Team Go Dog, Go! Modified Partial Streamliners

[wobblywalrus]

The pressure waves travel down to the final expansion point and they are bounced back toward the intake valve at opposite polarity.  This is what i call the "end effect" 'cause it usually happens at the end of the system.  Pressure waves travel at the speed of sound and this is related to the temperature of the gas.

Gas temperature drops as it goes through the system with it being hottest near the exhaust valve and coldest near the end.  The relationship between the magnitude of this drop and the length of the system is the temperature gradient.  A short system with a big temperature drop has a high gradient.  Gasses that go from a hot to a cold environment sort of "stack up" on each other as they he decelerate.  The less dense hot gasses collide with the slow moving cold gasses and this creates turbulence.  There are swirling pockets of hot gasses next to cold gasses.  This f's up the wave action because waves travel at different speeds gasses of varying temperatures.  This is why it is a good idea to insulate the exhaust system.  The headers are wrapped sand sixteen gage stainless is used on this system to give some degree of insulation.  I have that "base covered" as they say.

An open ended megga on a large diameter system is the devil's playground in terms of temperature control.  The O2 sensor pipe was stuck more than a foot into the system and it indicated lots of fresh air intrusion with turbulence between pockets of it and hot exhaust gas.  This creates a temperature differential across the cross-section of the collector with it being especially bad in the megga.  This completely destroys useful end effect wave action.  Note how the turbulence creates the warbling effect on the torque and power curves.

The blooey pipe has a lot less taper.  The O2 sensor indicates fresh air intrusion, but less of it.  It has less of a problem with temp diff than the megga.

The header, alone has the least problems.  It has less fresh air intrusion, but some cold air does get in.

This is a big muffler.  The end effect happens before the end of the muff and it is in an area of hot gas with minimal temperature differential across the opening where expansion occurs.  It bounces a pressure wave back with a strong signal.  This end effect wave can be used to make HP, unlike with the other systems.

[Interested Observer]

Wobbly, your reply #2850 seems to be just a construct to try to build a mental picture of the results of the recent dyno testing.  However, I think there are some holes in the analysis and your thinking about what was going on.  You might consider the following comments.

“The pressure waves travel down to the final expansion point and they are bounced back toward the intake valve at opposite polarity.”   The pressure waves travel to any and all expansion points, the first and probably the most important of which is at the collector.  This is why header length is critical to the tuning possible in the exhaust tract.  The reflected negative wave starts back there, and should be timed to achieve the best effect.  Generally, a megaphone immediately follows the collector which, by providing a gradual expansion of area tends to spread out the reflected wave in time, broadening the rev band over which the effect is felt.

“Gasses that go from a hot to a cold environment sort of "stack up" on each other as they he decelerate.”
Are we talking about gases or waves here? Presumably waves.  In which case, they can’t overtake one another since at any point the temperature is the same and the wave velocity would be the same.  They may slightly approach each other (in space), but how would the trailing wave overtake the leading one?

“The O2 sensor pipe was stuck more than a foot into the system and it indicated lots of fresh air intrusion with turbulence between pockets of it and hot exhaust gas.”
Postulating that atmospheric air has traveled upstream against a very robust exhaust stream strains my credulity.  What physical evidence is there that this is happening?  Was there a smoke generator at the exit that showed anything like this was going on?
It is far more likely that the O2 sensor is telling you that there is evidence of incomplete combustion, ie., residual oxygen in the exhaust, probably inlet charge lost during overlap.  All of which brings into question the appropriateness of the tuned lengths and configurations of the various tested arrangements. 
It is clear from the torque curves that the non-muffler configurations work at lower than desired revs and that they just are not right for other rev ranges.  That the muffler works better may just be a happy coincidence of longer length working in conjunction with the header/collector length and some increased back-pressure having a serendipitous effect on inlet charge capture.

[wobblywalrus]

You are probably right on this.  A day spent breathing carbon monoxide, partially burned toluene, and listening to all of that racket might have affected my brain.  I might not be completely wrong, either.  This is a very large diameter system for this displacement engine when comparing it designs using other common methods.       

