can someone please explain what causes rasp? i am in the works of creating my own custom exhaust ideas and dont want there to be rasp, so i guess i need to understand the concept of what it is that causes rasp first.

 

I also am curious what causes that as well.

 

no one can explain this?

 

Rasp can be caused by many a things....

Loose elements in a cat converter, can cause rasp.
Piping to close to other parts, can cause rasp, the exhaust needs .5-1 inch to move under hard acceleration.
Bad welds can cause rasp.
Believe it or not, to many "tone" restrictors can cause rasp. I.E. If you have 2+ resonators, AND a muffler, you might get a top end rasp at WOT.

People say that diameter to big for your application causes rasp as well. Look at MOST hondas with rasp, 2.5" piping or more, not needed on a bone stock motor.

On the other hand if the diameter is to small you could also develop rasp from the motor straining.

SOOO many elements play in to effect. You want to build a good exhaust, that sounds phenominal, and nets you the gains that you deserve for the money.

WELL, there are companies out there that do this already for you. Granted you will save a ton of money building it yourself, especially if you have a welder, and good welding skills.

My advice, start from the block and go to the rear of the car. After all, what is the point of a great flowing exhaust, being restricted by stock exhaust manifolds, and better yet stock cats??

Equal Length headers, mmm. Then test pipes, or HFC's. Then Mid pipe. Then axle-back.

TRUST me, in the end you will net the gains you want for your money, with all the time and effort you put into the car you will appreciate it more. PLUS you almost completely eliminate the "RASP" you don't want, because your exhaust is COMPLETE.

Example of a setup:
Stock Car:
Equal Length headers (4-2-1 with a 2.5" collecter...4-1 also but 4-2-1 is more common)
Test pipes/HFC's depends on emmisions and where you live but 2.5" diameter piping.
Midpipe section, a good Flowmaster muffler, and 2.5" piping here as well.
Axle-back 2.5" piping into your tips.
(Note: Throw in another muffler, or resonator to deaden the sound more if needed)

Modded Car: (Intake, Plenum Spacer, Intake Manifold)
Equal Length Headers(see above)
3" from the header back, throwing in HFC's if wanted, Mufflers, and resonator.

BEFORE people attack me and call me a noob because this is my 2nd post here, and I am advising 3" on an N/A application. Think about it. You have 3 Intake mods, so you are taking in more air, and causing more turbulence on the intake side, but you are running 2.5" exhaust. Taking in an abundance of air, but not releasing much, doesn't sound so free flowing anymore does it?

Hope this helps.

Reguards,
Brandon

 

"think about it" ...
are you talking about Long tube headers? If not, 3" from headers back will do nothing but lose all sorts of power...torque will be terrible and i doubt you'll make back anywhere close to what you lose in the top end. I bet top end suffers as well.

ALSO, having intake mods doesn't create turbulence.

The intake from factory is 3". With 1.75" header inlet, 2.25" header outlets. There is a reason that infiniti designed it this way.

The cats are 2.25" in and 2.25" out. 3" in and out here would be awful with rasp all over the place.


rasp is generally due to piping diameter and air velocity

 

They designed it that way to pass emissions, and cut down noise. The car was originally built to be a luxury sports car.

Long tube headers, not quite understanding what you mean. Equal Length headers generally have longer tubes if that is what you mean.

I do suppose turbulence was the wrong term used on my behalf, but you are forcing in more air, then are releasing with intake mods.

I don't know much about the G35 as I am still learning, I am going off of my past builds, and have had great success with my formula.

I.E. Honda Prelude H22. Started with DC Sports 4-1 header, and a BuddyClub SpecII exhaust. 70mm TB, CAI, Skunk2 Manifold. 227WHP. Went to a custom made Bishimoto equal length header, and a 3" BuddyClub SpecII exhaust and netted 13hp.

Note this was also on a 2.2L, I don't see why it would not work the same with a G35.

 

Do it...and you'll see why.

 

For sake of argument, will do.

 

the Motordyne exhaust i have is 3" back ...from the Y-pipe. Any earlier without a very large turbo and I bet you lose power.

Depends on your headers though. There aren't a lot of long tube options. 2 that I'm aware of unless you custom do it yourself.

 

I personally will be buying my header back from Motordyne when they come out with there test pipes. I guess I will have to look more into these cars, totally didnt put into affect the fact that they are true dual.

By any means you wouldn't need a really large turbo setup to see gains, infact any turbo setup would be sufficient enough for 3".