Port Job Opinions


20 replies to this topic
  • ToXicD

Posted January 27, 2008 - 09:28 PM

#1

Hey guys some of you may have read my other post where i posted the pics of intake but since it mentioned nothing in the title i figured i would make a new one so more people can see it. Anyways i believe my xr650r motor has been ported and i just want to post some pics so everyone can give me their opinions on them. I would like to know if you guys think it looks pretty good, or if i should go ahead and have it re-ported when i send the motor in to Xr'sOnly to get rebuilt. Any comments or opinions will be appreciated, thanks dudes :cool:

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  • martinfan30

Posted January 27, 2008 - 10:05 PM

#2

I know I've posted on your last one, but that is really a nice port job! There is no more metal that needs to be removed on that head...

  • ToXicD

Posted January 27, 2008 - 10:15 PM

#3

cool, thanks. only thing i think i need to do is bore the opening to match the 43mm carb and use that xr's only intake manifold.

  • martinfan30

Posted January 27, 2008 - 10:59 PM

#4

Ya, and dont do anything to the exh. port. You dont want an EGR situation.

  • ToXicD

Posted January 27, 2008 - 11:29 PM

#5

Ya, and dont do anything to the exh. port. You dont want an EGR situation.


what do you mean an egr situation?? exhaust gas recirculation?? what kind of situation could i have??

  • crmc33

Posted January 28, 2008 - 04:28 AM

#6

I think MF30 means that if you machine the exh ports to match the headers then you may get exh gas reentering the exh port and baulking flow, particularly at low to mid RPM.
This is the theory behind having a step down into the exh header and even D shaping the port.

HTH

  • Nailpounder

Posted January 28, 2008 - 05:02 AM

#7

Who ever did that port work did a mighty fine job, it almost looks like a cnc cutter did the work.

  • sploogemonkey

Posted January 28, 2008 - 05:28 AM

#8

cool, thanks. only thing i think i need to do is bore the opening to match the 43mm carb and use that xr's only intake manifold.


Try hogging out your own intake manifold before you spend the money on the XR's Only manifold.

When I uncorked my 600R, one of the things I did was stick my finger inside the manifold and feel around for any imperfections. I found that the stock manifold was really narrow as compared to the intake port and not contoured the same way.

When I took the manifold off and looked at the side that touches the head, I could easily see the impression of the extra material that could be removed. I used a dremel and got to grinding away, and within 20 or 30 minutes of grinding, sanding, and fitting, I had a perfectly smooth and contoured manifold that matched the intake port perfectly.

I don't know how much the XR's Only manifold costs, but my manifold cost me less than a half hours worth of my time.

Your port job looks great, BTW!

  • sploogemonkey

Posted January 28, 2008 - 05:34 AM

#9

ToXicD,

Have you cc'd your intake port to check the volume? I don't know if the shop manual gives volume specs for the stock head, but if it does, you'd be able to determine how much porting was done.

  • martinfan30

Posted January 28, 2008 - 10:08 AM

#10

I think MF30 means that if you machine the exh ports to match the headers then you may get exh gas reentering the exh port and baulking flow, particularly at low to mid RPM.
This is the theory behind having a step down into the exh header and even D shaping the port.

HTH


Thats exactly what I meant! It was late...:cool:

Been on here alot lately.

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  • dldavis_66

Posted January 28, 2008 - 04:45 PM

#11

This is the theory behind having a step down into the exh header


Could you please elaborate on this "step down" thing??

I get the part about "D" shaping the opening of the exh port with throwing some weld in there and shaping it, but...

The only thing I can figure is that...uh...is...uh...hmmm.

Maybe extending the glob of weld for the "D" shaping so that it kinda protrudes into the header pipes a little....??? I mean, I think I got a pretty good picture in my head as to what you might be talking about...

  • martinfan30

Posted January 28, 2008 - 04:56 PM

#12

From what I gather the flat part of the "D" would be at the bottom of the port. So if you look at the port from the front, you see a "D" on its back.:cool:

Nothing protrudes into the header pipe space.

When the piston is at EXHAUST TDC, it begins to move down.. Exhaust valve still slightly open for a time. This can cause the exhaust gas to kind of "recirculate" back into the combustion chamber and dillute the next incoming air/fuel charge. So if you matched the exh. port to the header, this effect would be enhanced... Undesireable! So the "D" port helps prevent this.

