...Provided that the wastegate can freely flow out all the excess pressure and exhaust volume from the exhaust manifold. This has got me thinking yet again on the benefits of a wastegate-priority exhaust manifold coupled to a wastegate with a large (44 mm+) diameter diaphram and a tiny, tiny turbine housing. The exhaust wheel should be of a just large enough diameter to be able to spin the compressor wheel effectively without the need for excessive exhaust manifold pressure, thereby less backpressure/reversion and more horsepower. The compressor wheel would be taylored to the specific need for the most HP/Psi and midrange power. Compressor surge due to the earlier spool-up could be delt with via a ported shroud compressor cover with great sound effects as a bi-product.

Do you guys see any flaws that I am missing?

 

and why wouldnt the turbo manufactrers pick this up?

 

You are missing one important detail, the exhaust turbine needs energy to make boost from the compressor side. Where does the energy come from? Heat, pressure and MASS FLOW across the turbine wheel.

If you reduce either of the three, you have to increase one of the other two to continue making boost pressure. If you decrease the mass flow rate thru the turbine wheel (smaller turbine wheel and housing) you MUST increase the exhaust pressure or heat differential to continue making the same boost pressure. Temperature differential has to do with the turbine efficiency. I guess if you could find a 100% efficient isentropic turbine, you could get a little ways with this theory. Unfortunately, the best turbines come in around 75% thermal efficiency.

So the only place left to really regain that lost power is thru increasing the exhaust back pressure. This reduces engine VE.

From my own personal experience, here is how it works out.

Too little turbine wheel (or housing): The turbo will make all kinds of boost and spool fast but won't make that great of power. Exhaust backpressure will be very high but boost pressure will never really fall off.

Too much turbine wheel (or exhaust housing): Turbo is laggy with poor transient response. Exhaust back pressure can be very low, but the turbo will not hold boost very well. There basically isn't enough exhaust pressure or mass flow for the turbine to draw enough energy from. This type of turbo will make great HP numbers for a given boost level but may have difficulty reaching high boost levels.

Just the right amount of turbine: Turbo is responsive for it's given size. Exhaust back pressure is higher then the too large turbine, but is not considerably higher then the boost pressure. If the turbo drops boost, it's because it's out of compressor wheel flow. This turbo will make excellent power at any boost, but will also be able to run very high boost levels if the compressor wheel can support it.

 

i started a topic on this yesterday

 

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<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b16hybridsol &raquo;</TD></TR><TR><TD CLASS="quote">i started a topic on this yesterday </TD></TR></TABLE>
Oh ****! I knew I shoulda searched before posting. Fu-ku-i-n-gu n00b mistake.


I think I can grasp the concept that the turbine need energy applied to it to be able to spin the compressor wheel, and that energy could be chocked off when running a too small turbine wheel and/or housing. The turbine gets more energy applied to it by the pressure differential, heat differential and mass flow - sounds right.

 

your thread is getting more action than mine tho, so i'll throw what i had to say in here

My thought is, why not use the small ar housing with a dual large gate setup for better all around power. With a smaller ar housing you are going to get a faster spooling turbo. Now once you reach your desired boost level the gates open and the majority of the exhaust gasses can flow freely through the gates to limit the backpressure in the manifold and thus still allowing the motor to hold/ make power, because with the smaller housing and smaller wheel it will take less exhaust gas to keep it at the desired boost level.

i think a larger ar housing with a smaller trim wheel would also be more prone to reversion issues then a smaller ar housing with a big wheel. Because with a larger housing you'll have less velocity than a smaller housing

another thought with the smaller ar bigger wheel setup... a bigger wheel will carry more inertia, so it will take less flow to remain at your desired pressure.

P.S. if you guys haven't picked up on it yet the idea behind my thread came from the t3/t67 h.o. vs. the T4 combination housing guys. there was a thread up the other day of a car making 750whp on the t3/t67 h.o. setup which way more than enough for a street car, but its still got a very good spool time