b16hybridsol

Which is better for a streetable setup and why. and just for sake of starting this off i'll give my thoughts on it.

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.

(edited had example setups but i think the discussion will go further without them)


Modified by b16hybridsol at 9:33 PM 1/9/2006

Tony the Tiger

Although turbine housing does greatly affect the amount of exhaust gases it can flow through, don't forget that the turbine wheel causes the majority of the restriction as well. With turbos, there are so many combinations that only testing is the best way to find the a good combo.

In some cases, it is probably better to step down to a smaller turbine wheel but run a larger A/R turbine housing to gain both spool and better top-end. Or perhaps increase the turbine wheel size to gain flow through the wheel, but reduce the turbine a/r to allow more exhaust gases to hit the blades sooner. It's all about finding the perfect balance and finding the perfect powerband for each application. We've seen that the GT28RS with T3-drop-in is a perfect example of using a larger A/R housing but using a relatively small turbine wheel to gain both spool and top-end. There are also examples of factory turbo upgrades which consist of modifying the turbine wheels to gain more flow at high RPM but they still using the same turbine housings.

Using a larger wastegate or dual WG's to allow more exhaust flow sounds like a plan, but if the turbo is indeed correctly sized, it will most likely need all the exhaust from the engine to maintain that boost at redline. If the turbo can hold ie: 10 PSI all the way up the redline but still have 50+% of the exhaust going through the WG, it is a sign that the turbo is way too big for the appplication. If the turbo is so big anyway, why bother working around a flawed combo to gain something that can be achieved as easily as getting a smaller turbo that suits the specific power level?

Teglove2

Very well said Tony.........Chad my thoughts on the matter are simple. The dual gates are a great idea no doubt and that sounds like it should be employed but like Tony said it just sounds like trying to correct a problem but no going to the source being the small a/r. Even though you are venting a lot of that exhaust threw the wg's after desired boost the smaller housings still offer more backpressure before given boost pressure is reached vs a larger a/r. If there is really a backpressure problem then the turbo sizing was done unintelligently. Most of the time it is better to upgrade to next size a/r than stuff a "larger trim" wheel into that housing due to the larger a/r offering the exhaust gasses to expand and impinge on the wheel. Large trim small a/r housing have been found to lose efficiency points by doing so and is usually advised to run the next size housing to solve the spool up issue and gain top end. Also, the added "flow" of the larger a/r is also going to give the turbine more "torque" as I like to call it, to drive the compressor wheel. The larger a/r turbos just seem to "HIT" so much harder and offer less reversion in the chamber which if not tuned properly can cause detonation. Not sure if I answered all ?'s the best.......with the cars I've built and tested those seem to be the most pleasing way to go.
Ryan
Not to mention dual gate setups tend to cost just a little more......

b16hybridsol

wouldn't a larger ar housing with a smaller trim wheel be more prone to reversion issues then a smaller ar housing with a big wheel. Because with a larger housing you have less velocity then a smaller housing

and the dual gate setup isn't much more expensive than a single big gate. but i think it would be geared more toward the divided tang setups

b16hybridsol

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 this 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

Teglove2

Most of the time we are debating/discussing on here about stuff like this. What books say and what real life dictates are always contradicting.....if you haven't noticed. I don't know if this contradicts what I said earlier(its late) but yes it is always better to put a larger a/r and a smaller trim wheel to solve spool up time. And yes, it is usually better to put a larger trim wheel in instead of a bigger wheel and lose a couple of points of efficiency rather than putting a larger wheel in and gain more lag causing inertia! Right on the $ mang! Trial and error Chad! Hows your car anyawys?
Hit me up whenever we gotta talk!
Ryan