Big holes mean big power right?

[BC]

Work is a little slow today so....

Banshee intake port configuration has always been an intriguing facet of engine building to me- not so much in the technical aspect but more in the aspect of what the customer's impressions influence engine builders.  My stance on Banshee intakes is a reshaped intake- not made much larger versus stock.  Floors are dropped and corners squared up some.  The piston skirt spends nearly 300 of the 360 degrees of revolution in the intake port- and when the skirt does clear the port- the negative pressure in the case is fairly low.  Certainly there is some aspect the inertia of the incoming intake flow to continue pulling some fuel-air charge in, even as the piston approaches TDC. 

Reed configuration does influence me to some extent.  A single pyramid cage like the stockers Im not nearly as concerned about the roof height as the majority of the flow is towards the center, but there is still some component of when the reed is fully open there can be a pattern of flow in the upper area- albeit small.  Whereas with V-force reeds, the double pyramid configuration- I do get concerned about the flow pattern, as the upper half of the cage does aim directly at the step in the intake port roof.  I reshape that step to become a ramp to influence the intake charge by providing a smooth transitioned surface and to aim the charge downwards.  The intake charge has to go to the base of the cylinder in order to be swept into the transfer tunnels and ultimately wind up in the bore.  Some of my thinking is to provide a clear(er) path for that charge to get connected with the transfers.   

I've always looked at and try to provide some assessment of other engine builders work.  Trying to discern why did they do this or do that- is this something I would incorporate into my own work or do I know from my own testing it is not something of benefit.  Ebay has always been a good source of pictures of cylinder port work.  So here are a few recent pictures that are of interest to me.

In this photo- the bike has been ran some time and in such a flow pattern has "washed" the reed box walls showing where the flow is at.  Patterns such as this can be found on the piston crown, case wall, transfer tunnels- pretty much anywhere there is some flow within the engine, given some time a pattern will develop.  These patterns have had some great influence to my decisions in choice of porting alteration.


In this photo- these intakes are pretty typical of the work I do.  The step is removed and a ramp is formed.  The center divider is not narrowed as there is a tremendous amount of thrust from the piston skirt on that section of the intake.  The floors are dropped and feature lower corners squared up.  This intake configuration would be capable of making 90 some HP on a stock stroke alky build.  If you add up the intake area as compared to the diameter of the carb and/or the available area of the reed cage at reed full lift- you'll find the stock intake port area is greater than 35mm carbs are.


In this photo- its the infamous huge intake port with the tiny stick of an intake bridge.  This is the instance I mention in the beginning- how engine builders may be influenced by customers.  Customers want to feel they got their money's worth in what porting they got.  The funny thing is- that cutting intakes takes about 20 minutes typically.  So of the 5 or 6 hours it takes me to do a typical duner spec set of cylinders from start to completion- the time spent on intakes is only a fraction of that.  I call it the WOW factor- customers go "WOW you ported the shit out of those things."  Engine builders like to hear that- they feel they have provided what the customer wants.  Little do they know that it makes for tweaky tuning as the signal to the carb is weak.  Ever wonder why some guys run 55 pilots in their scooters- this is why.  The huge intake has such a weak signal to the carb you have to run such a massive jet to get enough fuel to dribble out of it.  This intake configuration violates some pretty solid foundations of flow- that a diverging angle will decrease pressure.  Granted pressure and volume are inverse to one another, the factor of time is critical to me.  At 9000 RPM that is 150 revolutions per SECOND- not much time for your bulk flow to move the nearly 6 inches from the cage to the transfer port window and into the bore.  I opt for the pressure(velocity and inertia) to move the flow thru that distance.


