Test pipe vs. cat

6962 Views 20 Replies 17 Participants Last post by Nate, Sep 26, 2010

Sedan

Discussion Starter · Sep 8, 2008

Tonight I acquired the final piece of the puzzle for the exhaust I'm putting on my 8-valve, naturally-aspirated '85 900S notchback.

At Carlisle I purchased a lightly used 8-valve MSS header that had been specially ordered with a 4-bolt flange so that a turbo cat and cat-back exhaust could be used with it. At SOC I bought a brand new turbo cat and gaskets from one of the vendors. Tonight I bought a lightly used stock cat-back exhaust and test pipe that a friend ran on his '88 SPG for a few thousand miles before parting it out. Between all of this, I have $130 into it, not too shabby.

What I'm wondering is if there would be any performance gain from running a straight pipe vs. a cat? All along I'd been leaning towards a cat and was pretty happy finding a brand new one with gaskets for $30, then this straight pipe just fell into my lap. With the N/A 8-valve I need all of the help I can get. No emissions testing in Kentucky. Any opinions?

1 - 20 of 21 Posts

Castor Troy

· #2 · Sep 8, 2008

iirc you'll lose some power by running w/out a cat, as you need a certain amount of backpressure

Palmer

· #3 · Sep 8, 2008

Straight pipe.

No cat = greenhouse gasses
With cat = smog

Pick one.

saabkid37

· #4 · Sep 8, 2008

Castor Troy said:
iirc you'll lose some power by running w/out a cat, as you need a certain amount of backpressure

theres a huge argument ongoing in the honda world

my view is...let the header do the scavenging and run catless

Castor Troy

· #5 · Sep 8, 2008

i'd like to see nick do some tests on his T5 n/a car with custom 4-2-1 header, see what happens

Palmer

· #6 · Sep 8, 2008

...i would like to hear a c900 with an MSS header and no cat!

It's a win win!

mike d

· #7 · Sep 8, 2008

saabkid37 said:
theres a huge argument ongoing in the honda world

my view is...let the header do the scavenging and run catless

if your car is a turbo there is no debate on cat vs no cat,, no cat simply makes more power.

on the NA cars, my feelings are that you have the proper amount of back-pressure via muffler, headers, and the normal twist and bends in the exhaust. besides, one could argue that a straight pipe weighs less than a cat

Jack Straw

· #8 · Sep 9, 2008

Well really, you're not going to get an ideal setup if you don't have a 'custom tuned' exhaust anyway, so you might as well go for the one that sounds cooler. It's not just "a little backpressure = more power" per se. It's some sort of balance with the exhaust system size/shape making it so that the exhaust pulses create a resonance pattern through the exhaust that helps pull air through the cylinders. Of course, this is beyond the shade tree mechanic's scope, just trying to give a nice justification for you to yank out the cat

Sweed Speed

· #9 · Sep 11, 2008

The untimate exhaust is an equation between cylander volume and expansion chamber size in exhaust behind header.

call Nat Wentworth at Erikson (sp) transmissions. He spend a good amount of time doing this and the result is an awesome sound with maximum power.

My short opinion... no cat

c900

· #10 · Sep 13, 2008

Sweed Speed said:
The untimate exhaust is an equation between cylander volume and expansion chamber size in exhaust behind header.

call Nat Wentworth at Erikson (sp) transmissions. He spend a good amount of time doing this and the result is an awesome sound with maximum power.

My short opinion... no cat

My 81 turbo car (8V) has no cat and I think that if it had cat the performance would be diminished. Not sure how this applies to 16V's as I thought all 16V cars had a cat due to the tougher emission standards that came about in the mid-80's in most countries where Saab's are/were sold.

Craig.

Eliteforeignauto

· #11 · Sep 13, 2008

fu*k cats thats all i have to say....
3 years 1990 spg no cat...

AutoXer01

· #12 · Sep 16, 2008

No cat for sure. Simply running with headers and an exhaust provides plenty of backpressure. I don't believe in cats too much anyway...I used to have a 01' tiburon with no cats (came with 2 for cali emissions) and it still passed emissions every year I had it (5yrs).

Make sure you get some sort of straight through muffler or resonator though or else you will sound very riced out. The only thing a cat does is wipe out a lot of high frequency noise.

jarnold88

· #13 · Aug 2, 2010

If the car is turbo then you can run with no exhaust! the turbo is the back pressure. As for N/A i run straight pipe and gained quite a bit high end power nothing noticable until on the highway.

86notchback

· #14 · Aug 3, 2010

I found you josh about time.....oh and for my 2 cents im gonna be running sans cat on my 85 8V valve as soon as I deal with the exhaust....its gonna be wicked

94cde

· #15 · Aug 4, 2010

look at the power ratings on the turbos w/ and w/o cats.. good for 10bph from the factory w/o cat.... not that the n/a will make that much powa but its worth a shot if you got it for a song....

Jack Straw

· #16 · Aug 4, 2010

94cde said:
look at the power ratings on the turbos w/ and w/o cats.. good for 10bph from the factory w/o cat.... not that the n/a will make that much powa but its worth a shot if you got it for a song....

That's because they are fueled differently. You will get a small gain in power though.

86notchback

· #17 · Aug 11, 2010

may not look pretty but sounds great and I swear I have more powaaarr...

See less See more

turbo1992

· #18 · Sep 5, 2010

86notchback said:
may not look pretty but sounds great and I swear I have more powaaarr...

Did you cut that from a stock section and just clamp it? Does it perform better than a gutted cat?

skoart

· #19 · Sep 14, 2010

response for palmer

i have a 91 900 non turbo with a mss header/straight thur cat and rebuilt mss exhaust system. for your infro/when was the last time you were at the airport and heard a ww2 fighter take off!!!!! that's what it sounds like.

bare

· #20 · Sep 21, 2010

A 4 ! cylinder fighter

1 - 20 of 21 Posts

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