Nissan Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
106 Posts
Discussion Starter · #1 ·
I put on a MagnaFlow cat-back exuast with 2 1/4 " piping on a while ago and was wondering if it would give me enough back pressure to give me a horse power gain. Somebody told me that some tips dont have enough back pressure and can actually create a loss in power, can anybody help me with this?
 

·
neutral handling is cool
Joined
·
180 Posts
I have a 2.25" exhaust and I gained 7-11 hp all over the curve. 2.25" is pretty optimal, but 2.5" is also good I heard.
 

·
Registered
Joined
·
413 Posts
91SERHondaKiller said:
I put on a MagnaFlow cat-back exuast with 2 1/4 " piping on a while ago and was wondering if it would give me enough back pressure to give me a horse power gain. Somebody told me that some tips dont have enough back pressure and can actually create a loss in power, can anybody help me with this?
Absolute horse doodoo! I have a custom 2.25" stainless catback piping with a Magnaflow SS 2.25" muffler and don't have any issues whatsoever!

If you installed larger than a 2.5" cat-back on your NA car, then I can see you having an issue. A standard 2" to 2.5" straight through exhaust is fine with your NA. Especially with your mods.

Your power loss has to be from something else going wrong.
 

·
neutral handling is cool
Joined
·
180 Posts
I have the pacesetter muffler that came with the exhaust...it looks ok, but since the exhaust is painted black and the tip is very shiny(chrome polished), it looks like just a tip. If you put a 2.5" cat in the middle of the 2.25" piping exhaust, theoretically you'll have a power loss because of the relationship between pressure, volume and flow velocity...stick with a 2.25" cat for a constant exhaust stream velocity.
 

·
Registered
Joined
·
413 Posts
gottabfast said:
... If you put a 2.5" cat in the middle of the 2.25" piping exhaust, theoretically you'll have a power loss because of the relationship between pressure, volume and flow velocity...stick with a 2.25" cat for a constant exhaust stream velocity.
What? :rolleyes: Theory doesn't always seem to be correct way to do things.

The OEM Nissan stock catalytic has a 2.5" inlet/outlet. It is quite substantial for the basic bolt-on mods and even basic turbo upgrades.

Stick with an OEM or an OEM direct bolt on replacement with the same diameter inlet/outlet as OEM.
 

·
Icy Hot Stunta
Joined
·
2,366 Posts
91SERHondaKiller said:
I put on a MagnaFlow cat-back exuast with 2 1/4 " piping on a while ago and was wondering if it would give me enough back pressure to give me a horse power gain. Somebody told me that some tips dont have enough back pressure and can actually create a loss in power, can anybody help me with this?
I have proably written this a million times in many different places but backpressure never helps, it always hurts.

What makes a car with big pipes slow is a loss of velocity in the exhaust system. You need velocity to help scavange the charge on overlap. Veloctiy also helps create a vacume behind a closed exhaust valve so when it opens the exhaust is sucked out as well as pushed out.

So what you want is the lowest backpressure and the highest velocity in the exhaust. Thats why straight thru pefforated core mufflers work the best and why you don't want to go crazy and spec too big of an exhaust pipe on your NA ride.

Mike
 

·
neutral handling is cool
Joined
·
180 Posts
Ok, when I had the 2 catco cats, they were 2.5" inlet/outlet and I put down 134/122 to the wheels...3 weeks later I put it in the shop to replace the clutch, add a lightened flywheel and replace the crappy/busted catco cat...when I went to pick it up from the shop the dyno showed 142/128...the new magnaflow was 2.25" inlet/outlet. I'm pretty sure not all 8 hp was lost to the old clutch, or maybe the catco cat was that crappy...it wasn't busted when it was dyno'd the first time.
 

·
Icy Hot Stunta
Joined
·
2,366 Posts
91SERHondaKiller said:
I have a 2 1/4" to a 4" tip, should I downgrade the size? And if I do, what would be the best one to buy?
No 21/4 is pretty good for an SR20
 

·
Registered
Joined
·
118 Posts
thats not completely true if you get a perforated tip, it will lower the decibels some, im trying to get my hands on a sebring stainless steel perforated tip
 

·
You get what you pay for.
Joined
·
156 Posts
Re: Re: Back Pressure

Mike would you agree that the correct velocity to obtain would be approximately 250 Ft/sec ?

morepower2 said:
I have proably written this a million times in many different places but backpressure never helps, it always hurts.

What makes a car with big pipes slow is a loss of velocity in the exhaust system. You need velocity to help scavange the charge on overlap. Veloctiy also helps create a vacume behind a closed exhaust valve so when it opens the exhaust is sucked out as well as pushed out.

So what you want is the lowest backpressure and the highest velocity in the exhaust. Thats why straight thru pefforated core mufflers work the best and why you don't want to go crazy and spec too big of an exhaust pipe on your NA ride.

Mike
 
1 - 13 of 13 Posts
Top