Today I Learned: Turbo'd Carb & Dizzy Relocation

On the last post, i mentioned about Nico, a friend i met in Lampung. Nico rides a KE20 but this one is not your ordinary "humpback" Corolla.

Here's why:

That's a 4A-GE (rough guessing from the spark plug leads, bigports) converted to carb and turbo. This being the my first time to see a running carb turbo engine in person, to say i'm amazed was an understatement. I have always wondered how can carburetor work with positive air pressure coming from a turbo and now i get the chance to learn how it's tackled.

After seeing Nico's engine in detail, i learned that the key in allowing turbo carb is this (see arrow):

That is called a rising rate fuel pressure regulator. This is what's stopping you from pushing pressurized air into the carb jets and subsequently pushing those fuels out of the float chamber. This works by sensing the air pressure on the charge pipe and via some membrane and spring system, ensures that the fuel pressure from the pump is always above the air pressure coming to the carb. Typically it's set to 3-4 psi above the air pressure. Here's a short yet good writing about rising rate FPRs.

That's not the only thing i learned from Nico's 4A-GE. Notice where the dizzy is on the engine? Since the engine's converted to carb, the stock distributor is useless since it's designed to work with the ECU. One way to solve this is to use a point-and-condenser dizzy. I don't know what engine's distributor is usually used but i think this one's from a K-series engine. Correct me if i'm wrong. Anyway, that's not my focus now. I'm more interested on where the dizzy is.

Although usually dizzy relocation is more of a 20V RWD conversion thingy as this will keep you from ruining the firewall, it's a good idea also for turbo application as you're now moving the melt-prone dizzy cap away from the turbo heat. You'll also be spared from leaky distributor oil seal.

Seeing it in person, it looks simple. The most complicated work i believe is modding the dizzy shaft so that it'd match the slot you that you machined on the cam sprocket bolt. I think Nico's slot was too wide as i still see a small gap that would allow a small play on the dizzy. This is not ideal as your ignition timing won't be firm but since you're already using a mechanical point dizzy, i guess precision ignition timing is not really what you're after, now is it?

So, imagining myself doing the same work, here's, in order, how i would do it :

1. Make a slot the cam sprocket bolt.

2. Mock up the placement of the dizzy mounting plate. This is so that you can measure how much you need to cut the dizzy shaft.

3. Once you shorten the dizzy shaft, make the key on the shaft that match the slot on the sprocket bolt.

4. Mount the dizzy, done. Make sure the mounting plate is thick enough and firm to withstand the vibration.

Last but not least, Nico also took me to my new playground here in Lampung. I've been looking for a junkyard here and finally i found one! Here's one view of the junkyard..

This is a great find for me.. Why? See the pic above. Hint: this will solve my gearbox problem. Got it? Well, this junkyard have some W58 gearboxes! Now i don't have to hunt one in Jakarta!