So I want a 3 Inch Downpipe... where do i go? - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Prefabbed Turbo Kits A place to discuss prefabricated turbo kits on the market
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools
Old 01-31-2007, 03:03 PM   #21
Elite Member
iTrader: (24)
 
kotomile's Avatar
 
Join Date: Oct 2006
Location: Monterey, CA
Posts: 7,578
Total Cats: 40
Default

That's all good info if we were naturally aspirated T25... but with turbos I'm afraid bigger really is better.
kotomile is offline   Reply With Quote
Old 02-01-2007, 12:36 AM   #22
Junior Member
 
Join Date: Dec 2006
Posts: 85
Total Cats: 0
Default

Quote:
Originally Posted by Brian View Post
T25...do some reading on turbochargers...you're all wrong. Well, not all wrong, but mostly wrong.
Turbochargers change the equation slightly, but not much. On a stock 1.6 I would laugh at anything bigger than 2.25". On a turbo 1.6, a well sorted full 2.5 is going to be a screamer, and be cheaper than a custom (probably not well thought out and built) 3".

A well built 3" DP MIGHT be worthwhile but NOT, and I repeat, NOT a full 3". And it seems that because it is a waste of time, there isn't a well built one available.
t25miata is offline   Reply With Quote
Old 02-01-2007, 12:39 AM   #23
Elite Member
iTrader: (5)
 
Atlanta93LE's Avatar
 
Join Date: Sep 2006
Location: Marietta, GA
Posts: 2,198
Total Cats: 1
Default

Here I was thinking this whole discussion was entirely about downpipe size. I've been listening because the DP sitting in my garage is 3" with a step to 2.5" right at the cat.
Atlanta93LE is offline   Reply With Quote
Old 02-01-2007, 12:43 AM   #24
Junior Member
 
Join Date: Dec 2006
Posts: 85
Total Cats: 0
Default

The cat will cool and therefore compress the gasses, so 2.5 after is all you need.
t25miata is offline   Reply With Quote
Old 02-01-2007, 12:48 AM   #25
Senior Member
 
Join Date: Dec 2004
Posts: 1,450
Total Cats: -1
Default

Turbochargers change the equation a bit more than slightly...first off, you have a huge restriction in the exhaust directly after the primaries...a naturally aspirated car doesn't have that. This basically means exhuast gas velocity and pulse tuning are a moot point, unlike in a naturally-aspirated car. You no longer have defined pulses because they've all be chopped up and thrown into one big gas plume by the turbine.

Why do you think a turbocharged car spools better when it's running merely a downpipe and no cat-back? Funny thing is, after the primaries are properly collected on an N/A car's header, you actually want the pipe to open up as much as possible there as well (assuming smooth transition). Say your N/A car's header primaries collected into 2.5"...a smooth, short transition from 2.5" - 4" into open air would make more horsepower at no expense in torque compared with a full 2.5" cat-back. Same goes for the exhaust dia. post turbocharger.

Here's something for you to chew on since, basically, the burden of proof rests on you, as you're going against all modern thought on the topic: since a turbocharger relies on a pressure differential across the turbine to spool and produce boost, explain to us why you wouldn't want the largest diameter possible exiting the turbine?
bripab007 is offline   Reply With Quote
Old 02-01-2007, 02:53 AM   #26
Senior Member
iTrader: (1)
 
Join Date: Mar 2006
Location: Tucson "it's 110º" Arizona
Posts: 1,017
Total Cats: 0
Default

Quote:
Originally Posted by t25miata View Post
The cat will cool and therefore compress the gasses, so 2.5 after is all you need.
You would be right here if you weren't so wrong
UofACATS is offline   Reply With Quote
Old 02-01-2007, 11:49 AM   #27
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

man, all those dragsters and race cars running 4" diameter dump pipes are sure gonna be mad they forgot to run an exhaust!



y8s is offline   Reply With Quote
Old 02-01-2007, 12:00 PM   #28
Miotta FTW!
iTrader: (24)
 
Splitime's Avatar
 
Join Date: Jun 2006
Location: Chicagoland, IL
Posts: 4,295
Total Cats: 26
Default

t25... you really are off base. A turbo is happiest with NO piping at all, just something to smooth exit gases and the open air make it happiest.

I run a full 3" DP on my 1.6L civic... and will be running a full 3" on my 1.6L miata. Its an easy size to get piping in and it has proven gains over smaller piping.

If I could fit 4"+... I would use it.
Splitime is offline   Reply With Quote
Old 02-01-2007, 12:29 PM   #29
Elite Member
iTrader: (14)
 
Join Date: Mar 2006
Location: Edmonton, AB
Posts: 4,921
Total Cats: 0
Default

I don't think the question should be: Is a 3" DP and exhaust better than 2.5?

