This thing ain’t stock. Dubbed the 520R to signify the different engine and its power output that falls midway between the 420R and 620R, there were a lot of changes made during the build to make it more mine. Some were minor, some significant. But many will likely polarize. I’m sure the ardent purists hate me, but I’m okay with that given I’m not overly fond of them 😊 3D printing was used extensively throughout this project. Unless otherwise noted, all printing was done with a Carbon Fiber impregnated Nylon that can handle various automotive fluids and under-bonnet heat.
Engine
When speccing the car, my initial plan was to simply swap engines with the Westfield which had very special 2.0L Duratec: forged rods & pistons w/12:1 compression ratio, more radical cams than the 420R, headwork, fully balanced bottom end, Jenvey 45mm DTHTBs, etc. However, when looking into this more closely, I discovered that the 420R engine wouldn’t fit the Westfield due to the positioning of the intake system. That meant I would need to buy another set of Jenvey’s and all the associated gear to make it work, including an unlocked MBE ECU. There was also a lot of effort required to make the wiring harnesses compatible. Bottom line, this would be a PITA and expensive. It seemed better to either rebuild the 420R engine to the Westfield specs or go a little different direction. Given the Caterham was a little heavier, and the amount invested in the purchase, I wanted a noticeable power increase. I wanted to go faster. That meant a switch to a larger Duratec.
Enter the Esslinger 2.4L short block. It’s a 2.5L block coupled with a forged 2.3L crank, custom forged rods that are slightly longer than the 2.3L, forged 12:1 pistons, various block upgrades, upgraded fasteners, and a bottom end fully balanced with my flywheel and pressure plate. Attached to the block are a 2.5L head extensively reworked by Progressive Automotive and fitted with Esslinger’s Stage 4 cams and valve springs, 50mm Jenvey DTHTBs, light flywheel, heavy duty clutch, dry sump, etc. An unlocked MBE 9A4 allowed for a custom engine map.
In theory, the engine could get to the 280+hp range. More than I want or need. The goal was 260-270hp with the knowledge that if I initially kept the stock 420 exhaust system, the power would cap in the 250-260hp range. Simply put, that exhaust is undersized at these power levels. After tuning it on the dyno, the graph supports this restriction. Assuming a 15% loss, flywheel horsepower comes in at 255hp, so right in the middle of expectations. If I decide I do need a little more power, or just want to have a little more urgency at the top of the rev range, I’ll tackle the exhaust.
Engine
When speccing the car, my initial plan was to simply swap engines with the Westfield which had very special 2.0L Duratec: forged rods & pistons w/12:1 compression ratio, more radical cams than the 420R, headwork, fully balanced bottom end, Jenvey 45mm DTHTBs, etc. However, when looking into this more closely, I discovered that the 420R engine wouldn’t fit the Westfield due to the positioning of the intake system. That meant I would need to buy another set of Jenvey’s and all the associated gear to make it work, including an unlocked MBE ECU. There was also a lot of effort required to make the wiring harnesses compatible. Bottom line, this would be a PITA and expensive. It seemed better to either rebuild the 420R engine to the Westfield specs or go a little different direction. Given the Caterham was a little heavier, and the amount invested in the purchase, I wanted a noticeable power increase. I wanted to go faster. That meant a switch to a larger Duratec.
Enter the Esslinger 2.4L short block. It’s a 2.5L block coupled with a forged 2.3L crank, custom forged rods that are slightly longer than the 2.3L, forged 12:1 pistons, various block upgrades, upgraded fasteners, and a bottom end fully balanced with my flywheel and pressure plate. Attached to the block are a 2.5L head extensively reworked by Progressive Automotive and fitted with Esslinger’s Stage 4 cams and valve springs, 50mm Jenvey DTHTBs, light flywheel, heavy duty clutch, dry sump, etc. An unlocked MBE 9A4 allowed for a custom engine map.
In theory, the engine could get to the 280+hp range. More than I want or need. The goal was 260-270hp with the knowledge that if I initially kept the stock 420 exhaust system, the power would cap in the 250-260hp range. Simply put, that exhaust is undersized at these power levels. After tuning it on the dyno, the graph supports this restriction. Assuming a 15% loss, flywheel horsepower comes in at 255hp, so right in the middle of expectations. If I decide I do need a little more power, or just want to have a little more urgency at the top of the rev range, I’ll tackle the exhaust.
