 3 races.

So a frustrating end to the weekend.

 

Decided to see if 17" wheels would fit.

Probably not without a lot of cutting...

 

 

[Hyperblade]

Found a new rear housing and have 3d scanned it.

Now to work out how to make a bolt on bracket to move the shifter forward.

Bit hard as don't have the current gearbox out of the car, so will see if I can make something that has a some adjustment.

 

Has to move a long way forward.

 

[Hyperblade]

Housing has been scanned and chopped up virtually to move the shifter as close to where I think it needs to be compared to old one (without taking the current gearbox out).

 

Everything is still a very rough work in progress to get the overall shape of it (fillets etc will come later), and the intention is to get it 3d printed in metal rather then CNC as I think the machine costs would quickly add up.

 

Currently I've got a flat base to mount the shifter too. The challenge with this bracket is all going to be in mounting the shifter housing itself to the bracket as it's all curves, and I'm not sure yet what space I have within the shifter for bolts.

 

 

 

 

 

 

 

 

Getting better with the scanning, and super happy I managed to get it all aligned in 3d space really well, which has made things a lot easier.

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I've been hitting the rev limiter at the end of the straight in 6th (209km/hr), into the hairpin in 5th and in 4th into the 1st Esses.

One of the changes while the rear axle is being straightened is to change the diff ratio (current 4.55) to improve this situation.

I just happened to have a 4.1 spare so have installed that as a "no cost" fix.

Then an opportunity came up to buy a rebuilt gearbox with the same AP1 gearset but AP2 reduction gear (plus carbon syncros) since my gearbox has to be pulled apart anyway to replace the housing it seem like a good opportunity to switch and put my current gearbox back to original spec and sell it.

It's almost too nice to cut the housing up on the new one, but has to be done.

 

Here's the diff ratios vs gears vs tyre diameter

 

Finally got the old box out to sort it out, the white paint here is the crack around the housing.

Wasn't far away from having the whole thing fall off.

 

 

 

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Feels wrong to cut up another perfectly good rear Honda S2000 transmission housing, just to shorten the shift lever position, but here we are.

 

Prototype V1 of the bracket to verify hole locations, overall positioning, easy of getting on and off.

 

As a CAD noob, it's a lot more tricky then it looks, as the bracing is not on simple planes.

 

Absolutely stoked being only 2mm off on a couple of the main holes just from the 3d scan.

 

Needs a lot more strengthening to take loads front and rear, but side to side is looking really good considering it's just printed in pla for now with only 4 walls and 15% gyroid infill (so effectively none).

 

My approach here was to deliberately do it as light as I could to visually see where it wants to flex (which is pretty obvious in hindsight, but I often just need to see it) and also to work out if the overall concept of mounting will work.

 

So next step will be to add more bracing into where I think it needs it, I will also make the main braces thicker in the forward/backward plane.

 

I figure if I can get that pretty solid, then once I had chamfers into all the corners, thicker walls, proper grid infill and a couple of other tricks, then that should be looking pretty good for the loads.

 

 

 

Short video of the flexing:

 

 

[Hyperblade]

So my goal with the prototypes is to get something that sits in the right location, and also has basically no movement in plastic, therefore I know the aluminum it will be ultimately done in will handle the loads (I don't have the skills or access to generative design at the moment.)

So version 3 of the bracket.

Printed in PLA 5 walls, 25% rectilinear infill (so close to overall internal geometry in how it would be printed in ali).

I added another smaller cross brace which helped a lot. I then added fillets everywhere, and an outer 2x20mm edge to the side to stiffen it forward to back.

Overall it's a lot better, there is however significant force with the gear lever (being longer then normal) which means you can see the movement.

You can see the forward to back movement here.

 

Interesting the twist is worse now as the front is strong, so the front of the bracket doesn't move, but the rear does.

The front to back movement I know I can solve by bracing back to the webbing. 

The side to side is trickier challenge, because of the height of where the cup sits to the bolts. there isn't much angle on the side braces, which means it's easy for it to twist.

The bracket is also overhanging a lot compared to it's mounting bolts, which does not make things easy.

