Offroad-Express

churchill wrote:
What I can't understand is what keeps the turbo spinning to provide to 20psi to the cylinders when the fuel is reduced. Perhaps the kinetic energy of the engine spinning and pumping air is enough? Doesn't make sense seeing as full throttle was required to do this initially so if you cut the fuel you would expect to see a reduction in boost as the turbo slows down.

Wastegate... This basically bypasses the turbo once it reaches boost pressure. So max fuel not much gas going through turbine and minimum fuel all gas going through turbine...

Ahh, yes. So boost starts to drop off, wastegate closes and redirects engine air through turbo using the kinetic energy of enigne to keep the turbo turning and boost up.

Ok, I understand now how the system doesn't lose all it's boost in general applications. In saying that there are certain applications a BOV can be used effectively as we discussed.

Yeah but it's still exhaust gas as there will still be combustion even on minimum fuel.

I have heard turbo chargers surging many times on ships engines during high load change conditions. For example the prop comping out the water in heavy seas. Doesnt sound very good coming out of a turbo bigger that your truck but have never experienced any ill effects from it. It is a rare occurence though and I'm sure if it happened all the time then the thrust bearings etc would suffer. At full load our engines are running at 80psi boost. If you go from Full ahead to all stop in one swift movement the turbos would be barking like a pack of wild dogs..

I understand about the fuel still being burnt off throttle. I didn't add it because I thought it would be neglitiable when compared to the rotational kinetic energy held by the engine at high rpm.

After more research it looks like BOV's will keep the turbo spinning faster between gear changes but the gain is minimal compared to the expense of fitting them hence why they are not fitted for that purpose.

Tweake's comment on 4x4patrol.com

"its possible to fit BOV on diesel. i know of a few who have them (on toyotas) and they work ok. helps with quick gearchanges. but its a lot of $$$ for bugger all gain and fairly pointless on a stock vechile."

Thanks for thrashing that out with me, I'm new to the Diesel engine and I also like to understand the reasons behind why things are done the way they are.

Sorry about the thread hijack Heath but hopefully this helps with some of your questions.

But is the $$$$ worth the cool factor????????

churchill wrote:Ahh, yes. So boost starts to drop off, wastegate closes and redirects engine air through turbo using the kinetic energy of enigne to keep the turbo turning and boost up.
....

in normal use yes but with sudden drop in drive pressure its a bit slow.
the boost in the manifold keeps the wastegate open while the boost is causing the turbo to stall. its not until after the stall that the boost has dropped and wastegate closes.
keep in mind that boost is always trying to go backwoulds through the turbo.

DieselBoy wrote:But is the $$$$ worth the cool factor????????

I want on of these when I fit my turbo

DieselBoy wrote:But is the $$$$ worth the cool factor????????

Yep that priceless look you get from the ricer next to you when you blip the throttle and get the psst like he does - expensive gimick.

If you want a wow factor get a duck caller and glue it to your BOV. It would be 5 seconds of shock then 10 minutes of rolling on the ground pissing your self.

When I worked at transmission and diesel in Auckland years ago, I used to do a bit of work on our race truck (1200hp 38psi 8v89 2 stroke weapon) and other teams trucks(rebuilding or adjusting the allison transmissions)

None!! of the race trucks ever run BOV, as Diesel boy and Ice4x4 perfectly explained a Blow off valve is not required and if anything detrimental to a TD Diesel performance.

my 2cents

only 38psi? thats a bit low.
a car or light 4x4 is a little bit different than a truck.
just because its not useful in one application doesn't mean it will never work in all applications.

tweake wrote:only 38psi? thats a bit low.
a car or light 4x4 is a little bit different than a truck.
just because its not useful in one application doesn't mean it will never work in all applications.

Yeah agreed, BUT the only reason I can see for fitting a BOV to a Turbo Diesel engine is to protect the turbo from damage cause you have set the boost at such a level that it is way beyond the design parameters of the Turbo charger.

Why would you want to do that??

Diesel engines running high boost pressures are designed and engineered from the get go to run under those conditions. Wee car engines aren't...

