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P90a VS. ported ZN47


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I'm helping a friend of mine build a turbo motor. We are getting ready to order some stainless valves aside from where to order them from, the other question is which head would be better. He is wanting to use a very mildly ported and polished ZN47, while I'm wanting him to use the head I have. It's bone stock P90a that has soild lifters NOT hydo. Also he has a COMP CAM 280S cam he wants to install in one of these heads. Would this be a bad,good,great idea for use in a turbo motor with a upgraded turbo about like a holset.

 

Thanks for any help and advice

Jason

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I'm sorry I haven't been here in quit a while. I remember the N47 head being the Z N47 and know one really knew that the maxima head was any different. People started calling the new found maxima head the MN47 so I thought maybe the N47 from the Z became the ZN47. Sorry about the confusion. But isn't the N47 one of the worst flowing heads dispite the small combustion chamber and larger valves that the pre E88 heads.

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Actually, The earlier heads *in theory* should flow better, as the P79 and P90 heads have a sharper short side radius. Whether it means anything in practice, you'd have to get BRAAP or 1FastZ to answer.

 

Besides that, stock for stock, the Z heads are nearly equivalent in flow performance. Everyone wants a P90 because it has no exhaust liners, and the high quench chambers, AND the large valves.

 

The head swap probably stems from the compression ratio change-the N47 with stock turbo pistons would put you about 8.4:1 compression, and the P90 will put you at 7.4:1 compression. Higher compression off boost means more response off boost, but lower compression means higher overall boost, given that all else is equal.

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Yes, the PORTED P90 (his personal uberported P90, I belive) flows a little more than the PORTED E88 that has smaller intake and exhaust valves. I can expect that.

 

But stock for stock, the heads flow similarly. I've had 4 E88, 2 N42, the infamous EARLY E88, with E31 chambers and different porting, and a P90 all flow tested. At stock levels, having just been through the hot tank to clean everything, the early E88 with E31 chambers and the different porting skunked them all, by as much as 7%. Believe it or not, the P90 in that bunch was third from the top, the order being Early E88, N42 #1, P90, N42 #2, then the rest of E88's. All of these heads flowed within 10% of each other.

 

AGAIN, this was stock heads. I don't have numbers, the tests were done by a local shop who was asked to rank them by flow, and give me percentages. To me, the numbers didn't matter as much as percent increase in flow. Unfortunately, that shop is no longer in buisiness and I can't get the digits for you, or I'd have them in a heartbeat to back up what I've said.

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