DTM - weird wah, wah, wah noise

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BajaT4
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DTM - weird wah, wah, wah noise

Post by BajaT4 » Tue Jul 25, 2006 7:27 am

First let me preface this post by saying that the DTM is the best thing since sliced bread. My engine has never run cooler.

Since day one though, I've had this wah, wah, wah noise that sounded like an out of balance fan that starts at about 2400 rpm. There was some runout in the original welded fan so I replaced it this year with a non-welded stock fan but I still have the same noise.

I'm not sure if the alternator is bad, if the placement of the fan at the extreme end of the shaft is the problem, or if something is out of balance with the engine. The engine was balance by RAT when it was in the original Type 4 cooling configuration but never rebalanced when I switched to the DTM (the difference being the pulley at the end of the crank.)

I'll try to record the sound and post it later. Just wondering if anyone else has experienced anything like this.

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Post by MASSIVE TYPE IV » Tue Jul 25, 2006 8:37 am

Glad the DTM is doing it's job- people have to experience it to believe that it works so damn well!

It sounds like one of two things..

1- The alternator, sometimes they do make noises... You can isolate the problem for troubleshooting by removing the belt. If the problem goes away it's alternator/fan related... If it does not it's interna.

2- The fan can sometimes scrub the shroud if things are not adjusted right, with the belt removed turn the alternator and if the fan scrubs you'll know it!

The DTM has some fan noise compared to a stock system, but its not loud..

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BajaT4
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Post by BajaT4 » Wed Jul 26, 2006 10:21 am

http://www.bakerb.com/Tom/lifter/engine.wav

This was recorded this morning, typical on ramp to highway acceleration up to 80. It isn't as pronounced in the recording as it is when actually driving the vehicle but maybe it's a sound that you've heard in the past. I've never heard anything like it in 20 years of VW related engines.

I did check it without the belt on and the noise did seem to go away but there was a high frequency vibration right at an indicated 3400 RPM.

There was no interference with the fan shroud when turned by hand.

Oh yea, 95 degree ambient yesterday, 3800 RPM, both head temps were less than 300 degrees and within 15 degrees of each other.

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Post by MASSIVE TYPE IV » Wed Jul 26, 2006 10:41 am

Damn!
I have never heard a sound like that in the car, nothing even close!

I have heard it on the dyno with some exhaust systems when the engine is heavily loaded and off the cam, before it started to pull good.

What exhaust are you running? What cam? Was this ever present before the shroud was installed??

I can say that if it has something to do with the shroud it would be VERY odd!

I'd say that you should do a short test with the belt off driving the car to see if it goes away. Since you have head temp gauges you should be safe for a few minutes of test time to see if it goes away loaded or not..
My guess is that it will not..

The pulley difference in balance should not make that sound..

BTW- The DTM is doing it's job exactly as it should... What temps did you see before??

Also I'd like to add the only time I have heard this noise was with some exhaust systems at or around peak torque or just before the cam and heads started to really come on... Thats with a heavy load that I don't think any car could place on the engine, unless you were towing three busses behind you..

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BajaT4
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Post by BajaT4 » Wed Jul 26, 2006 12:56 pm

MASSIVE TYPE IV wrote:Damn!
I have never heard a sound like that in the car, nothing even close!
I'm running a split duration WebCam (163/86B I think). I didn't get the noise before I put the DTM on 3 years ago BUT I also changed the exhaust at the same time.

I've used the stock J-tubes with both the stock shroud and DTM. Before, I had a quiet pack muffler for each J-tube. Now, I built my own equal length header from each J-tube which goes into a collector. The collector dumps into a Flowmaster 40 series that sits between the engine and bumper. I really wanted to go with a true header but at the time there was nothing but garbage out there. The engine makes great power, runs cool, gets around 25 mpg on the highway but makes that annoying wah, wah, wah noise!

Does anyone out there make a GOOD and QUIET offroad exhaust system?

I've suspected that the combination of the exhaust, engine RPM and fan RPM are all working together to make the cacaphony that I hear.

