Low-end porting shld be done via the aux ports

[georgieboy]

Hi all,
been a while since i posted last time but i have this question about low-end porting and i don't find the answer via the search button.
I am looking at this husqvarna CR125 cilinder and one thing i find interesting is the amount of transfer ports. Two mains, ofcourse but 4 aux ports. Or you can say 2 middle and 2 smaller at te back, and then at last a boost port.
The thing is i want more low-end although it is not to bad compared to a CR125 honda from 1996. ;)
I notice from all the pictures out of Eric's book and other sources that the most of the port work is done via the aux ports and not so much via the mains.
One way of creating more low-end is rerouting the flow to the back of the cilinder with higher flow rates since there is so little gas speed at lower rpm's.
Is it safe to say that i have to epoxy/jb weld the aux for more angle towards the back of the cilinder hence creating more gas speed and better scavenging?
Pls elaborate with me on this....... any one.
O btw, i already did the home work by making sure all the ports open the same time :)

 

[georgieboy]

To all,
I do realise the difficulty in answering a question like this, considering i don't give any data about the cilinder in question.
I have done some math on the cilinder in calculating blowdown?Ta's etc and what i came up with is that the blowdown, compared to major bike brands, is minimum. Blowdown with open exh valve is 28 degrees, so with closed valves even less. Is it safe to say that this cilinder wld benefit with faster scaveging? I wld almost say this cilinder is made for low-end was it not so that the aux ports are angled towards the exhaust rather steeply.
This is a 99 cilinder but as everybody knows the design is not changed in all these years and nowadays everybody raves about the wr125 huskie, although this is a cr but cilinders are the same.
And Marcus don't say again that this my project from hell, pls....

 

[Pete Payne]

What is the timing of the exh port and transfers after top dead center?

 

[georgieboy]

Pete, with closed PV the exh open at 101 degrees atdc.
The transfers open at 116 degrees atdc.
Blowdown is 15 degrees.
With open PV exh open at 88 degrees atdc.
Blowdown with open PV is 28 degrees.
The ktm 125 are famous for there low-end aswell so are the rm's. What wld be there blowdown with closest PV?
Wld liffting the PV for another mm do some good?

 

[Pete Payne]

If you deck the cylinder .95mm the exhaust timing would be 90deg. ATDC(power stroke of 30.85mm, stock power stroke was 29.9mm)) and the transfer timing would be 118deg ATDC. blow down timing would be 28.6 deg.
This would be a much more bottom end set up .
don't froget to compensate for the cylinder deck , must remachine the cylinder head also.

 

[georgieboy]

Pete, thx for yr fast reply.
You put my data in yr computer programm, didn't you?
Since you are only talking about lowering the cilinder wld that mean that narrowing the transfers to speed up flow is an endless road. Wld it have the same outcome?
Or rerouting flow to the back of cilinder more?
When i ask too much to make public, let me know.
I already am very thankfull with this data. :)

 

[Pete Payne]

Yeas , I pluged a few #'s into the TSR software.
Give me the width's of all transfer ports and approx. roof angles and I will see what zone they work in and if we need to narrow them some.

 

[georgieboy]

Pete, i get to work and respond later, but in the meantime can you tell does TSR take into account powervalve heights?
I ve got a trials bike aswell and that one is without a powervalve and still has 26 degrees blowdown. A trialsbike is famous for their lowends, so how does that compare to a closed powervalve with only approx 15 degrees blowdown?

 

[georgieboy]

Pete, read the angles counted from the exhaust towards the back.
The main transfers are angled 55/65 towards the back.
And the flow is hitting with 55 degrees dead in the center of the cilinder. The 65 flow is hitting 12mm from back.
The 5ths ports are angled 65/90 towards back.(can you also calculate for 65 back/55 front, as that was the original angle)
The 7ths ports are angled 55/35 towards the front. And boost port is offcourse angled towards the exhaust opening.
In total i have got 6 transfer ports and one boost port.
About the widths. For the exhaust i have a mean width, but since it is a butterfly/bridge type port i give the biggest width also.
So exhaust mean width:20mm, biggest width is:30mm at opening.
Main trfports mean width:18mm(also a sort of butterfly shape, so a lot smaller at the beginning of opening, about 12mm)
Mean 5ths ports (are square):14mm
Mean 7ths ports (are square):12mm
Mean boost port(is square): 17mm
Can you do some calculation with these figures, Hope so.
Can you also say something about the PV heights as in my previous question?

 

[Pete Payne]

You have more than enough transfer area. I think it would be a good idea to narrow the rear transfers (the ones that are 14mm wide ) down to 12mm wide and reset the flow angle to appose each other , more of a straight across flow , insted of toward the exh port.

The programs allow for port roof opening times , so to see were the exh valve comes into or leaves off you can plug in the timings/area's and see were it kinda runs out of area . one thing we know for sure is the powervalve helps the bottome end so I would not be too concerned about it just yet.

 

[georgieboy]

Thx for yr help, Pete.
Good to know that i have enough port area.