The Turbo JB74 Jimny!

The Turbo JB74 Jimny!

I’ve had this car since 2019 and have done all sorts of trips.

When I go adventuring, my favourite kind of trip is to head into the mountains for 3 or 4 days with no plans, but the goal is to see how far we can get into the mountains. This means I’m taking a bunch of gear with me, and a mate with all their camping gear. Now I’ve added these 33” tyres and a big lift, so more power is definitely going to be helpful.

As you can tell, I quite like modifying my Jimny, so the turbo conversion has been a great project, not just because I need more power, but because I like to see what we can do with these wee Suzukis. To see what issues I’d face, how to overcome them, and to share what I’ve learned to help other people who might be considering a turbo conversion.

Turbo Jimny

We initially did a dyno tune on this car in standard form and found that we had 74hp at the rear wheels. Now we’ve done the turbo conversion we’re up to 162hp at 8psi, over double what we started with.

The plan was to tune the car with a flash of the factory ECU, and I was aiming for 140hp at the wheels.

We’re using the Greddy turbo kit which comes with the Mitsubishi TF035 turbo, all the required piping, the Greddy intercooler and the air filter. We’re using a Walbro 500 fuel pump and the factory injectors are doing great. We’ve also kept the factory exhaust, clutch, even the factory spark plugs.

A flash is where the fuel and timing maps within the factory ECU are rewritten to suit the turbo. There are several tuning shops here around the world that are offering flash tunes for the factory ECU for a turbo conversion, literally you ship your ECU to them, they load their prewritten maps into your ECU and they ship if back to you. As the tuning shop started to tune the car, they soon learned that the factory MAP sensor couldn’t measure positive manifold pressure and the factory ECU wouldn’t work with an aftermarket MAP sensor.

 

It turns out that the flash tunes you can buy are having to override the factory MAP sensor, so the ECU is just guessing the manifold pressure. To me, that seems risky and as I’m aiming for a reliable car long term, I needed to do something better than that.

So we looked at the option of a full aftermarket ECU, but this came with all sorts of issues, as there is only a couple of ECUs on the market that can manage everything. If we replace the factory ECU, we need a way to manage things like the hill start assist, stability control, even the speedo. This was going to be an expensive ECU, and even more work to have it all wired in.

Even more annoying is the electronic throttle control, an aftermarket ECU was going to need to manage that, too, and most ECUs aren’t set up to do.

I got talking to a very clever tuning guy here, a young guy who wanted to have a go at getting it all working with a combination of an aftermarket ECU and the factory ECU. He suggested we use a Link ECU. The Link would manage fuel, timing, boost etc, and the factory ECU to manage everything else.

The only thing we’re without is cruise control, because while cruising the factory ECU normally would cut fuel to bring the revs back down to maintain the speed, but the Link is managing fuel now.

Turbo JB74 Jimny

We’ve recently added the lift kit, the 33” tyres and the gear reduction, so it’s hard to get an exact comparison of how it drove before, but it’s such a fun car to drive now. Sure, it was cool before, but now it's come alive. It feels like it never comes under load as I’m getting around town now, it's just cruising.

I’m a fairly slow driver anyway, so it doesn’t come up to full boost as I’m around town. Even when we come up to 2 or 3psi of boost, it gets up and goes, it feels like a completely different car.

Like anything, if I drove like an idiot, it be braking things like diffs, driveshafts, gears maybe. If I went flat out, maybe it’d heat up and cook the engine, but we’ve given it a really safe tune, it’s not going to detonate or spike the boost. Driven casually, it should be totally fine.

For safe offroading I’ve installed air lockers to help look after the diffs, so the factory slip assist system thing isn’t going to be loading up all the power to 1 wheel and smashing things.

I was worried that temperatures were going to come up during open road driving, but all is fine, even at motorway speeds. These Jimny's don't have a temperature gauge, which was a worry, but the Link computer has a bunch of safety precautions built in, incase the temp does come up. It'll reduce boost and the rev limit. 

Moving forward we still need to connect the intake to the snorkel, which is going to be a mission. We'll try and run an intake pipe across to the snorkel inlet and house the filter within an airbox. If that doesn't work, we'll need to build a custom snorkel and run it out the left side of the vehicle. That just means we'll need to remove the snorkel on the drivers side and fill in the holes that we've made installing it - bummer!