Gollum Posted April 8, 2008 Share Posted April 8, 2008 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. Quote Link to comment Share on other sites More sharing options...
Calgary280ZT Posted April 8, 2008 Share Posted April 8, 2008 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.... Quote Link to comment Share on other sites More sharing options...
oerna Posted July 24, 2008 Share Posted July 24, 2008 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. Quote Link to comment Share on other sites More sharing options...
Midnitz Posted July 26, 2008 Share Posted July 26, 2008 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. Quote Link to comment Share on other sites More sharing options...
Z2000 Posted July 26, 2008 Share Posted July 26, 2008 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. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted July 26, 2008 Author Share Posted July 26, 2008 Man, I am supprised to see one of my initial threads! Man, The flow numbers are a ton better now than they were back in late 2004, thats for sure. As far as the real life experements and flow bench numbers, I have both. I track race both my NA car and my Turbo car, both represent decent numbers. I use stock valves, to maintain port velocity. There are tons of tricks that get done to my heads, that I dont tell, thats just my nature. Like a quote from BRAAP. "My customers keep coming back, so I must be doing something correct". Quote Link to comment Share on other sites More sharing options...
sweetiemattZ Posted July 26, 2008 Share Posted July 26, 2008 Can you send me some pricing on porting heads. I have done only a few and it's been mild work, nothing to great to brag about. It helps that you have a flow bench to test with.. Dude, where have you been!!! Matt Quote Link to comment Share on other sites More sharing options...
Midnitz Posted July 27, 2008 Share Posted July 27, 2008 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. ------------------------- Flow rate is a good guideline to help establish flow characteristics based on what the engine will be used for. You are indeed right that raw, large numbers can be deceiving. One must perform portwork keeping physics in mind. Larger volumes will indeed slow the port velocity down at lower flow rates....effectively moving the VE% window up the RPM ladder. This is one reason I don't open the port size up too much. Most of my work pertains to work in the upper radius and valve pocket as well as the valve seat and guide areas. I also like to use clay to help model the port before I add material. My work mostly ends up being the equivalent to a Stage 2 cylinder head. Flow benching helps verify that the ports are balanced. Flowbenching also helps as a verification tool. The pressure differential Pitot probes are good when you want to break the port down into "moments" of flow WRT port position....and yes it does take the portwork up a notch qualitatively. But one must setup a flow bench properly to make sure the port is going to receive the amount of flow it would see given RPM increments. Your readings are only as good as your setup. This is also why I asked if the flow work was broken down in increments. Good Discussion! Quote Link to comment Share on other sites More sharing options...
Z2000 Posted July 28, 2008 Share Posted July 28, 2008 -------------------------Flow rate is a good guideline to help establish flow characteristics based on what the engine will be used for. You are indeed right that raw, large numbers can be deceiving. One must perform portwork keeping physics in mind. Larger volumes will indeed slow the port velocity down at lower flow rates....effectively moving the VE% window up the RPM ladder. This is one reason I don't open the port size up too much. Most of my work pertains to work in the upper radius and valve pocket as well as the valve seat and guide areas. I also like to use clay to help model the port before I add material. My work mostly ends up being the equivalent to a Stage 2 cylinder head. Flow benching helps verify that the ports are balanced. Flowbenching also helps as a verification tool. The pressure differential Pitot probes are good when you want to break the port down into "moments" of flow WRT port position....and yes it does take the portwork up a notch qualitatively. But one must setup a flow bench properly to make sure the port is going to receive the amount of flow it would see given RPM increments. Your readings are only as good as your setup. This is also why I asked if the flow work was broken down in increments. Good Discussion! Some good points, I use clay as well, but I disagree with big ports moving powerband up the rpm ladder. High rpm capability is mostly piston speed, geometry, valveterain capability, and cam porfile. Most of the engines that see 16,000 to 20,000 rpm actually use a port to valve sizeing that generaly falls about 10% smaller port than we see on most race engines that dont see more than 10,000 rpm. For example the newest street bike engines are increasing displacement, REDUCING port sizes (intake and exhaust), reving higher and making more power than ever. I agree! Good discussion! I would like to hear more... Quote Link to comment Share on other sites More sharing options...
HowlerMonkey Posted July 28, 2008 Share Posted July 28, 2008 Hmmm.........I wonder if the appearance of liners was at the same time that they blocked some holes in the head gasket? Quote Link to comment Share on other sites More sharing options...
Midnitz Posted July 29, 2008 Share Posted July 29, 2008 Some good points, I use clay as well, but I disagree with big ports moving powerband up the rpm ladder. High rpm capability is mostly piston speed, geometry, valveterain capability, and cam porfile. Most of the engines that see 16,000 to 20,000 rpm actually use a port to valve sizeing that generaly falls about 10% smaller port than we see on most race engines that dont see more than 10,000 rpm. For example the newest street bike engines are increasing displacement, REDUCING port sizes (intake and exhaust), reving higher and making more power than ever. I agree! Good discussion! I would like to hear more... ---------------------------------------------- You can have all of your mentioned factors in an engine....but if the cylinder head, intake and exhaust systems are "restrictive" for the desired powerband, then i'd say one would have a non-optimized or de-tuned engine. Street bikes (as well as high dollar multiple valve per cylinder engines) do indeed use smaller ports and valves...but the number of valves/ports filling/scavenging that cylinder are increased (this leaves a larger valve surface area than one large valve)....designers have used this to keep port flow velocity higher at a wider range of valve lift and over all rpms. Re: big ports = moving powerband up the rpm ladder , I was making reference to the L28 head where one has a single intake and exhaust. Typically, the larger one makes the intake or cyl head port, the slower the port velocity at the given rpm and valve lift....this usually kills low end torque, with the expected payoff being in the upper midrange to top end. Notice I haven't even mentioned cams...it's usually the lower # LSA, higher duration and lift units that will move the powerband to a higher rpm range. This is why I advocate looking at the engine design as a complete assembly, using parts with characteristics that are compatible. Breaking things down into moments wherever possible. The pitot probe is a good addition, but don't discount the flowbench as a verification tool. Just be sure that the person performing the testing, knows the proper test setup. Cheers, RL Quote Link to comment Share on other sites More sharing options...
Daeron Posted July 30, 2008 Share Posted July 30, 2008 1fastZ, I am curious about the two different port grinds you posted priginally in this thread... I know you said your numbers have come a long way, but I was looking specifically at the curve of each of your ported examples. It appears that you specifically built two port flow profiles; one more aggressive and higher flowing by the end, than the other. The curves definitively part from each other at high valve lift. What would you say the relative characteristics of these two curves are, as it translates to the engine as a whole? I am asking a rather complex question here.. I can see the differing points, and have ideas as to how they translate to real world, but I would love to hear the answer from the horse's mouth before I start developing my ideas and wind up with some sort of misconception on my part. Thanks! Quote Link to comment Share on other sites More sharing options...
Midnitz Posted December 3, 2009 Share Posted December 3, 2009 Get that N47 head and have Rebello perform portwork on it. These old nissan castings also have port taper issues....an intake port needs to decrease in volume leading up to the roof and floor radii. Intake ports on N42s grow up until the valve guide and open up into the pocket...this is not good for making power or good low valve lift flow. The volume growth makes the air charge slowdown. The exhaust ports also need welding and reshaping to flow decent numbers.When flow benching, be sure to check flow at .5in valve lift incriments. Quote Link to comment Share on other sites More sharing options...
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