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Lsn2this
Dodge Dakota
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9/13/2006
17:48:57
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 Subject: RE: cat removal =HP?
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OBIO3 thank you very much! Thats what i was trying to say from the beginning about back pressure. and can also agree about the 2 stroke and 4 stroke comparisons... there isnt one. reeds NEED the backpressure to function properly. where as a 4 stroke DOES NOT need any. im not saying take off the exhaust, but an exhaust that offers zero backpressure is best.
Oh and leave the insults at home where they belong 2000dak :) this is a discussion :)
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N56629
Dodge Dakota
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9/13/2006
21:25:15
| RE: cat removal =HP?
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"take the manifolds off start your motor and try and rev it with 0 back pressure it will break up and sputer and not rev over 2000rpm"
That's not really a valid illustration because you have just eliminated all scavenging effects.
I agree that the cats are not restrictive but you definately won't lose on the low end just because you remove it. The only thing valid here is that there is absolutely no reason to remove a perfectly good functioning cat with the mistaken notion that you are gaining performance. If anything you may lose something because the computer is missing some important information and may be the cause of eventual poor performance. However, that lose isn't do to a lack of backpressure. Of course we all know that there are O2 sims that can eliminate problems caused by the removal of the cat.
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stevedak
Dodge Dakota
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9/14/2006
13:53:03
| RE: cat removal =HP?
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My dakota was without a cat for several months, used a straight pipe. Yeah, I know, I should surrender to the EPA, pay a million dollar fine and burn in hell, yada, yada, yada... Anyway, I just installed a magnaflow cat. Their is definitely no loss of performance with the new cat. It might be a little better torque off the light but in general, no significant difference. I don't see any reason to remove a cat in good condition.
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GB2000
GenIII
9/14/2006
14:42:44
| RE: cat removal =HP?
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stevedak...did you notice any gains whatsoever or a deeper exhaust tone (as compared to your factory cat)? Just curious as I got a Magnaflow cat sitting in my passenger seat now waiting to be installed...lol
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stevedak
Dodge Dakota
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9/15/2006
10:23:47
| RE: cat removal =HP?
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GB2000 I had a straigth pipe, no cat when I bought the truck used, so I never had the stock cat and can't make a comparison. I noticed a very slight gain in torque (I think...) but nothing to get excited about. The main thing is that I didn't lose anything, didn't lose torque, HP or MPG. I already had a deep exhaust tone due to no cat, minor exhaust leak and a high flo muffler. I added the cat, fixed the leaks and now it sounds sweet
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BP guy
Dodge Dakota
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9/16/2006
09:20:27
| RE: cat removal =HP?
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I absolutely love debating the whole back pressure issue and I'm glad most of my competition has no clue how it works.That only helps me win more races.
Obio3 -not only have I read about the differences in 2 and 4 stroke design,I have also built many engines.yes both 2 and 4 stroke.They both have a point in the power cycle where intake and exhaust are both open.Pull the head off of a 2 stroke.now move the piston down from TDC(that's top dead center incase you don't know)you'll see a point where exhaust port and intake port are open.Next,go buy a camshaft for a 4 stroke engine.wait,you don't even have to buy one.Read the specs on one (ANY ONE)and you'll see there are a few degrees on the cam where both the exhaust & intakes are open at the same time.Regardless of engine design,this is the most critical time for making the exhaust most efficient.As different as their basic designs are they are both piston engines that pump air in and out.Likewise they will both suffer if they are not given enough area to expell used gas or if they are given an area so large that there is not enough charge inertia (that's the momentum of the exhaust gases in case you didn't know)
Every time I hear about somebody installing a high flow "whatever" I have to wonder where everybody gets the idea that more flow equals more horsepower.Funny how most heads and intakes which do the POOREST on cfm flow bench seem to perform better on dynoes than a higher cfm rated comparable part.Oh hmm let's see how could that be possible?
One of the best things I've read that deals with what I'm trying to say is on the Grape Ape Racing site.These guys are world renowned for their racing products,so why then do their components flow so much less on the bench than competitors,yet far surpass anything on the track?
but hey I could spew forth my ravings all day long,and it still won't amount to a hill of s&^% with most of you guys on this site.So go ahead and put on those 4" exhaust pipes and use your butt dyno to swear to the world that you have a mean machine now.I'll stick with the formulae that I've used for 18 years now....
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BP guy
Dodge Dakota
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9/16/2006
17:41:56
| RE: cat removal =HP?
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oops I forgot a few things....
when somebody says "With all due respect,you best do some reading on engine design"
and
"Do some reading at the library and learn what's real. then bring it here to share."
then says something like
"The reed is the only help a 2 stroke gets and I'm not so sure they all have a reed. In days past none had one" in the same paragraph, I have to wonder ,if you're "not so sure" about what I need to read up on,which library you've been to?
the reed is the only help a 2 stroke engine gets for back pressure???? where did you read that?
the reed(s) which are in front of the carb produce absolutely zero back pressure.The converging end and stinger of the expansion chamber(exhaust pipe) are what create back pressure, my friend..The reeds prevent fuel from flying back into the carb when the piston displaces the fuel charge inside the crankcase on it's down stroke and have ABSOLUTELY NOTHING to do with back pressure..
BTW...
ever heard of a piston-ported 2-stroke?
Take the carb off your weedeater..I challenge you to find the reeds.
"Drill a hole in the exhaust pipe directly in front of the cat to hook a pressure guage to. Guess what. Most pressure you will have at any given time is 1 &1/2 lbs of pressure. Almost none at all"
Have you done this?with a calibrated gauge?Have you taken the cat off then measured again?Have you used different mufflers and tested the pressure again?If you have ,you probably get a different reading everytime.Not much difference probably,but do you ever really gain or lose a whole lot of power changing muffler types?see my point?Let's say you're absolutely correct-1.5 pounds(I assume you mean PSI)this may seem small to you but it is pressure nonetheless.I guarantee if you reduced that pressure 33 percent or so with an exhaust component(then that'd be 1 psi in your example)you'd see a noticeable difference in engine performance.2 OR 4 stroke
so many questions ..so few people with the correct answers...
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