cygnusx1 Posted August 12, 2008 Share Posted August 12, 2008 Last night I measured the intake ports on my stock P90A solid lifter version. The ports on the head are roughly 1-3/8" in diameter. Then I measured the ID of the stock manifold intake runners. They are only 1-1/4" in diameter. That is a huge difference. Now why go through all the trouble of porting the head if you are going to leave the stock intake alone? I understand that the head ports have a complex shape and the air has to contort to get around the valve but wouldn't the relatively narrow intake manifold runners be a much better place to begin your porting work? At this point with my limited tools and porting experience, all I would be able to do would be to bell out the intake runners, from about 1" deep, to a slightly larger ID to more closely match the head ports. Would that be at all beneficial to flow between the runners and the head? Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 13, 2008 Author Share Posted August 13, 2008 Bueller? Quote Link to comment Share on other sites More sharing options...
woldson Posted August 13, 2008 Share Posted August 13, 2008 Since it is not the head your working on, I would say go for it!! Obviously there are some powerhouses here that know more than I, however it stands to reason that the lip would cause vortexes that would possible inhibit flow. Quote Link to comment Share on other sites More sharing options...
mom'sZ Posted August 13, 2008 Share Posted August 13, 2008 I know this may not make sense logically, but the intake runners being smaller then the port in the head may actually help. Here's why: As the gasses flow thru the ports, as you probably know, there is a period of time when both intake and exhaust are open. The effect of this is different at different RPMs. At some RPMs reversion occurs, in other words flow actually tries to reverse and exhaust gasses try to push the intake charge back up the port. It doesn't actually do so, but it can hinder intake flow. The step between intake manifold and head may actually help inhibit this reversion. Also, any attempt to 'port match' the intake to the head must also include some work making sure the intake mounts positively. Slop in the mount holes may allow some misalignment once the intake actually ends up bolted in place. Your perfect port match job may end up creating a lip on the head side. Understand that porting works different and has different effects at different RPMs. Opening up the ports may help high RPM flow, but create a 'dead spot' at lower RPMs, where the charge actually stalls or has greatly reduced flow. Think about where your engine operates, at what engine speed. With earllier model cars, such as our zcar engines, often great gains can be made by just cleaning up sloppy castings from the factory. There is a lot of information out there about head porting. Lots of good books and stuff on the interwebs. The most improvement can usaully be made working in the bowl area of the port, just behind the valve. If your car is a turbo car (cygnusx1's is I think) opening up the exhuast side and polishing it can almost never hurt. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 13, 2008 Author Share Posted August 13, 2008 I also thought about the anti reversion properties of having a 1/16" step. I had heard about AR in the exhaust tract but not in the intake. I think Nissan may have used that step as tolerance control as well. Just making sure that there would be no step working against the intake air even if the manifold were to be slightly misaligned. Discuss.... Quote Link to comment Share on other sites More sharing options...
JustinOlson Posted August 13, 2008 Share Posted August 13, 2008 This is the reason I had these custom flanges machined for the L28. Now I have 1.5" intake runners that are raised for a larger radius SSR. Justin Quote Link to comment Share on other sites More sharing options...
2126 Posted August 13, 2008 Share Posted August 13, 2008 Correct me if I'm wrong but, with a step in the intake track (as described), would you not decrease the fuel/air velocity? Tom Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted August 13, 2008 Administrators Share Posted August 13, 2008 Correct me if I'm wrong but, with a step in the intake track (as described), would you not decrease the fuel/air velocity? That's why God invented match-porting... Quote Link to comment Share on other sites More sharing options...
