so currently i have a 2.5" test pipe on my car, but i have a cat layin around from my dx, and was wondering if you guys think i could get some more back pressure if i install the cat? my car feels like it doesn't have enough back pressure till i rev it a little bit, then it's good (all top end power?)

here's my exhaust setup:
stock z6 4-2-1 header, --> ebay test pipe, --> sir exhaust w 2.25 piping all the way back. is this too much for a tiny little d15b1? lol

thanks in advance!

 

you can feel backpressure? and you LIKE it?

 

https://honda-tech.com/forums/tech-misc-15/backpressure-vs-exhaust-velocity-explained-2077910/ check that out.

 

idk i was just wondering how to make my car feel less gutless in low rpms... but perhaps i'll mess w the timing some more. i'm no pro when it comes to the performance world of cars, i'm just a n00b tryin to lear stuff.

 

Save your money and do this

 

^ lol

 

^^ lol


Actually, a test pipe on an ef doesn't amke power, i'd run a cat if i were you

 

^^seriously? I put a test pipe on my crx and it dropped my quarter mile times, so I think it helped.


Ok, well you have a d15b1, they're gutless. That's all there is to it. Trust me, I had one in my crx and it was gutless down low. They're only a 1.5 liter and are all top end power (not much power, but that's where they work best).
Now I know putting a cat on your car (especially a stock one from a dx) will only hurt power, so don't do it. If you have to run a cat put a high flow cat from Random Technology or something. What you need to do is do a head swap to a vtec head, it'll bump your compression to 10-10.5:1 and you'll have the advantage of vtec. Which will give you a better bottom end and a more aggressive top end as well. Or just throw some nitrous on it and call it a day. (I did both, LOL)

What other mods do you have on your car? And what car do you have by the way?
Nice to see some one else from Oregon here too, Lol.

 

wasnt there a comparison of test pipe VS H/F cat? with the test pipe making a huge + 1 hp over the cat ??? i think i rember reading that somewhere IDK..???
im running 4 -2-1 header with greddy evo 2 and when i swaped cat for test pipe i noticed a major power lose down low, and really dont know if i gained anything up top but nosie.. WTF? backpressure!!??

 

[QUOTE=got_no_sol;38639125]wasnt there a comparison of test pipe VS H/F cat? with the test pipe making a huge + 1 hp over the cat ??? i think i rember reading that somewhere IDK..???
QUOTE]

It's true..it's like a 1hp gain. For any of those who say they've gained more, it would only because your old cat was plugged or restricted from age or a bad running engine

 

change to a diffrent aftermarket headder leave the testpipe

 

Ryan, give me an offer for my header, (your WAY lucky i left you the SiR exhaust, i miss that thing a SHIHITE load!) and go from there

 

NEVER!! i like my stock z6 4-2-1 header. the car i'm talking about is an 88 hatch std, but from the looks of it you'd sware it's a dx. it's mpfi swapped with z6 manifold, b7 cam, ls tb, injen intake pipe with an autozone cone filter, running a pm6 ecu, and then the exhaust stuff i said. i'm thinking swapping to a 5spd will help me a little bit more since i'm rockin the insanely tall 4spd now. but i have to get a new clutch first. lol

i replaced my dizzy with another one i had laying around and now my code nine went away, no more cel, and it seems to respond quicker. i've got an a6 mini me that i'm rebuilding now, and i guess it's a jdm d15b that i have to have some machine work done to, which i will mate up to a z6 head and give it some boost maybe.

 

haha

 

Buy my d16a6 cam and through that in there. It really made a difference for me when I had my d15 with the mpfi swap (I swapped to a y8 head so that's why I don't need it anymore). I'd just leave the test pipe, the low end power isn't worth it anyway, get a better si tranny and you'll be havin a good time.

 

lol Ryan, mom is right, IT STINKS LIKE HELL! lol dude, i think the kid that did my rings on the B1 messed up, cause he did them in like 5 minutes lol thats why its smoking like mad when you get on it! hahahahaha

fine, keep your oem header, see if i care haha

 

anyone seen them twister de-cats


the inners of this stainless decat are rifled so as to create a vortex and therefore draw exhaust gas from the manifold, creating better flow!

lol

 

your useing a stock header hiflow cat and the back to a 2.25 in exshaust . your power is being bottle necked cause it start off from a small header to a largehi flow cat them back to a smaller exshaust . get a better header 2.25 cat and youll be fine

 

I recently purchased a 1994 Honda Civic LX. When I originally bought the vehilce, the previous owner was running a stock exhaust system with no catalytic converter. I wasnt concerned because I had intentions on replacing the whole exhaust system anyways. I bought headers, a resignator, hi flow cat and a muffler. I took these parts to the muffler shop and im pretty sure they put 3" piping in between. At the time I didnt even know that they had different pipe sizes and that it made a difference. Now i'm not exactly sure if my exhaust system is the problem but my car is extremely low on power. I can barely get up hills. In fact I cant gain any speed up hills all my spedometer does is drop along with my rpms..even when I switch into a lower gear I still cant get up them. And its not only big hills its any slope thats not level and i mean ANY. Its ridiculous because if im at a stoplight and i try to accelerate normally my car will just run backwards until i get up into the 4000 rpm range and then it will slowly make its way up but only when I ride the clutch! Please someone help me. Could this be because of my exhaust system or is there another underlying problem. And what are my options in fixing the issue.

Thanks in advance.

 

wtf? ^^

 

Not this one again

 

I have a SOHC ZC cam thats no use to me, interested?

 

Back pressure, Exhaust velocity and scavenging.

The myth: “engines need some backpressure.”


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 its consequences are. I'm sure many of you have heard or read the phrase "engines need some backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.


How the myth came about:


It is easy to see how this misunderstanding arises. Lets’ say that Max puts a 3-inch system on his normally aspirated car. He soon realizes that he has lost power right through the power band. The connection is made in his throbbing brain….

Put on 3" pipe = loss of backpressure = loss of power.

Max erroneously concludes that you need backpressure to retain performance. He has ignored the need for exhaust gas velocity to get that scavenge effect.


The other myth: “engines can get burned valves from not enough backpressure”



How this myth came about:

The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.

The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.

Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.

Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust for his.

Once these vehicles received performance mods that reduced backpressure, they tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.

Some basic exhaust theory

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficiently. 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 pulses 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.

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 its 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 power band is located 2-3000 RPM you'd want a narrower pipe than if your power band 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.

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).

Conclusion.


SO it turns out that engines don't need backpressure, they need as high a flow velocity as possible with as little backpressure as possible.

 

Wow. very good read