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Hi flow Cat or Straight threw cat? 

 

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Posted: Thu Aug 14, 2008 8:07 am 
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running with an hollowed cat does make the the engine smell its running rich and leaves black crap(petrol) on the ground at the exhaust tip
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Posted: Thu Aug 14, 2008 10:33 am 
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if any one is interested, there is a group buy on ford forums for cats in the Au section, $165 for 2.5 inch cat metal core magnaflow. they have other sizes available.
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Posted: Thu Aug 14, 2008 11:46 am 
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Quote:
I also noticed that there was not enough backpressure to the engine, which caused me to have a massive flat spot.


if your cat was fully hollowed the problem was the larger volume of the cat slows down gas velocity when it enters the cat, which is wider and fatter than the pipe, hence the fix being some straight pipe of the same diameter as your exhaust. for example, a 2.25 inch exhaust will have better exhaust gas velocity at 2000 rpm than say a 3 inch exhaust, because the gas has less time to expand and cool becoming heavy and clogging the system. however the 3 inch system will be more efficient at 5000 rpm, where the 2.25 chokes. so until your revs got to the point where it could overcome the velocity drop in the gutted cat you would find your flat spot.

backpressure regards flow, and velocity is another animal. velocity tends to help torque and flow helps HP. which is why gutted cats do give higher hp.

 

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Posted: Thu Aug 14, 2008 2:44 pm 
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i had a hm headers high flow cat and with the turbo it was a huge restriction,im making way more power w/o a cat and it sounds the same with straight through pipe on my car

 

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Posted: Thu Aug 14, 2008 3:37 pm 
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madeaspack wrote:
i had a hm headers high flow cat and with the turbo it was a huge restriction,im making way more power w/o a cat and it sounds the same with straight through pipe on my car
just dont tell the cops or the EPA that fast though!... :!: :shock:

 

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Posted: Thu Aug 14, 2008 6:49 pm 
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madeaspack wrote:
i had a hm headers high flow cat and with the turbo it was a huge restriction,im making way more power w/o a cat and it sounds the same with straight through pipe on my car


how do you run HM Headers with a turbo? I've never seen them make a turbo manifold, only extractors.

 

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Posted: Thu Aug 14, 2008 7:56 pm 
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twr7cx wrote:
madeaspack wrote:
i had a hm headers high flow cat and with the turbo it was a huge restriction,im making way more power w/o a cat and it sounds the same with straight through pipe on my car


how do you run HM Headers with a turbo? I've never seen them make a turbo manifold, only extractors.


"hm headers high flow cat", I'm guessing its a cat made by HM :?

 

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Posted: Thu Aug 14, 2008 9:27 pm 
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i remember booting my car few yrs back and blowing out my cat's guts, had no idea it blew all it out till recently when i got a 3 inch exhuast lol, found a hollow cat...and a blocked up muffler

 

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Posted: Fri Aug 15, 2008 8:55 am 
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i have a proper 3 inch cat now

 

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Posted: Sat Aug 16, 2008 3:53 pm 
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krisisdog wrote:
I've smelt a few cars with gutted cats now, and they smell the same, maybe a bit rich if anything.


Wouldn't the R.S.P.C.A get up ya for gutting cats? :lol: :lol: :lol:

 

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