Remembering obviously that anything Nissan designed into the engine was based around the power target they had in mind at the time of design, also passing emissions testing, reliability for warranty purposes and a number of other factors. Sure the spark plug boss may have been put there to improve the position of the spark plug tip while reducing potential detonation issues BUT in what? a stock engine with a generic off the shelf tune in an ECU that's now over 25yrs old with a trigger system that's pretty hit & miss when it comes to getting the most out of the engine. At this stage in the game it really comes down to the fact that the finner details of the engine design are either out of date or of no use if you are changing so many other things on the engine. Replacing the turbos, manifolds, injectors, tune, changing the port shape, pistons, rods, camshafts, pipe work, intercoolers, exh system, flywheel, diff ratio & what ever else turns you on but leave the little boss around the spark plug because Nissan designed it to be there???? Does it seem kind of silly when someone puts it that way?
Mungy, There are many reasons for cylinder chamber designs. When I was experimenting with getting my engine to pass the emission targets for road registration I found a lot of very interesting things with the combustion process in the chamber. The points with the turbos, manifolds, etc, they are all external to the combustion phase, when the flame front propagation is paramount. There is a book by Sir Harry Ricardo which is an awesome read. Also some research on the Jaguar V12 HE head design also goes a long way to explain the criticality of a slight head design modification. As for the VG30DE spark plug boss. It is clearly there to limit the chance of cracking. It is common issue that the VG30DE crowd have not had to deal with much, and for a simple reason, we have a little more material where they are likely to form
The point was what ever the reason Nissan had for putting it there is now long out of whack with the rest of the engine. The combustion process alters with different cylinder pressure, temperature, fuel mixture, fuel atomization, fuel dispersal, fuel type etc etc etc. Unless someone is going to ask Nissan directly what the boss was for then all anyone can do is guess or educate themselves with literature then guess. OR look at other examples around & guess or follow. Case in point R35GTR Alpha heads as modified by AMS (not the Canadian guys) = no spark plug boss, who cares if it was there to start off with or not, it is not required & those guys are making power that makes the VGs look like Tonka toys.
Rob, not looking to reinvent the wheel at all. Just want to do all the standard stuff and do it right. That's why I'm asking whenever I come across something that conflicts. I've done a heap of digging and spoke to the engine builder too. Looks like the boss is coming off.
If you do open up the injector ports make sure you leave the gasket face intact it it won't deal properly I think sim300 went through that with some heads that were opened up to much
