More power out of a JB74 Jimny

I have been called a lot of times in recent months about mapping a JB74 to get more power. I have no clue how to do it, however....

I have just seen this link from someone who has done it. They found that the ECU system is identical to a Suzuki GS1000 motorbike. They found 12hp more.

m.facebook.com/groups/1480549812004311?v...&id=3090453451013931

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I've never heard such a high gain claimed from a naturally aspirated engine with no modifications. Without seeing a dyno printout to back it up I am very sceptical of that claim! It's more likely to be a high reading dyno.

I have where the engine has been "de-tuned" for the application, specifically in my experience in boats.

I can see a scenario where the engine is running in a different tune so it meets emissions for that class of vehicle, puts in a torque curve and power peak in a different place etc. Aftermarket tuners do not have to worry about this so can find the original peaks and ignore emissions and ignore what might be best for the vehicle.

I've got a 1998 Z3 1.9 pre facelift- Fitted with the same M44 engine used in the BMW E30 318ti.

The Engines been meticulously maintained. It left the production line with 140BHP, I had it remapped in 2018 due to having a new Stainless exhaust fitted. It now produces 154bhp - a record of the dyno results were provided by Avon tuning in Thornbury (South Gloucestershire).

I must admit I was surprised to get that kind of gain out of a 20+ year old engine, but the technician Echo'd what martin has said. Most engines are tuned from the factory so that they fall within the nearest emissions band. (Usually de-tuned)

The car has been running sweet as a nut ever since, fuel economy seems to have remained the same if not slightly improved.

It cost around £300 for a full dyno re-map which took about 3-4 hours. Not bad value, but I can't say I'm itching to get the JIM re-mapped anytime soon, but I understand that people with added weight/larger wheels may feel obliged to do so. I'd highly recommend Avon Tuning to anyone in the south west!

All versions of the K15b engine produce the same power, so it's not been de-tuned for the Jimny. Normally to meet emissions the fuelling is set on the lean side, and a re-map to richen it up can gain a few %. That would be 3-4hp. Add a more free flowing exhaust and you might net another 5-6%, which explains the BMW gaining 10%.
But 12% with no supporting mods still strikes me as far fetched. I'd love to be proven wrong with before and after dyno printouts though.