What are the differences?

[2toneNV]

I see when looking at turbos there is the .63 and the .85 A/R, what does this describe and what are the major differences and is there a better one for a stock motor? How about a TA60

 

[budget_crx]

A/R is the ratio that determines gas velocity from the turbo. It is the Area (A) of a section of the compressor divided by the Radius (R) of that section from the shaft. A larger A/R (in this case .85) has a higher flow rate, while a smaller A/R (.63) will keep the gas's velocity higher. So its a trade off on a quicker spool or more flow. Hope this illustration helps, its the best i could find

 

[2toneNV]

I appreciate the engineering explanation. I am still wondering if you want a high 10 to mid 11 sec. car which one is better? Also, I was looking on Precision's site and there are alot of combos. Which of these turbos would you go for: TA53, 54, 52, PT61-T350-E, PT52, 53 or 54?

 

[XxDarkSidexX]

I think it really isn't a matter of worse or better, but what application(.63 or .85) will work best for your motor. The bigger the ex. housing the more lag there will be. So if you take into account for example a dual ball bearing VS a single journal bearing, the dbb could handle an .85 housing with not to bad of lag. But on the non ball bearing, the journal brass bearing turbos, .63 would be a better choice because it takes longer to spool a non ball bearing. So a smaller ex housing would give you quicker spool. I hope this helps.

Also gear raitos, exhaust system, heads, cam, tire size. These all have an effect on turbo lag too.

but yes that was good info to start

 

[RUQWKNF]

Here's a little more info.
With regards to which A/R is better for say a low 11 to high 10 second car, here's my take on it. If you have a car that does not have cam, heads or intake, but just a large turbo (PT6176E through T64E) then the .63 A/R would be advised due to quicker spool up needed to help reach your ET. But if you used the same models of turbos on a built 109 motor that is a lot more efficient due to free flowing heads, nice sized cam, ported and matched intake, larger t-body and plenum, you could run the .85 A/R housing. One thing to remember, on non ball bearing turbos, when you go from a .63 to a .85 on these size turbos, your stall speed requirements will go up. The small shaft P-trim turbos such as your 6176 and the 6776 journal bearing turbos like to see a converter that can flash stall to 3400, in order to have some really snappy acceleration from a punch.

The large shaft P trim equipped turbos, these being the T63E (TE-45), T64E (TE-45a), PT6876H, PT7076H like to have a flash stall of around 3500-3600, especially with the journal bearing versions. The larger shaft of the P-trim turbine wheel, does add some rotating mass to the rotating assembly. This is also true when going from a TE-44 - PT6152 sized turbo and graduating up to a PT70 GT-Q. It's a night and day difference in rotating mass. Where as before your 3200 stall converter would spool those smaller turbos up just fine, it's no where near enough to spool up a monster 7080H.

It's when you add the dual ball bearing cartridge that these general rules get thrown out the window. In which case, lets say you have a dual ball bearing PT6776RS turbo but you only 1/8 race and you want the quickest spool up period. Then you should opt for the .63 A/R. If you had the same turbo but raced at a 1/4 mile track and you want to be able to get close to making 700 rwhp, then definitely opt for the .85 housing. Where as before this turbo with journal bearings, needed a converter that would flash stall to 3400, now, you might get away with only needing 3000-3200 flash stall. Here is some good reading material from Garrett's site that talks about not only turbine housing A/Rs, but also compressor cover A/Rs. Scroll down about 1/3rds the way down the screen.
TurboByGarrett.com - Turbo Tech102

And for the advanced Jedis in training...
TurboByGarrett.com - Turbo Tech103

With my personal car I run a .63 A/R ratio, eventually, I step up to a 6776RH turbo and will still keep a .63 A/R turbine housing, even with my goals of low 11s. In the old days, we used to tell people, once you get into the mid to high 10s with a full weight Turbo Buick (625-650 fwhp range) is where you will see some significant gains from a .85 A/R housing. This is only relevant to 231-235 CI V6s and not for 240+ CI motors. Once you go stroker or Stage II, the .63 housing can become a restriction, or cause back pressure to rise. This is where having a back pressure gauge setup will tell you if the turbine housing is a problem or not. I would not recommend running a .63 A/R housing on a 270+ CI V6. Makes no sense melting your headers off the motor.
Steve10.flv - Video - Photobucket - Video and Image Hosting
Not saying that is his problem, just using the video as an example of how our headers glow when making serious power. The Buick starts walking at 1:20 and you can see the headers at 1:22.
Hope some of this helps and sorry to ramble.

Patrick

 

[XxDarkSidexX]

Yea i heard your not making enough power until you can lit a cig off your dp


listen to pat he's turbo nutz!