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240Z Turbo

P90 Head Porting realizations

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Well, some know that I run the P90 on my turbo motor. I had a spare head and decided to chop it up to look at the port cross section. The inlet on the head is roughly 1.375" and the valve seat has an ID of roughly 1.525". This is not a good scenario when the port needs to taper from large to small, not small to large as the stock configuration. In looking at the cross section just before the valve guide the port is actually quite large. It is only the 1st 2" of the port that are really suffering from what I can tell. As far as the cross sectional wall thickness, it looks to be between 3/16" and 1/4" on average. I am sure most of you remember the pics of Franky's massively ported N42 head. This is what needs to be achieved to make the big power we all so desire. However, a custom intake will be a must to take advantage of this port configuration.

screen

If we take the inlet from 1.375" to 1.625" that is a 40% increase in cross-sectional area and according to Corky Bell, a 95% increase in flow potential. This is not to mention that we know have a scenario where the port tapers from large to small increasing port velocity. I am ordering a 1.625" 4-flute end mill and will practice on the other half of the head I did not slice up. What I hope to do is use the endmill to come into the head at an angle to punch it out and then smooth the rest of the transition by hand porting. I see alot of potential to get some drastic increases in flow #'s. I have heard 290cfm from the intake ports is possible. I will post some pics soon of the chopped up head.

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Guest JAMIE T

James, 290cfm. Holy smokes, that IS awesome. Definatly keep us informed. I was once told by the guys at Brownfield heads(high end alum. head maker for chevy's) to shape the port the way you WANT it, then worry about the holes you've created in water jackets etc... Weld them up! Or like these on the intake side, you can use epoxy.

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My buddy with the Turbo mustang([email protected]) has the epoxy on his intake ports. The ports maxed the flow bench at 400cfm and he has had no problems with the epoxy leaking from the water jackets and massive boost. However, the Epoxy from Morosso is about $50. 290cfm would be an ultimate goal and I have no idea if that will be achieved from doing this, but it can only make it flow better in my opinioin.

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Be sure to flow bench and dyno a before & after to give us some concrete results. If you are going to epoxy be sure you are not restricting any cooling passages with the epoxy, don't want any hot spots in the head.

 

Not sure why the port is smaller than valve inlet. Perhaps it might be to increase velocity to create a tiubling effect ?? Mabey it might be just the limitation of engineers working with an outdated design ??

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Ok, I cut the head long ways down the port to get a better understanding of the angle of attack. The 1st pic shows the stock port configuration. Disregard the notch at the port inlet as this is the injector cutout. You can see the port inlet is roughly 1.350" and the valve seat ID is roughly 1.525".

ipdim.jpg

What I will do I run a 1.565"(1-9/16") end mill into the port and then smooth the transition. The necessary angle appears to be 17deg. At the port entrance I will make the inlet 1.625" by hand porting. This will allow for a good transition from 1.625" at the port inlet to 1.525" at the valve seat. Here is a pic of what I mean.

ipmod.jpg

Below is a pic of the exhaust side of things, looks can be deceiving, but it does need some work.

exhaustport.JPG

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Now those are the money shots I was hoping for as I started reading this thread. :D James, is that intake runner unmodified at this point? I'm impressed if this is the case! As far as the valve guide goes anyway, its really well incorporated into the runner, providing less restriction than a lot of heads I've seen. The exhaust on the other hand... :shock: Sure looks ugly to me. Problem is, with the exception of shorter valve guides, what can you do?

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WOW great post but I have to ask why hand port out to 1.625 when you could do most of it with a mill and then smoth the transistion by hand. that way your inlets stay round and don't loose shape from hand porting. What I'm saying is mill the 1.525 and then mill teh 1.625 and just don't mill as deap as the first time. It's just my 2 cents on this. Keep us posted, if all works out I might not swap a DOHC RB20 head to my motor.

 

 

tbs

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I was looking at the exhaust port and guide area and that is a real problem for the head in my opinion. The intake can be done easily enough to get the flow up.

The exhaust port on the other hand is a different ball game. I printed the picture of the port and here is a possible solution to improve the flow. The first thing that can be done is to shorten up the guide, but with that you run the risk of a quick failing guide. The thing that occured to me was to move the guide up say 1/2". Weld on the top in the spring area to provide added support for the longer quide. That would have to be figured out just how much weld could be built up so that the spring retainer would not hit, but I think you could get away wil about 1/2" Then machine the weld so that it would not touch the spring and accept the seal. After that is completed then you can remove the chunk of material in the port and still maintain the guide strength so that it will not wear out quickly. That would free up allot of space in the port. then on the lower side of the exit you can remove some of the radious above the water jacket and free up some more space. The question is tho, how much can you build up the valve spring seat area in the head, and would you, and or, how much would you have to shorten the guide.

