EXHAUST FLOW

[trimless]

Maybe I'm simple minded... Can someone explain how you can increase exhause flow with headers or cat-back exhaust when the same catalytic convertor remains in place? It seems to me that the Cat is the bottleneck and no increase in flow can be achieved unless you remove or upgrade the cat! So if I'm wrong, please explain why. Thanks!

[woody1]

If the Pre/After-Cat and Y-pipe is more restrictive than the Cat, it makes sense when they are replaced you get more flow. However, after the CatBack, Headers and cross-over are replaced THEN the CAT is obviously the restrictive part remaining and the next item in line for replacement. Don't have any specific stock flow ratings for the parts mentioned to back this up (maybe some of our techs do) only what I've seen as results from my own and others experiences reported in these pages.

[GeneralTJI]

The more restriction you have the more power will be taken away. So if your cat and muffler restrict flow.. relieving the exhaust system of some of that restriction by replacing the muffler will allow more flow because there is less fighting flow= more power. Decrease all the restiction by removing your cat or getting better one and you will gain some more power.<br /><br />Exhaust will only give you so much, dont belive those who tell you, you can get 25-50 hp from a better muffler ! BS !

[trimless]

Thanks for the imput. But I'm still not convinced. MY theory is that the exhaust system is like a funnel. Picture this: The exhaust manifold or headers is the top of the funnel, the Cat is in the middle, the muffler is the bottom of the funnel. On the typical exhaust system, the funnel looks like an hour glass because the Cat is usually the most restrictive part to the exhaust system. If you "open up" the top with headers and the bottom with a better flowing muffler, you are still limited in your flow rate with the cat no matter how much better the two ends are flowing. So in theory, if you make the top and bottom opening of an hour glass shaped funnel "bigger" , the flow will remain the same because the "middle" (Cat) remains the same opening size. I know a few folks have claimed better performance on the Tundra when installing Cat Back exhaust or headers. But i haven't seen any real numbers yet. Only an opinion of the driver that the truck "feels" faster or has improved performance because of a race with two different vehicles. I'm not disputing the claims, but it would be nice to see some real numbers. I'd love to hear from someone that has a G-Tech or similar measurement device with before and after numbers. I'm debating on whether to spend the money to remove a perfectly good exhast sytem. Convince me to do it!
Thanks-Long Dong

[HockeyFreak]

LD,
If your statement is true, how can Borla and the other Cat-back manufacturers claim a hp and torque gain? These companies obviously know what they are doing, that is why they have been in business for so long. Why don't you call them and have them explain it to you. If you replace your stock muffler with a high flow muffler you reduce your OVERALL exhaust restriction.
hockeyfreak

[pakalas]

But if you get the Bassani Xhaust system like I did, you get rid of the restricted Y and the third cat or resonator that is before the muffler. I live in Hawaii so it was a resonator not a cat. With straight pipes coming out of each side of the engine, into the muffler, than out, I'm sure I got hp increase. No numbers but I can feel the difference! One bad thing about getting rid of the Y, you lose some low end.

[Tundra_Jules]

My Tundra seems to pull much smoother now and there is no "fall off" of power in the mid to high rpms. It feels more like a direct linkage throttle than the drive by wire system that is on the truck. Ever notice how when you press on the accelerator that it doesn't seem to increase speed proportionally? This was really noticeable to me, probably because my previous car was a modded Mustang GT. Throttle response was much better on that car. Changing the exhaust on my truck definitely improved throttle response and improved performance. The problem with most factory exhaust systems is that they are too restrictive and it isn't because of the cats. The manufacturer likes to make quiet cars and trucks because most people don't want to listen to the drone of a high performance exhaust system. They make them restrictive to make them quiet. They also go the cheap and fast route when bending pipes to make them fit under your vehicle-some of the bends in a stock exhaust are very restrictive. In doing so, they rob horsepower. I replaced the headers on my '94 Mustang GT along with the mufflers and there was a noticeable improvement in throttle response and acceleration. I don't have numbers but it IS noticeable. Same with my Tundra. That stock Y pipe is very restrictive, I have photos of it after the shop cut it out of my truck along with the custom Y they fab'd for me. I would be happy to e-mail the pics to you if you like. Have you ever watched any of those high performance shows on TNN? They are always replacing factory parts on cars and trucks and slappin' em on a dyno. I remember they took an S-10 pick up truck and replaced the factory airbox and exhaust system and I think it made like 10-15 more rwhp as a result. I don't remember the exact numbers but it was a noticeable improvement. Fact is, the catalytic converters are not the most restrictive part of the exhaust system. I don't need a dyno to prove what I already know though. I'm satisfied with the results I got for the money I spent.

