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240Z Turbo

P90 Head Porting realizations

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Guest Nic-Rebel450CA

Just stumbled across this thread. Just to be sure, are we talking 290cfm per port, or for the intake side of the head?

 

What are the stock numbers?

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Guest zline

what about 89mm big bore? think he could simulate that too?

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Well, as most machinists go, he too is not prompt, but has been frank that he has yet to do the testing. He was held up a bit because he needed to create a jig specific to the 86-88mm bore commonly used on our engines. I hope to hear something new by the end of next week.

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I was reading the "Smokey Yunick's Power Secrets", and he said that all of the stress on the guides is at the spring side of the head, and that the port side can be cut way down, but he also said that it did close to nothing for port flow. He explained that if you could shink down and stand in the port that the air is still at the stem guide area.

 

These are his exhaust port thoughts:

 

"Many, but not all of the concepts that apply to the intake port will also be valid in the exhaust. Exhaust flow is initiated when the exhaust valve opens, and the relatively high pressure in the cylinder moves toward the relatively lower pressure area in the exhaust system. In addition, the pressure inside the exhaust system in a racing engine is usually pulled "artificially" low by the functioning of the headers. Therefore, it is generally possible to exhaust the chamber quite successfully with a rather small port.

The flow leaving the combustion chamber must get around the head of the exhaust valve before it enters the port, and the valve is the most important element in exhaust flow. Once again, it would be advantageous to have the port angle more nearly in line with the centerline of the valve, and the long and short sides of the port should be as nearly equal as possible. The flow will cone around the head of the valve as it leaves the chamber, but chamber-wall shrouding will sometimes break up a portion of the cone and reduce flow very considerably.

If at all possible, the exhaust port entry should be straight and concentric to the valve centerline for at least 1/2-inch before the bend towards the exit begins. If you cut away the short side radius and try to bend the flow right off the seat area, you will rip the side out of the cone and knock the flow down by at least 20-30 percent. Just as on the intake, the max flow will be achieved if the cone forms completely around the periphery of the valve head. If you set up the valve head and face properly, the cone can be shortened quite a bit, and once the cone closes up around the back of the valve head, you can pull the flow around the bend and send it out of the head."

 

He goes on in great detail more, and the intake discussions are in a complete differant direction that I would have ever imagined, ports are tricky, and common sense doesn't always do the trick here. I saw your cutaway pics on your site a couple of weeks ago and had been thinking about chopping up a head prior to that, but you pics did the trick, looks like your on track with the intakes, I think some narrowing on the valve half of the port might be benificial, but only testing will tell, I might have access to a flow bench soon, and I'm trying to get an engine Dyno together in the near future to try lots of things out, that's the only way to find the power, try anything and everthing and learn from failing which then becomes a gain, I'm sure there are lot's of things to be learned, so let's go!

 

Chris

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James I know your as egare to get the flow numbers back from this as anyone but I can't wait any longer in about a week I'm going to be reshaping my p-90 for increased flow and try to keep velocity up and trublance limited. Your half cuts really help man and so did talking to a few guys that run there own speed shops that really knew the ins and outs of port shaping, texturing and chamber mods. I hope you get the head back soon. :)

 

 

 

 

 

tbs

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Guest HBskinheadZ

Bump :wink: just picked up a p90 head today at the JY so I hope we see some progress with this.

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Very intresting, and overwheliming, you gearheads make me feel rookie ( witch i'am) but still absorbing man, just gave me a reason to keep the spare p90, and i hope to start a job, when i graduate cause this shit cost :)

 

 

 

thanks for this great thread :D

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Guest FinalRights

Does anyone know if the S20 head will fit the l28 block? Might be hard to find one in good condition though.

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No, it will not (the LY SOHC head will, as will the OS Giken DOHC head. Both are rare as.....).

 

FWIW I spent a fortune getting my P90 ported last year (will post pics) and it flowed ~350CFM with manifolds attached. I don't have the flowbench data handy, but will try to get hold of it.

 

A very interesting thread, but have patience - these things take time :-D

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Well I was looking at the turbo exhuast. and wow I thought that the ports were bad! If you want to port you really have to go custom manifolds! I've done a bit of work to the inside of the intake manifold and smoothed most of the obstructions. That is all I really want to go for. A lot of work needs to be done just to start to see any affect. I hope this thread continues to bring good information about the p90 head. Thanks Guys

 

Ray

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