Fueling system
Caterham uses a dead head system with an in-tank pump that is marginal at target power levels. The in-tank fuel assembly module drops in from the top of the tank at a slight angle, and because the floor of the fuel tank is also at an angle (~15 deg), the fuel pump misses out on about the last 1.5 gallons of fuel. Add in the notoriously inaccurate fuel level sensor and various changes were in order. To address these and to accommodate -6AN lines, a new assembly was fabricated from a 3D printed top, aluminum stock, Centroid capacitance fuel level sender, 255 LPH positive displacement pump and a Holley Hydramat. Goodridge 910 Aramid braided PTFE hoses feed fuel from the assembly to an external fuel filter (strangely Caterham doesn’t use one) attached to the under boot floor support by a 3D printed bracket, then to the engine and a combination fuel pressure regulator/damper from Radium Engineering before roundtripping back to the tank. Although pricey, the Goodridge lines are light, very flexible, and the hose end installation is a lot easier than most other lines.
Caterham uses a dead head system with an in-tank pump that is marginal at target power levels. The in-tank fuel assembly module drops in from the top of the tank at a slight angle, and because the floor of the fuel tank is also at an angle (~15 deg), the fuel pump misses out on about the last 1.5 gallons of fuel. Add in the notoriously inaccurate fuel level sensor and various changes were in order. To address these and to accommodate -6AN lines, a new assembly was fabricated from a 3D printed top, aluminum stock, Centroid capacitance fuel level sender, 255 LPH positive displacement pump and a Holley Hydramat. Goodridge 910 Aramid braided PTFE hoses feed fuel from the assembly to an external fuel filter (strangely Caterham doesn’t use one) attached to the under boot floor support by a 3D printed bracket, then to the engine and a combination fuel pressure regulator/damper from Radium Engineering before roundtripping back to the tank. Although pricey, the Goodridge lines are light, very flexible, and the hose end installation is a lot easier than most other lines.
Under bonnet
Given I wasn’t using the factory airbox or a heater, this gave flexibility on the firewall layout. The brake/clutch reservoir was moved to the driver’s side, freeing up space for a custom fuse and relay box making those items accessible from under the bonnet rather than from under the scuttle which requires contortionists’ skills I don’t possess. This was another 3D printed part. The battery is still in the stock location but was replaced with a much smaller and lighter Lithium battery from Antigravity. The stock battery mount was reshaped to accommodate the size difference and incorporates a 3D printed hold down. The last big change was the coolant reservoir. The factory places this under the nose cone where it’s harder to access and it’s…well, not overly attractive. I went to Radium again for a solution and mounted this in the center of the firewall where the heater would normally reside.
The Jenvey underslung throttle linkage interferes with the factory upper radiator hose, so that was replaced with a combination of a silicone 90 deg bend and a flexible, convoluted hose. An adjustable 3D printed bracket keeps the hose away from the idler pulley.
Because the 420R is known for overcooling the oil on the street, I fabricated an oil cooler block-off cover from aluminum sheet. The U-shaped cover slips on from underneath and is secured by zip ties making removal and refitment an easy process.
Lastly, and purely for aesthetics, the ugly and unfinished top of the rear coolant manifold was topped with 3D printed cover that matches the ribbed design of the battery hold down and fuse box covers.
Given I wasn’t using the factory airbox or a heater, this gave flexibility on the firewall layout. The brake/clutch reservoir was moved to the driver’s side, freeing up space for a custom fuse and relay box making those items accessible from under the bonnet rather than from under the scuttle which requires contortionists’ skills I don’t possess. This was another 3D printed part. The battery is still in the stock location but was replaced with a much smaller and lighter Lithium battery from Antigravity. The stock battery mount was reshaped to accommodate the size difference and incorporates a 3D printed hold down. The last big change was the coolant reservoir. The factory places this under the nose cone where it’s harder to access and it’s…well, not overly attractive. I went to Radium again for a solution and mounted this in the center of the firewall where the heater would normally reside.
The Jenvey underslung throttle linkage interferes with the factory upper radiator hose, so that was replaced with a combination of a silicone 90 deg bend and a flexible, convoluted hose. An adjustable 3D printed bracket keeps the hose away from the idler pulley.
