Discussion and questions related to the course Road Tuning
Is it possible to get a decent flex tune on the road?!
My concern is that when running high ethanol contents I may not be knock limited, How would i know if I tuned passed MBT?! (Assuming I am not monitoring EGT).
I would guess fuel overlay tables etc would be straight forward, But not sure how the IGN tune would work out.... Ideas?!
You're concerns are valid. Tuning on a quality fuel such as E85 or a race fuel can mean your engine is not knock limited. Your only option is to apply a somewhat conservative approach to your ignition tuning. Of course if you're not knock limited then having the ignition timing over advanced is not going to damage the engine but it will result in less torque. Generally if we look at how torque is affected by ignition timing we see that the torque is relatively flat over quite a wide range of timing so there is a fairly wide 'target' that you can be in and still produce close to maximum power.
I base my ignition timing in these instances on how heavily knock limited I was on pump gas, and experience with similar engines on a dyno. What I mean by this is that if the engine is very heavily knock limited then you're going to probably end up adding quite a lot of timing to reach MBT on E85. If on the other hand the engine isn't actually that knock sensitive on pump gas then the timing map on E85 won't be vastly different.
It was probably a bit naughty, but I actually got my head around flex fuel tuning using a mates S14 Silvia and road tuning - dyno hire was going to be difficult and expensive to acquire as is and at the time I did this there was basically no one I knew of anywhere, let alone in my country who had done "proper" flex fuel tuning so I knew I was going to have to anticipate and resolve any issues I encountered with the platform I used.
I used Brad Barnhill's Virtual Dyno software to determine MBT at moderate boost levels on different ethanol contents and built the maps from there to a pretty conservative level and just confirmed them with the knock block at petrol blends I anticipated knock to be a potential risk - given basically we didn't really want to do too much road tuning and were going to hit a dyno eventually.
When we finally got it to the ACTUAL dyno to dial the tune in "for good" it turned out that most of the maps were pretty much where I had intended them to be and the session turned out to be more of a confirmation session than an actual tune session - so Virtual Dyno etc had actually worked pretty well for the purpose I used it for.