Custom Stainless Steel Exhaust

Make it go fast! Kick it up a notch. Post tips in here.
User avatar
4uall
Posts: 4145
Joined: Mon Sep 26, 2011 12:09 pm
Your car is a: 1980 Fiat Pininfarina Spider 2000 F.I.
Location: Ottawa, Ontario, Canada

Re: Custom Stainless Steel Exhaust

Postby 4uall » Wed Aug 05, 2015 8:01 am

So Cal Mark wrote:1.75? is this supposed to be a performance exhaust?


I did not ask for a performance exhaust, nor did he inform me of such. I just asked for some details to post here :? As far as performance goes, the exhaust comes out only at the end (which is not how it was before lol) and sounds great doing so.
Jay

Fiona
1980 FI 2000 Spider
ITZEBTZE

https://goo.gl/photos/eNKaX7hrXhBu9fmp6

FINN (FN-2187)
2014 Jeep Wrangler Sport
MYTHERPY

davery
Posts: 804
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Custom Stainless Steel Exhaust

Postby davery » Wed Aug 05, 2015 9:48 am

4uall wrote:
So Cal Mark wrote:1.75? is this supposed to be a performance exhaust?


I did not ask for a performance exhaust, nor did he inform me of such. I just asked for some details to post here :? As far as performance goes, the exhaust comes out only at the end (which is not how it was before lol) and sounds great doing so.



This brings up something I have thought about for a while. If the outlet from the exhaust manifold or the inlet or outlet of the converter is 1.75", does it really matter what the diameter of the rest of the pipe is?
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

vandor
Posts: 3996
Joined: Sat May 23, 2009 1:23 pm
Your car is a: 1971 124 Spider
Location: Texas, USA

Re: Custom Stainless Steel Exhaust

Postby vandor » Wed Aug 05, 2015 11:46 am

It depends on a lot of things. There are 'cat back' systems available for a lot newer cars and supposedly they add some power. Only dyno testing would tell the truth.
Csaba
'71 124 Spider, much modified
'17 124 Abarth, silver
http://italiancarclub.com/csaba/
Co-owner of the best dang Fiat parts place in town

User avatar
Redline
Posts: 631
Joined: Sat Aug 29, 2009 4:34 pm
Your car is a: formerly a 1971 Fiat 124 BC Coupe
Location: Switzerland

Re: Custom Stainless Steel Exhaust

Postby Redline » Wed Aug 05, 2015 11:48 am

Roughly speaking (and depending on how you want to do all the numbers), 1.75" could flow enough for a 125hp motor. 2" could flow enough for about 160hp. Exhaust velocity is also a consideration.
http://www.124bc.com
La Dolce Vita: Joy and frustration at the speed of smoke

davery
Posts: 804
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Custom Stainless Steel Exhaust

Postby davery » Wed Aug 05, 2015 12:19 pm

vandor wrote:It depends on a lot of things. There are 'cat back' systems available for a lot newer cars and supposedly they add some power. Only dyno testing would tell the truth.


But is the "improvement" from an increase in the pipe diameter or less restrictive muffler? In theory I just don't see how a 2.25" inch exhaust is an improvement if it has even one choke point of 1.75" diameter. Once the gases have to slow down to fit through the smaller pipe, does it really matter how much larger the pipe afterward is? Which is why I have never purchased a header and 2.25" performance exhaust for my car. If the outlet of the header is 1.75", what is the point?
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

User avatar
Redline
Posts: 631
Joined: Sat Aug 29, 2009 4:34 pm
Your car is a: formerly a 1971 Fiat 124 BC Coupe
Location: Switzerland

Re: Custom Stainless Steel Exhaust

Postby Redline » Wed Aug 05, 2015 1:44 pm

To be pedantic, the flow (velocity) will actually speed up through the restriction. The total volumetric flow rate through the system will depend on the sum of resistances along the whole chain, so in principal opening it up after the restrictive header could still be beneficial. As for the restriction, it will depend on how long that restrictive section is. Breathing through a 10" long straw feels a lot different than through a 1" one.
http://www.124bc.com
La Dolce Vita: Joy and frustration at the speed of smoke

TX82FIAT
Posts: 1814
Joined: Mon May 03, 2010 11:04 am
Your car is a: 82 Fiat Spider 2000 CSO
Location: San Antonio

Re: Custom Stainless Steel Exhaust

Postby TX82FIAT » Wed Aug 05, 2015 2:26 pm

Good discussion about velocity through the tubes and restrictions. There is a ton more that goes into performance exhaust such as header design, shape, length. The width of the pipe from the header back or some other point such as CAT back. For a true exhaust performance gain I would think you need to go from the head back. So is there such a think as too much or too wide an exhaust... yes, there need to be some backpressure.

I had to install a resonator after taking the CAT out before the muffler. it was just too loud.
Buon giro a tutti! - enjoy the ride!

