Chii, I apologize for not getting a response to your e-mail. We do receive a very high volume of e-mails and although I searched diligently through my inbox, I couldn't find an e-mail that seemed like it would be from you.
After having read through this thread, I can see you have somewhat more realistic expectations from a naturally aspirated build. As many members here have pointed out, Nissan has done a pretty good job of getting quite a bit of naturally aspirated power out of their V6 with a nice broad power band.
As most people here have pointed out, it doesn't make financial sense to do an all out N/A build on this engine. In fact, we have a G35 here that the owner has dumped copious amounts of money into chasing the big N/A build. In the end, we're putting our supercharger on it because that car has no bottom end torque and just doesn't make a lot of power, especially for all the noise it makes. All bark and no bite.
If you are really set on doing an all out N/A build on a 370Z, we can do it. Sure, it hasn't been done and very few would follow you because the cost/benefit ratio is a real turn-off when compared to FI.
Yes, we can open up the ports for more flow and install larger valves, but remember they have a cost: lost torque at low rpm's. Sure, you'll make up some of that lost port velocity with the added displacement and higher compression, but there is always a trade-off.
Now, I noticed some people have thought of ditching VVEL and going with HR (or God forbid, DE) heads and aggressive cams, but you're really throwing the baby out with the bath water with that move IMO. The VHR heads have a lot of improvements over the HR heads. Better combustion chamber design, better cooling jacket design to increase resistance to detonation and better port design as well. Sure, the VVEL system is complicated and is a bit of an unknown variable when trying to build an all out N/A build, but since it hasn't been attempted, I honestly think it's worth it to see how it plays out...at least once.
I'll be honest with you. I usually steer people in the direction of forced induction because most inquiries related to N/A builds are people trying to get an extra 100bhp for a couple grand. It's just not going to happen. The other argument I hear often is "reliability" and as several people in this thread have said, once you open up that motor, you have lost some of that OEM reliability. Especially when you start running higher compression and spinning the motor to high enough rpm to start making power.
Currently, we are working on a project in our shop that the customer put no limit on the expense to build a 500hp N/A engine. Here are some of the specifics of the engine:
2008 350Z HR
GTM Competition Engine with 3.8L of displacement and 9,000rpm redline and 14:1 compression.
Custom Cams
All variable cam timing is completely disabled
Individual Throttle Bodies
Dry Sump Oiling system
This engine alone is $35,000 and the whole project is in the high $50k range. It is a full race engine build and can only drink race gas and will have a peaky, narrow power band. Such a build is not street-able at all.
That's to give you an idea of what it takes to get 500hp at the flywheel on a naturally aspirated V6.
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