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View Full Version : Anyone Straight Pipe 7th Gen?



nitsua93
02-18-2012, 06:13 PM
Has anyone done a straight pipe on their Celica? I've thought about doing it but I kind of would like to keep the stock cat.

vip09
02-18-2012, 08:04 PM
Just unbolt the rear section of your exhaust. I had mine like that for a long time. Enjoying my stock exhaust now.

MCcelica
02-19-2012, 12:03 AM
I had it mostly open for a while. It was just too loud for me. Wound up switching it for an Apexi WS2.

nitsua93
02-19-2012, 04:11 AM
Just unbolt the rear section of your exhaust. I had mine like that for a long time. Enjoying my stock exhaust now.

That would be the dumbest thing ever. Like I said, I'd like to keep back pressure. I'm probably going to put a 1.5" pipe with a 3" tip. That will keep a lot of back pressure and sound legit.

T-spoon
02-19-2012, 04:32 AM
That would be the dumbest thing ever. Like I said, I'd like to keep back pressure. I'm probably going to put a 1.5" pipe with a 3" tip. That will keep a lot of back pressure and sound legit.

Actually, THAT sounds like the dumbest thing ever. At least what he did didn't cost any money. What you want to do would be expensive, as well as pointless and sound like garbage. I'd have been more gentle, but if you're going to pull out attitude as one of your first posts.....

nitsua93
02-19-2012, 09:34 PM
Actually, THAT sounds like the dumbest thing ever. At least what he did didn't cost any money. What you want to do would be expensive, as well as pointless and sound like garbage. I'd have been more gentle, but if you're going to pull out attitude as one of your first posts.....

I apologize for the attitude, but unbolting will take away almost all my back pressure. Thus reducing gas mileage and reducing power. If I spend maybe $300 for a 1.5" mendrel bent pipe that would probably be the best straight pipe scenario.

CollapsedNut
02-20-2012, 02:42 AM
Why bother.. there is nothing to gain aside from ricer sounds.

Hipster Lawrence
02-20-2012, 04:28 AM
That back pressure sure stuff is a myth. This has been floating around the bet for a while. It's not a bad read.


--------------------------------------------------------------------------------

Backpressure: The myth and why it's wrong.

I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?
I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s)."

bloodMoney
02-20-2012, 11:28 PM
Good read Jessie.

Now, I'd only half of the general population knew what that meant.

Seriously though, Abby is going to have a 1/2" true dual exhaust system this year.... I gotta keep all the back pressure up!

vip09
02-21-2012, 12:55 AM
That would be the dumbest thing ever. Like I said, I'd like to keep back pressure. I'm probably going to put a 1.5" pipe with a 3" tip. That will keep a lot of back pressure and sound legit.


You are retarded. You will gain power by removing the rear section. Adding back pressure will kill your power.

nitsua93
02-21-2012, 05:17 PM
You are retarded. You will gain power by removing the rear section. Adding back pressure will kill your power.

I never said I was going to add back pressure. I said "I'd like to keep back pressure". I know it's there for a good reason, so why change it too much?

Thanks cavemanlarry! That was a good read. Can you tell me where you got it from?

vip09
02-21-2012, 06:05 PM
A straight 2.5" exhaust will be the best thing you can do. Unbolting the rear exhaust section at the rear suspension and removing it will give you a straight 2.5" exhaust for free. It is loud, and you will gain power. Whatever you do, don't mess with the stock collector between the exhaust manifold and the cat. Also, if you delete the cat you will get a CEL.

renegadex
02-21-2012, 06:21 PM
It's retardedly loud without the rear section. You will make yourself def and pray to god you don't have any passengers in the back seat.

Hipster Lawrence
02-21-2012, 07:14 PM
It's all over the net. Just google back pressure myth. As for the original source I haven't a clue. I'd bet it's from a hot rod mag though.

nitsua93
02-21-2012, 08:22 PM
A straight 2.5" exhaust will be the best thing you can do. Unbolting the rear exhaust section at the rear suspension and removing it will give you a straight 2.5" exhaust for free. It is loud, and you will gain power. Whatever you do, don't mess with the stock collector between the exhaust manifold and the cat. Also, if you delete the cat you will get a CEL.

I see people say "CEL" all over. What's that mean? Is that just a computer code?

I'm going to unbolt my exhaust when I'm at our company's shop in the middle of nowhere. Doing that in my neighborhood does not seem like a good idea :P especially since it's mostly old people. I'm not going to leave it unbolted though, I'll have to get a full 2.5" pipe all the way through, or maybe I can bolt a pipe into where I unbolted the stock exhaust. I know someone who can program ECU/ECM (whatever it is that they program) to make the computer not care that I removed the CAT and CAT sensors.. I can reset/disable the OBD codes that I'll receive by removing the CAT.

Luni
02-21-2012, 08:26 PM
CEL is Check Engine Light.

If you remove the cat, youll pull a CEL. If you just unbolt the rear part of the exhaust, you wont.

And I doubt anyone you know is going to be able to reprogram your Toyota ECU to not care about the code. They might install an O2 simulator, but theyre not reprogramming that ECU.

nitsua93
02-21-2012, 09:05 PM
CEL is Check Engine Light.

If you remove the cat, youll pull a CEL. If you just unbolt the rear part of the exhaust, you wont.

And I doubt anyone you know is going to be able to reprogram your Toyota ECU to not care about the code. They might install an O2 simulator, but theyre not reprogramming that ECU.


Hmmm... is a Celica's ECU different than the standard programmable ECU? I could put the O2 simulators in myself, I've thought about doing that anyway/

UtahSleeper
02-21-2012, 10:38 PM
You could use 2 spark plug anti foulers on the second o2. It pulls it out of the stream to "trick" the ECU that the cat is burning some of the excess fuel. Did this on a protege with a gutted preCat and recieved no CEL.

Anyone know if there is any truth that the best exhaust size for a NA (small) 4 banger is 2 1/4? I know you cant say for every motor, but it seems llike a reasonable generic diameter. Saw it posted all over the protege forum I use to frequent.

vip09
02-22-2012, 02:05 AM
From what I've seen, the O2 simulators don't work well on the 7th gen.

And no, your friend cannot program your stock ecu.

Hipster Lawrence
02-27-2012, 01:34 AM
I don't know about the celica but lots of newer cars use the post cat o2 to fine tune fuel trims. I'd just run a cat if in doubt.