turbo upgrade?

[60GT]

I'm looking to upgrade my turbo as I will be putting an aluminator in this spring, I am looking at the precision billet wheel turbos, specifically the 7675, my question is do I go for the .81 AR or the .96AR, I will probably not be spinning the engine passed 6500. If I understand AR correctly, in simplest of terms that relates to the spool time Vs. volume of air it is pushing. If this is totally wrong its cause I honestly dont know what I am doing when it comes to turbos . If you have any other suggestions feel free to share, I like the precision because I have been hearing a lot of good stuff about them. Planing on keeping the stock heads and cam for know.

 

[JeremyH]

What is your power goal and is a street or drag car?

 

[60GT]

mid 500's pump, mid 700's race gas, street/strip more street.

 

[SteveP]

i'm running the precision 67 billet wheel on the hellion system and i'm 657rwhp. will be 720ish when i do the fuel system.

 

[60GT]

I have a feeling i didn't need to go that big, but when i was looking at the compressor maps for a t76 it put me at like a 80%, the smaller ones I would have been hitting the surge limit. I think I need to call precision and have them send me a few compressor maps because I think there shit is way different.

 

[60GT]

steve, is that the 6765 or the 6768 and whats the A/R on that?

 

[JeremyH]

Precision doesnt advertise their maps for the billet wheel turbo but believe me they are around 20-25% more efficient. In easy to understand terms a 65mm billet turbo will make power like a 70 but spool like a 60mm.

Street or drag car?

 

[60GT]

ok, that sounds about right lightblade, Its def. a street car that will be seeing some track days this year, but for all purposes assume its a pure street car.

 

[JeremyH]

I would go with the precision billet 6765 or comp billet 6765 with a .81 ar.

Info on ar size

Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.
Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.
When deciding between A/R options, be realistic with the intended vehicle use and use the A/R to bias the performance toward the desired powerband characteristic.

 

[Nickoli]

I strongly recommend Precision. I went from a master power 70mm to a Precision 76 and it was like night and day. If I were you I would go with the 76 now since we all know you will want more one day and the 76 will take you as far as you will ever want.

 

[60GT]

Thanks , appreciate all the info, that looks like the root I will be taking.

 

[Bobby]

have you considered comp turbo. i think it is the best.

 

[CPRsm]

I'd do a 67/66. Their new turbines are showing power and spool gains. You'll close on maxing the turbo at 700rwhp.
I haven't had a chance to try a Comp yet, though heard good things. I can get ya a Precision if you go that way.

 

[ChiDiddy]

have you considered comp turbo. i think it is the best.

They are very good turbos also. And dont forget Borg Warner

 

[Bobby]

No compairson.

 

[Thekid760]

what nake them so much better than borg warner and precision?

 

[Nickoli]

Look at bullseye also...

 

[Bobby]

They have some new technology the others don't. I would rate the up there with precision but not borgwarner or bullseye