Of note in that photo is also the addition of Boyesen port or as some call them "boost" ports.  They work well in engines that are designed for them.  Of chief design factor is the distance of the reed cage to the piston skirt.  In Banshee engines the reed cage is rather close to the piston skirt- this helps with peak power- it shortens that distance the flow has to travel under that time constraint I mentioned above.  In slower rev'ing motors like 250Rs, the cage is set further back as there is more to flow and a main design decision was to focus on mid range type power.  If you add these ports to Banshee cylinders- again a great WOW factor- it can create all sorts of tuning nightmares.  As the reed cage is close(r) to the Boyesen ports there is a certain amount of reversed flow (spit back).  This reversed flow is aimed right at the reed cage.  This can cause the reversion to extend into the carb and "double dip".  The reverted flow is more like a jet stream of flow, not a bulk flow that would cause the reeds to shut, instead it can sneak in past the reed tips.  Wherein the reversion flows back into the carb, picking up additional fuel and then as the reversion ends that overly rich "double dipped" mixture creates a wicked rich condition that cannot be tuned out.  There was a certain builder that featured a 9 billion port port job on the forums recently- some of the customers had a nightmarish time tuning their low to mid range RPM.  In my opinion this was due to the addition of the 9 billion other ports to the cylinder.  Why did some have a problem and others did not.  It had to do with the intake they chose to use.  I noticed some builds featured stock and stock like intakes without reed spacers.  On some builds there were stock intakes and thick reed spacers.  Other builds had the BOSS intake which is a massively thick intake nearly an inch thick.  Those with the reed spacers or thick BOSS intake did not have problems as the carbs were spaced far enough away from the flow reversion to cause difficulty in tuning adequately. 

[Pete]

I think I have pics of my cylinders on my computer at home, but they look a lot like that 2nd picture anyways.  I was curious about those '12 port' portjobs that certain builder does.


dude, don't forget about these awesome portjobs!!!

[Ben]

Holy Shit. The 2nd and third pictures, awful looking. If i got a set of cylinders back that looked liked that, i would be none to happy. Looks like there is 0 consideration for smooth flow, all just focused on BIG HOLES!.
That toothpick of an intake bridge is quite scary too. What motors have exhaust bridges? i always see the note in the wiseco pistons box that tells you to drill holes in the exhaust bridges, i have never seen one though

Those Boyesen ports. Do they go into the bore or down in to the case?

That washing is very interesting too. I was reading on that site you have on your webpage, powersports tuning or whatever you call it, and read a whole thing about the wash marks on piston faces, very interesting.

I have a whole new respect for velocity over maximum volume of airflow, basically either a big hole or small hole, i think it makes a huge difference from things i have read and seen, and most people never take it into consideration. If i had my choice, i would go for velocity. Especially for rideability reasons. Seems like changing shapes of ports and such makes a better difference then just changing the size. Even on Dannys and Jens cylinder heads, when i ported them i wasnt aiming for maximum material removal, i was focused on trying to think out how the air would be going through and how i could make it flow as smoothly as possible

BC, you had perfect timing with this post, its slow here too 

Also, you always see the ad for the monoblock cylinders, CUTTING EDGE 13 PORT DESIGN!!!! what are the 13 ports, and how is it that it has an uneven number, when you would think it would be split evenly between the 2 cylinders?

[Pete]

it's most likely 13 ports per cylinder.  triple port exhaust and 10 port intake.

[BC]

The single cylinder ATVs are bridged.  In some cases I cut the bridge out entirely- it can create some issues with piston seizures.


Here is a shot of a 250R cylinder- this is the later '87 - '89 type cylinder with a bridged intake.


Here is a shot from the base of the cylinder showing where the Boyesen ports are from relative to the transfer ports and the cylinder base.  Intake side to the bottom


What the cases look like.  Intake side to the right.



13 port:
1 main exhaust port
2 sub exhaust ports
6 transfer ports
2 intake ports
2 boyesen ports

[Pete]

The single cylinder ATVs are bridged.  In some cases I cut the bridge out entirely- it can create some issues with piston seizures.


Here is a shot of a 250R cylinder- this is the later '87 - '89 type cylinder with a bridged intake.


Here is a shot from the base of the cylinder showing where the Boyesen ports are from relative to the transfer ports and the cylinder base.  Intake side to the bottom


What the cases look like.  Intake side to the right.



13 port:
1 main exhaust port
2 sub exhaust ports
6 transfer ports
2 intake ports
2 boyesen ports

hey, that first picture looks pretty familiar!  Some cool dude wrote that article...

