S54 Header Design talk

[3staxontheradio]

That's super interesting. In that sim at least, its not a huge difference between taper and step but the general appearance seems to show the tapered runner having a stronger wave signal but less spread out than the steps. Is that how you read it too? Your runner is shorter than the pipemax calced one so not surprised its looking a little more top end heavy? Could you try with a 480mm runner and also can you show the torque across RPM for a full idle to maybe 8500rpm sweep?

Also can you help me understand that valve pressure chart? Is it at a specific RPM? Seeing whats happening before EVO is cool

On the power trace the 38mm straight runner just outperforms the taper. The stepped runner is at least holding more power on the far left but its only one point on the sim and maybe not enough to show a trend.

[digger]

That's super interesting. In that sim at least, its not a huge difference between taper and step but the general appearance seems to show the tapered runner having a stronger wave signal but less spread out than the steps. Is that how you read it too? Your runner is shorter than the pipemax calced one so not surprised its looking a little more top end heavy? Could you try with a 480mm runner and also can you show the torque across RPM for a full idle to maybe 8500rpm sweep?

Also can you help me understand that valve pressure chart? Is it at a specific RPM? Seeing whats happening before EVO is cool

On the power trace the 38mm straight runner just outperforms the taper. The stepped runner is at least holding more power on the far left but its only one point on the sim and maybe not enough to show a trend.

i just used 450 mm as a round number so each step was 150mm, i can change the length. you can see that the changing the pipe size also needs a length change to ensure the scavenge wave arrives at the same "time"

Its probably not much value to do full rpm sweep with open primaries (no collector and not realistic) and haven't set up variable cam timing. i was just using the model to see the impact on the wave at an rpm when the pipe is in tune

Also it appears 35 mm is likely too small overall for this hp level, 38 mm ID is probably better as a minimum so i might add 44 mm (ID) and see if a step 38-41-44 is "better" than a single pipe size once the size is more appropriate

The taper does produce a slightly better suction wave with less pumping loss. I don't understand why the step header having the higher peak pressure, maybe it is something to do with a difference in residual pressures at EVO

It is also worth noting that there is approx less than a 1% change in VE, so the power differences for the most part are pumping loss differences between BDC and TDC as they are all scavenging well enough during overlap (0.5-0.6 bar "suction" or about 200" H20 ). Adding a collector and other piping is likely to degrade the scavenging at this rpm

The model is also rough if you can tell me the following to double check i could improve it

Inlet port
- min CSA and distance of the min CSA from valve (if not the throat)
- port entry area / diameter equivalent

Exhaust port
- min CSA and distance of the min CSA from valve (if not the throat)
- port exit area / diameter equivalent

Inlet manifold
- area/diameter at the head
- overall length of the cast throttle body section
- overall length from head flange edge of trumpet
- trumpet inlet ID

[3staxontheradio]

Cool. I can get all of those measurements to you soon