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I get to tune some cars that had a turbo conversion from NA, the engine is stock and it is known that the stock internals can hold around 33kgm.
While tuning on a dyno I get to a point that this max known torque is achieved at retard spark compered to MBT or as close as I can get to it.
Does it make any sense ?
I get on the dyno, tuning spark, max required torque is achieved before I get to the best advance for that area in the map.
What would be the right course of action ?
- Leave it at that
- lowering boost and advancing till MBT or as close as possible
Is it bad for the engine/egt when the spark map is not fully optimized because of the engine internals limitations ?
I hope it is clear.
This webinar might be helpful explaining the effects of AFR and ignition timing on your EGT's:
Personally I would tune for as little boost as possible and try and reach power goals with ignition timing whilst avoiding knock limits etc.
Are you saying you are getting knock before you are reaching MBT? Would be a effect of the relatively high compression of the N/A motor I imagine. Does it have a upgraded Cam to suit an N/A
No, I'm saying that I reach the max desired torque for this stock engine before MBT or knock.
If you need to limit engine torque in order to ensure reliability, there's two ways you can do it - retard timing from MBT, or reduce boost. Each has pros and cons.
For instance if you retard the timing around peak torque, this will result in higher EGT and under sustained operation this may potentially damage components. Typically though you would only need to retard the timing around peak torque and then you can ramp the timing back in as the rpm climbs.
Reducing boost might be the obvious answer as it would then allow you to run MBT timing (or at least as close as you can get), however if you want to maintain a flat torque curve once you're past peak torque, you will need to ramp the boost up at higher rpm. This can be the more difficult option to achieve repeatedly and accurately.
A while back we tuned an EVO IX drag car that ran a stock block and the customer was going to try for a stock block 1/4 mile record. We ran 38 psi boost on E85 with a Garrett TO4Z and produced around 500 kW atw. In order to give the engine the best chance of surviving we used both techniques, ramping the boost up as rpm increased as well as retarding the timing around peak torque.