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View Full Version : Open'd exhaust. How much did you gain?



Dave
04-13-2006, 08:35 AM
Just curious. By placing a cut out after the downpipe we've consistently removed 3/10 of a second off the 1/4. What have you all progressed from opening your exhaust?

We usually had either a TII or TI setup running mild boost with fair traction.

Anyone have any dyno-proven improvements?

-Bryan

Keito
04-13-2006, 07:06 PM
You are correct on the 3/10's
I added a cutout to the SRT-4, wen from 13.80 to
13.52.

R/T
04-13-2006, 10:30 PM
My Son's ( SC 2.5 ) 88 Shadow ES automatic;

We were running an open 2.25" stock downpipe, went to a 2.5" from an 89 Shelby Daytona and picked up 6/10ths and 4 MPH.

The Mitsu has the big swingvalve, it *really* likes a big downpipe.... :thumb:

turbovanmanČ
04-13-2006, 11:22 PM
On that note, full 3 inch mandrel system with a Magnaflow, I can't see gaining 3/10's??????????

Dave
04-13-2006, 11:45 PM
On that note, full 3 inch mandrel system with a Magnaflow, I can't see gaining 3/10's??????????

Of course you still got the restriction of a 3" diameter vs. an open downpipe's amount resistant pressure being only barometric pressure.

There's literally no restriction in an open exhaust, just about how fast the engine is cranking it out.

Whorse
04-14-2006, 02:35 PM
What d'you have for an exhaust manifold and turbo SV?

Dave
04-15-2006, 08:18 PM
I have a MoparzRule heavily ported exhaust manifold and a stock 2.25" '88 SV.

GLHSKEN
04-16-2006, 07:05 AM
2 1/4" ran a 13.97 @99.98mph Over the winter opened the stock downpipe. Ran 13.27 @ 106.7mph 1st pass. Changed to a Rick D 2.5" ported S/v and open 3" downpipe. Ran 12.85 @ 109.7mph

On the dyno, full 3" system with a cat and a cutout before the cat. Lost 22ft lbs abd 11whp with the cutout closed.

Dave
04-16-2006, 07:45 AM
2 1/4" ran a 13.97 @99.98mph Over the winter opened the stock downpipe. Ran 13.27 @ 106.7mph 1st pass. Changed to a Rick D 2.5" ported S/v and open 3" downpipe. Ran 12.85 @ 109.7mph

On the dyno, full 3" system with a cat and a cutout before the cat. Lost 22ft lbs abd 11whp with the cutout closed.

Wow.:clap2:

JuXsA
04-16-2006, 11:33 PM
I am running no exhaust now... just open turbo :D freaking awesome!!!!

86Shelby
04-17-2006, 12:43 AM
My R/T gained 20-25 hp over the entire pull with the cutout open. it's at the end of the downpipe 8-10" before the cat.

It's a 3" mandrel bent system and at the time the car had a cat on it. Pushed it from 29x whp to 322whp.

turbovanmanČ
04-17-2006, 11:17 PM
Nice gains but full 3 inch and Magnaflow, can't be loosing that much. Will have to try that on the dyno. Any bets?

BadAssPerformance
04-17-2006, 11:45 PM
'87 T2 shadow

Open stock downpipe, cut in front of converter = 13.00's

Full non-mandrel-bent (read: crimped corners) 3" after downpipe, no converter thru a 3" Dynomax Race Magnum Oval muffler, exit out the back = 13.00's

Dave
04-28-2006, 07:41 AM
'87 T2 shadow

Open stock downpipe, cut in front of converter = 13.00's

Full non-mandrel-bent (read: crimped corners) 3" after downpipe, no converter thru a 3" Dynomax Race Magnum Oval muffler, exit out the back = 13.00's

What were your 60's and 660's like on both passes? Can you get me both entire slips? That doesn't seem right at all. Either one's pulling real hard on the bottom or the other real hard on the top. Restriction is restriction. And you still had 9.42" x Y (y being whatever the length of the exhaust) of backpressure versus 0 being open.

