Blow off valves
- Thread starter Abbott
- Start date
powerboatr
living well in Texas
what year 6.0 do you have?
if your needing a pop off for it, your going to have a whole lot more problems than settign a defuel condition.
can you say head gaskets
if your needing a pop off for it, your going to have a whole lot more problems than settign a defuel condition.
can you say head gaskets
Hoss 350
My GSP, Dutch
I am recycling an old post from a couple months ago as my reply. Ignore anything irrelevant to the topic at hand. THis is a discussion of why a blow-off valve, as they have them on gasser turbos, is not useful on a diesel engine...Abbott said:
"Blowoff valves in gassers are little more than a large spring-loaded poppet valve that are set to open at a certain psi to bleed off boost. The pressure in the intake spikes when the throttle valves snaps shut, creating air hammer, oscillations, and all sorts of bad things that can and do hurt turbos, pop seals, etc. The pressure spike in a gasser from the throttle snapping shut is what pops open the BOV and causes the Pshsst sound that you are referring to. The BOV is set to a pressure that is just slightly higher than or the same as the maximum boost pressure that the turbo/engine combination can make. That way, when the spike occurs, or an over-pressure situation occurs, the valve pops open, and voila, problem mitigated. (Not eliminated, mind you, because the small BOV cannot IMMEDIATELY bleed off the pressure, but it certainly reduces the problem.)
In a diesel, however, there is no throttle plate. Consequently, there is no pressure spike when you let up off the throttle, and therefore, nothing available to open a BOV. As a result, a traditional BOV will not work on a diesel engine. What is more, the condition creating purpose behind having a BOV does not exist on a diesel engine (no throttle plate) and therefore, beyond making a cool noise, it serves no function whatsoever.
For people that are interested in adding a part to their truck that does nothing but bleed off any accrued boost when they let off the throttle, forcing the truck to start over again building boost when the throttle is crammed back down again, just for the sake of having a cool noise when they let off the throttle, there is a diesel-capable BOV available in the aftermarket. It is electronically controlled off of the trucks MAP sensor, and an electric solenoid actuates it when you let off the throttle. I cannot remember where I saw it, but it is quite expensive (like $400 bucks or something). Keeping in mind that it serves no purpose whatsoever, and functions simply to create a BOV sound at shifts, I would not recommend anybody waste their money on it, unless, to them, the BOV sound is worth $400 bucks, because that is all you get out of it.
What is more, I am not completely convinced that it doesn’t REDUCE performance by blowing off boost that you otherwise could have kept if you shifted quickly enough, forcing the turbo to start all over again building boost.
Anyway, just my .02 on the matter. BOV’s are for ricers. Real trucks don’t need ‘em."
scotty7751
Big Daddy
lol that made me want to get up and shout AMEN!
kiarasue
The RamSmoker
Blow off
I have the dual blow off system. It is a little slow but does do the job. SP diesel sells a intercepter harness plug that stops the pcm from ever reading over boost. Its about the same dollars as the dual valve like mine.
I have the dual blow off system. It is a little slow but does do the job. SP diesel sells a intercepter harness plug that stops the pcm from ever reading over boost. Its about the same dollars as the dual valve like mine.
Hoss 350
My GSP, Dutch
Okay, it looks to me like we are all talking about two different things.kiarasue said:
The MAP blowoff as others are talking about keeps the PCM from defueling because of overboost.
A blowoff, in the terms of what most people talk about when tey are discussing turbos, is what i posted about originally.
So, I guess we need to know which one he's talking about.
kiarasue
The RamSmoker
If blow off valves don't work on diesels then what are the big valves that release boost on the Cummins trucks? I was at the drags a few weeks back and they open about the 60ft mark and can be heard to the finnish line.
Hoss 350
My GSP, Dutch
I think those are boost limiting devices, (poppet vavles) that bleed off excessive boost to prevent overboost in twin-turbo high HP engines. They are not blow-off valves like most people mean when they say blow off valves. In my experience, most people mean the valves that they hear and see on gasser turbos, because they sound cool and obviously perform a safety function, people tend to want to add them aftermarket. The problem is that they do not perform like that on a diesel.kiarasue said:
What you described is a different, yet similar, item, performing a completely different function.