Pros and cons to diff. turbine housings...

[LTUSPE]

What are the different pros and cons to 7cm and 8cm turbine housings on turbos? Specifically for the FP Green, as that is probably the next turbo I am going to get with my tax refund. I'm not just looking for 'it flows more'....

Thanx,

Justin
'99GSX

 

[2gTurboS]

More lag the bigger you go, I know that much.

 

[2-0turbo]

Originally posted by LTUSPE
What are the different pros and cons to 7cm and 8cm turbine housings on turbos? Specifically for the FP Green, as that is probably the next turbo I am going to get with my tax refund. I'm not just looking for 'it flows more'....

Thanx,

Justin
'99GSX

Justin, well basically the larger turbine housings just flow more. :laugh: No really, they do. In Mitsubishi turbos, the 7/8 cm spec gives the AR ratio: Area/radius ratio. On garrett turbos, this is stated in a decimal like .48, .63, .8X, 1.08 (going from memory here). The R (radius) is somewhat fixed by whatever turbine housing family you choose (T3 for example). As that number gets larger, the area gets larger for a relatively fixed radius. Simply put, it flows more. The larger area is going to represent less back pressure. It also means the velocity of the exhaust gases are lower, so they don't have as much "push" on the "pinwheel" of your turbine.

In real life, larger exhaust housings (8,9, 10 CM and 1.08, 1.15) are going to flow more air and spool later. But, they usually make more top end power. Those Supras that you see with the big single turbos that make 800 HP...they are using turbos with large AR ratios. The boost comes on real strong between 4500 and 5500 (depending on a ton of factors) and they run like the wind up top. Turbos are not a free lunch. They are a compromise and like a camshaft, must be chosen for a range of performance you feel is important to you. If you pick a low AR, it makes boost at low RPM's but that turbine wheel/housing becomes a cork to flow at higher RPM's.

Pick smaller turbine housings and lower AR's for quicker spool at the expense of top end power. Pick larger turbine housings and higher AR ratios for more top end power when lag is less important.

 

[LTUSPE]

Thanks Matt, that's pretty much what I'm looking for. Seeing how I'm AWD, lag really isn't much of an issue because I can pull on most people leaving the line anyway. I know there are some on here that'll tell me to get the biggest exhaust housing and just use the naaaaawwwwwwwwws to spool it.... ;-P

 

[candela]

A/R =The Area / Radius ratio
A = Area of throat at intake
R = radius of scroll in the housing of either the compressor or exhaust turbine

TRIM -turbine wheel trim can effect an increase or decrease in turbine pressure for a given housing A/R





Well in any case really, or most I should say, greens are cool with 7cm housings. you can always port it out really nicely if you desire. But the green is simply a awesome turbo, one of the best hybrids in my opinion. People have had lots of luck with them in the past and have run 10s with them also. Not saying you will but the 7cm housing is a better choice for a street driven car if you ask me. 7cm housings are used on most all hybrids and when ported is just fine in most cases.


Austin

 

[candela]

A/R =The Area / Radius ratio
A = Area of throat at intake
R = radius of scroll in the housing of either the compressor or exhaust turbine
This is measured from the cneter of the inlet
TRIM -turbine wheel trim can effect an increase or decrease in turbine pressure for a given housing A/R





Well in any case really, or most I should say, greens are cool with 7cm housings. you can always port it out really nicely if you desire. But the green is simply a awesome turbo, one of the best hybrids in my opinion. People have had lots of luck with them in the past and have run 10s with them also. Not saying you will but the 7cm housing is a better choice for a street driven car if you ask me. 7cm housings are used on most all hybrids and when ported is just fine in most cases.


Austin