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Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by PGL4VT, Nov 29, 2002.
Some say removing it kills torque due to loss of back pressure. Opinions?
There is that school of thought. However, overall I THINK the generally accepted idea is it'll help. An engine is nothing but an overgrown vaccuum, so less restriction everywhere is a good thing. I think tho, that a small amount of backpressure does help torque, but I'm not an expert on it, or on much for that matter!! I gutted it and the precats in my 96 MX-6 with a Ford logo and I noticed a diff. Remember it can actually be bad tho, alot of turbulence can end up in there, as well as it can make a stupid noise. If you can do a test pipe, great, or if there's a chance it'll be looked at I've known people to put a pipe the same diameter as the exhaust thru the cat and weld the edges. Or a pipe that just fits. looks stock but alot less reisitance. Good luck!
I personally don't really buy into the backpressure idea, (look at really fast vehicles, they run specially tuned headers, not cats to manage exhaust : )
and I don't buy into stock cat converters restricting flow either necessarily. To tell you the truth, any claims or "testing" I have seen, have all been USED stock catsagainst brand new "high flow" cats. There was an article in Corvette Fever that did exactly that, and it's not a fair comparison at all.
"I personally don't really buy into the backpressure idea, (look at really fast vehicles, they run specially tuned headers, not cats to manage exhaust : )"
Well, really fast vehicles usually have really big horsepower, so their 4" straight exhaust supplies enough backpressure. You wouldn't put 4" exhaust on a 275 HP engine most likely.
(I think this is right, I'm a newbie so if I'm wrong then lemme know...i can take criticism..)
I have had people tell me back pressure is good for your motor I say thats 110% BULLSH*T. Here are 2 Examples I have had with motors. Lets Start with my 4 stroke 4 wheeler. I had a straight through exuast pipe on it which was loud but the motor loved it. The engine was very snappy and had great torque no matter what Rpm. I put the stock pipe back on to make it less noisy and to see if i would gain more torque. Well it had less torque and exceleration. Now My 86 K5 Has a 350 Which makes 300 Hp. I have dual exhaust and had to put 2 cats on for inspection. After installing the cats I felt my motor was not as snappy and a little slower.
If I had my way Every engine i owned would have straight through exhaust. /forums/images/graemlins/wink.gif
/forums/images/graemlins/grin.gifJust my 2 cents. /forums/images/graemlins/grin.gif
<font color="red"> 86 K5,6" Lift,35 BFG,10 bolts,4:56,Hotted 700-R4 </font color>
Everyone I know that has gone to "oversize pipes" in 1/4 mile cars has been faster, or has shown more total power on the dyno. You might lose some low end (which you see with headers too most of the time) but the gains higher up are worth the trade off. You don't lose much down low, but you gain a lot up high.
There are different schools of thought on this, no matter how technical people get, you'll still see people disagreeing on it. : )
Pulling the cat on my S-10 way improved high end, but it lost it's balls at 2,000 RPM.
1/4 mile cars use it because horsepower is what they need, torque is for towing vehicles. Also, yeah they make gobs more torque, but it's at about 3,000 RPM higher.
Small tubes help low end, big tubes helps high end...it's up to you
Actually, checking on desktop dyno2k (just for general indication what change X will do to HP/TQ numbers) headers are a big step up from manifolds even at 2000RPM (and all the way beyond) on a "torque" built motor.
Manifolds create LOTS of backpressure, (restriction) if it was a good thing, the TQ numbers wouldn't be better with less restriction (small tube headers) than with the manifolds, at least in my thinking.
I haven't any links to cat/no cat dyno comparisons, and even if I did, I still don't think you could draw many conclusions from it, since there are still too many variables. I *will* say that a properly operating cat converter is not enough of a restiction to worry about hollowing it out just to do it. Most of us aren't timing ourselves in the 1/4, or putting our trucks on dyno's, so we won't notice it.
Problem is, there is no easy way to know if the converter is flowing at its potential, or if its clogged or internally broken, you've got to pull it off to check, and even then you really can't know if its hurting a little bit.
I have a feeling what we are talking about here, for most motors on this list, are small differences that aren't going to be noticeable.
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