82 Fiat Spider 2000
03 BMW M3
07 Chevy Suburban

User avatar
4uall
Posts: 4145
Joined: Mon Sep 26, 2011 12:09 pm
Your car is a: 1980 Fiat Pininfarina Spider 2000 F.I.
Location: Ottawa, Ontario, Canada

Re: Custom Stainless Steel Exhaust

Postby 4uall » Wed Aug 05, 2015 2:55 pm

Image
Jay

Fiona
1980 FI 2000 Spider
ITZEBTZE

https://goo.gl/photos/eNKaX7hrXhBu9fmp6

FINN (FN-2187)
2014 Jeep Wrangler Sport
MYTHERPY

User avatar
v6spider
Posts: 1035
Joined: Tue Feb 28, 2006 6:57 pm
Your car is a: 4.3L V6 Powered 1972 124 FIAT Spider
Location: Mount Vernon WA

Re: Custom Stainless Steel Exhaust

Postby v6spider » Wed Aug 05, 2015 8:26 pm

Volumetric efficiency of the engine plays an important role here.. IE how quick you can get air through the engine. Typically intake cfm on a street performance machine is lower than exhaust.. Otherwise low rpm response would be not so streetable.. Even with 1.75" header opening. A 2" or 2 ¼" pipe will flow better. Down side is it will be louder..

Rob
http://www.v6spider.com
4.3L V6 Powered 1972 124 FIAT Spider

davery
Posts: 804
Joined: Sun Apr 15, 2012 8:51 pm
Your car is a: 1985 Spider
Location: Ohio

Re: Custom Stainless Steel Exhaust

Postby davery » Thu Aug 06, 2015 1:40 am

This is a really interesting thread. So it would appear whether the header is a 4-2-1 or a 4-1 the area of the collector will be less than the total area of each of the four pipes leading into it. If the collector is 1.75" then the area of a cross section is about 2.4 sq in. Divided by 4 would be .6 sq in. This would mean each of the 4 pipes would be a diameter of less than 1/2 in. That can't be right, so the collector does restrict the flow. How much? I have no idea what the inside diameter of each pipe is, but assume it is 1". That would mean the area of a cross section would be .785 sq in. Since there are 4, that would mean the total area of all four cross sections would be 3.14 sq in. So through the header the total area decreases by about 20%. This would be a gradual decrease, so I assume this acts as a merge collector to create back pressure. The question is after the pipe goes to a 2.25" pipe after the merge collector, is any additional decrease in area of of the cross section (say at the converter) really needed? For example, would a straight pipe provide the most horsepower? I'm probably missing something or making this too simple. I'm just trying to understand the mechanics of the exhaust system.
Last edited by davery on Thu Aug 06, 2015 1:49 pm, edited 1 time in total.
Don Avery
Dayton, OH/Sarasota,FL
1985 Pininfarina
2011 Eos
2012 Mercedes E550 Cabriolet

User avatar
So Cal Mark
Posts: 13839
Joined: Wed Jan 25, 2006 3:45 pm
Your car is a: Fiat
Location: upland, ca.

Re: Custom Stainless Steel Exhaust

Postby So Cal Mark » Thu Aug 06, 2015 1:54 am

generally the tubes are at least 1.5" and the collector is 2.5". Our header steps from 1.5 to 1.75 per tube into a 2.5" collector. Dyno testing has proven a substantial hp and torque improvement with no other changes to the engine. At peak hp we had a 10% increase, peak torque was a 15% increase. What is really telling is the power and torque increase at 6000rpm. The stock hp and torque curves begin to drop at 6k, while our header/exhaust kept the curves nearly flat so that we had a 15% hp increase and 20% torque increase at 6k. This indicates the stock exhaust system doesn't flow enough at high rpm
Mark Allison
allisonsautomotive.com Fiat and Alfa Romeo parts and service. Performance parts our specialty!
Headers, ignitions, wheels, cams, flywheels
starsmark@hotmail.com 909-981-3566

131
Posts: 672
Joined: Sun Nov 14, 2010 1:13 am
Your car is a: 1982 131 Superbrava warmed 2.0 litre.
Location: Tasmania, Australia

Re: Custom Stainless Steel Exhaust

Postby 131 » Thu Aug 06, 2015 4:14 am

TX82FIAT wrote:there need to be some backpressure.


No there don't.
Mick.

'82 2litre 131, rally cams, IDFs & headers.

Squidders
Posts: 91
Joined: Wed Apr 29, 2015 6:20 am
Your car is a: 1980 Fiat 124 Spider
Location: Sydney, Australia

Re: Custom Stainless Steel Exhaust

Postby Squidders » Thu Aug 06, 2015 8:00 am

Sweet sounding. Not loud at all! congrats.

User avatar
toplessexpat
Posts: 1183
Joined: Fri Aug 31, 2012 2:29 am
Your car is a: 1976 Spider 1800
Location: Houston, TX

Re: Custom Stainless Steel Exhaust

Postby toplessexpat » Thu Aug 06, 2015 8:48 am

TX82FIAT wrote:I had to install a resonator after taking the CAT out before the muffler. it was just too loud.


I haven't yet put a resonator on the 1800. Abarth Headers -> 2.25" -> Magnaflow backbox -> Twin pipes ..... it's a little on the loud side, and I suspect the boss is going to insist eventually.

On the 2000. Stock Manifold -> 1.75" -> Cat -> Resonator -> Magnaflow backbox -> Twin pipes ..... and it's a glorious note.
---
Many classic Fiats - it's a disease!
www.mirafiori.com

Squidders
Posts: 91
Joined: Wed Apr 29, 2015 6:20 am
Your car is a: 1980 Fiat 124 Spider
Location: Sydney, Australia

Re: Custom Stainless Steel Exhaust

Postby Squidders » Thu Aug 06, 2015 8:55 am

Sweet sound. Congrats.


Return to “Performance”

Who is online

Users browsing this forum: No registered users and 17 guests