The S is Silent
04-28-2006, 08:38 AM
What were your 60's and 660's like on both passes? Can you get me both entire slips? That doesn't seem right at all. Either one's pulling real hard on the bottom or the other real hard on the top. Restriction is restriction. And you still had 9.42" x Y (y being whatever the length of the exhaust) of backpressure versus 0 being open.

I think he's saying the backpressure in a full 3" exhaust is comparable to the backpressure from using a stock dp. Or at least that is what I read from it.

Dave
04-28-2006, 08:40 AM
I think he's saying the backpressure in a full 3" exhaust is comparable to the backpressure from using a stock dp. Or at least that is what I read from it.

What I got out of his saying is that an open downpipe is equivalent to a 3" mandrel bent exhaust.

The S is Silent
04-28-2006, 08:44 AM
What I got out of his saying is that an open downpipe is equivalent to a 3" mandrel bent exhaust.

Stock open DP = 3" NON-mandrel bent system

BadAssPerformance
04-28-2006, 10:33 AM
Stock open DP = 3" NON-mandrel bent system

yep, that is what I said...

Stock open DP = full 3" non mandrel bent with 3" race magnum oval w/o converter

Entire timeslip is similar for both setups even tried with and without the back seat in the car with the full exhaust setup. Launch at 4000-4500, 1.83-1.85 60'... 13.00-13.10 @ 103-105 mph....

MiniMopar
04-30-2006, 10:04 AM
It sounds like you were still using the stock DP in both setups? Another way to look at it is that the restriction of the stock DP is such that adding the 3" system had no real effect on backpressure.

BadAssPerformance
04-30-2006, 11:06 AM
It sounds like you were still using the stock DP in both setups? Another way to look at it is that the restriction of the stock DP is such that adding the 3" system had no real effect on backpressure.

Yep, stock turbo, SV & DP in both. So after that cork, a 3" flowed as good as the open DP :thumb:

gti_7
04-30-2006, 06:38 PM
This is an interesting post:thumb: I do have a question though. If you had a full 3" system but used 6 inches of 2.5" pipe after a 2.5 inch SV how much of a loss would this roughly net versus using a full 3 inch downpipe after the 2.5 inch SV?
5-10whp? maybe? less? perhaps more?

thanks
bernard

BadAssPerformance
04-30-2006, 11:00 PM
Not sure about that one... 6" of 2.5" vs. a full 2.5" DP?

btw, forgot to mention the Shadow also has a stock Garrett T03 ('87 T2) turbo on it so it has a 2.25" SV

gti_7
05-01-2006, 07:02 AM
Not sure about that one... 6" of 2.5" vs. a full 2.5" DP?

btw, forgot to mention the Shadow also has a stock Garrett T03 ('87 T2) turbo on it so it has a 2.25" SV


sorry, i should have clarified it better. If i had a 2.5" sv with 6" of 2.5" pipe attached to it, welded that six inches of pipe to a 3" pipe, then to a 3" cat, and 3" race bullet and 3" all the way back after that, vs using a full 3" dp on a 2.5" sv with a 3" cat, race bullet and 3" after that.

BadAssPerformance
05-01-2006, 08:16 PM
Not sure that 6" is gonna kill too much HP. I had a similar setup (maybe 9") on my Z before making a full 3" DP for it but unfortunately I changed a few other things at the same time (as usual) so I dont have a direct a-b reference on it.

MiniMopar
05-02-2006, 12:02 AM
The biggest cork will be the cat. From what I have seen (Dynomax and CatCo), the cross sectional area of the cat is the same for 2-1/4", 2-1/2" and 3". They just put a bigger flange on it.

Recently, the Dynomax Super Turbo muffer on my CSX exploded (rust). I have a new SS 3" system for it, but no time to work on it. I tried patching up the muffer up a couple of times to get a couple more weeks out of it. That thing creates quite a bit of back pressure at WOT, given how easily it blew open again. I got it strapped together now. I think part of the reason is that the inner tubes are not perferated at all. So the expanding exhaust has to funnel back through the end of the final tube to get out.

