Another person was looking into this. Some sort of insert to help with back pressure. To my knowledge, Titan has never done any dyno testing on any of the engines they fly.I ran into a exhaust restrictor on a 70's Rolls Royce one time. It was located between the manifold and pipe, and the center hole (from memory) wasn't any bigger around than my thumb. The back pressure it must have had something to do with it's ability to scavenge.https://en.wikipedia.org/wiki/Scavenging_(automotive) I don't know how they got it right on the merlin, but it seems Titan could have started out with long stacks, and incrementally shortened them to find the right mix on the dino.
Yes, I think so. While we did lose some power with the short stack Mustang exhaust, it is better than we first thought.That will be fun.
Someone suggested lengthening the tubes a bit. I was reading also that you don't want the diameter of each tube to be too large, as it will actually slow the velocity down.20hp drop at 4500rpm? Not a huge deal. If you have the budget, you could play with headers as you may be able to find more power with a different header bore.
Best option: Make up a straight set of the required length, maybe start a bit bigger than the titan pipes. Do dyno pulls while progressively sleeving them down internally by inserting bits of pipe. Once you know best diameter, make some proper headers.
Cheaper: try sleeving the straight bits of the titan headers. Restrictive washers won't work half as well as sleeves.
edit: Looking at the curves, the titan headers may be a wee bit small. Sleeving what you can get at 1/8" would confirm that with a bigger power loss. Power above 4500 won't matter in your plane, but gives tuners an inkling into what is happening.
The only real loss is above 4000 rpm. We can live with that as most of the flying will be done below that figure. The dyno shop told us to expect up to a 50 hp loss.The short stack loss was predictable as the sunrise. Exhaust scavenging on a NA engine is very important, and these pipes are killing it. The camshaft change probably made it even worse. The Merlin gets away with it for one very simple reason - it is supercharged, so the intake charge is going to get into the chamber unless you weld the stacks closed.
While I remember those articles vaguely, were they single pipe per cyl or in pairs or 4 to 1 collector. I do remember doing some exh testing on a 2L Pinto powered Hydroplane with both 4/1 headers and 4 individual stacks (both with anti reversion steps @ port face). Engine ran nicer on the 4/1 setup but was actually fastest @ top end on individuals, albeit being a pig @ low RPM and slow off the mark.Kent Paser experimented with exhaust nozzles on a 320 CI Lycoming. With a 1 1/4” nozzle on a 1 3/4” exhaust, he gained about 5 MPH at 7,000 feet. He lost HP below 6,000 feet.
I believe that's called a fish tail exhaust. I can't tell you its technical merits just know that's what it's called.