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Throttle Pedal, stop, and cable equals 'Max Power'!

Looking back through my build blog I now realize I didn't cover the installation of the throttle cable. I can't recall any particular reason for the omission, so if you've been searching for the topic then I apologize.

Making the most out of this post does require a little understanding of the throttle cable installation. I suggest a quick recap is in order and with a bit of luck there's some benefit in this post for those building their 7 too.

Let's look at the basics first, cable routing. The throttle cable is essentially laid flat on top of the engine and it arcs forward from the passenger side to the driver's side. On the passenger side, the cable is secured into the sprung loaded throttle position assembly using the cable end which finishes with the thin cylinder shape. The cable is then clipped into the cable adjuster as shown.

Caterham 7 blog throttle cable
Throttle cable setup passenger side

Once looped around the cable passes through the circular aperture in the side of the pedal box where it's secured into the top of the throttle pedal.

Caterham 7 blog throttle cable
Throttle cable entering pedal box and secured into throttle pedal

In the image shown the pedal box cover is removed. Removal of the cover is straightforward but I recommend removing the battery if it's your first time. There's a hex bolt on the inner lower side near the battery which secures two p-clips holding two copper brake lines. You'll be working blind with the battery in place as you can't get a sight-line, plus space is limited so it's easy to back the bolt out and get a ratchet stuck. If you do keep the battery in place, just back the bolt out a little and switch to an 8 mm spanner.

The next tricky bit is to actually get the cable into the top of the throttle pedal. You need to manoeuvre the cable down into the pedal's hollow construction, passing the cable end out through a hole. Then seat the cable bulb into the pedal while allowing the cable to drop through the rear channel. With the cable and pedal as supplied it's next to impossible. I ended up widened both the exit hole and rear channel. If you do this make sure you debur or file any rough edges. I've also used some self-amalgamating tape and heat shrink to reduce cable on pedal friction. I've noticed at maximum pedal throw or full throttle the cable has a tendency to catch against the very bottom of the rear channel. I suspect over time it would result in a failure. Heat shrink has been added to the cable, and the tape to the pedal, thus reducing metal on metal contact.

Caterham 7 blog throttle pedal
Protected throttle pedal, heat shrink and tape, limiting metal on metal wear

Before you fit the cable into the pedal you need to bend it forward! Yes it's in the build manual. As supplied the pedal doesn't provide sufficient throw for adequate cable movement on the Duratec or Sigma throttle assembly. To bend the pedal, wedge it against the throttle pedal stop with a block of wood. Make sure the pedal stop is at the highest position. Insert a screwdriver into the throttle pedal and bend. It's one of those jobs you'll hate, especially as you do not want to damage the foot-well front panel. Avoid creating a curve in the pedal too, you need to keep it straight to maintain linearity of pedal motion.

During my build, I'd managed to bend my pedal as far as I could, ultimately the rear structure of the pedal box housing limits the movement of the inserted screwdriver. With the pedal bent, I'd also placed the pedal stop at the lowest setting and set the throttle adjuster. The adjuster ensured the throttle rested against the throttle stop, but with a slight amount of slack in the cable. With this setup I was aware I couldn't quite achieve 100% rotation or throw on the throttle, it was about 90% give or take. I'd made a visual inspection of the butterfly valve and it seemed to be horizontal, and so I'd accepted the situation, but it needed confirmation.

Step in Easymap again!

Using Easymap I've been able to confirm the maximum throw of my throttle pedal generates a Site value of 14.2, whereas manually moving the throttle assembly generates a Site value of 15.2. Based on 15.2 representing wide open throttle and if the Site value is linear within the map, the current setup may well be limited to 90% throttle! It's reasonable to conclude the car is down on power.

Having recently corrected my idle issue with the aid of Easymap, I decided to leverage the tool once more and ensure maximum performance was available. During my work correcting the engine's idle I'd become well aware no additional travel was left in the cable adjuster. It was time to take another look at the pedal box.

Over the weekend I spent about an hour trying different methods to further bend the throttle pedal, all failed. Even though I was trying to bend the pedal I wasn't convinced it would result in the extra movement needed. I felt bending the pedal simply changed the start and end positions, but the delta or deflection remained the same. It's the delta which directly translates into the throttle rotation. If I wanted more rotation in the throttle assembly through greater movement in the cable, I needed more travel in the throttle pedal. What dictates throttle pedal travel? The throttle pedal stop!

I knew I'd lowered the pedal stop to its lowest position during the build, so decided to remove the stop and investigate further.

The design of the pedal stop is pretty simple. A threaded bar with a plate welded on the end is passed through the foot-well panel and then held either side by a two shaped collars, two spring washers and two nuts.

Caterham blog throttle stop
Throttle stop exploded diagram

The shaped collars compensate for the foot-well panel being at an angle and thus ensures the stop meets the pedal in the right location. Having a spring washer and nut on both the inside and outside permits the threaded bar to be biased against the panel as required. This provides the height adjustment for the pedal stop.

I decided I didn't need the height adjustment, I just needed the stop as low as possible. Since the inner nut and washer supported the ability to raise the stop I opted to remove both. Removing the nut and washer would lower the stop by their approximate depth of 8 mm and with a bit of luck provide sufficient additional travel. The stop would still be secured in placed by the split washer and nut positioned on the outside of the panel.

Caterham 7 blog pedal stop
Inner nut and split washer removed from the pedal stop

This approach worked a treat, the extra travel gave ample additional cable movement, in fact more than needed. Initially the cable pulled the throttle a little too tight causing the throttle to fully extend and create a metal on metal noise as it hit the maximum. To prevent this the throttle adjuster was used to gradually adjust the cable and ensure the pedal stop was hit before the maximum on the throttle cable, but still ensuring a Site value of 15.2 was obtained. Thanks again to Easymap.

I've since been out and driven the car, I can confirm it feels more aggressive when at full throttle. Of course it's difficult to say just how much power might have been missing and subsequently restored. Absolutely worth doing though!

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