Hey guys, I’ve been driving my turbo 5.3 87 firebird for years now and I’m always playing/changing the car and setup. Quick question- how come I lose all my turbo spool with my cutout closed even with a high flow 4” cat back exhaust? my 5.3 is stock 99 SBE with a custom blower cam and ported stock heads and the normal upgrades to support cam. Running a modified CX racing front mount turbo kit with a 2.25” crossover and 3” down pipe (custom made mandrel to under the pass seat) then into a 3” eBay cutout and right off the cutout it’s adapted to a 4” hawks sinister catback with a 21” vibrant SS straight through 7” round muffler In the stock location and single 4” driver exit. This past winter I recirculated the WG to help with noise and it helped a lot. With the VS billet gen 1 78/75 it has super loud turbo spool with the cutout open and no other changes. When I close the cutout the exhaust gets quieter as you can imagine but I loose like 95% of the turbo spool noise. The car still makes basically the same power (maybe alittle less) but it seems to be flowing great. I was thinking of ditching the muffler and running a delete that came with the sinister exhaust but the point was to have “tame” with cutout closed and “wicked” with cutout open which it does, I just didn’t expect to loose all the turbo spool with the 4” massive exhaust as I swapped out the 3” thinking it was killing the sound. The spool with the cutout closed comes in very early like 2k starting and gets loud by 2500/3k which logs show is when I’m typically in boost by and the car is super fun on the street at 8-15psi.

so I guess what I’m asking is if I remove the muffler it will get louder but will I gain some spool noise back? Does the spool noise come from the compressor side (intake side) or do I hear it out of the exhaust which is why it’s so much louder bc it’s right under the pass seat and it’s pointless to remove the muffler bc the sound will be coming out the back of the car which is too far to hear and pointed away?

 

My buddies single turbo 5.3 is crazy loud with a comp. turbo. mine twin turbo setup is stupid quiet 🤷🏻‍♂️ Both have exhausts. Just makes mine more of a sleeper.

 

my single is pretty loud when the cutout is open but very quiet through the exhaust. What kind of exhaust is he running? I don’t mind the sleeper but it does get kinda boring lol

 

he just has 3” all back till a muffler.

mine is 3.5” from firewall back on each turbo.

its going to just be turbo design. He had a Vs racing single before he got the comp and the comp is just super loud.

 

I removed the muffler and swapped in the delete pipe, it got louder and seems like I got back alittle bit more turbo whine. The cutout is still louder but big time turbo whine vs catback. Car seemed a bit more peppy too with the muffler out. The vibrant street SS muffler really took a good bit of the bite of the exhaust and made it deeper.

 

You are looking at only one side. You could completely silence the turbine/exhaust, but still have the compressor side scream with the right combo

A recirculated/ported compressor housing is usually the biggest contributing factor to it

 

Yea I don't disagree but the compressor is already LOUD with the cutout open. Once its closed you loose like 80-90% of the compressor spool sound. Which means that the catback is causing something that kills the sound. Its not like the compressor is quiet all the time and I just want more... its already loud but only when I have the cutout open. So what is changing once I close the cutout that is affecting the compressor side... my guess is spool/backpressure but the car doesn't really seem that much slower or noticeably different through the 4" exhaust. So maybe its exhaust velocity is reduced?

 

Lol what?

 

My turbo spool/compressor whine is very loud with my electric cutout open under the pass seat. When I flick the switch to close it and push the exhaust through the 4" catback I lose 80-90% of the spool/compressor whine with no other changes. I can close it while I'm making the noise and its like hitting a mute button or reducing the volume to almost nothing.

What I'm saying is if I know the turbo is loud bc the cutout proves this why does it go almost dead quiet going through the 4" catback? IDK how it could be back pressure since the DP is 3" into a 3" cutout and then its stepped up right to 4" for the back half of the car.

 

My question is what makes you believe all the noise just comes from the compressor side?

if you muffle the exhaust of the turbo... and the intake side is fully plumbed to a intake...

the only part of the entire turbo freely open to atmosphere is the intake. So it’s gunna be quiet.

i guess I’m confused why someone is disappointed that their cut out does exactly as intended lol

 

I believe my first post/thread start was asking if the spool noise came from the intake or exhaust side? My assumption was that its the noise coming from the compressor wheel as it spins up to speed and begins to get into the boost zone. Since the intake side remains unchanged with the cutout open or closed I have to assume that the additional 10ft of 4" tubing and associated bends is affecting turbo whine. Turbo whine is probably the only cool thing about diesels for me, love that you can hear it spooling all the time. I can even hear my wifes CRV spool alittle bit and its cool that I can hear it come down when coming to a stop.

I'm not disappointed that the cutout works, I'm happy that it works as intended and I was hoping that I could gain some turbo whine back even with the cutout closed. I guess it doesn't matter that much, I just enjoy hearing that turbo so much I guess I was hoping to get the whine without the exhaust being full open at the cutout. Kinda like how Diesels get it but I also believe that the turbo size would have to be smaller for insta spool like it is on the diesel.

 

side note, how much power does your combo make?

 

An uncorked exhaust you can hear the turbine every bit of not more than the compressor

The exhaust is irrelevant to the compressor sound/ noise level other than if the turbo doesn't make the same shaft speed when the exhaust is closed up

 

No dyno numbers, going off logs and my fuel inj duty cycle looking back at a log I did in April here is some math.

60lb at 43psi running 93 pump 1:1 reference and a walbro 450 in the tank, additional 750cc of water/meth wiper fluid 20% meth
192kpa (13psi) I was at 87.5% INJ duty = 700hp crank or about 600hp wheel
192.8kpa (13.2psi) I was at 89.6% INJ duty = 720hp crank or about 612hp wheel
186.5kpa (12.5psi) I was at 81.3% INJ duty = 650hp crank or 560hp wheel

This is with an online calculator so I'm sure the numbers are somewhat accurate. FIC said these 60lb @ 43psi would be about 72lb at 58psi and would support about 850hp on pump. If I convert 60lb at 43psi to 58psi I get 70lb flow which at 80% duty would be about 862hp crank and 733hp wheel. I believe these numbers to be a little high using the online calculator but this is using a turbo setting fuel calculator.

I basically am always between 8-13psi as its pretty easy to hit those numbers with my EBC on the street setting. power setting would net 15+psi which I have only been to once and will get my INJ duty in the 90's% when I bump the pressure to 58psi and reset the injector flow in the tune.

 

Gotcha. So you think I'm hearing the turbine through the cutout an not the compressor. Then when I close up the cutout I lose the turbine noise and thus can only hear the compressor?

 

Yes correct

The actual compressor and housing design make the noise and sound of different compressors and levels vastly different

 

Show a picture of your actual compressor and housing

 

Just your standard VS racing Gen 1 billet 11 blade 78/75

 

"I was hoping that I could gain some turbo whine back even with the cutout closed".
Record it open, put it on a Bluetooth device, and play it back, thru your stereo, when you just have to hear it...