USDM Single Scroll vs. JDM Twin Scroll Setup

ShinobiDGM · 03-09-2008, 03:20 PM

I'm not sure where to post this thread exactly, so if this is in the wrong section, I apologize in advance and request to have this moved to the correct one....

I'm new to the turbocharged boxer community so in my quest to learn more about this wonderful technology, I've looked at the other threads (via notice) regarding the differences between the EJ20 and EJ25's stock turbo setup and all of them seem to say that the twin scroll is the superior of the two (if not by much).... However, within the threads I've looked into, I could not find any advantages that the Single Scroll setup has over the Twin Scroll besides less moving parts and complexity/price... I'd imagine that if a twin scroll turbo was used on the EJ25, then the "off the factory" performance of the 08 STi would be noticeably better... Am I right to assume this? Are there any other reasons why EU/US STi's use the single scroll setup on their 2.5L's?

**Turninconcepts.com** · 03-09-2008, 04:45 PM

The performance is about the same. We changed over to a vf37 twin scroll setup on our 04 sti after the vf39 cracked and was dead. Power wise is the same as any other stock size turbo that comes on the sti's. Transition over boost threshold is smoother, but other than that it is about the same.

IMO, it's not worth the amount of money you would spend on it. You need to change the headers, UP, turbo, and DP. That normally sells for 2000-2500 and would give you pretty much the same results as just tuning your stock setup.

Tony

ShinobiDGM · 03-09-2008, 06:51 PM

Sounds like a lot of work... and I agree with you about the change being a waste of money just to make the same power...

I guess contemplating on why we get a single scroll over a twin scroll when the performance is almost indistinguishable is futile.... Thank you for your insight ^.^

tshrey · 03-10-2008, 04:49 AM

If you have the 2.0 liter (JDM), the twin scroll helps with spool. The size of the stock USDM STI turbo along with the larger 2.5 liter motor makes the twin scroll less important.

speedball3 · 03-18-2008, 08:14 AM

Quote:

Originally Posted by tshrey

If you have the 2.0 liter (JDM), the twin scroll helps with spool. The size of the stock USDM STI turbo along with the larger 2.5 liter motor makes the twin scroll less important.

So does this mean that if Subaru decided to give the USDM a twin scroll, they could increase the turbo size and "easily" up the power of the STI while maintaining similar power delivery?

**Turninconcepts.com** · 03-18-2008, 01:06 PM

Yes, but at an increased cost. The twin scroll setup is more complicated to manufacture.

03-09-2008, 03:20 PM	#1
ShinobiDGM Junior STI Driver Car: DGM GRB STi Fav Mod: My broadway mirror Location: CA Posts: 161 Join Date: Feb 2008 Trader Rating: (0)	USDM Single Scroll vs. JDM Twin Scroll Setup I'm not sure where to post this thread exactly, so if this is in the wrong section, I apologize in advance and request to have this moved to the correct one.... I'm new to the turbocharged boxer community so in my quest to learn more about this wonderful technology, I've looked at the other threads (via notice) regarding the differences between the EJ20 and EJ25's stock turbo setup and all of them seem to say that the twin scroll is the superior of the two (if not by much).... However, within the threads I've looked into, I could not find any advantages that the Single Scroll setup has over the Twin Scroll besides less moving parts and complexity/price... I'd imagine that if a twin scroll turbo was used on the EJ25, then the "off the factory" performance of the 08 STi would be noticeably better... Am I right to assume this? Are there any other reasons why EU/US STi's use the single scroll setup on their 2.5L's? This ad is not endorsed by this member. Please register or login to hide this ad.

03-09-2008, 04:45 PM	#2
Turninconcepts.com Authorized Vendor Posts: 4,748 Join Date: Jul 2003 Trader Rating: (50)	Re: USDM Single Scroll vs. JDM Twin Scroll Setup The performance is about the same. We changed over to a vf37 twin scroll setup on our 04 sti after the vf39 cracked and was dead. Power wise is the same as any other stock size turbo that comes on the sti's. Transition over boost threshold is smoother, but other than that it is about the same. IMO, it's not worth the amount of money you would spend on it. You need to change the headers, UP, turbo, and DP. That normally sells for 2000-2500 and would give you pretty much the same results as just tuning your stock setup. Tony

03-09-2008, 06:51 PM	#3
ShinobiDGM Junior STI Driver Car: DGM GRB STi Fav Mod: My broadway mirror Location: CA Posts: 161 Join Date: Feb 2008 Trader Rating: (0)	Re: USDM Single Scroll vs. JDM Twin Scroll Setup Sounds like a lot of work... and I agree with you about the change being a waste of money just to make the same power... I guess contemplating on why we get a single scroll over a twin scroll when the performance is almost indistinguishable is futile.... Thank you for your insight ^.^

03-10-2008, 04:49 AM	#4
tshrey STI Driver Car: 08 STI Fav Mod: Removing the window sticker Location: Underground Atom Smasher Posts: 218 Join Date: Feb 2007 Trader Rating: (0)	Re: USDM Single Scroll vs. JDM Twin Scroll Setup If you have the 2.0 liter (JDM), the twin scroll helps with spool. The size of the stock USDM STI turbo along with the larger 2.5 liter motor makes the twin scroll less important.

03-18-2008, 01:06 PM	#6
Turninconcepts.com Authorized Vendor Posts: 4,748 Join Date: Jul 2003 Trader Rating: (50)	Re: USDM Single Scroll vs. JDM Twin Scroll Setup Yes, but at an increased cost. The twin scroll setup is more complicated to manufacture. This ad is not endorsed by this member. Please register or login to hide this ad.