Thinking about keeping stock exhaust. - 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 10-07-2007, 04:23 PM   #1
Elite Member
Thread Starter
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default Thinking about keeping stock exhaust.

I was just doing some thinking about my turbo setup. My question is how much spool up and response will I lose if I keep my stock exhaust with cat and use a begi downpipe? and if I ditch the catalytic?

I dont want to spend a lot of money on the whole kit initially and wouldnt mind swapping the rest of the exhaust out later.

Thanks
Saml01 is offline   Reply With Quote
Old 10-07-2007, 04:47 PM   #2
Elite Member
iTrader: (3)
 
Mach929's Avatar
 
Join Date: Oct 2004
Location: lansdale PA
Posts: 2,500
Total Cats: 0
Default

either way it will kill performance horribly
Mach929 is offline   Reply With Quote
Old 10-07-2007, 05:08 PM   #3
Elite Member
iTrader: (11)
 
Trent's Avatar
 
Join Date: Feb 2006
Location: Louisiana
Posts: 1,625
Total Cats: 5
Default

You can run with the stock exhaust for now if you're keeping the boost very low, but your turbo kit will be severely, SEVERELY hindered by it. For the cost investment, it's a BIG bang for the buck to invest in a 2.5" exhaust.
Trent is offline   Reply With Quote
Old 10-07-2007, 05:31 PM   #4
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

That plan will work just fine. By the time winter rolls around you can swap that **** out and have a vastly improved car come spring time
magnamx-5 is offline   Reply With Quote
Old 10-07-2007, 05:34 PM   #5
Junior Member
 
Join Date: Jul 2005
Location: Alexandria, VA
Posts: 125
Total Cats: 0
Default

The cat is a bigger hinderance than the stock exhaust. Get rid of it now, and upgrade the cat-back later as budget allows.
MiaTurbo is offline   Reply With Quote
Old 10-07-2007, 05:37 PM   #6
Elite Member
Thread Starter
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Alright so I guess i'm going all out right from the start. Money isn't the issue here, its taking the smarter approach.

Heres a question. Do exhaust flanges differ depending on the diameter of the pipe used?

I ask because if I get a begi DP which is 2.5inch and thats bigger then the factory exhaust, doesnt the step down at the flange create a bottle neck? What happens if I want to upgrade the rest of it?
Saml01 is offline   Reply With Quote
Old 10-07-2007, 05:44 PM   #7
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

Yes the flange changes relative to the size. I progressive step down is no more a flow restriction than the cat, muffler, or even the 2 someodd inch pipe we run stock.
magnamx-5 is offline   Reply With Quote
Old 10-07-2007, 05:56 PM   #8
Senior Member
 
Join Date: Mar 2007
Location: Denver, CO
Posts: 564
Total Cats: 0
Default

I made 280hp on my Talon with stock exhaust and gutted cat. Was it the right way to do it? No.
jwarriner is offline   Reply With Quote
Old 10-07-2007, 09:27 PM   #9
Elite Member
Thread Starter
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Quote:
Originally Posted by magnamx-5 View Post
Yes the flange changes relative to the size. I progressive step down is no more a flow restriction than the cat, muffler, or even the 2 someodd inch pipe we run stock.
So if I decide to go with a 2.5 inch all the way back to match the begi DP, how would I obtain the flange necessary to mate the rest of the system to Begis piece?
Saml01 is offline   Reply With Quote
Old 10-07-2007, 09:29 PM   #10
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

The local muffler shop should have them in stock it is only a 2 bolt flange.
magnamx-5 is offline   Reply With Quote
Old 10-08-2007, 05:01 PM   #11
Elite Member
Thread Starter
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Does the flange that comes with the begi DP if mated to the stock exhaust create a bottleneck? Will it have to be replaced or opened up if a new exhaust is installed?
Saml01 is offline   Reply With Quote
Old 10-08-2007, 05:17 PM   #12
Elite Member
iTrader: (39)
 
