924Board.org

epsylon · Posted: Sat May 31, 2003 2:53 am Post subject: is this sound normal

now that my exhaust leak is taken care of i can hear my turbo spoil up, very cool, and the lovely rumble of the audi 2.0. One of the noisiest motors i have ever owned.

but sometimes i hear what sounds like air escaping when i take my foot of the accelerator when the turbo is in mid spoil up. almost like the car is dumping the pressure at the turbo since i am no longer accelerating. is this normal or is something not functioning right. i have never owned a turbo and my 924 doesn't make this sound ever.
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'82 931
'78 928
Howell Henderson
South Padre Island

Lizard · Posted: Sat May 31, 2003 3:36 am Post subject:

should be fine it is a mix of the POV and the wastegate dumping extra pressure
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3 928s,

924 turbo · Posted: Sat May 31, 2003 5:02 am Post subject:

Mine does the same thing.
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Jon Furst

epsylon · Posted: Sat May 31, 2003 5:07 am Post subject:

cool. for a second there i thought something might be wrong with the turbo system. you never can be to careful with noises. seems like a better system would somehow keep the boost / pressure so it wouldn't have to build up again. but hey what do i know. i am just amazed at how fast the 931 is compared to the 924.
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'82 931
'78 928
Howell Henderson
South Padre Island

924 turbo · Posted: Sat May 31, 2003 5:13 am Post subject:

epsylon · Posted: Sat May 31, 2003 5:19 am Post subject:

"The system does keep the pressure up. It cycles the air in a circle. The sound you hear is not air escaping, but cycling."

how and where does the air cycle to, what circle. i thought the waste gate simply dumped into the cat. forgive my ignorance.
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'82 931
'78 928
Howell Henderson
South Padre Island

924 turbo · Posted: Sat May 31, 2003 5:27 am Post subject:

There is a bypass valve at the front of the turbocharger, seen here:

It has a sensing line that is attached at the bottom of the intake manifold. When it senses vacuum, it opens the bypass valve, allowing air that has passed the compressor to cycle back before the compressor. It does this to keep the speed of the compressor fan up for quicker spooling during shifts.
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Jon Furst

924RACR · Posted: Sat May 31, 2003 5:29 am Post subject:

Speaking of noisy, I know someone here who had contact with someone who'd been involved in dynoing a bunch of motors, including the 924NA when it came out. They said it had the worst vibration of any motor they put on the dyno, including the outboard marine motor!

No wonder Porsche went for the balance shafts on the 944! LOL
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

Lizard · Posted: Sat May 31, 2003 5:49 am Post subject:

the 931 has less than 1/10th the vibrations of the 924 NA,
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3 928s,

epsylon · Posted: Sat May 31, 2003 3:48 pm Post subject:

1/10th of the vibrations with 1/5th more HP. cool.
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'82 931
'78 928
Howell Henderson
South Padre Island

Joes924Racer · Posted: Sat May 31, 2003 5:34 pm Post subject:

They are noisy also[924na] I remember when I first started talken to porsche engine builders besides saying they didnt know because they
didnt know anything about the early na they specialized in 944 and air cooled motors a few said one in particular hes in a california shop
and he had experience with em, he said they were the loudest of all porsches and for the money involved couldnt yeild that much power.
Even with a header that doesnt leak and a copper collector gasket
its still loud.
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1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

78 924 N/a · Joined: 20 Mar 2003 Posts: 769 Location: Pacific N.W.

epsylon · Posted: Wed Jun 04, 2003 3:52 am Post subject:

i think the motor mounts might be of the newer type. the turbo muffles the exhaust some, so it sounds less noisy. but once the turbo starts dieing all sorts of fun sounds come from under the hood. sometimes at idle my turbo ticks. once i increase the engine RPMs a little the sound goes away. sort of has me freaked out right now so i am not driving the car much until i replace the turbo.
_________________
'82 931
'78 928
Howell Henderson
South Padre Island