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Low RPM high load.

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what is the best way to tune a engine with a supercharger or small turbo.

for example, last i driving a 1.6 supercharged mini fully forged engine and bigger supercharger.

and was taking a look at the logs. it has some knock at low rpm high load. (2000-3000 RPM and +/- 200 Kpa)

i would say take ignition out. but i'm worried i have to take out a lot of ign adv. to perhaps 8 degrees.

is it a option to limit the E throttle. so the electric throttle body isnt fully opend and the boost is kept at 160 kpa. with sensible ign adv.

(see picture)

Correct me if i'm wrong, just wondering what could be the options and if i'm right.

Cheers

Attached Files

Can you not reduce your boost down to 160kpa with your boost control system? Do you have a wastegate on your intercooler pipe to control boost with the supercharger?

IMO with a turbocharger you don't want to reduce boost by that level closing the throttle, its not the most efficient way especially when it comes to maintaining turbo speed for response.

Throttle based boost control features as such do exist in some ECU's, however its used to correct very small errors such as 10 mbar etc, so the throttle movement is minimal, thus not effecting turbo speed/response.

There is no blowoff on the system only a bypass valve. All is mechanical, no electronics in the boost system. So i’m Limited to ignition which seems the way to go, or the method abovè. But I’ve never heard or seen that method.

cheers for the quick response

I can't see why not, if you don't want the extra pressure / don't need it / causes knock, seems reasonable to not open the throttle all the way.

The ultimate solution would probably be a better fuel that isn't so knock prone but there's no reason you can't limit the throttle opening to achieve less boost. You may however find that just retarding the timing in that area is also going to be fine. You're not going to be sitting at 200 kpa/2-3000 rpm in steady state and the engine will pull through that rpm range very quickly meaning the timing is only going to be retarded very briefly.

I've mapped supercharged FA20's which required very low ignition angles (~5*) to stop det at low engine speeds (below 2500rpm). You should be conscious though that the window for det/knock is longer at slower engine speeds so I would recommend in the first instance as above to retard the spark enough to stop the det, monitor exhaust temperatures to ensure safe, and if not safe then look at additional control measures, again such as throttle angle or bleeding the supercharger off.