Effects of secondary sizing

White Knight

White Knight

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Aug 18, 2007
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I'm curious how the size of the secondary turbo in a set of twins effects all out performance. Considering everything else remains the same, does a larger compressor wheel on the secondary make any more power? For example, consider an s480/96-1.32 primary, and the same 71mm turbine exducer in a .80 housing with a 50mm wastegate on the s300 based secondary on the same mid 700hp fueled truck. Which secondary compressor size would make the most power? Drive the best?

I've heard that keeping secondary compressor inducers between 70 and 75% of the primaries inducer size provides the best results but have never seen this discussed. Is there any fact to this?
:charger:
 
I forgot to add would there be a noticeable difference by stepping up from 62mm to a 64 or a 66?


Besides being a restriction I'm not sure how a larger secondary would increase power. As I understand it, when under boost the secondary turbo just increases the pressure of the flow of air from the primary. But that's just my logic
 
no experience but one would think that the housings and wheels choosen would depend on the application

drag race vs sled pull

take it this is not going to see the street at all, right?

i am also curious about twin combinations

so thanks for starting the thread

don
 
Back when I was running a K31 primary, I tried a couple of different top chargers. Bell WSB, Dodgezilla, 62/65/.7 and .8, 62/71/.8, and a 64/71/.8, 13ss, and 16ss. Alot of difference.
 
Depends on what you're doing with the truck...

for a DD, I'd rather crutch a set of towing twins to make big numbers than crutch race twins to tow.

I prefer a smaller secondary for good spool and throttle response, but ported & gated enough to exhaust everything the primary compressor can supply at max power.

An imperfect analogy to old school SI engines is the difference between spread-bore & square bore carbs.
 
White Knight said:
I'm not sure how a larger secondary would increase power. As I understand it, when under boost the secondary turbo just increases the pressure of the flow of air from the primary.
Click to expand...

A larger secondary can move more air, which makes more power (assuming enough fuel), and while it is true that the secondary just operates at it's compressor map's relevant pressure ratio, generally speaking a smaller compressor produces more expansion boost compared to a larger one at a particular CFM flow rate.

Quality boost (cool pressure) makes more power.

Of course, the difference isn't nearly as much during "normal" driving conditions, when boost isn't very high.
 
XLR8R said:
Depends on what you're doing with the truck...

for a DD, I'd rather crutch a set of towing twins to make big numbers than crutch race twins to tow.

I prefer a smaller secondary for good spool and throttle response, but ported & gated enough to exhaust everything the primary compressor can supply at max power.

An imperfect analogy to old school SI engines is the difference between spread-bore & square bore carbs.
Click to expand...

X2

I've been trying to figure out how to make my 62/71/13SS over S480 tow nicely with a tight TC, and 3.55's...just not enough air in OD at towing speeds. So, I'll probably rebuild them with a couple ball bearing chargers I have, 60mm and 80mm maybe:D

Chris
 
Good topic. I think I'm ok for towing though. Will have to hook up to a trailer to see. On the highway unloaded I run 5-6psi boost @ 70mph. No heat issues in town or on the dyno.
 
Get a 64/65/13....or 62/65/13 even...

IdahoCTD will get on this one soon to explain.
 
RonA said:
Back when I was running a K31 primary, I tried a couple of different top chargers. Bell WSB, Dodgezilla, 62/65/.7 and .8, 62/71/.8, and a 64/71/.8, 13ss, and 16ss. Alot of difference.
Click to expand...


Can you elaborate some more on what you liked and didn't.

I'm really curious about the difference between the 62/71 and 64/71.

Sometimes I think about upgrading to a 64/71, but I think it would be smarter to switch my primary to a S480 or GT80 or bb garrett if my budget allows.
 
80mm is little big for a 60-62mm on a DD/towing... more toward the race or competion side of the road.
doable yes...
75mm would be better and easier to make work smoothly with said small turbo.
 
Signature600 said:
X2

I've been trying to figure out how to make my 62/71/13SS over S480 tow nicely with a tight TC, and 3.55's...just not enough air in OD at towing speeds. So, I'll probably rebuild them with a couple ball bearing chargers I have, 60mm and 80mm maybe:D

Chris
Click to expand...


Curious how a tight convertor makes a difference when your in OD. Aren't you usually locked up?
 
bsmith said:
Can you elaborate some more on what you liked and didn't.

I'm really curious about the difference between the 62/71 and 64/71.

Sometimes I think about upgrading to a 64/71, but I think it would be smarter to switch my primary to a S480 or GT80 or bb garrett if my budget allows.
Click to expand...

I loved the k31 with the 62/71/.8. I swapped in the 64/71/16 and picked up 40hp on top with only a fraction of a second slower spooling. I have been running the 64 ever since, but have gone through more primaries than I like to think about. I am currently running a GT4788 primary. It tows well with the 64/71/16ss, but i can't tow in OD locked(not enough rpm). Tows fine in the flats unlocked in od. In the hills I run 3rd locked. No problems or egt issues. 13mm p-pump Mach 7 injectors.
 
malibu795 said:
80mm is little big for a 60-62mm on a DD/towing... more toward the race or competion side of the road.
doable yes...
75mm would be better and easier to make work smoothly with said small turbo.
Click to expand...

What about the 3rd gen guys? I see lots of 62/71/13ss over S480 setups.
 
bsmith said:
What about the 3rd gen guys? I see lots of 62/71/13ss over S480 setups.
Click to expand...

haveing the tunability of the CR over mechnical, adjustable pulse width, timing etc makes it alot easier

if it was a choice between a 60 or a 62... i would go with the 62
 
malibu795 said:
haveing the tunability of the CR over mechnical, adjustable pulse width, timing etc makes it alot easier

if it was a choice between a 60 or a 62... i would go with the 62
Click to expand...

I have a 62/71/13ss over S475 already that I like, just want more.
 
zstroken said:
Curious how a tight convertor makes a difference when your in OD. Aren't you usually locked up?
Click to expand...

I meant for spool up issues...once we're moving she don't do bad, but at 1750 cruising in OD locked, it doesn't like towing!

Chris
 
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