View Full Version : Possible to route a blow-off valve to the exhaust ?

08-10-2006, 08:44 AM
Hey ,

I know this sounds odd , but I think it makes sense in the long-run.
Just want to get some feedback, thus my post..

All of my buddies are going the forced induction route lately, so of-course I want to hop on the bandwagon with my 55. A few days ago I was driving my somewhat quiet 55 next to a buddies Procharged 1999 camaro, and I couldnt even here myself think becasue his blowoff valve was so friggin loud ! He has a Vortech Mondo on their, with some stupid large outlet.

My idea for my future setup would be get a blowoff with a smaller outlet, then run a 10 or 12an line to a bung welded in the exhaust. This way the "blow-off" would be routed into the exhaust, and help keep the noise down under the hood. Good idea ?

Dont get me wrong, as I am ALL ABOUT noise, but I would much rather listen to the sweet sound of the blower itself than the blow-off while cruising around... .. .

Is this idea possibile / workable ??

08-10-2006, 01:42 PM
Is it the blowoff valve or the wastegaste? The blowoff valve should only open during quick throttle closure (shifting). If he has the wastegate discharging to the atmosphere, then yes, most people route the
wastegate discharge to the downpipe. Ideally you want it to seam into the exhaust at least 12" from the turbo outlet. It will be quiet then.

08-10-2006, 01:52 PM
As far as I am aware he has a blow-off valve on his car, but maybe I am wrong. All I know is that while he is just crusin along at say 45-50 mph all you hear is constant blast of air under his hood
(which sounds horribile in my opinion)

So my "crazy" idea makes sense huh ?

Would their be any benefit to T the line to each exhaust, for eaqual pressure in both pipes, or am I over-thinking this ??

08-12-2006, 04:42 AM
Must be the wastegate. The blowoff makes a swooosh shound when shifting.

08-12-2006, 04:16 PM
No wastegates on a centrifugal blower setup. You might be hearing the blower gear whine, or the bypass valve whistling if it is a steady sound on the highway. The Procharger gears whine like crazy - even worse at idle.

Depending on how he has the Mondo bypass set up, it could also whistle on the highway as a lot of air is passing through it at those loads (low load, high vacuum, bypass is fully open).

You can make the bypass quieter by routing it back into the intake of the blower. That's what I did on mine and I barely hear anything at highway speeds. Also, I installed the super-quiet Vortech V-2 SQ S-trim blower because I don't like the gear whine and my car is, in theory, a sleeper 4DR.

Some pix of the setup and bypass valve at my site:




08-13-2006, 03:35 PM
My bad, I though it was turbo not procharger.

08-13-2006, 05:20 PM
Depends where the bypass valve is routed, and some are louder than others. For example, the Procharger "race" poppet-style bypass valve is rather loud because the air slams into the valve then has to make a 90 degree turn and exit out some machined orifices, whereas the butterfly-style Bosch bypass valves (procharger standard) are relatively quiet. I haven't heard a Vortech Mondo but it appears to be a poppet style, and if so-- it will be loud.

I have my bypass valve venting at the very front of the car under the radiator support by using flexible aircraft ducting (spiral spring wound into a silicone hose.) Can't hear it at all in the car. Works mint. Also drains any water from my water injection setup right under the center of the car which is WAY better than in line with the tires!

When I used to have the engine with the blow-through carb the bypass valve was dumping right near the master cylinder and it was very annoying in the car.

Recircing the bypass is the quietest way to do things but I don't like it as then you keep recycling warm air through the supercharger. If you dump the bypass, you get a steady flow of cooler air through the supercharger (especially if you have a cold air induction of some sort) which helps keep the supercharger cooler. The constant flow of air does dirty up the airfilter quicker though.