Can we talk backpressure, cats?

[starchland]

Ive been doing some reading on replacing my cat due to reasons of some odd noise. But the question lies in backpressure, when i installed my magnaflow catback I did notice somewhat of a drop in low end power(butt dyno). Ive read that lack of back pressure means less torque is just a myth, but im not sure what to believe?

[zipcreature]

http://auto.howstuffworks.com/
http://www.flowmastermufflers.com/backpressure.html
I will attempt to explain it as I understand it. *These answers are by no means correct nor accurite in any way. I got most of them from a fortune cookie today at Wong's Express/Italian Sub shop.

Searching owns you. Less back pressure on a stock car can mean a drop in trq due to the scavaging (sp) effects of the exhaust. What that means is since there is more vaccume on the exhaust side, some of the air/fuel mixture is sucked out. This is bad because it burns in the exhaust making a hotter exhaust. It also can lean your cars a/f mixture out which is bad because it means your losing trq through less engine combustion pressure I believe. It also means your combustion temperatures will be alot higher which can damage your car by frying your rings, and blowing the welds on your intake manifold. Something I think we all want to avoid.


- Zipcreature


- Zipcreature

[h22sparkle]

lol Thats messed up welds on the intake manifold. Unless your turbo. Btw I have a catalyc converter by magna-flo for sale.

[starchland]

Im looking for information geared more towards cb7s and hands on information as to what the affects are to our cars, not in general. Thanks for searching for me though

[Fearit22]

You really should search for this because I've personally commented on it at least 10 times. I won't flame you Zip since you just got this information from someone else, but I will say the people at Flowmaster are retards. The thing about losing torque is partially true, but totally irrelevant. You lose torque down low because the exhaust is more free flowing so there is going to be more turbulence in the low rpm's decreasing flow velocity. Once there is enough air flowing in from higher engine speeds the max flow velocity is increased which will result in an increase in power. So basically you gain power where you need it in the upper rpm's and lose very little down low. Whenever you race you never do it below 3500 rpm's which is where the loss would be. If you want low rpm torque with a Honda then you should just give up and get a v8 anyway.

Now for why these people are stupid. Look at the size of a piston compared to a valve. Which one does it look like would cause more suction? There will be some pull from the exhaust, but it wouldn't apply in almost any street application. Which is why the only time you really feel/see an exhaust being extremely hot is off something like a pro dragster. You don't see too many Honda's driving down the road shooting out fireballs. You basically need a lack of an exhaust system and very high engine rpm's. Besides those facts from their diagrams you would think they would even be able to tell the angles of their flow is stupid. The valves point at about 60 degrees downward so they are fairly close to being parallel. So according to a magic forcefield in their diagram the intake charge suddenly changes direction by 120 degrees. Which is even more illogical considering how much larger (weight and volume) the piston is than a valve. The force from the air of the valve would have to be considerably larger than that of the piston for the intake charge to flow out without having first been combusted.

One of the main good aspects of upgrading the exhaust on your car is that it keeps your car cooler. There is more surface area on the exhaust and air in it to dissipate the heat more quickly. So pretty much any street application of an exhaust is going to do nothing but good for the engine. Flowmaster you get a big

[starchland]

...One of the main good aspects of upgrading the exhaust on your car is that it keeps your car cooler...

by pulling heat away from your engine, which is a good thing
Just about to correct one of the earlier posts that said you may 'fry your o rings' . because of this.

[koolkoreanked]

You don't see too many Honda's driving down the road shooting out fireballs

LOL mine does. Just little ones when the engine is decellerating but thats just because my exhaust dumps at the flex pipe. I've been meaning to get this fixed but I dont want to lose the extra power and mpg I've been experiencing. fearit22 hit it right on the head with what he said. If it was me in your situation I would just replace the cat with a test pipe and be done with it. but thats just me.

[zipcreature]

Fearit22 - I want 3 of everything...lol Right on about "Whenever you race you never do it below 3500 rpm's..." And thank you for clearing that up I'm sorry for the misinformation.
Eliot explained intakes and exhaust by saying "yes you lose low-end power, but gain more max hp and trq". It is all about tuning the power curve - where you want the power to be.


- Zipcreature

[Fearit22]

Fearit22 - I want 3 of everything...lol Right on about "Whenever you race you never do it below 3500 rpm's..." And thank you for clearing that up I'm sorry for the misinformation.
Eliot explained intakes and exhaust by saying "yes you lose low-end power, but gain more max hp and trq". It is all about tuning the power curve - where you want the power to be.


- Zipcreature

Yeah, you got that right ... just shifting the powerband. No harm done at least you presented some info even if the people at flowmaster don't have a clue what they are talking about.

[starchland]

thats a good point zip about tuning the power curve, even if your not really picking up much hp or tq, the curve is more useful.