Hi,

posting new thread rather than turbo/boost as looking for a swiftish answer.

My mate purchase an sr20det 180 yesterday just wondering in regards to the turbo intake set up, apparently it has no BOV and we can't see one yet you can hear the pressurised gases being expelled but my question is where??

Originally we thought they were being pushed back past the intake valve but shouldn't the compressor and pressurised gases stop it heading back out the intake??

Also thought it could do with the wastegate but i dont have the experience in turbos... although i will.

Also through reading im a bit worried that the lack of a BOV may cause rapid fluctuations in compressor speed, do i have reason to be worried?

Thanks for all help and inputs of relevent info

peace out

aj

I would say its the wastegate actuator doing its job :)

The wastegate is a valve that opens up 'vents' your exhaust gasses.. it stops the turbine from spinning too fast and shattering the fins :)

When you let off the throttle in a turbocharged car, the excess pressure thats immeadiattly built up between the throttle doby and turbo has to go somehere. If a BOV is not fitted then it will just go back through the easiest route of escape, and thats the turbo, this will cause the turbo to slow down. The sound compressor surge makes depends on few factors. These can inlcude the type of air filtration fitted (i.e. pod filter, airbox with panel, deign of airbox etc...), intkae piping lenght and routing.

But as you mentioned sometimes wastegates make a similar sound. If he is running a standard tubrocharger (T28), then it will be internally gated (harder or somtimes imposible to hear).

Edit: well Bain backs the wastgate assumption. :)

compressor surge makes depends on few factors. These can inlcude the type of air filtration fitted (i.e. pod filter, airbox with panel, deign of airbox etc...), intkae piping lenght and routing.

But as you mentioned sometimes wastegates make a similar sound. If he is running a standard tubrocharger (T28), then it will be internally gated (harder or somtimes imposible to hear).

Edit: well Bain backs the wastgate assumption. :)

If it is compressor surge it should be fairly loud.. And if it is.. Well, its not nice having bent fins in a turbo..


Lets hope its just the wastegate!

I would be extremely surpised if Nissan didn't have a pressure relief valve after the compressor lol. I'm not familiar with the 180s but it would most probably have a recirculating type bov. This is where the pressurised air after the compressor is vented back into the intake in front of the compressor. This type of system ****s over a atmospheric bov as the airflow meter will only read the amount of air going into the engine.

Also the recirculating type is much better if you have an air flow meter in front of the compressor. See here (http://www.aussiemagna.com/forums/showpost.php?p=535865&postcount=90)

Bain - if it from him backing off the throttle then i doubt its the waste gate making the noise - and more likely compressor surge coming back through the intake (pod or filter)

wastegate will only redirect exhaust gas, not intake air.

wastegate will only redirect exhaust gas, not intake air.
Correct.

You can get flutter when you take your foot off the accelerator or in between gear changes due to the change in exhaust pressure. - My car does it.

Possibly a leak between the turbo and manifold, when the boost spikes when throttle suddenly shuts its enough pressure to leak out?

If it is compressor surge it should be fairly loud.. And if it is.. Well, its not nice having bent fins in a turbo..


Lets hope its just the wastegate!

A small amount of compressor surge will not bend any fins, although it will add to boost lag between throttle openings.

for those that don't know it's a red top sr20det so not originally in the car. Thus aftermarket cooler piping and cooler etc

It's got a very pretty boost gauge that indicates no spiking

And yeah it flutters" from on load to off... so i think the air must being pushed back through the turbo, like my original thoughts... it's only running 5/6psi but still i can't see it as being good for the turbines. In reading BOV were fitted to remove the noise from stocko expensive turbo cars (wikipedia).

He's defs getting the plumback BOV when he can afford it (recirculating as stated).

Might give it a rev today and see if the noise comes from the wastegate or pod.

i can convince the turbo diesel Jeep Cherokee to make a BOV sound when its stalled up on the brakes in gear, yet, there is very little to suggest it has a bov, what ever is cousing the noise the the jeep, may be the same as the nissan.

if it does infact not have a BOV, which should be easy to see with aftermarket piping, then my money is on compressor surge.

i didn't think there was a turbo nissan in the world without a stupidly loud, obnoxious BOV...

MAte just had a 180sx very simialar to the question posed. ie front mount, no BOV, and pod filter. The surge back through the turbo was rather loud and similar to a BOV with a flutter. The pod filter provides very little noise mitigation.