Noddle Posted August 14, 2008 Share Posted August 14, 2008 I though he was after information about standard manifold and port matching, and not these nice ones that JustinOlson had done I would agree with 2126 but I'm no expert. Nigel Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 14, 2008 Author Share Posted August 14, 2008 Yeah the original question was WHY did Nissan give us 1.25" intake tubes and 1.375" holes in the side of the head and what can we, should we, or shouldn't we do? ...how do we make lemonade?...so to speak, without a custom fabrication peice. To port and match the manifold interface with a bevel or leave the step-up in diameter which slows the air stream before the valve. A or B is better? Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted August 14, 2008 Administrators Share Posted August 14, 2008 A or B is better? The step you speak of is to be found in nearly every production car ever produced. Its cheaper to manufacture and the power trade of is usually marginal. Some people will tell you that the anti-reversion qualities of "A" may offset the slight penalty in high RPM flow. Some (successful) people do it intentionally. JeffP is making well past 600 hp with, what I'm told, is about a .050" step. Hope this helps. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 14, 2008 Author Share Posted August 14, 2008 OK thanks Ron for the words of wisdom. It's just so tempting to grind anything I can find when I have my dremel in hand. I will resist the urge, stick to the basics, and the tried and true. Quote Link to comment Share on other sites More sharing options...
woldson Posted August 14, 2008 Share Posted August 14, 2008 "At this point with my limited tools and porting experience," Since it really won't hurt ethier way, practice, practice, practice:) Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 16, 2008 Share Posted August 16, 2008 I can't comment on normally aspirated stuff but I've always heard from machine shops that "B" is better for turbo. Every car I've worked on (turbo or N/A) has a step from the factory (never dis-assembled Ferrari, Porsche, etc. though). I think it's more to make SURE that during the normal production variations, the reverse step isn't experienced (step DOWN in diameter, call it C). In that case, only sometimes getting B is better than sometimes getting C. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 16, 2008 Author Share Posted August 16, 2008 It most likely is to avoid tolerance stepping in the wrong direction. Nissan really went out of the ball park with almost 1/16" all the way around. Although, it is two casting processes with no post corrective machining, so I suppose 1/16" isn't that big a target. I bet beveling it up like B, and getting a perfect alignment wouldn't yield much gains anyhow unless the entire manifold was ported up to match. It's just so tempting to dremel it that I might anyhow. I have no way to quantify the gains or losses but at least I'll feel like I tried something. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 16, 2008 Share Posted August 16, 2008 It most likely is to avoid tolerance stepping in the wrong direction. Nissan really went out of the ball park with almost 1/16" all the way around. Although, it is two casting processes with no post corrective machining, so I suppose 1/16" isn't that big a target. I bet beveling it up like B, and getting a perfect alignment wouldn't yield much gains anyhow unless the entire manifold was ported up to match. It's just so tempting to dremel it that I might anyhow. I have no way to quantify the gains or losses but at least I'll feel like I tried something. You'd need dowels or some way to center or mark the alignment of the intake manifold to avoid ending up with a step, too. The stock setup leaves a lot of alignment slop. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 16, 2008 Author Share Posted August 16, 2008 I bet there is about 1/16" slop. Quote Link to comment Share on other sites More sharing options...
z-ya Posted August 16, 2008 Share Posted August 16, 2008 I find that the OEM intake/exhaust manifold gaskets match very well to the head. If there are any slight differences, I open up the head ports to match the gasket. Then I use the gasket to mark the intake manifold ports. I use the 4 stock shoulder bolts to align the gasket on the manifold. Then I scribe it. Matching the intake ports is easy, and is certainly worth the effort. Pete Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted August 19, 2008 Author Share Posted August 19, 2008 There you have it. I could no longer resist the urge to port. Not sure if I did any good or bad but I fit the gasket to the head and checked the port alignments. Marked the gasket in a couple of spots that needed trimming. Trimmed it, flipped it onto the intake all while centering the stud holes to the gasket. I decided to split the difference and hog out about half of the step. Here is a photo showing two runners left to do and one of the ones completed. Quote Link to comment Share on other sites More sharing options...
woldson Posted August 19, 2008 Share Posted August 19, 2008 LOL bravo!! In that pic that step looks huge!! I guess its just me but I don't remember any of my intakes haveing what looks like a liner in it. Nice work, now polish up the intake on the head;) Quote Link to comment Share on other sites More sharing options...
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