engine noise at high RPM
 

Okay so I ahve a question about the engine in my 94 Civic. It's a D15B7, sohc non-vtec. I have not done any engine mods, and it runs great. The thing is, I am wondering what exactly it is my engine is doing around 4200 rpm. At this point, usually only noticable in 2nd or 3rd gear, the engine makes a sort of high-pitched "whirring" hummm to it, similar to the sound of a turbo spooling up. It's amost like a hair dryer getting turned from "medium" onto "high." Could this be from the increasing speed of my valvetrain (cam in particular)? If it were just the sound, that wouldn't be so curious, but this sound is also accompanied by a noticable boost of acceleration from about 4200-5500 rpm. It seems to be the sweet spot of 2nd gear, but I don't know why -- I have no VTEC or anything. I'm not complaining, it makes for quite a fun 102 HP, but I just don't have any idea why I get this kind of noise and power at such a specific RPM from an econobox engine. Any thoughts?

Re:engine noise at high RPM
 

it's probably just your intake/throttle body sucking in more air at higher rpm's, i'm sure that's what it is ;D

Re:engine noise at high RPM
 

thats the sweetspot of your cam.

Re:engine noise at high RPM
 

d15b7 = 16 valves...
VTEC works with 8 valves, then at high RPMs switches to 16 valves, because at higher RPMs, u need more valves to take in the air, which is why at higher RPMs your car works better.

Re:engine noise at high RPM
 

hmm, time for some Vtec 101

http://www.geocities.com/gkurka2001/VTEC/VTEC.htm

Jeff

Re:engine noise at high RPM
 

ok Robo Wop, you got me interested with "d15b7 = 16 valves", but then you got crazy and started talking about vtec. As Jeff pointed out, your vtec info is a bit off, and my car doesn't even have vtec so it doesn't matter (i refer you to the place where i twice mentioned not having vtec).

As far as vtec goes, all 16 valves are always working, but when the engine hits vtec RPM, the VTEC rocker arm locks to the other two next to it and the valvetrain is suddenly being controlled by the more aggressive cam lobes. so it'd be fair to say that at non-vtec the engine is controlled by 16 lobes, but at VTEC it is controlled by only 8.

But on my original question, is it just the speed of my cam?? It sounds more like a turbo than my friend's WRX.

Re:engine noise at high RPM
 

maybe someone put one of those electric turbos in there!

Re:engine noise at high RPM
 

maybe its your alternator whining, they whine when they are working hard, like if your battery sucks or you leave your lights on.

Re:engine noise at high RPM
 

awww crap I better go check and see if some shmuck put an electric turbo in there. From what I've seen on the Tech section og HMT, maybe I'll just take it out and give it to Jeff. He knows what to do with them.

Oh and my alternator... if that were the case, why would the whine have anything to do with my engine speed? Do my headlights get brighter at high RPM because the alternator is working harder? Or perhaps you are just giving me crap...

Okay I'll just assume it's my little overworked camshaft getting his freak on. Poor guy has a full 16 lobes on him. Good thing he's not VTEC, it'd be 24 lobes.

Re:engine noise at high RPM
 

it is just where your cam hits its sweet spot. when the cam timing and intake resonances match up you engine is able to cram more air into the cylinders, creating more power. what you are hearing is the engine reaching a speed where its volumetric efficiency is good, creating more power. if you take a look for power outputs you will find that your engines torque peak is in about the same place.