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My Head Flow work and graphs.


1 fast z

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You DO NOT need a P90 head, that is just something that most think. Any head would work, espeacially if you are going to be using dished top pistons. P90 does absolutly nothing on a P90, you loose ALL of the quench. Best bet for econimy is to use a P79 with flat tops at about 10 PSI. Square ports flow EXACTLY the same as round ports stock for stock.

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Well Turbobluestreak, you obviosly havent ever flow tested these L series heads. The linered heads flow EXACTLY the same as the square port heads. I have perfomed these test many times on all L series heads. You must have your words backwards as well because the P90/P79 Lowers compression when compared to other heads but Increases Quench. Belive me, and I can get a linered head to flow about 138 at 25 " at .55" of lift.

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I have a bare head I would love to get ported, but Im not all that impressed with the flow numbers. I guess Im used to Honda heads though. It's very nice that someone has a flow bench and can do their own porting. I'd love to take this spare, bare head and build it up for a 7500+rpm large turbo monster. Do you know where to get a performance upgrade for the internals, a cam, the springs, retainers, over sized valves, etc.

 

I've heard that oversized valves, in most applications aren't the best thing to do for boost, and usually they don't help create any more power. I derno.

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  • 3 weeks later...
Guest mongrel

Why the odd 25" waterpillar? 10" or 28" are more common and 25" makes for some guesswork when comparing flow!

 

Have you tried raising the floor of the exhust port? I bet that would dramaticly improve flow!

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  • 6 months later...

I'm thinking of using a P79 on a flat top turbo motor. I know that the turbo exhaust manifold ports are square, and P79s are round. From what I've read hear the P79 flows as good as the P90. Is it worth removing the liners in the P79 so that there is a smooth transisition between the head and the manifold? Or should I just leave the liners and smooth the transition as good as I can with them in there?

 

Also, how is the P79 cam for turbo applications? Is it similar in profile to the P90? I'm building a budget turbo motor, and I have the P79 sitting on the shelf, so I would like to use it.

 

Thanks in advance,

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  • 2 years later...

I think that removing the liners is generally a bad idea....most of the work needed on these heads is at the valve bowl and the valve guide, unshrouding the valve is also a must with the newer heads as the valves are larger.

 

Flowbench work is also a must as balanced flow is important.

 

In some cases, I have welded the N42 exhaust ports because of the cast core shift is so bad and the ports are too large for practical header flange interfacing....Effectively raising the exhaust port floor up by up to 2 mm in some cases and adding up to 2mm to the sidewalls to make up for shifts in the cast cores....

 

Also I have discovered that leading up to the valve guide on the intake side,

there should be a splitter that progreesively tapers air around the guide such that the guide itself doesn't produce unwanted turbulence and cause the air to tumble.....

 

This is why being able to weld aluminum and perform clay work along with a flow bench is so necessary. To find out what works at given valve lifts.

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I'm new at this, so be gentle if I post something incorrect or stupid...I just had Rebello port my P90 and the numbers are: 1) intake at 25 psi is 209; 2) exhaust at 25 psi is 150. This is the full race port, not the street port. Dave said this head flowed really really well. I'm hoping to get around 300-325 hp at 10 psi with my T3/T4.

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  • 2 weeks later...

Calgary280zt,

 

The numbers for airflow are decent, but what are the valve lift vs airflow at .100 inch incriments? 0.050 incriments?

 

By knowing the dynamic flow characteristics of a cylinder head, the camshaft designer/grinder can zero in on the cam duration/lift profiles and LSA design.

 

In most cases, a typical Turbo cam profile emphasizes the exhaust side duration and lift to help mitigate turbo lag while LSA usually won't dip under 112.

 

In most cases a thorough flowbench analysis can yield you lots of good info to help you design the supporting components. Insufficient good data can leave you building a "detuned", powerplant.

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I have a N47 in my 280Z right now, I'm looking to either get a P90 or get some head work done to the one I already have. Do you think that with the right porting I can get similar results with my N47 or should i try to find a turbo head? I already have a header for my N47, so keeping that would be a plus.

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