I think the question should be: Is a 3" DP and exahaust worth the trouble and expense?
jayc72 is offline   Reply With Quote
Old 02-01-2007, 12:42 PM   #30
Senior Member
 
Join Date: Oct 2005
Location: Knoxville
Posts: 1,168
Total Cats: 0
Default

I don't know this trouble everyone speaks of. I have a 3" exhaust, and it wasn't difficult at all. the downpipe is the hard part. there's pics in my garage.
Al Hounos is offline   Reply With Quote
Old 02-01-2007, 12:51 PM   #31
Elite Member
iTrader: (14)
 
Join Date: Mar 2006
Location: Edmonton, AB
Posts: 4,921
Total Cats: 0
Default

Quote:
Originally Posted by Al Hounos View Post
I don't know this trouble everyone speaks of. I have a 3" exhaust, and it wasn't difficult at all. the downpipe is the hard part. there's pics in my garage.
Some would say that having a custom exahaust made is more hassle than buying an off the shelf 2.5" exhaust. Is there anyone making a bolt on 3" exhaust?
jayc72 is offline   Reply With Quote
Old 02-01-2007, 12:52 PM   #32
Senior Member
 
Join Date: Oct 2005
Location: Knoxville
Posts: 1,168
Total Cats: 0
Default

oh, i see. but they'd still be wrong. it's easier than intercooler piping.
Al Hounos is offline   Reply With Quote
Old 02-01-2007, 12:55 PM   #33
Elite Member
iTrader: (14)
 
Join Date: Mar 2006
Location: Edmonton, AB
Posts: 4,921
Total Cats: 0
Default

Quote:
Originally Posted by Al Hounos View Post
oh, i see. but they'd still be wrong. it's easier than intercooler piping.
I'm sure if you have access to the tools and skills to use them you would be correct.
jayc72 is offline   Reply With Quote
Old 02-01-2007, 01:20 PM   #34
Guest
Thread Starter
 
Join Date: Mar 2006
Location: So Cal
Posts: 407
Total Cats: 0
Default

I dont know what you guys are saying... I have a bunch of friends that have had evo's,sti's,GTI's all with big downpipes. You lose lowend but top end pays off for it. One of my buddies was running a GTI 1.8T with a gt30R and a 3 inch turboback. Car ran amazingly. I remember he made my 350z look like it was stopped on the freeway.
krayzrac3r is offline   Reply With Quote
Old 02-01-2007, 01:31 PM   #35
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 dont lose low end from a big exhaust. if you run a GT30R on a 1.8 you lose low end.

large downpipe improves spool which improves low-end.
y8s is offline   Reply With Quote
Old 02-01-2007, 01:38 PM   #36
Senior Member
 
Join Date: Dec 2004
Posts: 1,450
Total Cats: -1
Default

You would certainly lose low-end if you want from a log- or short-runner tubular manifold to a super long-runner manifold (like this: http://www.turbotechnologyinc.com/pr.../e&e/e&e02.jpg ), on the same engine, with the same turbo with the same downpipe size.

Post turbine, however, you want the larger MF'n diameter you can get.
bripab007 is offline   Reply With Quote
Old 02-01-2007, 02:21 PM   #37
Elite Member
iTrader: (2)
 
Join Date: Jun 2006
Location: ABQ, NM
Posts: 1,850
Total Cats: -8
Default

Quote:
Originally Posted by Al Hounos View Post
oh, i see. but they'd still be wrong. it's easier than intercooler piping.

If it's so easy and so little hassle you should make some up, there's at least one guy in this thread who'd buy it.
BenR is offline   Reply With Quote
Old 02-01-2007, 02:32 PM   #38
Senior Member
 
Join Date: Oct 2005
Location: Knoxville
Posts: 1,168
Total Cats: 0
Default

All i'm sayin is it took a 6ft straight pipe, 1 u-bend, 1 muffler, 1 or 2 sets of flanges, and four or five cuts to make. i then took the whole lot to a muffler shop and had it welded. It really isn't too bad. IT even clears a 7" diff without modifying the rear subframe brace.
Al Hounos is offline   Reply With Quote
Old 02-01-2007, 05:20 PM   #39
Elite Member
iTrader: (2)
 
Join Date: Jun 2006
Location: ABQ, NM
Posts: 1,850
Total Cats: -8
Default

Have you seen how far back a greddy is mounted on the manifold?
BenR is offline   Reply With Quote
Old 02-05-2007, 10:26 PM   #40
Junior Member
 
Join Date: Dec 2006
Posts: 85
Total Cats: 0
Default

http://www.bellengineering.net/Pages...peupgrade.html

Read it. I am happy to stand corrected on several of your points. Dragsters are not road cars, don't use them to back you up cause they are so different they aren't comparable. And if they use 4", what makes you think that a pissy little 1.6 needs 3" :gay:

Like I said, I stand corrected on some things and have learned a lot in this thread, and also laughed at a lot of comments. Don't put me down because of **** you have read on forums. ********* like us post on forums, what makes what we say right? I'd trust Begi though, they research.

Quote:
Engines do not like exhaust gas back pressure. Getting the exhaust gasses smoothly out of the system with a minimum of back pressure is therefore crucial to producing power. Turbocharged engines like it even less. Yet, it is very clear that just “bigger” is not the answer to “better.” We are stuck with convertors and mufflers, but there are other areas that can hurt power just as bad if not handled properly. Specifically, “handling” is the treatment of the gasses passing through the turbine and those vented through the integral wastegate.

The problems to solve are:
~Matching flow intersections to smooth changes
~Expanding flow area based on aerodynamically correct expansion rates
Avoidance of dumping the exhaust gas into a sudden cavern such as “the middle of Grand Canyon.”
t25miata is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
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
Partial Turbo kit for a 1.6 and dual headlight kit. Andifer Miata parts for sale/trade 8 09-23-2015 06:43 PM
Replacing one tire nigelt Wheels and Tires 7 09-22-2015 01:32 PM
Megasquirt 2 or 3 ? TheNomad Engine Performance 3 09-21-2015 11:20 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 06:31 AM.