August 10, 2022

Bodged not bought

A basic diagram to explain why velocity stacks/ trumpets are required. These allow the fine tuning to where the power comes in the rev range. Bike carbs are designed for the torque to kick in high in the rev range as most bikes rev to around 11000. As car engines do not rev as high we need to extend the trumpet to increase the velocity further and allow this to be usable in the rev range. The conical shape increases the air pressure as the diameter decreases which makes the air travel faster due to being more dense. For example the without my trumpets on you can feel the torque kick in around 6500 rpm put with them on it kicks in closer to 6000rpm. If there is not room for trumpets then a plenum may be implemented to increase the velocity of the air travelling in to the engine.[/caption]

I always planned on putting a 2.0 Zetec e in the fiesta. One thing I was unsure on was whether to retain fuel injection or convert to carbs. This is what gave me the idea to convert the 1.6 to carbs prior to the transplant.

I wanted to find out if the ford ecu would be capable of running the ignition if various sensors were not plugged in. I also wanted to know if the ignition would be retarded to a point where the carbs would not make a decent performance gain.

cbr 600 carbs photo 476.jpg

I got hold of some CBR 600cc bike carbs that I intended to use on the 1.8 mk3.5 Fez. I thought as they were not oversized this would work well on the 1.6 but on the 2.0 would give decent fuel economy too.

cbr 600 carbs photo 476.jpg

I picked up a standard 1.6 manifold from the scrap yard to ensure if it did not work successfully I would be able to return to standard induction with ease.

This it the inlet with the plenum chamber removed.

The chopped inlet CBR 600 carbs and a Malpassi injection to carb fuel regulator. Its a clever bit of kit, It uses 1 inlet and 2 outlets for the fuel. This allows the possibility to reduce the fuel pressure to the required 6psi level from 1 outlet while the extra fuel is sent to the tank. Another way to achieve this is by using a motorcycle fuel pump instead of the standard fuel pump. A basic way to attempt to achieve this is to T off 1 of the fuel line to the carb to reduce the fuel pressure. I would not advise this method.

cbr 600 carbs photo 301.jpg

Trial fitting to see how well the carb line up with the inlet ports. In between the ports there is 2 tubes. These were originally for the oil breather pipe. I used the standard pipes to join this to the brake breather for the servo.

I then routed the engine oil breather to a catch tank.

cbr 600 carbs photo 393.jpg

Had to use quite long pieces of silicone to ensure I didn’t have to re space the carbs. Dont cut corners like this as I found later that the pipes flex loads on idle.
When I fitted them to the engine I used 8 jubilee clips to secure each end of the silicone hose’s.

The engine with the stock inlet removed.

Due to the long hoses the carbs sat quite close to the bonnet. this meant I had to remove the velocity stacks. I ran this set up for approximately 2 weeks as a daily runner and taking it out for a play on the evenings. Then It was time to move towards the 2.0 swap




Post Engine mount and conversion info


parts required etc

External Links

Ford radio code generator: M W Sstewart: Valuable source of information with great knowledge and explanation