Because the 420R is known for overcooling the oil on the street, I fabricated an oil cooler block-off cover from aluminum sheet. The U-shaped cover slips on from underneath and is secured by zip ties making removal and refitment an easy process.
Lastly, and purely for aesthetics, the ugly and unfinished top of the rear coolant manifold was topped with 3D printed cover that matches the ribbed design of the battery hold down and fuse box covers.
Suspension
Meteor Motorsports has a great reputation in the UK among Caterham owners for their suspension expertise. Given this engine would be very torquey and I drive on a lot of uneven roads, losing traction while overtaking was a concern. The Westfield is not as nuts and does have IRS, so this has never been an issue with that car. The Caterham, however, was an unknown and I had been advised they do have issues in this area with 250+ hp engines. Opting to throw money at an unconfirmed problem, I worked with Simon at Meteor to come up with a package to help keep the drive tires in contact with the road: different spring rates coupled to single-adjustable CORE dampers. The front dampers are digressive and mated with fixed rate 275 lb springs, while the rear dampers are not digressive and are mated to 150 lb progressive rate springs. In contrast, Caterham’s Sport suspension features 170 lb front springs and 140 lb progressive rears.
Interior
This was another area of significant change. To my eyes, the factory dash layout looks like someone sneezed the switches and gauges into place; very haphazard, impairing both functionality and aesthetics. The factory dash was replaced by a carbon fiber blank dash from Westermann Motorsports in Germany (quality is not great). An AiM MXS 1.2 Strada display was mounts on a custom 3D printed base that angles the screen towards the driver’s eyes rather than a foot over their head like the factory gauges. This not only improves readability, but significantly reduces glare. Freewheel wireless steering wheel button system operates horn, turn signals (and hazards when pressed simultaneously) high beam/flash to pass, and odometer reset. The remaining switch needs are handled by five 620R toggles in the center of the dash. The plate that mounts the steering wheel buttons was also 3D printed to place the buttons precisely where I wanted and to provide hidden channels for the supporting wiring.
I optioned heated seats to help offset the lack of a heater. The switches are normally fitted to the top of the transmission tunnel cover ahead of the gear lever, however, because I custom ordered a plain black leather tunnel in lieu of the standard carbon-fiber-look vinyl, these switches were not fitted. This was an opportunity to mount them on the tunnel sides which makes them less visually obtrusive and is every bit as convenient and functional.
To add a little storage, a glove box was 3D printed from Carbon Fiber PETG, covered with matching leather to blend in with transmission tunnel and affixed behind the gear lever. It features a magnetic door latch and a switchable 12v+ port with a dual USB insert.
This same material was used to 3D print covers for the upper damper mount bolt access ports. These are left uncovered in R-spec cars which don’t use carpet on the rear bulkhead.
Lighting
To increase visibility without having to remember to turn off the headlights when stopped, I decided to give DRLs a try. I found some very small, very bright LEDs, then designed and printed brackets which attach to the license plate bracket found in the lower grill of the 620 nose cone. A relay powers them with the key and turns them off when the headlights are turned on.
A 3rd brake light was added to the top of the rollbar and is controlled by a BackOff module that flashes it five times upon initial brake application.
To increase visibility without having to remember to turn off the headlights when stopped, I decided to give DRLs a try. I found some very small, very bright LEDs, then designed and printed brackets which attach to the license plate bracket found in the lower grill of the 620 nose cone. A relay powers them with the key and turns them off when the headlights are turned on.
A 3rd brake light was added to the top of the rollbar and is controlled by a BackOff module that flashes it five times upon initial brake application.
Miscellaneous
The 3rd brake light doesn’t interfere with the full hood but does prevent a half hood from cinching down around the top of the roll bar. Working with Thundersport, a custom half hood was made that could accommodate this protrusion while remaining watertight. An Element Firestick is mounted above the passenger’s knees where it is out of sight yet easy to access from the driver’s seat.
The 3rd brake light doesn’t interfere with the full hood but does prevent a half hood from cinching down around the top of the roll bar. Working with Thundersport, a custom half hood was made that could accommodate this protrusion while remaining watertight. An Element Firestick is mounted above the passenger’s knees where it is out of sight yet easy to access from the driver’s seat.
