Donate!
Welcome, Guest. Please Login or Register :: View Members
Pages: 1 2 3 4 
Send Topic Print
Big Bore Engine - Part 2 - Head (Read 306 times)
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Big Bore Engine - Part 2 - Head
Reply #45 - 07/19/20 at 23:47:41
 
I measured the combustion chamber volume after reassembling the head.  It is now 55cc.  Those new intake valves take up a little extra room.  I will need this value to confirm my static compression ratio.
Back to top
 

Ready_to_Go_2_2.JPG

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Big Bore Engine - Part 2 - Head
Reply #46 - 07/19/20 at 23:48:29
 
Remember that spring retainer clearance issue?  I was worried about the retainer hitting the underside of the rocker arm.  Now it’s time to check that.  Install the camshaft along with the head cover and rocker arms.  The cam must be in the TDC compression position.  Use a few head cover bolts to make sure the head cover is up hard against the head.  You need about .060” clearance between the spring retainer and the underside of the rocker arm.  This .050” copper wire passes through with plenty of room to spare.  Good to go.  If the wire had not passed through, I would have ground the underside of the rocker arm just enough to allow the wire to pass through.  Check this at all four spring retainers.
Back to top
 

_050_Copper_Wire_Spring_Retainer_Clearance_2.jpg

Knowledge is power.
  IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Big Bore Engine - Part 2 - Head
Reply #47 - 07/19/20 at 23:49:32
 
I’m not an advocate for polishing.  I prefer to test it with the flow bench and look for significant, measurable improvements in flow.  The finished ports are relatively free of imperfections.  There are no big chunks of stuff sticking out into the air stream.  Good enough.  Let’s face it, after a few miles of operation the crud is gonna start accumulating and that pretty mirror finish will be buried.
 
The completed cylinder head flows much better than the Stage II.  It can handle a cam with up to .420” lift.  It’s ready to install on the big bore engine.  I’m chompin at the bit to give it a try.

I hope you find this report informative and I welcome your questions and comments.

Knowledge is power.

Mike
Back to top
 
 

Knowledge is power.
  IP Logged
RocketScienceSmurf
Senior Member
****
Offline

SuzukiSavage.com
Rocks!

Posts: 268
Sweden
Gender: male
Re: Big Bore Engine - Part 2 - Head
Reply #48 - 07/20/20 at 03:53:54
 
Your level of skill and knowledge is nothing short of amazing! I am very grateful that you share both the information and the pictures with us Smiley
Back to top
 
 
  IP Logged
Armen
Serious Thumper
*****
Offline

Half-Witted
Wrench-Jockey from
Jersey

Posts: 1430

Re: Big Bore Engine - Part 2 - Head
Reply #49 - 07/20/20 at 06:18:49
 
Amazing!
Thanks for sharing your hard work.
Back to top
 
 

In theory, theory and reality are the same. In reality, they aren't...
  IP Logged
FinnHammer
Junior Member
**
Offline



Posts: 85
Denmark
Gender: male
Re: Big Bore Engine - Part 2 - Head
Reply #50 - 02/05/24 at 14:36:01
 
Mike,

A short revival of this thread, related to the modification of the exhaust port.
This port is the first one I am going to try my hand at, and there is one detail I don't quite understand.
It is the flat part, the one that makes the port into a "D" instead of a round hole.
What keeps you from rounding the port by grinding into the floor of the port?
I am opening up to a 1.65" ID header.

Cheers, Finn Hammer
Back to top
 
 
WWW   IP Logged
DragBikeMike
Serious Thumper
*****
Offline

SuzukiSavage.com
Rocks!

Posts: 4071
Honolulu
Re: Big Bore Engine - Part 2 - Head
Reply #51 - 02/06/24 at 00:06:51
 
Finn, it is my understanding that the "D" port is intended to mitigate exhaust reversion.  The hot gas flows easily over the bottom edge as it exits the port, but any reverse wave (acoustic or pressure) will run into the flat face on the bottom.  In effect, it should reduce the reverse flow (it serves as a dam).

I have seen articles and books that discuss problems associated with exhaust reversion, and it can get so bad that it actually forces the fresh intake charge back out of the carburetor.  Reversion that bad is usually associated with open headers (straight pipes).  It can be a real torque killer since a carb doesn't care which way the air is flowing, so each time the charge reverses flow it picks up more fuel.  The mixture goes grossly rich.  In severe instances, it can change direction several times before the exhaust valve closes.  Long duration cams with high TDC lift and lots of overlap aggravate the condition.

Another reason to leave the bottom of the port alone is the exhaust gas tends to run along the top of the port, so opening up the bottom only increases port volume, which decreases gas velocity.  I suspect that in the case of an exhaust port, the differential across the port is so high that the gasses are going to fill that port regardless of the inertia developed in the column of hot gas.  Even though the mass will want to run along the top of the port, the pressure will force the mass to fill the port top to bottom.  But as the pressure bleeds off, the smaller port volume will start to yield dividends by maintaining gas velocity and dragging the burnt charge out of the cylinder.

I don't have any hard evidence that this "D" port theory works any better than a round port.  I just know that a number of reputable head porters use "D" ports, and their heads are generally recognized as good performers.  Jerry Branch, HeadQuarters, and Edelbrock all use "D" ports.

The "D" port isn't going to result in better numbers on the flow bench, but it shouldn't hurt flow either.  If it mitigates reversion, then I think it's a good idea.  

Back to top
 
 

Knowledge is power.
  IP Logged
FinnHammer
Junior Member
**
Offline



Posts: 85
Denmark
Gender: male
Re: Big Bore Engine - Part 2 - Head
Reply #52 - 02/06/24 at 12:25:17
 
Mike,

Thanks for the explanation which makes some sense. One more reason for asking is I saw this port from a KTM 250, and actually, at the time, I took it to be a round port, but now that you mention it, even this port has a bit of "D" to it. A "D" port it will be, then!.

Cheers, Finn Hammer
Back to top
 

5-KTM_2024_SXF_250_stock_cylinder_head-exhaust.jpg
WWW   IP Logged
Pages: 1 2 3 4 
Send Topic Print


« Home

 
« Home
SuzukiSavage.com
03/28/24 at 15:34:32



General CategoryRubber Side Down! › Big Bore Engine - Part 2 - Head


SuzukiSavage.com » Powered by YaBB 2.2!
YaBB © 2000-2007. All Rights Reserved.