I would like to go boost but feel 7lb is way too little and building the motor is too complex.

What I understand about good tuning requires:

intake/exhaust (headers, ported throttle body, y-pipe)

engine cooling (bigger radiators, heat vents, bigger intercoolers, colder spark plugs)

delivery (fuel rails, larger fuel pumps and injectors)

computer management (air/fuel controller for appropriate mixture, lower timing advance, strick strick strick monitor and management of knock retard and ping)

higher octane or race gas

If all attributes above mentioned are paid to attention with detail, why can't you boost higher without blowing a motor? Are the pistons just exposed too much stress at that high level of compression ratio?

 

There are A LOT of people boosting higher than 7 psi without building up the motor. I myself am running 9 psi. There are others a lot higher.

 

I have been running 8 PSI for quite a while. Both single turbo kits run 8 PSI or more out of the box...

 

Ok let's now change the topic to why not 12.

 

At 12 PSI even with a return fuel system you are pushing the stock rods beyond their limitations. Most of the info I have heard from Nissan QC Engineers (Mike Kojima etc) is that past about 480 Crank HP the rods are likely to fail. Of course there are several people getting close or past that on stock motors and to be honest no one really knows why the motors are letting go. Most of it appears to be the stock ECU advancing the timing so far that it cause detonation. But who knows. After a couple years the mystery of this motor will be unravleld but in the mean time the consensus is that it is the rods that are failing.

 

Rod failure is due to knock retard,pinging, and hot spots on the engine. So would it be correct in theory to say that no knock+more boost= VQ beast@12++ lbs of boost? Add a wild lopey cam to that and that would help out wouldn't it?

 

True however the pressure added by the turbo or turbos is also going to increase cylinder pressure which could also lead to rod failure. Sure many have done exactly as you are descibing with success. Would I risk it....no...this motor costs to much to start pushing to the limit. Unless you have the cash for a new built motor buried in the back yard I would run the out of the box boost on whatever kit you get. That is my plan until next year. Then its built motor and tons of boost for me... Now if I just could find that $17k I stashed somewhere

 

You can do that, I've seen stock VQs handle 12psi or so. But your real and main question should be what can it handle reliably and consistently? What's better 600whp 1 time pull or 450whp for 2 years. I think decent power that lasts a couple years is better. Who knows 450whp might be way too much. But i hope not!

"knocks on wood"

 

This is one of those impossible questions to answer. Thermal loads, inertial loads, etc. increase nearly exponential as RPM and pressure rise. At some point, the stock con rods will fail, as will the pistons. You can tune around some of this, but there are physical limits to keep in mind, even with a perfect tune...and even with forged internals.

As mentioned, making one dyno pull at 500whp is one thing. But doing this consistently, on the road, for thousands of miles, is a totally different thing. Your margin for error increases dramaticallyas boost pressure increases. A little bit of knock on a stock N /A motor is very tolerable. On a forced induction motor with very high peak cylinder pressurs, the stock internals can take VERY little knock before you crack a ring land.

Lack of ECU options are another factor that make it challenging to make safe whp beyond certain limits. And lets not forget to mentioned the cooling system (both oil and coolant) and possibly the physical flow of coolant through the block....all can play a role in engine failure.

 

Good explanation in detail..Real answer "no one knows".