[Tundra_Jules]

I just found this on http://www.magnaflow.com/02problems-a-restrictions.htm This is an example of why the stock exhaust system on the Tundra is so restrictive. Once look at that Y pipe and you can see what I'm talking about. "PROBLEM: Pipe diameter reduction is a common problem with OEM style bent tubing. In a sharp bend, this reduction may be as much as 20%. A 2" diameter pipe may see a flow reduction equivelant to a 1-3/4" diameter pipe. In effect, this reduces the entire system's flow capacity to the smaller dimension and increases backpressure."

[KLS]

Every fluid flow system, including intake air and exhaust gases, must be engineered for a particular flow rate. There is no way a system can be improved for all flow rates, i. e., rpm ranges.The narrow Y-pipe on the Tundras helps low rpm performance. At certain rates of flow the right amount of backpressure is beneficial. If you drive at high rpms, get an exhaust system engineered for high flow rates. If you mainly drive around town, or drive most often in the 1800-3000 rpm range, bigger, high flow pipes may lose performance.
Ken

[trimless]

Thanks for all of the input. I took a good look at the stock exhaust today and it looks like it could use some improvements! The Y-pipe has 2" pipe going from the manifolds to the muffler where it joins into a flow restricting mess right at the muffler, and a single 2 1/2" pipe from the muffler on out. This exhaust system was definately designed for low end torque. I've decided to go the custom exhaust route. The fact that I will have this truck only 3 or 4 years had a lot to do with the decision. Sure, I could spend $500 or more and have a nice pre-fabricated stainless exhaust, but that's a lot of money. I'm going to go with 2 1/4" mandrel bent pipe fom the Cat's into a single muffler with 2 inlets and one 3" outlet. Although a dual outlet looks better, I'm going with a single 3" for budget reasons. When completed, I should have a much better flowing exhaust and hopefully it will sound as good as those $500 systems. I'm not sure which muffler I'm going with, still in the research mode. I'll be sure to perform "before and after" test with my G-tech unit and post the results.
Long Dong

[Tundra_Jules]

I wish you could see my set up. I had it on my profile BTSC (Before The Server Crash). If you PM me with your e-mail address I will gladly send you a pic of the cut out of the stock Y pipe and a pic of the Y I have now (hell create a yahoo account if you're worried that I might spam you-I won't though) .Basically, the stock Y is two seperate 2" pipes which are each bent into a D shape where they meet. They match up along the straight edge of the D and this is where they converge into one 2 1/2" pipe (at best). So you have two 2" pipes going into one 2 1/2" pipe (more like 2 1/4" if you ask me). I may be off a bit on the tube diameters, I didn't measure them but the pics illustrate my point quite well.<br /><br />Mine is 3" from the Y to the muffler and 2 1/2" coming out of the muffler to the exit at the stock location. Other than the chrome tip and V8 rumble (not too loud) it looks completely stock until you crawl underneath it.

[Tundra_Jules]

Custom was by no means cheap though. The shop spent a good 3 hours doing my truck with 2 guys working on it at least 1/2 the time. Add to that the cost of the muffler and tubing and I spent $600 on the thing but it was worth every penny. Everything is welded, no clamps, they even sprayed on some high temp silver paint to protect the welds from rusting. Real nice work.

[rb280zx]

Originally Posted by HockeyFreak

LD,
If your statement is true, how can Borla and the other Cat-back manufacturers claim a hp and torque gain? These companies obviously know what they are doing, that is why they have been in business for so long. Why don't you call them and have them explain it to you. If you replace your stock muffler with a high flow muffler you reduce your OVERALL exhaust restriction.
hockeyfreak

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