So a buddy of mine has stepped up and offered to port my heads for me, and teach me in the process. He's been building engines with his dad since he was a kid, done many heads before and has the correct power/air tools. I'm looking for VG30 40P head specific advice. I know there's the basic "enlarge and it will flow more, go too big and you'll lose velocity" argument which is true of everything down to a straight pipe but may or may not apply in practice to some engines if they're especially restrictive. So if you've ported your heads, or had them done - how much was taken out? Where specifically should be attacked, or avoided? I read an article (that I can't find, annoyingly) a while ago discussing how the divider (correct term?) leading to the back of the two intake valves got progressively lower as the VG progressed to the 35 and 37 generation motors. I'm guessing this will be a good idea as well as knife edging what's left. The heads are stock as a rock at the moment, and once the porting's done they'll go to the engine builder to have the valves seated and full assembly, as well as remaining porting. Cheers guys -A
the most important thing is to pay for flow testing, flow them stock, then when you think you are done porting, then usualy adjustments will need to be made With the divider, dont knife edge it, bull nose it . Apparantly subsonic air flows faster around rounded surfaces
Head porting is a dangerous business. For the Vg30DE heads though it is very easy. Radius off the intake ports and smooth off the castings. The exhaust ports benefit the most, blend the radius from the transition from the valve seat on the lower edge. Also remove the guide valve boss. If you friend is very good this will seem obvious. Warning don't take too much off in the exhaust they are not overly thick and you don't need to enlarge much.
Flow testing sounds like a great idea - aren't there figures out there for 40P heads already though? I was aware that the port walls on the intake side shouldn't be polished to lead to the air flow tumbling and mixing through the fuel vapour, but am under the impression that knife edging is a widely accepted and beneficial mod. Thank you Dave, good tips.
I've heard that the S1 heads intake ports come very close to the water galleries. Does anyone have any photos or extra info on this to make it easier to miss?
One day when I get around to it I will be organizing CNC porting of some VG30DETT heads. To do this and make sure it's done right I will be cutting up some heads to ensure we know what to expect with wall thickness etc. There is a very reputable shop down sth that I will use for this, it may be a while before it happens as it's only likely to happen if the eng in my own Z needs to come out for repair. that one just seems to keep going though so who knows how long the wait will be ha ha!!
We got started today, and after a good and thorough checking out of the OEM set up it doesn't look like they'll be too hard to take on. One thing we're not sure about is the boss that surrounds where the spark plug protrudes into the chamber. Whether to remove it or maintain it appears to strongly divide people. There are heaps of accounts of people doing both. Black Beast passed on that it's there for heat dissipation/detonation prevention, and I'm sure Nissan put it there for a reason. How does it work though? Here's a pic of a head with them removed, one plug is TT and the other is NA (shows height difference) and here's a mental pretty EPR set up
i see , make sure you dont cut the exhaust side . i had a good set of ported heads here the i put in the bin , and heaps of other shit as well . all in the bin . lol
Cheers Tim, I'll pass it on to the buddy of mine I'm doing the work with. We kept going this last week and and am making great progress. We have a few more questions though. The first one he raised was opening up the injector port on the cylinder heads. In trying to find a pic online I found a direct comparison between S2 and S1 heads and it looks like Nissan did just that, so it's probably a good idea My accomplice said the RB heads he's done in the past have been much much wider. Then there's the question of opening up the injector ports on the lower plenum to suit. The OEM S1 ports honestly look like total shit; drilled holes that don't actually taper out. I tried to find some stock photos but all I could see was people that had totally gutted it, veeing out the area and removing the "drilled hole" completely. Still trying to find actual conclusive source for the function of the protruding spark plug boss.
Removing the boss looks like it may expose the thread on the spark plug which would be a potential detonation hot spot. It would also expose the plug to more heat again risking detonation. Considering the potential gains vs the potential risks I would leave it alone.
Once this is done you need to fit shorter NA plugs. The chamber on the left has had this done, the right chamber maintains the TT plug for a comparison only.
Remove it & run the NA style plugs, two main reasons: Lowers compression ratio by a tiny bit Removes obstruction from air flow around the valves Added bonus: Plugs are cheaper & easier to source in various heat ranges Makes polishing the combustion chamber easier
I've read Nissan has the spark plug boss to improve flamefront in the combustion chamber . Removing will deshroud the valves with a minimal increase of flow .. I didn't see the need to remove it . .normal deshrouding of bigger valves on the outer chamber and removing spark plug boss will lower comp a fair bit.. raising comp is better .. 9:1 should be standard for a rebuild Anti ...concentrate on the porting ,opening up the throat for bigger valves, deshrouding them and a good radius job . you don't need to reinvent the wheel.
That all sounds logical and makes removing the boss sound worthwhile. Is there any downside to the shorter plug? I read that Nissan USA had NGK make a longer plug range for the TT. The NGK PFRxB-11B range was designed to move the spark further into the combustion chamber than the PFRxB-11 range to improve combustion for emissions control.
Hey Anti, This may be worth reading - interesting at the least! http://www.twinturbo.net/nissan/300...0DETT-Cylinder-Head-Porting-Observations.html Cheers Jamie