As I understand it, Turbo Diesels are not fitted with BOVs, and thus Science you may have the same thing happening in your car. 4x4s running a pod or similar filter combined with running higher boost levels have a very pronounced throttle lift off flutter noise.

my ca18det flutter pretty loud, im not worried most sr's/ ca's have loud flutter from what ive seen when u turn the boost up,............its actually quite annoying feels like ur in a 15 year olds wet dream

if it goes bang ohwell its only a t25 ... well ur mate would have a t28..i want it yo lol

DOSE!!!! ULEH!!!

old thread, but who cares.


for those that don't know it's a red top sr20det so not originally in the car.
unless it was a 89-91 model 180sx then it did infact come with a red top sr20det in it. then from 95 onwards they went to black top, however the blacktop in the 180sx's was just a redtop with the black cover. the blacktop in the s14 and s15 silvias from the same time had variable cam timing.

the bov is fitted for emissions reasons other than to prolong turbo life, or for sound as many people think. pretty much all cars before 1990 that had turbo's had no bov from factory. with no bov, when you lift off the throttle the air comes back out the intake and through the airflow meter. since the AFM isn't smart it doesn't know that the air is going back out so it measures it and adds more fuel into the motor. this makes the car run rather rich for a second. so to cut emissions down they added the bov which keeps the air recirculating while the throttle is closed. atmo bovs will cause the car to run rich also. when the bov opens and the air from the piping escapes it draws fresh air past the AFM. the AFM measures this air and adds more fuel again, not realising that the air isn't going into the motor, but out into the engine bay.

the sr20 had a factory recirculating bov bolted to the side of the side mount intercooler. i have the stock bov from my old 180sx sitting about 2 feet from where i am now as a paper weight. however when front mount intercooler kits are put on this gets rid of the stock bov. most piping kits for front mount coolers have a provision in the piping for a bov on the pipe from the turbo to the cooler (which is a really dumb place for it, since it is so far from the throttle body). the ideal place for it is right next to the throttle body to keep the air flowing in the 1 direction.

if the car doesn't have a bov, when you lift off the throttle after hard acceleration you would get a flutter rather than the psssh of the bov, although some bovs are adjusted tightly so they flutter.

the wastegate will NOT make any noise. when you lift of the throttle the wastegate closes. the only way a wastegate can alter the sound of a car is if the car has a screamer pipe. this is when the pipe from the wastegate isn't plumbed back into the exhaust. then once the car comes on boost the wastegate opens and the exhaust noise is coming straight out into the open and doesn't pass through any muffler or the cat. the fine for having a screamer pipe if you get sent for an emissions test is the same as not having a cat, which is $$11,000 (220 penalty points, 1 penalty point = $50)


well ur mate would have a t28
all redtops in both silvia and 180sx and blacktop motors in the 180sx had t25 turbos. the black top in the silvias went to t28, and the GTiR pulsar had a t28 turbo. the ca18 had a t25 turbo, but it was smaller than the t25 in the s13's.

old thread, but who cares.


unless it was a 89-91 model 180sx then it did infact come with a red top sr20det in it. then from 95 onwards they went to black top, however the blacktop in the 180sx's was just a redtop with the black cover. the blacktop in the s14 and s15 silvias from the same time had variable cam timing.

the bov is fitted for emissions reasons other than to prolong turbo life, or for sound as many people think. pretty much all cars before 1990 that had turbo's had no bov from factory. with no bov, when you lift off the throttle the air comes back out the intake and through the airflow meter. since the AFM isn't smart it doesn't know that the air is going back out so it measures it and adds more fuel into the motor. this makes the car run rather rich for a second. so to cut emissions down they added the bov which keeps the air recirculating while the throttle is closed. atmo bovs will cause the car to run rich also. when the bov opens and the air from the piping escapes it draws fresh air past the AFM. the AFM measures this air and adds more fuel again, not realising that the air isn't going into the motor, but out into the engine bay.


yeah its a 90 model.

Also i cant remember if MAS or MAP sensor ie the turbo before the afm as map sensor and wouldnt have that problem.

He has a spare pipe for the bov which is pre-cooler but yeah hasnt bothered fitting it. Mainly because of our **** roads\coilovers he has a crack in some metal work and doesnt drive it.

I cant see compressor surge being good for a turbo...

ps wtf whenever i push the apostrophy and slash keys on amc sometimes they dont work and shortcut me to find ie control f, wtf also my arrows dont work.
So every time ive typed dont wouldnt couldnt blah ive got sent down to find... pissing me off
only on amc and only sometimes.... :nuts:

I used to own a Nissan Pulsar and could emulate a turbocharger using the torque converter

...

but then the gearbox died.

As for the topic at hand, I'm gunna go with compressor surge and say that your friend should maybe invest in a cheap, non-obnoxious, BOV. Hopefully the turbo is all good. But I'm not exactly skilled with this sorta thing.

the actual damage done by not having a bov is pretty minimal. look at how many VL turbos are out there without bovs. most of the japanese drifters run no bov. all of the japanese pro races cars run no bov. it is only air hitting the compressor and slowing it down, not really any different to the air hitting it on the exhaust side that makes it spin in the first place, just in the other direction.