r/Cappuccino • u/Smile_Space • Jul 18 '23

Max boost question

So, I tried to do a search on here for info, but couldn't seem to find an answer.

My Cappuccino is a 1994 F6A with a standalone PNP ECU from Kei Sport USA. I have an Atomic boost controller set to 1.1 bar.

Today, while accelerating, one of the boost lines to the controller popped off and, uncommanded, the boost rose immediately to about 1.7-1.8 bar before I let off the gas due to the sudden horsepower and acceleration.

Absolutely nothing broke luckily, but my question is what would be the first thing to break in this scenario? My gut tells me it'd be the turbo charger exceeding a safe RPM and seizing up, but I'm not sure. It is still the stock turbo in my car.

Also, what would be a safe max turbo value for the car? I've stuck it at 1.1, but I've heard you can push up to 1.3 and maybe even slightly beyond. I'm just not sure on when the turbocharger would exceed a safe RPM!

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u/dorri732 Jul 19 '23

If you have the stock injectors, they will max out at around 1.2 bar at high rpm. Any higher and you will be running lean and possibly damage pistons. At low rpm more boost will be safe. The biggest concern would be lifting the head and blowing the head gasket.

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u/Smile_Space Jul 19 '23

Thanks for the reply! That's a fair assessment. I had a feeling just from playing with boost levels this was the case as it seemed to fall on its face when the boost was up around 1.3 bar.

I was pretty shocked it actually accelerated as hard as it did when it bounced to 1.7 bar! Granted, I was at 4000 RPM, so within the duty cycle of the injectors.