I also have to be mindful that I need to be able to get the bracket on, the cup, the shift ball receiver, the main shift plate and ultimately the gear lever, so just adding in braces across the middle is not necessarily doable.

So the way forward.

• 3d Scan the new housing so I can get the position of the ribbing (old one had it all cut off)
• Try and get a more accurate picture of where it sits in the car, so I can work out how much ribbing is actually staying.
• Consider bracing the left side down to the next bolt lower.
• Consider bracing to the ribbing.
• Consider bracing to the gearbox cross member.

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On 18/12/2025 at 09:06, mjrstar said:

I would avoid flipping a rear steer arrangement to front steer it will ruin Ackerman.

 

Front steer has the balljoint outwards and rear steer inwards of the knuckle pivot point.

 

On 18/12/2025 at 16:42, cletus said:

Ackerman = the steering arms should be roughly inline with the rear axle center

So rear steer = the pivot points of the tie rod ends are closer together than the balljoints

If it's front steer they should be further apart, this is often a bit limited by other things

Flipping the spindles around so they are rear steer used in a front steer setup will  have anti ackerman where the outside wheel will turn more than the inside which is opposite of what you want 

So these comments popped up on the crazy RWD Platz build, 

 

And I was like hang on a second, I did that with my car, and then ohhhh fuck did the realization hit hard...

So to recap, we rotated the engine cross member around as we need to move the steering rack to the front to so the engine could sit down without affecting the sump. We then swapped struts and steering arms from each side.

Top of picture is towards front of car.

And then we managed to completely forget about the ackermann issue.

Your all going to be asking how? Simple answer is we had enough other issues getting the engine and drivetrain in + all the sheet metal changes, that it just slipped by and got forgotten.

But it explains one of the major issues I have with the car which is it wont turn in at all, it was very frustrating, but low down on the list of things to sort out as needed to get the car consistently reliable first.

Ok so how do we fix it?

Option 1:

Go back to a rear rack, completely redo the engine position in the car, go rack that goes through the middle of sump (can get kits now), but engine probably wont be in exact same position, which means issues with gearbox, headers, and length of driveshaft, not really liking this as an option...

Option 2:

 New steering arms to move the steering arm inwards towards the rotor (which is already thicker then most normal disks on an AE86) and all within a 13" wheel.

Option 3:

Sell the car, buy a GT86 race car and just bolt on parts to go faster...

Option 4:

?

 

So I think Option 2 is probably the only way to go at this point. But I will need to get into cad the measurements of what's there now, what it was before we swapped the arms and then how close to the rotor I can get something (I'm happy to get rid of the stupidly oversized T3 rods for something smaller so can claw back some space there.) then see what will actually work physically within the wheel too. Looking online around what ackermann you want in a racecar is a mine field, so may aim to go for as close to AE86 as I can get. 

 

I'll just add it to my current todo list which is already long enough

• Design new shifter mount, get it printed, put gearbox back in.
• Fit new harmonic balancer
• Design new cover plate on top of the pedal box for the giant hole i cut in the firewall (pics to come later)
• Rerun all the brake lines in the cabin as I ripped them all out in my pursuit of making the pedal box actually maintainable.
• Design and mount pedal pressure sensors.
• Design and get made new steering arms
• Fit new GPS unit
• Fit new 2 way radio unit
• Replace oil temp and oil pressure which are now flaky because of previous vibrations.
• Scan and create reducers for brake cooling inlets
• Design and Fit original kp side mirrors back on the car (biggest mistake was ever selling the originals and going to race mirrors)
• Move radiator and oil cooler (nice to have).

 

[Hyperblade]

So been a few months working sporadically on the S2000 Shifter relocation.

Been through a lot of iterations (understatement) trying to try and get the strength I need. But also so that it's easy bolt in, and also that it fits in the tunnel while also being easy to make. The whole shifter is moved 190mm forward is which is quite a lot.

Ultimately I've ended up with the following.

2x Front aluminum brackets which bolt to the gearbox housing.
2x Rear aluminum brackets which clamp and bolt to the ribbing on the rear of the housing.
1x Main Bracket which is going to be printed in PPA-CF.

I was originally going to 3d print the whole thing in aluminum, but when I ran through the costs it was getting up to be $1000 printed in solid aluminum (it was  going to be a lot more work to hollow and grid it all out internally to save weight so was a effort vs cost decision).

