Currencies spend 70% of their time ranging. Engine 3a exploits this with Connors RSI and Bollinger Bands on 4-hour charts — buying extremes and selling the return to normal.
Think of a rubber band. The further you stretch it, the harder it snaps back. Currency pairs behave similarly — when price moves far from its average, there’s a statistical tendency for it to return.
This isn’t guaranteed (the rubber band can break), but it happens often enough to build a strategy around. Unlike stocks or crypto, currencies don’t go to zero or to the moon. They’re anchored by central bank policy, trade flows, and interest rate differentials.
We tested trend-following (Donchian) on forex — it produced a 37.5% win rate. Mean reversion is a fundamentally better fit for how currencies actually behave.
Standard RSI measures momentum on a single dimension. Connors RSI is a composite indicator that combines three independent measures of mean-reversion potential:
A very fast RSI that measures how oversold or overbought the pair is right now. RSI(3) responds to just the last three bars, making it sensitive to short-term extremes that longer-period RSI would miss.
How many consecutive up or down bars have we seen? Long streaks of same-direction closes are statistically unlikely to continue. A 5-bar down streak is more likely to reverse than a 2-bar streak.
Where does today’s price change sit relative to recent history? If the current move is in the bottom 5% of the last 100 bars, that’s an extreme — and extremes tend to revert.
When all three components agree that a pair is at an extreme, and Bollinger Bands confirm the price is outside the bands, we take the trade. The exit comes when the pair returns toward its moving average.
Entry (Long): Connors RSI drops below the oversold threshold (20) while price touches or breaks below the lower Bollinger Band. This means the pair is extended on multiple independent measures simultaneously.
Entry (Short): Connors RSI rises above the overbought threshold (90) while price touches or breaks above the upper Bollinger Band.
Exit: When Connors RSI crosses back through the exit threshold (neutral zone), indicating the extreme condition has resolved and price has reverted toward its average.
Every trade has a defined stop-loss at 3× ATR. This gives the trade enough room to breathe through normal noise while protecting against the cases where the rubber band does break.
The champion configuration (os20/ob90/exit3/bbT/sl3.0) was selected through parameter sweep optimisation with a Calmar ratio of 5.87 — meaning the annualised return is nearly 6× the maximum drawdown.
Forex is uniquely suited to mean reversion for several reasons:
Range-bound behaviour: Major currency pairs spend the majority of their time
oscillating within ranges defined by macroeconomic fundamentals.
Deep liquidity: The forex market trades $7.5 trillion daily. Spreads are tight
and slippage is minimal even at scale.
24-hour market: Continuous trading means no overnight gaps that could blow through stops.
Natural anchoring: Central bank policy, inflation targets, and trade balances
create gravitational centres that prices orbit around.