[RansomT]

When are you going to hit the dyno again?

[wobblywalrus]

Sunday.  That muffler from Burns is their quieter model.  It is originally intended to be a convenience feature for the street based R and D.  I never figure on using it for racing.  It is screwed together so I take it apart to see what is inside.  It looks just like a monster size version of a US Forestry approved spark arrestor.  Primo!  I know exactly how to deal with one of them, as I wuz a dirt bike guy for most of my life. 

The muff is designed to be a wave dump.  In other words, it is designed to capture and neutralize waves.  This is my guess based on looking at the internals.  This is exactly what I have found to work best on Cosworth engines.

These motors have two intake and two exhaust valves in rows next to each other.   There is no high piston dome to separate them.  Any cam with significant overlap with funky exhaust has the potential to blow the intake charge right out the exhaust, or any of many bad alternatives, with no difficulty.   This makes tuning these motors a real pain in the donkey.  There are few exhaust dimension combinations that work and lots that perform awful.  The wave dump style mufflers seem to work well.  They dampen the intensity of the waves returning from the end of the pipe.  This seems to work best with these Cosworth engines.

This exhaust is tuned the way I have learned that works best.  The headers and collectors are designed using conventional methods.  Instead of a megga at the end of the collector, a subtle taper section is used to give gentle wave return.  It is located where the megga would start.  The collector end goes from 2.5 to 3 inches diameter in a few inches on this bike.  This limited expansion and gives a nice subtle back wave that does not pull or push the gasses too far between the valves.  The muff is beyond this and it is one that is a wave trap design.

The engine configuration in 2016 made 90 HP with #147.5 main jets.  This new configuration with the gentle taper and the dump muffler, at partial throttle, makes 101 HP with #147.5 mains.  This indicates the new setup does not under or over scavenge.

This summarizes what I have learned. It is to pay attention to wave effect intensity as well as timing.

[Interested Observer]

Wobbly,
It would be well worth your time to obtain and read, especially Chapter 6, the following book.

Design and Simulation of Four-Stroke Engines
Gordon Blair
publications@sae.org

In which he extensively examines the various parameters of a 2 liter 4 cylinder 4 valve (that is, 2x what you are working with) engine that has been very well developed and produced about 130 hp/liter.  Your inlet and exhaust seem to be in the neighborhood, but not all the info is in your build diary.  See attached pdf of the engine layout.  Dimensions are in millimeters.

[revolutionary]

Wobbly,
It would be well worth your time to obtain and read, especially Chapter 6, the following book.

Design and Simulation of Four-Stroke Engines
Gordon Blair
publications@sae.org

In which he extensively examines the various parameters of a 2 liter 4 cylinder 4 valve (that is, 2x what you are working with) engine that has been very well developed and produced about 130 hp/liter.  Your inlet and exhaust seem to be in the neighborhood, but not all the info is in your build diary.  See attached pdf of the engine layout.  Dimensions are in millimeters.

Great book with tons of usable information. Read up on the design of elliptical air inlets...

[wobblywalrus]

Fixing the throttle gives a few HP.  The final runs on Sunday were all 107 HP.  It was 87 HP the last time I was at B'ville when the bike went 146.  It might go faster this time.  Last time the rear sprocket was 38 teeth.  This motor winds out to much higher rpm.  A 40 tooth sprocket should work just fine.  40 / 38 = 1.05  There is another 5 % in tractive force in addition to the power increase.  This motor has street compression ratio, uses unleaded, has a muffler, and it idles and runs fine at low rpm.  A hot street motor is all it is.  Nothing special.

[RansomT]

If I read the AFR correctly, it looks like you need to move the needles up.  That should get rid of that ugly rich condition in the mid-range.  The jets are correct.  But of course, I could be wrong ... know a lot more about EFI than carbs.

