So I just got my Intense Power y-pipe and Crawford HFCs installed (which sound pretty damn good btw!) Anyways, when I punch it, it sounds sort of like a "whoosh" or a leak sound from the y-pipe. I took it back, we threw it on the rack and revved it up, and it makes the sound right before the y-pipe connects to the mid-pipe. They told me it was just back pressure, and made sure that everything was tight. Does this sound normal or what? If not, I'll just put the stock y-pipe back on. Thanks guys.

`John

 

the outlet of that y pipe is 3" and if you are on the stock mid pipe then there is pretty decent sized ring of restriction. you could either put the stock y pipe back on, get a reducer so there is a better transition between the y and midpipe or go with a larger aftermarket midpipe back section. a closer sized y pipe would be a tanabe or 5zigen.

 

ok so the sound it's making is normal? Not sure if I'm liking it, so I might just throw the stock y-pipe back on anyway. Damn.

 

It's called rasp

 

I don't recall this sound being that of 'rasp'. As it said, it sounds like an air leak, but I don't know.

 

Sound clip?

 

i'll try to work on that later today...I'll go over to my dads to pick up a digital camera and record it.

 

the other thing it could be since the y pipe is a lower budget one is that they use an unlined flex section. that would sound like a buzz or air leak but you should hear that noise from the flex sections and not the rear of the y pipe.

 

It's what happens when you jam air from HFC's into a 3 inch y pipe into a 2.5 inch stock b pipe. The "whoosh" sound is b/c of the bottleneck issue and a common complaint with this type of setup. Put back your stock y or get a smaller diameter one, until you put on an aftermarket exhaust, if u ever do.

 

Ok cool, I was just wondering what it could be. Just curious, with the HFC and y-pipe, am I hurting my performance at all due to the bottleneck? Basically, if I just left on the HFCs and put the stock Y-pipe on, would that provide better power? As for exhaust, this is all I ever have/had planned. I love the sound of the stock exhaust, and I just wanted to emphasize it a little more, not change it. So, with that known, what do you guys recommend? Keep it as is, or replace the y-pipe w/ the stock one?

BTW, I just took my car out w/ my buddy so I could hear it from the outside, and you can't even hear it. It's more noticeable on cold starts, and once the car is warmed up, it hardly does it. Thanks for all the responses so far!

`John

 

I think you are hurting the performance some. Depends more if you are turbo'd or using a superchrger or NA? NA needs back pressure but major flow issue in the exahust cant help. However a full 3" exhaust is definetly going to make youl ose low end power if you are not running a turbo setup (you would make much more power if you were turbod witha big exhaust like that).

To put it in a nutshell, NA needs back pressure with a smaller pipe, bottleneck isnt good. Turbo needs less backpressure, easier for exhaust to flow out, less back pressure.

 

Sorry if this has been covered but I'm wondering if anyone knows if the Intense perf. y pipe works on an X. 35parts.com just says it "yet untested"

 

Common misunderstanding of exhaust here. Back pressure is not good in any form. We want increased velocity and scavenging. Back pressure doesn't promote either. Look into why/how Tony (Hydrazine) designed his exhaust.


to the OP, HFC can have a "whoosh" sound with air flowing through them but you probably have a leak. I had a 3" outlet into the stock MP with HFC before and NEVER had rasp. Check for leaks. remove and reinstall the exhaust and make sure the bolts are tight.

 

Wouldn't the diameter of the exhaust piping be determined by the terminal velocity? In other words, having a 3'' exhaust would leave the n/a motor out of breath trying to push out all the exhaust.

I'm not sure if I'm making any sense, but try this. Take a large diameter pipe and blow into it. Now while you do that, does the air come out of the other side with somewhat equal or significantly lower velocity?

Now do the same thing with a smaller diameter pipe, see the difference of the air being pushed out between the two pipe sizes?


Or am I just re-explaining what you just typed.

lol, anyways, to the OP. Like the others said it does sound like the exhaust flow is being bottle neck'ed. You would probably hear a similar sound of a big v8/v6 with a very restrictive exhaust. It sounds more like the car is trying to push all the exhaust out rather than making nice sound that you were looking for.

 

I am not so sure I totally agree with the no back pressure statement but I think he is stating what I am thinking as well. What I believe can be important is the elimination of pulses which are present with piston engines. I think a better statement may be minimal backpressure. This is sort of like putting chlorine into a water system. If you smell it you have too much. If you don't you may not have enough. The pulses can cause a restriction of exhaust flow.

I don't buy this statement (except maybe the bottleneck):

'To put it in a nutshell, NA needs back pressure with a smaller pipe, bottleneck isnt good. Turbo needs less backpressure, easier for exhaust to flow out, less back pressure'

One of the effects of a turbine in the exhaust stream is that it tends to even out the pulses. Since you suck in more air, you have more exhaust to vent. Since you are compressing the intake air your temps can be much higher which also changes your exhaust requirements.

Nissan reportably uses on some vehicles a muffler design that has only one path at low rpms and two at high. Some performance cars use two totally different paths after the header. Us old folks had our lakers with cable operated cut outs.

The idea is that at different rpms you need a different size pipe to maintain velocity which is what contributes to your exhaust gas scavenging. The desired size of that pipe then in reality needs to change on a continuous basis based on the rpm associated with it. This is why some studies have shown that you may get a benefit with a removable resonator system where the resonator is left in for city driving (lower rpms) and taken out for track use (higher rpms). I personally think that a better method would be do to this closer to the front of the system instead of the tail. While we may have continuously variable exhaust valving the next step may be to do the same with the rest of the exhaust system. Even high humidy can affect the equation. Ideally one would think that you want to exhaust into as low of pressure as possible (ie atmosphere). However when water is present in the system it creates steam. When it condenses at the exhaust the water vapor it self creates a choke point to exhaust flow.

With modern systems this should not be nearly as hard since you can use various parameters such as rpm, load, and feed forward / feed back signals to modify the exhaust flow path.