I can't help but think that something important is missing here. 700hp is 700hp, yes, and the cylinder pressure is the *same* regardless of the bottlenecks before the cylinder but cramming tons of air mass through smaller ports (assuming small heads and higher boost) will generate heat in the charge that I imagine will lead to detonation quicker than if he had a free-flowing engine at low boost. This will require higher octane fuels, as mentioned in my first post. Is this guy okay with running C10 or e85 in the car? If so, by all means, go ahead but if he's stuck to 91-93 unleaded, I don't see why it would make sense to keep the current setup when he could get bigger stuff for very little money.
thousand dollar set of heads with a thousand dollars in machining vs selling the 170's for a thousand and buying 205's for about a thousand. Seems like a solution to me.
If he does stick with 170's on a 9.5CR 347 i doubt he'll make 700 through an AOD on 91-93 unleaded gas. If he does, he should write a book about it.
There's nothing missing. ~700hp with 347ci requires the engine to consume roughly 70-75 lbs/min of air mass at 6500RPM. That's regardless of the induction type. Volumetric efficiency is the variable here. Make the engine more efficient and the easier it is to attain that airflow goal after pumping losses.
The turbo is adding the most heat to the intake charge. What causes heat buildup in the turbo is backpressure and how hard the turbine is working. If the turbo doesn't have abnormally high backpressure on a "small" headed 15psi boosted engine then the charge air temps will be manageable. It's about the compressor more than it is about intake restriction as far as charge air temps are concerned. And a heated charge air is a good thing as long as the combustion event can be controlled which is where the tune comes into play.
And detonation has a bit more related to it than just high charge air temps. It's more about the thermal capacity of the charge entering the chamber. You can have high charge air temps and still control the combustion and make lots of power without detonation. That's what makes E85 so great in forced induction.
I daily drove a 10.4:1 347, TW170 heads with 10psi of boost on 93 octane through 3 Alabama summers. No overheating, and no C10 or meth injection required.
I'm just saying, the heads aren't "small" for a street car that is turbocharged which is why the turbo supplier, which I assume was Precision Turbo, told him the 170s would be okay for his application and power goal. It's more about the compressor efficiency combined with the volumetric efficiency of the engine naturally aspirated. If the heads aren't a restriction NA then they generally won't be once boost is added especially if we're talking 10-15psi.
I doubt he'd get $1000 for a set of used TW170 heads....