crasher2

getting ready to get a TII, thinking about doing mods to it, I need to know the differance between a blow off valve and a pop off vale? can anyone help here

CrackHeadMel

iTrader: (2)

i think a popoff valve is just a safty thing that stops you from running to high of bost, anda blow of valve kills boost when you let of gas

No7Yet

A blowoff valve vents extra pressure out of the intake stream when throttle is dropped to avoid compressor surge. I wrote a big long diatribe about what it does and why it's good a long time ago when some crackpot was claiming that his tuner had "reasons" for their being unnecessary.

A pop-off valve simply vents excess pressure in an overboost situation, as a last-resort, "oh **** I'm about to blow my engine" fail-safe. While it may save your engine, it's a purposely-introduced boost leak, and will overspin your turbo something awful.

Brandon

crasher2

ok, so would it be better to have them both or would you really need just one of them, and which one would be the best????

No7Yet

Uh, what? Did you read my post?

Besides, a TII has one stock. If you want/need a popoff valve, then get one.

Brandon

Angel Guard Racing Team

With a blow off valve you will never go overboost if you set it accordingly.

RETed

Bzzzt....wrong.


-Ted

PraxRX7

All a BOV does is vent the turbocharged air pressure.

Once you let off the gas (and the turbo is no longer pressurizing the system) then the BOV lets all the pressure out. (from my understanding), but the BOV uses vacuum to release itself properly, once your boost levels reach a low vacuum (letting off the throttle) then the BOV opens up and allow the air through.

Some BOV's can be adjusted to vent around certain pressures, but they should be set just above the highest pressure you will achieve, otherwise your boost will "leak" and your turbo will be over-spooling risking damage to the turbo (EX: in a closed system the turbo would be making 15 PSI while in a system with a leak your gauge only reads 12 PSI but the turbo is pushing more, and because it cannot pressurize to stop the turbo from over-spooling, the turbo will keep spooling in order to achieve maximum pressurization allowed by the air intake and exhaust system.

That is at least my understanding of a BOV. Any kind of extra pressure relief system should not be considered, because unless you drop off the throttle the turbo will spin, whether you are venting pressure or not.

One MAJOR thing to watch for is the vacuum line into the BOV, if this has anything wrong with it, you can get a compressor surge and cause damage to that as well. (That is why I got the APEXi BOV, just in case it can't vent normally it holds pressure in a second chamber to allow venting and more reliable venting or the pressure.

However, it is no substitue for the vacuum line.


I hope that helped, it sure confused me while typing it.

crasher2

yes this i know is wrong. No7Yet, I did a search and cant find what you wrote about this sbject. but thanks anyway

Evil Aviator

Best for what? Making cool noises, impressing your friends, what?

PraxRX7

a Pop-off-valve is not neccesary, only a BOV and a good wastegate. The Stock BOV is more than sufficient and is actually designed to blast the air back into the air intake.

crasher2

I am not worried about impressing friends or cool nosies, I am just looking for a way to keep the engine from explodeing on me. if it was cool nosies I would just clip a poker card to the back wheels to make nosies.

adamlewis

If youre not gonna run too much boost, just get an aftermarket BOV ... If youre GOING to run some boost, then get the BOV AND get your wastegate ported.

PraxRX7

With the STOCK setup, you wont need to upgrade any part of the system (unless it is an 86-88 Turbo II then you might want to consider porting your wastegate).

But even if you were to install a massive intake and a straight back 3" exhaust you wouldn't NEED an upgraded BOV (although any good BOV should be considered above 8.5 PSI in my books). What you would NEED is more fuel, bigger pump, bigger injectors, FCD, AFC, Ignition computer etc. The stock system is built for running stock number. If you want to get all crazy with mods get a Haltech and a bigger turbo/1600cc injectors and a massive Walbro Fuel pump.

No7Yet

Feel loved.



Brandon

Evil Aviator

How to keep the engine from exploding: Don't mess with it. Mazda put the CBV in there for a reason. If it's not broken, don't fix it.

Angel Guard Racing Team

My bad I meant Wastegate.

crasher2

Thanks guy for all the comments you gave, I should have added that it is going to be a street ported 87 engine with high flow injectors, fuel pump and other mods too.

But Really thanks again