MoTeC Global Forum

I have a 750bhp/550ft/lb twin turbo 3.4 ltr Porsche aircooled engine running twin k27 hybrids.

Transitioning from low boost to full boost happens over a very small RPM range. The engine dyno showed 100ft/lbs gain over just 200 rpm (no typo)...

So I need to tame the boost transition: Am I best to just pull ignition around that RPM range, or look at defining a ignition comp "smile" (for those of you in finance...) i.e. a dynamic ignition/fuel comp?

Help much appreciated.

You could do ignition retard based on say RPM and boost pressure, but that is not very good for engine heating, economy, etc.

You are best to limit the amount of boost delivered. Are you using the M800 boost control?? You might find the minimum boost pressure you can have is still too much, in that case it would be better to change the wastegate actuators so you can run low enough boost, rather than other methods of cutting power.
The boost control function contains many compensations, so you could do things like boost pressure controlled by the amount of time at full throttle and which gear you're in, for example.

Another option would be to replace the cable throttle with DBW, then the throttle opening can be controlled to limit power.

Thanks. TBH, I think part of the problem is with current springs we can't go below 0.8bar; so as you say i may have to swap springs.

I was wondering whether running rich before and through max boost might help. It only needs to tame about 500rpm and thought a table linked to accel enrichment and boost might take the sting out of the tail...

Yes I am using MoTeC boost control