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Discussion Starter #1
So after riding in my buddies turbo car with On3's 67mm(81 A/R) ceramic ball bearing turbo, I'm thinking of swapping my Precision 70mm(96 A/R) journal bearing turbo in favor of the On3 one this winter. I really love the "insta-spool" power that his car has. Anyone have any better recommendations? Anyone have a rough idea of what my Precision is worth(only has about 3000 miles on it since bought new)?
 

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Keep the precision and put a smaller exhaust housing on it. At your HP level a .68 will be fine and spool a lot faster then the .96
 

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Discussion Starter #3
Keep the precision and put a smaller exhaust housing on it. At your HP level a .68 will be fine and spool a lot faster then the .96
At my current power level, wouldn't a .68 be a little out of its efficiency range? Any idea what a smaller exhaust housing costs, roughly?
 

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Not really. On my old combo I ran a PT6776 at 12lbs with a .68 housing. Made 520 RWHP and 540 RWTQ. The thing spooled soooooo fast! You could also go with a .81 housing as well if you are worried about it.

As far as price they should not cost to much.
 

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I'm running 600-700 with a .68 ar housing. That being said the change from .96 to .81 to .68 is not that big I tested all 3 on my car on the dyno. Going from .96 to .81 spool changed maybe 50-100rpms and then another 100 rpms going to the .68. For an over all increase in around 200rpms, barely noticeable, power and tq had no change this was reving to 7k rpms. You dont have to go smaller if you go efficient ditch the cast wheel precision, I had a cast wheel 67 precision and it was very lazy. Get a billet wheel turbo and you will spool 1000 rpms sooner and you get instant boost repsonse when you hit the throttle no other changes and if you want the best repsonse you can get go ball bearing as well. I started with a cast wheel 67 precision and went to a Comp billet wheel 70mm tripple ceramic bb and it was night and day difference. I went from not making any boost till 2500rpms to making full boost by 2500rpms.
 

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The a/r of the turbine housing means nothing in terms of how much power the turbo will support. The turbine inducer wheel is what determines that
 

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Discussion Starter #8
So is it just the exhaust housing itself I'd have to change for a quicker spool?
 

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The a/r of the turbine housing means nothing in terms of how much power the turbo will support. The turbine inducer wheel is what determines that
That's not all true,at some point the exhaust housing becomes a restriction causing in decreased power output or over spooling the turbo out of its efficiency range.
 

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That's not all true,at some point the exhaust housing becomes a restriction causing in decreased power output or over spooling the turbo out of its efficiency range.
That is true if we're talking about huge T6 turbos and over 1000hp capability. But for a smaller turbo with a T4 housing and less hp, the housing won't be a restriction
 

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I agree on a t4 turbo on a motor that displaces 5 liters or less you can run any ar size doesnt really matter your not going to hurt power production so imho I run the smallest one to ge the best response. I saw no power loss at 650-700rwhp reving to 7k rpms going from .96 to .68 I decided to test it myself rather than just agree with what people posted on the internet about it. Everyone swore I needed a .96 and I would hurt power...

Like I mentioned the change in reponse/spool is only a few hundred rpm so not gonna matter on a track car but if you want lower boost threshold on the street get the smaller ar.

Its around $150-200 for a turbine housing so the swap on just that isnt really worth it if you want better repsonse and spool get a better turbo get a billet wheel that flows 15-20% more at the same size wheel. And get bb. then spec out the ar size etc when your order it.
 
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