Zabac's Avatar
 
Join Date: Sep 2007
Location: High Point NC
Posts: 4,854
Total Cats: 8
Default

i advise you do it right the first time and save yourself a lot of headaches...do the whole exhaust, you dont have to go all out, do a 2.5" cruch bent mild steel, and you'll be ok with your goals...
Zabac is offline   Reply With Quote
Old 10-08-2007, 05:36 PM   #13
Elite Member
iTrader: (5)
 
Atlanta93LE's Avatar
 
Join Date: Sep 2006
Location: Marietta, GA
Posts: 2,198
Total Cats: 1
Default

I noticed HUGE gains in spool and power just by going from a stock exhaust to a $140 mandrel-bent 2" ebay special catback.

Quantitatively: I was at ~75%DC on NB injectors at my AFR targets with the stock exhaust, redline at 7.5-8psi . Retuned with the nex exhaust, and now I run out of injector (100DC) at about 6k rpm at wastegate pressure. I had to set the overboost protection down lower and have to stay way out of high boost until new injectors arrive and get cleaned.
Atlanta93LE is offline   Reply With Quote
Old 10-08-2007, 06:55 PM   #14
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,363
Total Cats: 1,323
Default

Do it once, do it right. 3" or go home.
Savington is online now   Reply With Quote
Old 10-08-2007, 11:02 PM   #15
Senior Member
iTrader: (6)
 
Join Date: Mar 2005
Location: Sammamish, Washington
Posts: 1,396
Total Cats: 0
Default

I'm with this guy /\
Kelly is offline   Reply With Quote
Old 10-09-2007, 02:20 AM   #16
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

The stock cat is the greatest restriction. I measured it.
JasonC SBB is offline   Reply With Quote
Old 10-09-2007, 04:52 AM   #17
Elite Member
Thread Starter
iTrader: (9)
 
Saml01's Avatar
 
Join Date: Jul 2007
Location: NYC
Posts: 5,730
Total Cats: 2
Default

Quote:
Originally Posted by Savington View Post
Do it once, do it right. 3" or go home.
Whats the price difference of the pipe?

Besides isnt Begis DP a 2.5inch, does attaching 3 inches to it make that much difference? Unless I have to get a 3inch DP too. I think its marginal benefits after a certain point.
Saml01 is offline   Reply With Quote
Old 10-09-2007, 05:06 AM   #18
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,363
Total Cats: 1,323
Default

BEGI's DP is normally a 2.75", and they stepped it up right before the wastegate rejoins to a 3" for me for $30 extra. I then had a custom 3" midpipe w/ a 3" Magnaflow cat made to mate the 3" enthuza to the 3" BEGI DP.
Savington is online now   Reply With Quote
Old 10-09-2007, 09:19 AM   #19
Elite Member
iTrader: (2)
 
Join Date: Jan 2007
Location: Los Angeles, CA
Posts: 8,782
Total Cats: 119
Default

On my begi S5 downpipe 3" my gt3071 turbo spools about 700rpm earlier with catless 3" than with factory exhaust. power difference was also major.
Faeflora is offline   Reply With Quote
Old 10-09-2007, 10:05 AM   #20
Elite Member
iTrader: (8)
 
Join Date: Sep 2006
Location: Severn, MD
Posts: 1,927
Total Cats: 5
Default

My Begi DP does not mate well with my 2.5 FM catback. And it hits the K-member. I'm getting the catback reflanged and a testpipe made next week to mate better with the DP. Probably take the lower section of the DP off and hit it with a BFH.


Frank
fmowry is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Another Alternator thread ihiryu General Miata Chat 9 09-28-2015 11:22 AM
Recommended Tire Temp for best friction thumpetto007 Race Prep 4 09-27-2015 06:16 PM
Koni 1150 Coilover Kit drumman83 Suspension, Brakes, Drivetrain 2 09-25-2015 08:03 PM


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 11:38 AM.