The thing is that even if you did just the intake side of the head, the exhaust side will be the bottle neck and it will gain you nothing if you cant exhaust the same or close to the volume you can take into the intake side of the head.

What do you think James? That guide and radious side of the valve guide seat if that could be effectivly removed and keep a strong guide would really improve the flow, if you wanted to keep a close tolerance you could remove enough of the radious and make it the same size diameter as the valve.

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The valve guide on the exhaust side should be completely removed in my opinion. If you think there is a strength issue then compare it to the intake material holding the guide. There is roughly 1" of material holding the intake valve guide and 1.75" of material holding the exhaust valve guide. If we remove all the valve guide material from the natural path of the port it still leaves us with 1.375" of material which is .375" more than on the intake side. From all the info I have gathered thus far, the roof of the exhaust is key and the 1st part of the short turn radius. There is one advantage I see on the exhaust side. The piston will force all air out of the cylinder regardless, but that will take away from the power.

On the intake side it is key to keep the sort side radius broad as you see stock has done. That does not mean you cannot remove material from it, just keep the flow path curve as broad as possible. This is a high flow area. You want the roof to flow just as well as the floor. I have sent the pics to someone who is a professional doing head work/design for Top Fuel and CART. He is going to send me back the pics with the areas shaded that he feels need to be addressed. In the mean time Hoover is going to punch out the port as I have specified and flow the results on a spare head he has.

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Guest JAMIE T

Sure Doug. Bring that one that you have up to Richmond and I'll run it through the band saw :wink: . You know which one I'm talking about. The new, never used one. LOL

 

This is a GREAT thread. Nice job James. JeffP, that's some good food for thought. I have ported and polished dozens of sets of heads. Some VERY extensively modified. I'm talking about raising ports 1/4, etc... Great information here guys.

 

About raising the guide. I am looking at my springs(double) and retainers(both are Schneider), without a mic, I am guessing(with a ruler) that the retainer drops about .4"+ into the spring. I don't know how tall the stock guide is, as I don't have a head in front of me. My springs are for a 1.6" installed height. That minus the .4" leaves 1.2" to the spring seat. If the spring seats(and guides have not been modified on the pics James posted then it looks like the guide is only about .125 above the spring seat.(eyeball micrometer). So figure you've got about 1.075" of clearance currently. add to that a cam with well over .500" lift(that magic 290cfm is probably at .600"@ 28h20. That would leave you with .475" of clearance. figure for safety sake keep a .100" clearance between the guide top and retainer, you could probably move the guide up about .375". Why not just have new bronze guides installed and not set them down so far?

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James, what about the valve guide on the intake port? It seems to me that you open up the intake, but have a constriction there where the guide is, and then open it up again. Have you measured there to see what the spec is? Just curious.

 

I would like to see what happens with all this, since I am going to be doing a head soon. Perhaps I could send you one and be a guinea pig.

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The idea here is to move the guide up, so .375 would be good. I am not sure about the contact area of the guide to the cylinder head. I would like to see some of the contact area maintained for the exhaust guide by building up weld and then machining the welded area. Its important to remember here that the exhaust valve and guide get much hotter then the intake valve does, so that being said, I am reasoning more contact area would be a safer bet then to just remove all of the material and count on the knurl in the guide to hold it in place with less contact area. One thing to consider is that in my head I am running a exhaust valve that is 1.400 and not the stock 1.380 a slightly bigger valve, but it improves the flow of the exhaust.

That big chunk of material in the exhaust port is the key factor hindering flow, so if that can be removed, the guide moved up the suggested .375 then the flow of the port will be improved significantly. Then if you want to go really radical, then have a guide that fits a 7mm valve stem and gain some area that way. I called ISKY and they said they could make a valve spring retainer and locks for a 7mm stem.

These modifications will improve the hp output of a turbo application, and it will help out the N/A engine as well.

anyway, I am curious to see what the guy is going to suggest for improvements, post some pics James so we can see what he suggests.

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Although it is hard to tell from the pics of the exhaust side of things, there is a metal insert cast into the head around the exhaust valve guide. I have accented it in the pictures. This keeps the metal from expanding and loosening the guide which is your concern with having the knurl hold it. I do not think you will have a problem with as little material that needs to be removed and the ring that is cast into the head. I have drawn on the pic of the exhaust port to detail what I feel will free up exhaust flow. This does not address the floor of the port which needs to be modded right where it flows out of the valve, I just don't know what the best approach is at this time.

epmod.jpg

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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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