So I decided to thicken up the main spars in the bracket, and see how it goes with PPA-CF which cost me $200 for a roll (will use 75% of a roll). 

This way means it's all fairly low cost, and If I need more strength I can always redo the main bracket in metal later on.

 

Considering for the test everything is printed in PLA I'm stoked with the movement (I'm putting way more force through the extra long gear lever then it should ever take in real life)

The movement is also in the rear brackets, not the main one.

The key thinking behind the final design:

• No matter what I need to have aluminum brackets for the bolts going into the housing as these need to be torqued to spec. 
• Because I went with a rear clamp design, plastic creeps over time, so aluminum made sense here as well.
• As the main bracket is printed in plastic I need to ensure any bolt goes through it with compression limiters so it doesn't creep and loosen over time.
• I chose to double up on the 6mm bolts at each mounting point to give additional clamping load, but more shear strength on the plastic.
• I originally had the shift cup being bolted to an aluminum piece at the top of the main bracket, but unfortunately with how tight the tunnel is, I couldn't come up with a way where I could bolt through the plastic to it, the bolts would have had to go into the plastic, which for something which is taking lots of load and movement I just didn't want to do. So instead I've add extra ribs to the plastic around this area to get the strength back.
• By changing the design to have the rear mounting (something i was initially trying to avoid), it simplified the overall bracket, but also made it immediately stiffer as it was taking the natural load paths.
• Overall it's a lot easier to fit, the aluminum brackets stay on the gearbox, and then you can muck around with the main bracket.
• It's more flexible to change, if i need to make changes in the future, I'm not redoing everything.

So I now have some metal 3d printed brackets to drill/tap and fit.

And then I need to do another test print sized for the compression limiters and if that all looks good I will do the PPA-CF print.

Other key takeaways.

• Going direct to the 3d printing place in China can give you a substantial savings (vs through craft cloud) was $400 originally, ended up being $200 after discounts.
• Getting compression limiters in NZ is impossible, ended up having to go to the US and using Youshop, which hurt when they tacked on GST.
• Can save about $75 on Bambu lab PPA-CF by buying from Ali... $275 vs $200 (delivered)
• When dealing with Scans in Fusion 360, save them as an individual part which you get all aligned, then insert into another design, this improves the performance of Fusion as it doesn't have to upload the whole scan every time you save.
• Until it hits the track and is actually proved in the real world, it's all just speculation that this is the right design... it could end up being a colossal failure.

 

[Hyperblade]

So have printed the final version of the bracket in PPA-CF (Ignore the green it's support material I need to remove, somehow).

It's noticeably stronger then the PLA prototypes, and I think will work fine.

Currently need to anneal it (for about 20% more strength all going well), then fit the compression limiters, then wait for some new brackets to come (upload the wrong files like an idiot)

Then it should be ready to put together and back in the car.

 

While that's be ongoing.

I've started looking at the suspension and fixing the ackermann.

 

So I've 3d scanned and modeled some of it.

But I decided to just swap the steering arms over and see the clearance.

Well clearance is clearance even if it's only 1mm.

 

However the issue is that the vertical movement of it is limited, I would have to grind away a lot of the edge of the steering arm to give it clearance for the camber the struts are on.

 

But then you start looking harder at it, like the position of it in relation to the bottom arm ball joint.

The fact the starlet steering rack pivot points are 40mm shorter then the lower arm pivot points (factory standard???).

So I could keep persisting down this path, but I took a step back and looked at the whole, and the issue is I'm now getting far away from any factory off the shelf parts, that means repairs/replacements are an issue.

• Replacing a LHD starlet steering rack would not be easy in NZ.
• Custom steering arms are fine until you bend one.
• Also designing a steering arm from scratch is a lot of work.
• Long term trying to fit 10" wide rims on it all is not going to work without pushing them wide which means new flares, and not great scrub radius.
• Can put Quaife AE86 quick rack into starlet steering rack, but it's still too short by 5-10mm and also it's more expensive then a whole new escort rack, so an escort rack is the way to go.

If I'm putting in an escort rack, then may as well go all in and fit the capri front suspension...

