[ever_green]

Originally Posted by Madact

Well, I've been thinking about layout and I have one setup in mind where it would be feasible change the secondary lengths by about 6" without too much trouble, just using clamps...

Thanks for the links, should make some good 'light' reading tonight



That's exactly what I'd expect from the reading I've done, if the EL header was reasonably well tuned for high RPM - the reflected pulses would arrive at precisely the wrong time at lower RPMS, pushing gas back into the cylinder instead of sucking it out, which would explain both lack of torque and extra knock (as per the autozine article on the Mazda SkyActiv manifold linked earlier):



Conversely if there's a bit of valve overlap and new header is scavenging less at high RPM, the ECU could be expecting a slightly larger larger air charge, and adding the right amount of fuel for the expected intake mass... though I'd expect closed loop control to correct that? It would depend on how closed 'closed loop' is, there may be saturation values in there which keep either internal or control parameters within predefined ranges - this is a common control systems 'hack' to stop a closed loop system from going unstable if some physical parameters change in an unexpected way ... depends on whether the person programming the ECS paid attention when they covered finding poles of a z-transform, and how much they expect the - and how much they trust the physical parameters of the system to not change. Of course, I'm no expert in ECS specifically, so I don't know whether that applies in this case.

When people talk about installing headers for performance, it's often mentioned that ECU tuning is required to get the best out of it... but I'm not sure if that's because they take it out of the closed loop parameter envelope, or

Yeah I consistently self tune my ECU . the header did not give me much trouble with exception of slightly richer AFR under load or high rpm. Most of this was fixed with MAF and o2 sensor rescaling. However under closed loop it is still too rich off the target and for some reason the ECU does not seem to compensate for it. I'm just not sure why. When I target 14.5 its actually at 14.3-14.4.

UEL Headers let me improve BOTH performance and economy by running richer with more timing until MBT is achieved. This was done using dyno. Under 2800 rpm which is pretty reasonable for city driving the engine does not go any richer than 14.0:1 (under heavy load) and timing is about 10* higher wthan before hich is very significant. Stock it was 14.5:1 with 10* retard. You might argue that richer AFR demolishes BSFC. Yes it does but the slight sacrifice in BSFC is made up for by shorter acceleration times and more power from extra timing. The acceleration with UEL headers is very linear and controllable. The drivebywire has been tuned to keep the throttle nearly wide open at low rpms and we have the TCU short shift. This way an inexperienced driver can accelerate nearly at best efficiency while keeping up with traffic yet never exceeding 2000 rpm. This I found was not possible with EL headers. The engine would shudder and sometimes detonate and it just was too slow. It just felt like lugging and now it feels smooth and 'torquey'. My peak torque also moved lower slightly from 4600 rpm to 4100 rpm and peak power was raised to 5800 from 5600. There is a secondary peak torque from this resonance yoy were mentioning at 2200 rpm but its not substantial like the one with EL headers (that was at 2800 rpm). Its a very flat curve now from 1800-5200 rpm vs 2800-5200 rpm as before with lots of dips and peaks. I'm surprised how much difference in the curve was made just by changing exhaust manifolds.

You know hotter headers flow better and shorter uel manifolds have a tendency to run hot.