Please correct me if I'm wrong!

I also think crmc33 has a picture of one of his heads he had "D" shaped.

  • Graves

Posted January 28, 2008 - 05:10 PM

#13

Did this one myself. Didn't know how it would work out but...

Ah, there's the top end rush.

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  • martinfan30

Posted January 28, 2008 - 05:15 PM

#14

That is the intake side right? Very SHINY! Although a mirror polish is best on the exhaust side. Seems that a slight rough finish is best for intake.

  • dldavis_66

Posted January 28, 2008 - 05:43 PM

#15

I think MF30 means that if you machine the exh ports to match the headers then you may get exh gas reentering the exh port and baulking flow, particularly at low to mid RPM.
This is the theory behind having a step down into the exh header and even D shaping the port.

HTH


Like I said in my last response I totally understand the bit about D shaping the exhaust port, throwing some weld in there and shaping it to a sleepy D. Crystal clear.

This is the theory behind having a step down into the exh header



I believe this part of the sentence refers to something totally different: a step down into the exhaust header.

Here is the picture that I see in my head: the exhaust port on one side the header on the other, laterally speaking. The round inside space of both actually the same continual passage of flow (not actually seen as round, more like just 2 straigh lines in a side view). There is short and rounded mound of metal (like a Pitcher's mound I guess) and part(maybe most) of it is on the exhaust port side and the rest of it is on the header side.

Am I getting warmer crmc33????

  • dldavis_66

Posted January 28, 2008 - 05:59 PM

#16

That is the intake side right? Very SHINY! Although a mirror polish is best on the exhaust side. Seems that a slight rough finish is best for intake.


Exactly. Almost like a hone in the cylinder sleeve. Helps to vaporize the gas for a better burn.

  • ToXicD

Posted January 28, 2008 - 09:12 PM

#17

Correct, from what I have read you can get away with ported exhaust if you use a tapred down head pipe which creates a vacuum to such the exhaust gases out. I believe a reverse cone muffler will give you the same effect just not as efficient. I don't think people realize how criticle the muffler or silencer is for making maximum power and how much of a difference there is between all the designs and manufactures.

  • ToXicD

Posted January 28, 2008 - 09:17 PM

#18

Graves, could you post some other pics of your ports? Maybe some in natural light so you don't have to use the flash. Pics look awesome but it is hard to see the contours due to light from the flash being reflected off the mirror like finish, thanks dude :busted:

  • crmc33

Posted January 29, 2008 - 04:20 AM

#19

dldavis66,

I think the exh to header matching depends on the type of use the engine is for, but for general riding where you use a lot of low-midrange then the step down into the header helps prevent the exh gas reentering the port. Especially if the exh header has a tight bend downstream. The step down (eg header is 3mm bigger than the exh port) helps prevent recirculation.
I was going to make mine flush but then spoke to various tuners, read various books and came to the conclusion its best left with the mismatch for what In wanted. Ive never tested a exhaust with matched diameters tho, so I cant be sure of how much difference it makes till I do!

I would guess that for a engine tuned for top end power, youd probably make the daimters equal. The theory of the D shape is the same, apparently a D shape port flows better than a round one.

It would be interesting to have several heads of different spec to see the effect it makes. Ive got other things to do so its not a realistic option!!

I still believe for road riding, lightening the crank has a better seat of the pants effect than lots of porting work, but its worth doing some 'free HP' port work if you dont go to mad with the grinder and maybe read a few books on the subject!

  • Graves

Posted January 29, 2008 - 04:50 PM

#20

Let me interject a little flow theory here if I may. The reason that a rough surface will flow better is that the roughness will hold a layer of air, water… and air, water... flows best over itself, not over a shiny surface. Now I know that I’m the one who polished the ports, and I knew of this theory at the time. But like I said, I didn’t know how it would work out and figured I could rough it up if the results were unfavorable. The results were anything but unfavorable and the carb had to be completely re-jetted. This pig never had a top end and now it screams like a 80cc two stroke, not really but you get my meaning.

Exactly. Almost like a hone in the cylinder sleeve. Helps to vaporize the gas for a better burn.







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