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Ok, for those of you interested in the true purpose of this post, I can now share the results of my de-cat exhaust testing. At this point I should be clear I did not return to the dyno, the very limited testing was completed as safely as possible on the road, and data gathered using Monty's excellent EMU Black ECU. At this point I'll step back and let the legal eagle comentators debate taking Monty's Duratec to 7,258rpm on the King's highway.



Firstly it may help to explain Monty's sophisticated wide band lambda sensing provides a very accurate window into his combustion chambers, the oxygen in the exhaust being sampled as an average of all four cylinders by a fast responding Bosch LSU 4.9 lambda sensor placed at the entrance to the now empty void that once housed the cat core.

Prior to testing Monty had been carefully tuned to hit the 13.0:1 AFR target within Monty's lambda target table at full load above 3,000rpm, what we are looking for therefore are changes in short term trim that would indicate an enleanment condition, that in turn would point to increase in volumetric efficiency over the previous exhaust configuration. In simple terms, if the ECU is calling for more fuel to hit our 13.0:1 AFR target, the engine must be moving more air, and if we then match that additional air with more fuel in the correct proportion, we will make more power!

This is the principle that drives the EasyTune feature within the ECU software and while it is clever, it's certainly not magic. Changes to the VE table are simply suggested based on the target lambda table, a table of target AFRs that are of ones own making so it's really only as good as that. However, we do know best power in a naturally aspirated engine can be found around 13.0:1, and we do know Monty was hitting 13.0:1 at wide open throttle and full load with no correction on the catted exhaust, so any suggested corrections are a pretty good indicator of any extra power we may (or may not) have found from the de-cat?

Below on the left you can see Monty's unchanged VE table, a VE table is just a way of ilistrating the fuel we are applying at a given point in engine speed and load, in this case it is represented as Volumetric Efficiency (VE). On the right we can see another VE table, this is what the ECU is suggesting in order that the target AFR is hit, the difference between the two is therefore the percentage of enleanment or enrichment reqired to hit the target.



I've highlighted the full load cells at the problematic area where power was previosly failing to climb, what the table is telling us is that in these cells Monty is now calling for 4% more fuel. To be honest, I was expecting more, what the EasyTune table is telling us is the engine is moving 4% more air so it now needs 4% more fuel in order that the target AFR of 13.0:1 is met.

It's not an exact science, but 4% more air matched with 4% more fuel should deliver at least 4% more power, in my experience and when tested on the dyno the gains are typicallly more than the indicated percentage. However, I would be pretty confident in saying Monty's previous 182hp is now somewhere in the low to mid 190s, more acurately and if I was a betting man, I'd say what we're seeing here is an engine now making 193hp.

So it's still a long way off what we were expecting, and I now think the only way we'll find the missing horsepower is to fit a set of vernier cam sprockets and return to the dyno for a proper cam timing session.

Thanks for listening chaps

Dave.