How to fight exhaust reversion when the primaries are way too short

[Truckedup]

A couple of ideas if room is very tight,,,

Very short stub pipes from each cylinder that protrude into a tapering log manifold

With highly tuned 2 valve motorcycle engines ,reversion is generally a problem and will cause actual rich misfire at midrange RPM...The short stub pipe that protrudes into the primary pipe woks pretty well...

[ptuomov]

A couple of ideas if room is very tight,,,

Very short stub pipes from each cylinder that protrude into a tapering log manifold

With highly tuned 2 valve motorcycle engines ,reversion is generally a problem and will cause actual rich misfire at midrange RPM...The short stub pipe that protrudes into the primary pipe woks pretty well...

I played with two-stroke engines when younger. (Was wrong about most things back then, and the things that I was right about I don't remember any more.) Doesn't that hurt the torque at the tuned rpms?

In this case of four-stroke cross-plane log exhaust manifold, would you put such protruding pipe in the offending cylinder #3 or the victim cylinder #1 or both?

The problem with this manifold as far as I can tell is that the pressure pulse moves so much faster than the flow starts going. It's very difficult to control the pressure pulse with flow because the flow just gradually gets going when the pressure pulse has already done its thing. If there's no stopping of that pressure pulse from #3, the second best thing is to get it done and over with as early in the exhaust stroke of #1 as possible. Now how to do that?

[Truckedup]

A couple of ideas if room is very tight,,,

Very short stub pipes from each cylinder that protrude into a tapering log manifold

With highly tuned 2 valve motorcycle engines ,reversion is generally a problem and will cause actual rich misfire at midrange RPM...The short stub pipe that protrudes into the primary pipe woks pretty well...

I played with two-stroke engines when younger. (Was wrong about most things back then, and the things that I was right about I don't remember any more.) Doesn't that hurt the torque at the tuned rpms?

I really don't know because I don't use it on my race bikes...My bike holds the class speed record (land speed racing), the competition uses all sorts of tuned exhaust and intakes. My bike has the carbs close to the head as possible and two 34 inch straight exhaust pipes...So I have to figure all the tuned lengths don't matter on a 360 degree twin cylinder engine where maximum speed is important

[ptuomov]

Sorry I misread two valve as two stroke...

[Calypso]

Just brainstorming atypical ideas... Quarter wavelength resonator for the #3 at the frequency it begins to impact #1. Might be in the ballpark of manifold length at high rpm.

[ptuomov]

Just brainstorming atypical ideas... Quarter wavelength resonator for the #3 at the frequency it begins to impact #1. Might be in the ballpark of manifold length at high rpm.

A resonator tube is going to reflect a positive pressure wave back to #1 and #3. How do you reflect a negative wave to #1 in that manifold? (I've got a turbine corking the manifold outlet.)

[modok]

Run the turbo on 3cyls?
Pipe the odd one past the turbo, or to the other side?
Strategic wastegate placement?

[ptuomov]

Run the turbo on 3cyls? Pipe the odd one past the turbo, or to the other side? Strategic wastegate placement?

Brabus had at least a prototype of a turbo exhaust manifold that bypassed one cylinder to remove 90-degree exhaust blowdown interference.

brabus_biturbo_v8_exhaustthumb717x537998-1.jpg

There's no room for me to get a pipe past the turbos. Even the wastegate pipe must be integrated to the turbine housing to fit. So that's a "no go" for a number of reasons.

[cjperformance]

Just pop a flat plane crank in it!

[modok]

Do the heads have a crossover to heat the intake?

[ptuomov]

Do the heads have a crossover to heat the intake?

No. Fuel injected, four valve heads, nothing like that.

[user-23911]

Run the turbo on 3cyls? Pipe the odd one past the turbo, or to the other side? Strategic wastegate placement?

Brabus had at least a prototype of a turbo exhaust manifold that bypassed one cylinder to remove 90-degree exhaust blowdown interference.

brabus_biturbo_v8_exhaustthumb717x537998-1.jpg

There's no room for me to get a pipe past the turbos. Even the wastegate pipe must be integrated to the turbine housing to fit. So that's a "no go" for a number of reasons.

Well that's never going to get past the prototype stage.....dumbest idea ever with different VE for one cylinder of the bank..

[ptuomov]

Run the turbo on 3cyls? Pipe the odd one past the turbo, or to the other side? Strategic wastegate placement?

Brabus had at least a prototype of a turbo exhaust manifold that bypassed one cylinder to remove 90-degree exhaust blowdown interference.

brabus_biturbo_v8_exhaustthumb717x537998-1.jpg

There's no room for me to get a pipe past the turbos. Even the wastegate pipe must be integrated to the turbine housing to fit. So that's a "no go" for a number of reasons.

Well that's never going to get past the prototype stage.....dumbest idea ever with different VE for one cylinder of the bank..

It may not get past it, but I'd say that almost all if not all cross-plane V8's that come from the factory assembly line have significant variation between the VE of different cylinders. Unless you have long-tube headers from factory (basically only BMW of the big guys does something like that), that's just what you're going to have.

[Calypso]

Just brainstorming atypical ideas... Quarter wavelength resonator for the #3 at the frequency it begins to impact #1. Might be in the ballpark of manifold length at high rpm.

A resonator tube is going to reflect a positive pressure wave back to #1 and #3. How do you reflect a negative wave to #1 in that manifold? (I've got a turbine corking the manifold outlet.)

Maybe I’m way off, but wouldn’t 1/4 wavelength resonator connected to #3 be phase shifted to cancel out the wave action at the designed frequency. Of course, if the pressure in the manifold is higher than in #1, flow will still follow, but less in tune with that rpm. Thinking a dead end channel in the manifold.

[ptuomov]

Just brainstorming atypical ideas... Quarter wavelength resonator for the #3 at the frequency it begins to impact #1. Might be in the ballpark of manifold length at high rpm.

A resonator tube is going to reflect a positive pressure wave back to #1 and #3. How do you reflect a negative wave to #1 in that manifold? (I've got a turbine corking the manifold outlet.)

Maybe I’m way off, but wouldn’t 1/4 wavelength resonator connected to #3 be phase shifted to cancel out the wave action at the designed frequency. Of course, if the pressure in the manifold is higher than in #1, flow will still follow, but less in tune with that rpm. Thinking a dead end channel in the manifold.

It's my impression that in a logish manifold like this, each exhaust blowdown event is so violent that it effectively resets the whole system. Blowdown events happen as frequently as 400 times per second at 6000 rpm, since 90 degrees of crankshaft movement takes 1/(4*6000/60) = 0.0025 seconds. The speed of sound is of the order of 2000 ft/s in that temperature, so you have time to move about 5 feet (more in the direction of flow, much less against the flow) before the new "reset" pulse comes in 0.0025 seconds. I don't see how I could get a quarter-wave resonator to do anything beneficial in that sort of setting, can you sketch out your idea in more detail? Or have I misunderstood how it works?