Consisting of:

• Standard RHD Escort rack (quick 2.4 turns)
  • Off the shelf
• Capri stub axle
  • Off the shelf.
• Standard Steering Arms (maybe shorter if makes sense, but off the shelf either way)
  • Off the shelf
• Shocks, will bore out the Capri stub axles to take the lower threaded tube for my current shocks, so no change.
  • While there we will give extra clearance for 10" rim by boring at a small angle.
• Lower control arms
  • Off the shelf
• Brake calipers and hats for my current calipers and rotors.
  • Off the shelf.
• Hubs drilled to 4x114.3 and 60mm center bore
  • Off the shelf blanks, so easy as.
• Brake Cooling
  • Will likely have to redo this, might get lucky if can make minor adjustments to bolt it up.
• Sway bar
  • Will need to work out new mounting for it.
• Compression Limiters
  • New ones to suit lower arm.
• New Cross member to suit new lower arms and steering rack
  • Custom at this stage.
• Mount engine to frame rails directly
  • Custom, to simplify making the cross member.

Overall it moves the custom stuff to basically compression arm mounts, cross member and sway bar points. Everything else is pretty much off the shelf and in stock locally in Christchurch.

• It also means I don't need to get 3 new sets of rims, will all just bolt up.
• Can reuse the brake package.
• Can reuse the shocks

From a design point of view, it's simpler for me to manage I just need to work out position of lower arm pivots and where the steering rack will sit.

Additionally I can sell my old stuff, which would be useful to someone as a package if they want to go AE86 front axles in a starlet (the normal way around) so can get some money back.

[Hyperblade]

The Honda S2000 Shifter relocation is nearly done just waiting on 3d printed aluminum brackets to arrive in couple of days.

 

Work has been progressing on another pain point with the car, the pedal assembly.

 

 

Anyone with a starlet will know this, but putting a pedal box into them is a fair bit of work (made worse by a roll cage), the trouble really occurs when you have to work in that area. It is a full days job (a true 8 hours+) just to remove the pedals, master cylinders, pressure sensors and pipe work for me. And that's with an access hatch from the engine bay.

 

 

And don't even think about just trying to adjust the balance bar between the cylinders, not possible.

 

I need to make it easier to work on, and also add a clutch pressure sensor (for future fun stuff) so out with the angle grinder and I have a new access hole from the top.

 

 

I've now scanned it, and will design a 3d printed lid and top to go there to seal it back up (will be printed in polycarbonate flame retardant), technology these days is so cool.

 

Additionally I wanted to simplify all the pipe work, and make it much easier to change the pressure sensors if I needed to. So it made sense to just move that stuff to the passenger side (left) of the car, that gives a huge amount of room back around the pedal box.

 

So out with CAD and a 3d printed prototype bracket, then while i was there I made a whole system for mocking up the brake line bends and working out where to run the pipes...

 

 

Here's where I'm at with the lines, absolutely stoked with how they are turning out, cleanest job I've done so far.

 

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With the pressure sensors on the left now, it made sense to run the rear brake line along the left hand side of the tunnel.

Which then meant redoing my fuel lines...

3D printer comes in really handy... (brackets are just prototypes, will be redone in black.)

 

 

 

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Work continues on the brake lines, I need to get 3 to the master cylinders, and one over to the right front caliper.

WIP

[Hyperblade]

So the gearbox is finally in.

Bracket annealed and painted. 

Then a massive thank you to @Bling for helping me put the gearbox in.

What was meant to be a quick 15 mins morning job turned into a 2 hour morning job then turned into another hour in the evening to get it in.

Our first attempt was a failure because when we put it in the holes wouldn't line up, it needed to be rotated 3mm, but it didn't want to and we couldn't work out why, thought it was the dowel pins, input shaft being locked etc.

Turns out looking at the old gearbox, right at the top (of course where you can't see in the car) there was a mark, pretty minor looking (only 1.5 mm deep), but actually that's a deliberate indent to allow it to rotate. I probably knew this 5 years ago went I put the engine in, but clearly forgot it...

 

With that clearanced, it went in smoothly.

 

Even lines up with the shifter hole, which is a bonus...