[wobblywalrus]

This is a difficult deal.  Once I leaned out the needle to correct a midrange power drop and this burned a hole through the piston crown.  What I learned is that a heavily cammed engine can go "off song" at an rpm when the exhaust tuning is incompatible with the cam action and piston movement.  The mixture goes rich during this period.  I am not sure why.  When I compensate for this by leaning out the needle setting, the mixture when on the needle is too lean at "on song" rpm. 
I did raise the needle one notch for B'ville along with going two sizes smaller on the mains.  This dip in the middle of the powerband has given me problems since 2007.  What I learned is to keep the engine rpm above the dip.

This is not unexpected.  The wave action analysis showed me this would happen.  It was a tradeoff.  Big horses on top or less ponies and a smoother power curve. The triple step header and the mongo wide collector gave the most HP.  A two step header and reasonably sized collector gave me a smooth power curve but less on top.

The plan is to wind the little devil up till the tach needle passes completely through the red zone, bangs on the peg, then shift.  Messrs Carillo, Arias, and Kibblewhite will take care of the rest.

[RansomT]

and this is why I stick primarily to EFI...

and yes, the easiest work around is NOT to be in that RPM range.

[Koncretekid]

If I read the AFR correctly, it looks like you need to move the needles up.  That should get rid of that ugly rich condition in the mid-range.  The jets are correct.  But of course, I could be wrong ... know a lot more about EFI than carbs.

I thought about moving the needles up while experiencing the same richening at mid range during dyno pulls.  But what good would that do?  I am, and I suspect Bo is too, using a wide open throttle during the entire dyno pull.  That is the needles are pulled out of the main jets.  Dropping them down a notch would either not do anything, or if they interfered with the fuel flow, would lean up the entire pull, as I see it.

However, as we only need to pass thru that rpm range during 1st gear acceleration, we can slightly close the throttle when the motor starts to stumble, thereby leaning the mixture out until we achieve a higher rpm where the motor cleans up.  Then by keeping the motor to the higher rpm range, it need not drop down thru that rich zone again.

The exiting part is when in 1st gear, the motor cleans up suddenly and lights up the rear wheel.  Yes, it can happen with only 50 hp on tap.  Keep it on the boil once thru the offending rpm range.

Tom

[wobblywalrus]

Not much has been posted from me on this website lately.  This has been a minor thrash since Aug 2016, a moderate one for the last three months, and a major fiasco for the last three weeks.  It is best to not post a lot when one is tired and burnt out.  All of that is behind now.  We are on our way and should be there on Monday.  Things are looking good and I am a very happy little grasshopper.

The bike will be running without the big tail.  The FIM changed the rules this year and the back part behind the seat is too tall.  The AMA won't allow it to be used on a bike with a production frame.  So, it stays home.  This is not all bad.  I doubt if flow is attached behind the rider and it occupies an area of turbulence.  This is a situation that makes it useless.  It does move the CG back and this is never good.

The power curve refinement will be done this Fall when I have a decent computer model.   

[wobblywalrus]

This is Rose's first visit to the salt.  We stayed the first night at the Malheur Field Station.  Gretchen took her 250 off the trailer and rode ahead of us between Frenchglen and Fields along the base of Catlow Rim.  Then we went through Winnemucca and east to our usual camp at Angel Creek in the Humboldts.  The forest fire smoke is bad in eastern Oregon and western Nevada.  This morning we ate at Bella's in Wells and checked into the KOA at Wendover.  The paperwork is done and the bike has gone through tech.  We are in the third row across from Koncrete Kid.  Maj and Bones are further down in the pits.

It is a small meet with around 150 entrants, I hear.  One track is running.  A fellow who rode a rigid frame S and S Harley type of bike talked to me in the KOA.  He said the track is so rough that his bike broke up.  It seems the frame flexed to the degree that the secondary and primary chains put too much tension on the drivetrain and this broke the trans apart.  Not good.  I get similar stories from other folks and that is this is a very rough track.

This evening I went swimming to loosen up my back and shoulders.  The plan is to grip the bike with my knees, put most of my weight on the pegs and not on my ass, and ride with loose shoulders and arms, like in a desert race.  The bike will figure out its way down the track.  Tomorrow will be a challenging day.

[RansomT]

Best wishes ... be safe!