[Ben]

The single cylinder ATVs are bridged.  In some cases I cut the bridge out entirely- it can create some issues with piston seizures.


Here is a shot of a 250R cylinder- this is the later '87 - '89 type cylinder with a bridged intake.


Here is a shot from the base of the cylinder showing where the Boyesen ports are from relative to the transfer ports and the cylinder base.  Intake side to the bottom


What the cases look like.  Intake side to the right.



13 port:
1 main exhaust port
2 sub exhaust ports
6 transfer ports
2 intake ports
2 boyesen ports

im assuming you dont get the problems with intake bridges like you do with exhaust bridges since it stays so much cooler?

So those Boyesen ports connect the crankcase to the intake tract directly and arent affected by the piston at all? that doesnt mess with the crankcase pressure that pushes the charge through the transfers to the combustion chamber?

thats amazing how much different the honda looks over the banshee

do you have pics of the ports on a monoblock? like the sub exhaust ports and the boyesen ports?



i feel as though i can grasp this stuff pretty well once i get into it, but i read a whole thing on expansion chamber tuning, holy shit that made my head spin

[Ben]

are boyesen ports stock on a honda?

[Ben]

i actually found this, easy to see the ports

[Ben]

in that pic boost ports=boyesen ports?

the odd shape of the intake port, is it for making the same port act as a boost port also?

[BC]

A bridged intake is important- due to the rod angle and thrust it tends to place a higher load on the intake side of the piston skirt.  As it's bathed in nice cold fuel all the time it tends to not expand from the heat.

Yes all of the transfer tunnels, Boyesen ports, and reed box are all exposed to the same primary crankcase pressure. 

My view is that a piston either has holes in the skirt- like a Banshee piston does, or it has Boyesen ports- one or the other.  There are limited cases where I feel that even with Boyesen ports in it- they may not be big enough to totally omit the holes in the skirt.  Cheetahs and Cheetah Cubs are where I make that exception.

I have always used a 250R cylinder as an example against a Banshee cylinder for what is important for me to put my time into.  A 250R stock cyl is 66.00mm, a Banshee is 64mm.  There is at least double transfer port in a 250R cylinder than there is in a Banshee cylinder.  Granted their power outputs differ and therefore would need slightly different transfer sizes- but for the most part- taking the difference in RPM out of it- they still only have one and one only way of getting fuel-air charge into the cylinder.  Doesnt matter what fancy crap you might try to pull off with the intake or exhaust ports- the fact remains there is only ONE way to get fresh mixture into the bore.  The intake and exhaust are quick and easy to cut.  Any fool with a dremel or die grinder can go at it.  The shitty part of porting cylinders is bouncing around with a tiny assed cutter in a 90* hand piece.  It takes a fair modicum of skill to not even break the damn thing much less get a good port cut.

Here's a link to the CP Ind. website for Cub info.  On it are some pix of the port layout in the Cubs.
http://www.cpindinc.com/pub/view_product/37?lm=3&name=CPI-6858

[Ben]

i know i keep stacking these questions, but the exhaust boost ports, they just loop right around hook up with the main exhaust port? is it just a better way of getting the exhaust out faster without having a bigger exhaust port that would mess with the timing?

[BC]

No problemo...I can talk 2T stuff longer than you and Chris can about diesel stuff 

Sub-exhaust ports help in two ways.  1st is more time area for a given duration the port is open.  As you have more port area and the duration can remain lower- which will always help with power spread.  The other factor is that is helps vent the exhaust gasses from further back in the bore due to their location further back in the bore.

[Ben]

in that pic boost ports=boyesen ports?

the odd shape of the intake port, is it for making the same port act as a boost port also?

what about this? ^


Cheetah=powervalves and 250R reed cages, correct? whats the typical price difference between that and a cub?

looking at the CP link, the DMX cheetahs, those are rediculous CC sizes, do they really run all that well?

[Pete]

here is an '85-86 250R intake (lots of port pics in the 250R pics section FYI).  This was from my LRD 295 cylinder.  It wasn't very fast for me.




These are the transfers from my MP277 motor.  This motor ran quite well for me!