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My Head Flow work and graphs.

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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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But p79's have exhaust liners kill flow. That’s why everyone wants p90 or n42 and in reality yes p90 will lower quench but if you raise the compression you will have a more efficient motor. Efficient motors make more power and take more advantage of existing and future mods.

 

 

 

tbs

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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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Guest Cronic

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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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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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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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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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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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.

 

I used to think the same thing about the P90 head, that it was pretty much the best bet for going turbo charged. I've learned a LOT since then ;)

 

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.

 

 

I've now got 2 L28ET engines, and I think once I get my 75' running on megasquirt I'm gonna build up a mild 81-83 NA longblock, so flat top pistons with a P79 head. I'll probably get a mild cam and some good valve springs and leave the rest stock for sake of money. Then when I drop that in that shuold give me a pretty good street motor with good power off boost and good knock resistance.

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Midnitz, valve lift for intake at 209 cfm is .600. At .500 it flowed 201 and at .400 it flowed 198. On exhaust, I'm a bit of a noob and not sure how to read the data sheet. I have no idea what the grind is on the cam. Rebello chose the cam for the PO when they first worked on the head 4-5 years ago. My plan was to get everything installed, see how it runs, then down the road get a custom cam ground. Guess I better file away that data sheet where I can find it again....

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Has anyone compared P79 with exhaust liners

vs P90 regarding exhaust temperatures?

Have been on dyno with my 240z l28et(P79)

and it had high exhaust temperatures just

running normal,700 degrees c.When driving

it hard it raise to 820 degrees c so he thought

it was best giving it more fuel than he normally

would do.

Could it be the liners raising the temperature?

The engine runs really strong but he was shore

it could give more power when tuned down on fuel.

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Midnitz, valve lift for intake at 209 cfm is .600. At .500 it flowed 201 and at .400 it flowed 198. On exhaust, I'm a bit of a noob and not sure how to read the data sheet. I have no idea what the grind is on the cam. Rebello chose the cam for the PO when they first worked on the head 4-5 years ago. My plan was to get everything installed, see how it runs, then down the road get a custom cam ground. Guess I better file away that data sheet where I can find it again....

------------------------

You should have the head flow-benched by an outside vendor....the ports should have a progressive drop-off in flow (A place where the flow delta runs flat), Of course, things change when the force behind the valve is pressurized....

 

Things to consider in the long run:

1. define what the head does

2. finalize the boost level you will settle on

3. tune the cam to the intake-head flow.

 

In the end, it will be quite the beast.

 

Then you can work on keeping the rear tires stuck to the pavement....but this is a good problem to have. :-D

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I looked at the pics on your website... You got a pretty good grinder hand.

 

A good flow # doesnt hurt but the flowbench is one of the biggest blindfolds to the cylinder head porter. 99% of the time the flowbench leads porters to make their ports TOO BIG! Q. Why is that? A. big ports flow better on a flowbench. Making a port bigger slows the air down and that greatley reduces VE. This is so comon These days and its the main reason why so many "built engines" can pull an OK dyno # but they simply dont perform well on the track/street at all. This is the main category that keeps the pros so far ahead of the upcoming engine builders.

 

On the p90 pics page, the exhaust port exit is about twice as big as it should be (I dont care if its n/A or turbo) and the intake side needs some attention for port shape.

 

I would recomend investing in a pitot probe and see what the air is doing at port entry, short side, in the bowl, choke point, and past the valve into the chamber. This will be a big eye opener!

 

Please dont take offense to this post. Im just trying to help remove the flowbench blindfold. It will make you ten times the head porter you are now.

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