CamKing wrote: ↑Tue Oct 15, 2019 10:08 am
Increasing the exhaust duration can reduce temp in the cylinder, but will also reduce pressure, and power at lower RPM's.
For a towing application, where power below peak is more important then power past peak, increasing the exhaust duration is the wrong way to go.
If the engine has to pass a smog test, where they check the NOX levels, then the longer exhaust is a good idea, because it will reduce the cylinder temps, and reduce the NOX.
Mike
Would this also apply to wet exhaust marine engine from 1500-5000rpm powerbands direct drive?
I have seen many "towing specific" camshafts which appear to be single pattern with the same durations at .050" however, upon measuring them they are indeed dual-pattern camshafts with a more aggressive lobe on the exhaust side having lesser seat timing.
I always thought that it was because the exhaust valve was lighter but, maybe there are other reasons involved like keeping the exhaust valve closed longer so the pressure above the piston can do more work.
travis wrote: ↑Tue Oct 15, 2019 1:59 pm
but their stuff listed for moderate to heavy towing tends to be wider lsa with more and more exhaust duration/widening lsa as the towing weight gets heavier..
This would make sense for very heavy towing, where the trans downshifts, and the RPM's are pushing the redline. In that case, the engine is producing a ton of heat, and the longer exhaust duration will reduce the heat in the engine.
