3" downpipe - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


DIY Turbo Discussion greddy on a 1.8? homebrew kit?

Reply
 
 
 
LinkBack Thread Tools
Old 03-24-2008, 12:02 PM   #1
Newb
Thread Starter
 
Join Date: Jun 2007
Location: Vienna VA
Posts: 38
Total Cats: 0
Default 3" downpipe

So my parts collecting is going nicely and I finally have a Begi/ DP combo to mount my SR20 T28 on. However looking at this DP (2.25" outlet), I want to fab up something bigger, like 3" directly out of the turbo. The car is an 02 SE. Right now I'm trying to figure out how much clearance I have to play with between the turbo outlet and the "shelf" and trying to see how in the world to design this piece in such a cramped space. I'm thinking I may have to settle for 2.5" out and flare up to 3" later downstream. Just wondering what you guys have done and any pictures would be great. Thanks!
rcc-miata is offline   Reply With Quote
Old 03-24-2008, 12:06 PM   #2
Elite Member
iTrader: (13)
 
cjernigan's Avatar
 
Join Date: Oct 2006
Location: Atlanta, GA
Posts: 8,147
Total Cats: 6
Default

Y8s did exactly that. Flared it out like 8" after the turbo using a smooth transition piece. You could cut the end off your begi pipe and weld on a 3" transition. That wouldn't be all that bad.
cjernigan is offline   Reply With Quote
Old 03-24-2008, 12:21 PM   #3
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,908
Total Cats: 1,793
Default

its pretty common practice to match the turbine exit and then slowly step up teh exhaust.

for example, my outlet is 2.25", then steps to 2.75" then 3"
Braineack is online now   Reply With Quote
Old 03-24-2008, 12:29 PM   #4
Elite Member
iTrader: (5)
 
m2cupcar's Avatar
 
Join Date: Jan 2005
Location: Atlanta
Posts: 7,247
Total Cats: 291
Default

yep - in theory a gradual transition from the turbine outlet size to the dp size is best for flow.
m2cupcar is online now   Reply With Quote
Old 03-24-2008, 12:37 PM   #5
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,908
Total Cats: 1,793
Default

here, ive posted about it before:

The goal is flow; you want to keep the exhaust gases moving. A rapid decrease in temperature or rapid expansion and turbulence should cause the gases to slow. Starting with a matching port will keep the temps high and exhaust moving, as the exhaust cools the second it leaves the cylinder. This is also why we don't tend to port the exhaust on the head, but we do port the intake. Again, to keep the exhaust moving. It's really all a compromise. Throwing the 3" pipe on a 2" turbine outlet will cause both turbulence and a rapid decrease in EGTs, slowing the flow. But if you keep the exhaust moving out of the turbo with a matching port size the back pressure should drop more, since the area behind the turbo wants to keep moving rapidly into the stepped exhaust.
Braineack is online now   Reply With Quote
Old 03-24-2008, 01:19 PM   #6
Elite Member
iTrader: (21)
 
paul's Avatar
 
Join Date: Jun 2006
Location: Point Pleasant, NJ
Posts: 2,957
Total Cats: 2
Default

bell mouth 3" FTMFW!!! a la Turbo Tim






i got your turbulence right here... hangin
paul is offline   Reply With Quote
Old 03-24-2008, 01:34 PM   #7
Newb
Thread Starter
 
Join Date: Jun 2007
Location: Vienna VA
Posts: 38
Total Cats: 0
Default

Whoa! Sexy!! now that's what I'm thinkin. I'm not sure I've got the clearnace for that though. Once I get the turbo/ manifold mounted, I'll do some test fitting to see what works.
rcc-miata is offline   Reply With Quote
Old 03-24-2008, 02:07 PM   #8
y8s
2 Props,3 Dildos,& 1 Cat
iTrader: (8)
 
y8s's Avatar
 
Join Date: Jun 2005
Location: Fake Virginia
Posts: 19,038
Total Cats: 407
Default

you can measure the diam of the outlet and get a transition piece to go directly from that to 3" and that's going to be the best bet. The bellmouth is OK but you'd have (slightly?) better results to divde the wastegate portion out. somewhere someone posted that 11 degrees divergent angle is the optimum but i can't back that up with any data. maybe corky can jump in here.

anyway, chances are you'll be more limited by the angles of reducers available more than anything else. I picked up a 2 to 3" and cut it where the diameter matched the turbine exit.

anyway like chad said, i did the expansion a bit after the turbo because there was just no space to fit it with my turbo placement.

y8s is offline   Reply With Quote
Old 03-24-2008, 04:17 PM   #9
I'm Miserable!
iTrader: (5)
 
Join Date: Sep 2005
Location: SLC, Utah
Posts: 1,591
Total Cats: 0
Default

my next downpipe will be v-band, looks so much easier to take off when you need to.
zoom2zoom is offline   Reply With Quote
Old 03-24-2008, 10:58 PM   #10
Senior Member
iTrader: (2)
 
Join Date: Aug 2007
Location: North Cackalackey
Posts: 716
Total Cats: 2
Default

Quote:
Originally Posted by zoom2zoom View Post
my next downpipe will be v-band, looks so much easier to take off when you need to.
trust me it is a must have. easiest removal ever.
musanovic is offline   Reply With Quote
Old 03-26-2008, 09:51 PM   #11
Newb
Thread Starter
 
Join Date: Jun 2007
Location: Vienna VA
Posts: 38
Total Cats: 0
Default

Well the DIYer in me took control and I started to figure out a way to mod the DP to improve flow. Two big things bugged me about the DP. The fact that the wastegate gases didn't have a smooth exit and the pipe size was only 2.25". So here's my solution.

http://www.flickr.com/photos/[email protected]/2365386726/

http://www.flickr.com/photos/[email protected]/2364553833/

An improvement I'd say I need to actually mount it to see how soon I can flare to 3".
rcc-miata is offline   Reply With Quote
Old 03-26-2008, 10:03 PM   #12
Elite Member
iTrader: (9)
 
TurboTim's Avatar
 
Join Date: Jun 2006
Location: Chesterfield, NJ
Posts: 6,485
Total Cats: 248
Default

Quote:
Originally Posted by rcc-miata View Post
Well the DIYer in me took control and I started to figure out a way to mod the DP to improve flow. Two big things bugged me about the DP. The fact that the wastegate gases didn't have a smooth exit and the pipe size was only 2.25". So here's my solution.

http://www.flickr.com/photos/[email protected]/2365386726/

http://www.flickr.com/photos/[email protected]/2364553833/

An improvement I'd say I need to actually mount it to see how soon I can flare to 3".
Very good work there. Making that cutout piece is one of the things I really hate doing. You just gave yourself 5hp and 100rpm quicker spool, for sure. And maybe a little better boost control.
TurboTim is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Project Gemini - Turbo Civic on the Cheap Full_Tilt_Boogie Build Threads 59 12-15-2017 09:00 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Miata new person and a what's it worth! Model192 Meet and Greet 16 09-29-2015 09:50 PM
1996 Turbo Build Goldwar DIY Turbo Discussion 2 09-29-2015 10:20 AM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 12:57 PM.