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P90 Head Porting realizations


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Wow, removing that much of the valve guide makes me nervous, looks like an aggressive job but I'm not a porter so I dont know.

 

I suppose if the spring pressure isn't too insane, and you get a quality guide or guide insert along with possibly fresh valves, could be something that would last.

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Looks good James... man there is a lot of room for flow improvement there. Maybe consider machining some new valve guides out of a more thermally resistant material if you are going to shorten them up significantly. Is the outlined area cast into the head a steel insert around the valve guide? "metal" is a pretty broad term. ;)

 

Any plans to go up in valve size slightly? Seems to be lots of meat for it.

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Is the outlined area cast into the head a steel insert around the valve guide? "metal" is a pretty broad term. ;)

Any plans to go up in valve size slightly? Seems to be lots of meat for it.

 

Metal will do for now. I can send it to you and you can have it analzyed! :?

 

This "metal" insert wraps completely around the valve guide. I do not understand the thinking of spring pressure affecting the valve guide sticking out in the port. The spring works against the the valve seat, not the valve guide. There is more material than on the intake side even with the proposed porting. So you do a valve job every 3 years instead of 5 years. Most people break or upgrade in that amount of time. I don't see the issue with valve guides being affected in this case.

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Guest JAMIE T

I'm almost with James on this one. Why don't you port one like you want then port another with a minimal tear-drop shape around the guide(I'm sure you know what I'm talking about, so I won't bore you with that), leaving some of the guide that protrudes into the port. if the differance is a few cfm, then leave the extra material. If it is substantail, then grind it out. I have ground the guides completely out of some heads. Most others(like the ones on my LT1) I just contour around them and make them very small. Undercut valve stems would help here also.

 

Also, looking at the exhuast port, you could probably raise(port floor) it nearly as much as your removing from the top. You would need to TIG the extra material in the port floor. Then make it a nice wide "D" shape.

 

BTW, What is the length, and stem diameter of the P90 valves?

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You outlined almost exactly what I drew on your picture. The second surface acn have material removed as well, making the port the same diameter for a good even flow. The thing is that as exhaust exits the combustion chamber the port will promote a rolling effect of the gases because of the longer radious which will help the exit of the exhaust. Also like I said about the guide, you can take some of the material off and make the guide shorter, but you do run the risk of wearing the guide fast, so if you move the guide up some, you will be able to maintain a longer guide that will make a longer lasting part. I did not see the different materials, and the steel ring in the head is what is holding the guide for the most part, so it should stay in place provided the knurl is a correct debth and size.

I think this would work out well, but dont forget about the heat on the exhaust port and especially the heat dissipation.

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I do not understand the thinking of spring pressure affecting the valve guide sticking out in the port.

 

To me it is a matter of the valve wanting to work itself sideways increasing friction on the valve stem surface and the guide itself.

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Another note, if you look above the #6, #5, and #2 exhaust ports you will see a round spot on the head as shown below.

daylight.jpg

Directly behind these areas is the water jacket. As the old IMSA cars did, just drill through and tap 3/8" NPT. We would need to determine the best way to do this, but I think this should help. The last area that we need to discuss is the combustion chamber modifications. This can add 20% flow if done properly. I will post some pics shortly and detail what I propose to do. I think the P90 chamber will require the most mods to be done right, but I think it will yield the best results over all other heads because the valves are recessed and additional .080". Stay tuned.

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http://mywebpages.comcast.net/datsundoug/slides/Rebello2.html'>http://mywebpages.comcast.net/datsundoug/slides/Rebello2.html here is a pic that i scrounged up,,its on a n42 but this might help a little i have more at http://mywebpages.comcast.net/datsundoug/[img'][/img]

I feel this is the problem. It would seem a standard port job yields in the 190-200cfm range on the intake. I am not sure at what lift, but???? In the case of the pics you have shown we still have the classic case of the port entrance being smaller than that of the valve seat. It would seem that removing the casting flash and smoothing around the valve guide is the norm. I measured the ID of the intake runner on a RB25 today and it was 2". Holy crap, that is quite a bit larger than the stock 1.25" of the stock intake manifold runner ID. Let us figure this out. Hell, this technology on these heads is 20 years old. That's right, 20 years ago they were making over 700hp on these motors. As it is now, my setup kicks serious street booty. Hell, I raced a nova at 18psi and no nitrous and whipped it in a street race this past saturday. Yesterday this nova ran 11.4@119. If we can get a solid port job to yield 250cfm on the intake ports we can expect to get 400RWHP on pump gas without breaking a sweat at boost levels in the 15psi range. Of course this is with the proper turbo.

In recent times, TimZ had his head re-ported(not as drastic as I am proposing) and the results were in the 225cfm range. I have no doubt he will see 475RWHP on pump gas(smart bastard) :evil: . Anyway, I will post the proposed combustion chamber mods tomorrow.

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OK, here is what I am proposing for the combustion chamber mods. I went out and purchased some sculpting clay to reshape the chamber. I think the work required on the P90 chamber will be more than on any other head, but I also feel the results will be better. Because the valve is sunk into the head .080" further you have a better short turn radius on the intake port. You have a bigger squish area and the funnelling effect of reshaping the chamber will aid in air passing the valve. Here are some pics of what I propose. I could be dead-nuts wrong about this, but it would seem to make sense. BTW, I probably will not be a clay sculpter any time soon! :-D

cc4.JPG

cc2.JPG

cc3.JPG

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My only concern with what you have there James is the ridge between the valves, be careful about going too thin with it, so it doesn't create a hot spot.

 

What are your goals with the CC mods? Better flow in/out, higher CR, and higher detonation resistance? Or am I missing something else too?

 

Edit: meant higher CR, not lower CR. :bonk:

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What are your goals with the CC mods? Better flow in/out, lower CR, and higher detonation resistance? Or am I missing something else too?

 

You were bound to get the answer right and you did. Better flow in/out. I have heard the combustion chamber can enhance flow by 20% or more. The port shape only gets it to the valve, the combustion chamber shape helps get it out of the intake port and helps to funnel it back into the exhaust valve. Look at the how to modify Datsun book, the one with the engine on the cover and there are a few pics of the modified combustion chamber. It all adds up in the end....50cfm for opening the port inlet....10cfm for blending the valve guide area....20cfm for modding the combustion chamber....etc. In the end you have realized 80cfm more of flow. Although my numbers are made up you get the idea.

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