For the record, I put this original JRB 2.5" aluminized system on in 1998 and it started falling apart badly last year (got a few small holes the year before). I don't even drive it in the winter (except this past winter due to problems with the other beater). So if you live in the salt belt and you don't want to replace your exhaust every 6 years or so, just get a SS system.

BadAssPerformance
05-02-2006, 07:14 AM
The biggest cork will be the cat.

Word.

WickedShelby88
05-02-2006, 03:09 PM
Im with you. Ive got SS pipe and a high flow stainless cat and muffler. All still in the condition they were when put on last year. All on an 88 Shelby tona that saw 2 winters with that system.

gti_7
05-02-2006, 08:18 PM
Not sure that 6" is gonna kill too much HP. I had a similar setup (maybe 9") on my Z before making a full 3" DP for it but unfortunately I changed a few other things at the same time (as usual) so I dont have a direct a-b reference on it.


Okay, im game. What sort of gains did you get with the 9" of 2.5 inch pipe and what other things did you change at the same time? Im just wanting to see a rough guess at what id be loosing going this route over a full three inch.:thumb:

thanks again
bernard

gti_7
05-02-2006, 08:20 PM
The biggest cork will be the cat. From what I have seen (Dynomax and CatCo), the cross sectional area of the cat is the same for 2-1/4", 2-1/2" and 3". They just put a bigger flange on it.


Well, i sure wish they told you *that* when your ordering these things.. hopefully the larger size will be better for flow that what i have on there now at 2 1/4. This cat is supposed to be 3" ID :eyebrows: so heres hoping :)

bernard

BadAssPerformance
05-02-2006, 09:50 PM
Okay, im game. What sort of gains did you get with the 9" of 2.5 inch pipe and what other things did you change at the same time? Im just wanting to see a rough guess at what id be loosing going this route over a full three inch.:thumb:

thanks again
bernard

Changed a lot of things at one when that went on too... see a pattern? ;)

BadAssPerformance
05-02-2006, 09:51 PM
Well, i sure wish they told you *that* when your ordering these things.. hopefully the larger size will be better for flow that what i have on there now at 2 1/4. This cat is supposed to be 3" ID :eyebrows: so heres hoping :)

bernard

The 3" cats are 3" inlet and outlet but what Russ is saying is that the chamber and chunk of crap on the inside is the same as a smaller inlet/outlet cat.

gti_7
05-03-2006, 06:24 AM
Changed a lot of things at one when that went on too... see a pattern? ;)


ya ya.. "top secret" okay i get it.:nod:

thanks
bernard

GLHSKEN
05-03-2006, 07:29 AM
Only lost 11hp on the dyno through a 3" catco. Not too bad. It affected the torque more (22ft lbs)

BadAssPerformance
05-03-2006, 09:59 AM
ya ya.. "top secret" okay i get it.:nod:

thanks
bernard

lol, not at all, I just seem to change everything at once every time :thumb:

gti_7
05-03-2006, 01:33 PM
lol, not at all, I just seem to change everything at once every time :thumb:


okay, not wanting to divuldge are you :eyebrows: thats cool :thumb:

tell me this though.. any chance this http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8058841334&category=33633&fkxs=1#ebayphotohosting

would bolt to a 2.5" SV? the bends look right. the end is 3" the rest expands to 4 inches.. lol.. just curious

thanks
bernard

gti_7
05-03-2006, 01:35 PM
Only lost 11hp on the dyno through a 3" catco. Not too bad. It affected the torque more (22ft lbs)

Ken, actual numbers!:amen: :thumb: :D thank you thank you! its definetly a sacrifice, but im better off without those 22ft-lbs and 11whp than having my car impounded and fined 5k for not running one.. :nod:

thanks again!
bernard

turbovanmanČ
05-03-2006, 07:41 PM
okay, not wanting to divuldge are you :eyebrows: thats cool :thumb:

tell me this though.. any chance this http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8058841334&category=33633&fkxs=1#ebayphotohosting

would bolt to a 2.5" SV? the bends look right. the end is 3" the rest expands to 4 inches.. lol.. just curious

thanks
bernard

Nope, won't fit unless you modify it, guessing of course. Also, mounting flange is wrong.