When calculating a/r on a divided vs an undivided turbine housing, will a smaller undivided housing be "bigger" and a divided housing.

Say a .91 divided housing vs a .88 undivided.

Basically is the divide figured into the volume of the housing? Or is the calculation based on open air in each volute?

Jerod

 

the volume is based upon the overall size of the volute. Divided housings don't have the divided sectioning run along the entire volute size. Only the Garrett Ni-Resist, Borg-Warner EFR series, and Mitsubishi OEM volutes follow along the entire volute of the housing.

A .91 Divided housing uses a larger volute than the .88A/R undivided volute.

Standard Divided Housing (not a twin scroll)



true Twin scroll internal volute -Garrett Ni-Resist


MHI Twin Scroll Evo X volute


EFR Twin scroll complete volute

 

I think I follow. I'm comparing a shelf s366/73 .91 divided housing to a .88 divided housing. Since there is a divide this essentially take a away from the .91 (based on area of the divide) meaning essentially the .88 and .91/are nearly similar in volume/size?

 

No, one is clearly larger than the other. you don't "recalculate" when taking the first inch of divider out of the housing. It looks to the whole area/ratio of the volute. .88A/R is still .88A/R, as .91A/R is to .91A/R.

Bottom line, larger volute, more exhaust volume, less backpressure, more lag, but higher shifted top end power.

 

I spoke with a BW rep today and it was explained in the S series line that a divided .91 is roughly equivilant to an undivided .88. The divide is not taken into consideration of air volume. Rather entire inside volume is calculated. Meaning on the S series line the volume of the divide should be subtracted... Now the way he explained it, this is for the S series line. Not all manufacturers...

 

I've used BW for years. It still will respond differently. You can split the numbers anyway you'd like.

 

FP claims comparing undivided to divided is apples to oranges. The flow of a divided compared to a divided is .80*divided a/r. This is exactly what BW told me.

 

Well. At least now your question has been answered.

 

In terms of flow there's a tiny difference but it's nothing life changing.

The bigger the aspect ratio the bigger the volute regardless if the housing is dividedor undivided. The onlyexception to that is if you are comparing turbine housings belonging to two different wheel families... I.e. Garrett t3 to Garrett t4. If you were comparing those two families housings with the aspect ratio the t4 housing would be larger. This is mostly due to the change in housing centerline between the two.