Engine/Transmission (1994 - 1998) blow off valve question

[Centeno1]

k guys i'm gettin some of it down but I don't know what a blow off valve does but from what i read it's a good mod so what would it cost to do on my hx 40 and what is it's mechanical funcion ..... call it b. v. 101

thanks

 

[biggy238]

It releases excess pressure. Mostly gassers use them to save their turbos because of the pressure that builds when the throttle snaps shut. They work on diesels with twins also but someone with some experience will have to go into detail for you. On a single turbo I know they can and will reduce "turbo chirp" which I hear can break shafts in turbos.

 

[1dslram]

A BOV won't help with turbo chirp, or barking the turbo, that is a different valve. A BOV is used to release excess boost, In my case my BOV's there are 2 are set at 70# as I don't want to go over 75#. With a set-up capable of well over 70# mine release the excess well before I up-shift in second and third. If you want help with barking the turbo you will need a unit such as the BD Turbo Guard. Barking the turbo is caused when the throttle is closed quickly at high boost. When the throttle closes there is high pressure after the turbo and now no drive for the turbo, so the high pressure in the intercooler etc. forces the turbo to stop almost instantly and then makes the turbo reverse direction. This condition is well known for broken shafts on the HX35 & 40 turbo's they use the same shaft.

Bruce

 

[WDimig]

?

1dslram - i think you have them mixed up. a BOV will release the excess pressure, and keep a turbo from barking, and therefore help save the shaft from breaking. also when equipped on manual trucks, it keeps the turbo spooled up a bit,and builds boost quicker inbetween shifts. you talked of the BD turbo gaurd, that is indeed a blow off vavle, designed to release pressure, thus help keeping the turbo from barking, and or breaking at higher boost pressures. a pop off valve is what you are refering to. simply a valve that has a spring inside, and can be set at whatever boost pressure is desied, and will bleed the air once the preset limit is reached. the trouble with BOV's on our trucks, is they need a vaccum source for most of the BOV's to operate. there are some electric switches available, and are quite $$$$, which is another downfall to adding a BOV to our trucks. but i must say, can you see the look on some ricer's face hearing that turbo blow off at 40psi? it'd be priceless!



wes

 

[LaserBob]

I put a BD turbo Guard valve on a guy's '99, 5 Spd making about 550hp. It sounds cool and looks cool and makes him smile when he shifts. Poeple on their first ride with him always get a raised eyebrow when they hear it.

 

[WDimig]

laser bob - does the BD turbogaurd come with a tpps switch? how did you mount it to the intecooler piping? just curious cause im lookin to put a BOV on my 97' auto. i bark the turbo quite frequently and know its going to break sooner or later. pm if you haveany info. TIA.



wes

 

[RustyJC]

Barking the turbo is caused when the throttle is closed quickly at high boost. When the throttle closes there is high pressure after the turbo and now no drive for the turbo, so the high pressure in the intercooler etc. forces the turbo to stop almost instantly and then makes the turbo reverse direction.

No, the amount of rotational inertia in the turbine/compressor rotor won't allow this to happen. What one hears is flow reversal as the excess pressure flows backward through the compressor. When the pressure downstream of the compressor gets low enough, the compressor starts pumping again. This process repeatedly loads and unloads the compressor, thus subjecting the impeller and/or the shaft to cyclic fatigue failure.



Rusty

 

[JKouzez]

okay i guess i will chime in. My roomate and i (along with a local turbo shop with an owner going out of his way to help us out) are currently in the process of making a standard BOV work on our trucks. ( and be somewhat affordable) the problem is since our trucks dont have a throttle body to produce variable vacuum it will not allow the BOV to open and close. our vacuum pumps produce a constant amount of vacuum regardless of engine RPM, and while i am not sure the exact specs on our pumps we found out it is enough to open the valve on my BOV. Today we went to Grainger and ordered the pnuematic solenoid that i plan to use (should be in tommorow) between that and a microswitch and extra vacuum lines we are pretty sure it should work as intended without having a vacuum leak. This is all of course just theory but hopefully tommorow i should have some results.

 

[biggy238]

You should ask Scott Vorhees (BigBadDodge) about his setup. 1dslram ???? You've got pop off valves similar to air compressors from what you described. Like the others have said, they respond to pressure rather than vaccum.



Blow off valves also vent higher cfm than pop off valves. The underlying difference is the ability for the blow off valve to proportion itself to the vac signal if I remember correctly. I had all of this bookmarked... ... I think scott has the unit with a routable exhaust so that the compressed excess air enters the system ahead of the compressors again. You'll need a weldable bung provided by most manufacturers to mount one to your tubing. Look at the Blitz BOV's

 

[BPonci]

The popoff valve is a safety valve to prevent over boost if you blow past your w/g.

 

[TrqMonster]

I have drove a very fast AWD talon that had a blitz BOV lots of power, that thing was sweet. and sounded real cool when shifting or hitting the set PSI. Always thought it would be cool to install one on my truck



So is it my understanding that no one really makes a BOV for our trucks and modified ones are needed such as the Blitz and others that gassers use?

 

[LaserBob]

BD's valve came with instructions and suggestions on mounting it properly. Pictures are included for those like me, who need them. It is not a 30 minute install. It takes some time and welding and other stuff.



It does what they say when all is done. It is sweet!

 

[HoleshotHolset]

It is not a 30 minute install. It takes some time and welding and other stuff.

For $455, it should be a bolt-on.



Matt

 

[Centeno1]

but

but will the bd turbo guard stop the turbo from barking that is what i wanna know. I can just picture my truck stranded in nevada somewhere with one of my employees cause he snapped the shaft on the turbo. I'm not too worried on the time as long as it's straight forward and works right

 

[WDimig]

if installed properly, yes the design of the BOV will keep the turbo from barking. a good investment with a high priced turbo/ and or lots of boost



wes

 

[JKouzez]

If you can afford the BD turboguard i would definately recomend it unfortunately being 18 and in college i cant so thats why i am trying to find a way to make my little project work. and i understand that it is a little out there and some people say you just cant make it work reliably but that just makes me a little more determined, and if it still dosent work oh well at least i learned alot more of how these things work in the process

 

[biggy238]

Sweet, someone is younger than I am on here. What kind of BOV are you planning to use again??

 

[WDimig]

im 18 and in college as well. i try and foucus my income tworads my truck



wes

 

[DTroy]

You don't need to spend big bucks on a blow valve. Just pony up some Yen for this bad boy. .



http://www.takakaira.com/accessories/nightpager/nightpager.html

 

[biggy238]

That's just wrong. International redneck engineering.



I too am pulling college duty but i'm paying for the truck for now. I've got to find a money tree to put a dtt in this truck.



When I first started hanging around on here, more than one person told me that a BOV was useless on a diesel because they lack throttles.