Nagging whistling sound.

[whitehatspecial]

I have a 340 in my '68 with an edelbrock rpm and BG 650 Speed Demon. I've finally ironed out most of the performance problems I had from the engine rebuild and installation but there is still one nagging problem.

I get a fairly loud high pitched whistling sound when the RPM's are fairly high (at shift points) . It is difficult to pinpoint the source because I  only hear the sound when I'm driving.

I've disconnected the main vacuum line and plugged it. I have no power brakes or carb spacer. I have also sprayed carb cleaner all around the carb, intake and vacuum fittings with no increase in RPM's.

I know it sounds crazy but it almost sounds like it's coming from the tranny (904).

[mikepmcs]

Isn't there a vac line that goes to the 904??  I don't know but aren't some tranny's vac operated or something.

[Ghoste]

No, some of the GM and Ford tranny's were vacuum modulated but the 727 and 904 have that good old mechanical connection we call the kickdown linkage.
Didn't someone have a strange whistle on here quite a while back?  What was that one, something to do with loose throttle blades in the carb or something?

[Just 6T9 CHGR]

My friends 360 Dart does the same thing....very strange....I believe its air rushing through the venturi's in the carb.  it gets pretty loud when he hammers down on the loud pedal.......you can really hear it when you are next to the car

[mikepmcs]

No, some of the GM and Ford tranny's were vacuum modulated but the 727 and 904 have that good old mechanical connection we call the kickdown linkage.
Didn't someone have a strange whistle on here quite a while back?  What was that one, something to do with loose throttle blades in the carb or something?

This is funny, I posted the same exact question when Nacho had issues with his transmission and you were the first one to post the same response last time too.  Sorry I'm such a retard.

On subject, I'm looking for that thread that addresses this.

v/r
Mike

[firefighter3931]

Check to see if any part of the carb base gasket is overhanging into the plenum of the intake manifold. This will casue the whistle you're hearing. 


Ron

[John_Kunkel]

Vacuum is lowest at high rpm WOT so the whistle from a vacuum leak would be less noticeable at high rpm.

I agree that it could just be the air rushing through the carb especially if the air cleaner is unsilenced.

If the noise is originating from the trans, it could be a rapidly cycling pressure regulator valve which is more of an annoyance than a real problem.

[Ghoste]

And uh, Mike, that word does not describe you in the least.

[mikepmcs]

And uh, Mike, that word does not describe you in the least.

Thanks ghoste, that was a really nice thing to say!   I think

on subject... I think Ron has something right there.

v/r
Mike

[whitehatspecial]

Thanks, I will check the base gasket tomorrow. It is a Mr. Gasket and, from memory, it fit very well to the Edelbrock. Also I could not get the "sound" by manually operating the throttle.
The rapidly cycling pressure valve is something I'll have to talk to the tranny rebuilder about since the trans was just rebuilt.

[whitehatspecial]

Here's a picture of the carb base gasket. The arrows shows the edges of the gasket which protruded from about 1/16" to  1/8"  into the intake portion of the manifold. Do you think that's enough to create the sound I'm hearing?

[mikepmcs]

I don't know about the whistle but it could be enough to stick the blades on the carb a little.  That is what happened to me anyway.  Thanks Chryco for that fix!!!  Couldn' hurt to trim them up to give it a shot right.

Good luck, hope you fix it soon.

v/r
Mike

[whitehatspecial]

I don't know about the whistle but it could be enough to stick the blades on the carb a little.  That is what happened to me anyway.  Thanks Chryco for that fix!!!  Couldn' hurt to trim them up to give it a shot right.

Good luck, hope you fix it soon.

v/r
Mike

Thanks Mike. I just came in from clearing about 6" of snow from the damn driveway, so it will be a while till I get see if the trimming worked. WINTER SUCKS!
I was in the FL keys about a week ago and that really spoiled me.

[deathcharger71]

i have a 650 demon oval track and it whistles below 800 rpm, pretty loud too. but its a damn good carb so its worth it.

[mikepmcs]

The snow is just started flying here(saying 18 inches).  I will be plowing in around 4 hours and then again tomorrow early AM.   I'm done with it but I live with it if you know what I mean.

Sorry off topic but.....dang it is windy like a mofo here with blowing white stuff!!!

v/r
Mike

[deathcharger71]

also off topic....you wanna see windy and snowy, the place where i usually go boarding just had a storm with 159mph winds! and it was 20 degrees without wind chill factor, i love snow and mother nature at its best but damn that must have been intense.

[K9COP]

You want wind, come to see me in the Cayman Islands.. a cat 5 Hurricane is a constant threat here. Sept 2004 we had a doozy, and everything blew away! Mind you, we got new cop cars out of it..

Not much in the way of snow here tho.. it's hot hot hot!

You should check it out..

[MTPOCKET]

You might want to try a thinner gasket. Or a gasket that will fill the center on the manifold to carb to seal it from side to side.

[daves68]

Also, check around under the dash. 68 Chargers have a load of vacuum operated gizmos on them along with a virtual fistfull of vacuum lines running around. Some were spliced and had "T's" in them. Any connection, switch, or 40 year old hose can be guilty. I had a similar experience and it turned out to be the heater control switch than hangs under the dashboard was leaking vacuum. Omly whistled at higher speed. Drove me nuts finding it.
Dave

[whitehatspecial]

You might want to try a thinner gasket. Or a gasket that will fill the center on the manifold to carb to seal it from side to side.

I'm wondering if a 4-hole, 1/2" spacer with round hole gaskets will solve the problem.

[Just 6T9 CHGR]

You might want to try a thinner gasket. Or a gasket that will fill the center on the manifold to carb to seal it from side to side.

I'm wondering if a 4-hole, 1/2" spacer with round hole gaskets will solve the problem.

Let us know