Head temps with the stock shroud ran around 425, oil was about the same as it is now at maybe 220 max. I've been running an oil thermostat for the past year or so that has really helped get the oil up to temperature. I've only got about an 8 mile drive to work so it gets to around 180 on the way in the morning and maybe 200 on the drive home.

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Post by MASSIVE TYPE IV » Wed Jul 26, 2006 1:22 pm

So the DTM dropped the head temps 125 degrees??

I have an offroad exhaust system, email me at productdevelopment@aircooledtechnology.com for pics of it. It works very, very well.

The issue is the exhaust, I'll almost bet you that it is... Home brewed systems just don't cut it as the exhaust side of the TIV is odd. With this issue occured at 3500 RPM it is most certainly exhaust related! Thats where we see all the exhaust deficiencies most clearly time and time again.

The sound is being caused by the scavenging of the exhaust (or lack of) and the camshaft. That cam has 16 degrees of split duration and pours on the power, but it totally depends on proper exhaust.

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BigOlJohnson
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Post by BigOlJohnson » Wed Jul 26, 2006 2:25 pm

That is reverb in the exh. How much overlap is listed on the cam card?

I had a stock 429 with a set off those new-fangled turbo muffs that would do it out of only one side!

Drove me CRAZY!

Buy one of Jake's systems and it will magically go away!
8)

BOJ

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BajaT4
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Post by BajaT4 » Wed Jul 26, 2006 2:47 pm

Heck yeah the DTM dropped the head temps 125 degrees. If you've got the cash to afford a DTM, and don't buy one, you'll probably be buying a new set of heads sooner than you think.

I'll drop you an e-mail shortly Jake.

Thanks again for your help and expertise!

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BajaT4
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Post by BajaT4 » Thu Jul 27, 2006 8:31 am

BOJ -

I just checked Flowmaster's website and found the following description:

Standard 40 Series - Two Chamber Mufflers
This is the most “aggressive” sounding street/strip muffler that Flowmaster offers. If you're looking for attention, this one will get you noticed. The standard 40 series has an “aggressive rumble" and will generally resonate inside the vehicle around 1800-2000 rpm’s, and again at 2400-2600 rpm’s.

I wish they would have had the description when I bought my muffler. Those RPMs are for a V8 with dual mufflers. Double the RPM for a single muffler on a 4 cylinder and the resonance matches my RPMs.

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Post by MASSIVE TYPE IV » Thu Jul 27, 2006 8:50 am

Told ya so.... 8)

Note that cam and head specifics will change the resonance RPM and it's effects..

Did you get the pics of the header?

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BajaT4
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Post by BajaT4 » Thu Jul 27, 2006 9:17 am

I got them but wasn't sure if you wanted to discuss it here or offline. That is one nice setup! I may need to relocate my full flow filter setup though since its currently tucked in behind the engine. Drop me an e-mail or PM with the pricetag on that system.

You mentioned that you had pics of another system as well?

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Post by MASSIVE TYPE IV » Thu Jul 27, 2006 9:35 am

The other pics are gone, they were in my other computer that crashed a couple months back..

We only did one of them for a Manxter project that had a 2.4 Super Hero installed..

Thatsystem is not kept in stock and can be made to fit your cage/oil filter with some measurements. These run 850.00 and are awesome!

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BajaT4
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Post by BajaT4 » Thu Jul 27, 2006 9:47 am

Well worth it for sure. Let me build up my slush fund a little more and then we can talk specifics.

Thanks again Jake!

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BajaT4
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Post by BajaT4 » Mon Sep 04, 2006 4:52 pm

Finally had the time and a nice cool day to take the fan belt off and drive my Bug around the block.

Belt on (3200 RPM) - wah wah wah

Belt off (same RPM) - silence

This is the second fan I've put in with the DTM, both making the same noise. My thoughts are:

1. Bad alternator (doubt it)
2. Fan location on shaft (too far out). Its not rubbing on the shroud.
3. Firewall resonating

Now that I've really pinpointed the cause, I'm not sure what the solution is. Its amazing how much noise is caused by the cooling fan and how responsive the engine is when it isn't connected! Any ideas?

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