If BOV were a good thing to improove performance or reliabilty or give more power the manufactures would install them from new.
The best thing you can do to get more out of ya diesel is to help it breathe so big air in & big air out...then you will get complete burning of the fuel & get max bang for ya fuel.

tallsam66 wrote:If BOV were a good thing to improove performance or reliabilty or give more power the manufactures would install them from new.
The best thing you can do to get more out of ya diesel is to help it breathe so big air in & big air out...then you will get complete burning of the fuel & get max bang for ya fuel.

You could argue that for a car manufacturer the cost/benefit equation doesn't work out so they don't fit them. It doesn't necessarly mean there is no preformance gain to be exploited.

I wouldn't want to spoil a good discussion with facts but it would be good to see dyno charts and boost plots of the different setups.

would you want a bov opening underwater? or have another potential place water can get in all for the sake of wank factor?

i was under the impression that once your foot was off accelerator fuel shuts off and only air is being compressed thru the cylinders? so with no fuel and only air coming out, exhaust gases would be less but the air under boost is stil going into cylinders and not stopping causing compressor stall.the only time air would stop going thru the cylinders is wen the engine is shut off.

alot of petrol cars come out with factory bov's, but why dont diesels?

doesn't matter if a BOV opened under water. boost blows water out. if worried about it plumb it back to air cleaner.

but the air under boost is stil going into cylinders and not stopping causing compressor stall.the only time air would stop going thru the cylinders is wen the engine is shut off.

your forgetting pressure pushes in ALL directions. so you have air pushing towards the motor but its also pushing back against the turbo compressor. theres no one way valve or seal (like some superchargers), the only thing stopping it going back through the turbo is the turbo is throwing air out of it faster then it goes back in. but when the turbo can't throw air out, cause its got no exhaust pushing it, the boost wants to go back through the turbo.

factory diesels don't have bov because its not a major problem for them. a throttle butterfly causes a bigger problem thats worth them spending $$ on it. with standard diesel the problem is not big enough to spend the $$$.

mind you the navara ZD30 diesel runs a butterfly, 15psi+ boost and is also known for snapping compressor wheels. but nissan are to cheap to even fit an intercooler.

these days they use turbo back pressure for the egr system instead of intake butterflies.

Diesel engines running high boost pressures are designed and engineered from the get go to run under those conditions. Wee car engines aren't...

disagree with that.
tons of people here are running higher boost than the diesel engines where ever designed for, a lot of them pushing stock turbo's to the limit .........and some well past it
especially when fitting small turbo's to gain low down boost.

tallsam66 wrote:The best thing you can do to get more out of ya diesel is to help it breathe so big air in & big air out...then you will get complete burning of the fuel & get max bang for ya fuel.

when a BOV operates there is no (or minimal) fuel going in so the air does nothing anyway.
no need for dyno charts as BOV makes no difference to power what so ever.

tweake wrote:no need for dyno charts as BOV makes no difference to power what so ever.

Ok, a dyno chart with WOT, close throttle, WOT.

If a BOV does make a difference the engine should build revs faster on the second WOT.

churchill wrote:

tweake wrote:no need for dyno charts as BOV makes no difference to power what so ever.

Ok, a dyno chart with WOT, close throttle, WOT.

If a BOV does make a difference the engine should build revs faster on the second WOT.

why dyno, a quick drive down the road is far cheaper

i reckon screw the shitty bov idea, if you want your truck fast then your going to run high boost and no bov , if you dont want it fast then your going to run low boost and no bov any way as factory trucks dont come with them.....

high boost means your copromising engine longivity any way so why bother trying to make a turbo last ten seconds longer...

if ya want ya truck fast go petrol

Especialy if its got a turbo and a fuken BOV A.

tweake wrote: why dyno, a quick drive down the road is far cheaper

And more subjective... Depends how sensitive your ass is.

Been checking out the Le-mans racing Diesels from Pugeot and Audi and can't find any thing that suggests they have BOV's in them.

Go fast use petrol, yup. And boy you'll use petrol too, diesel gives you economy as well.

And haha mikee, I'm glad you know where to put a BOV.

Just a question since you guys are talking about this on this thread

I have a 1kz surf, iv disconnected the egr and, plated up, and cleaned the manifolds ect, but left both butterflies hooked up because i was under the impression thats where i get my throttle from because i dont have a manual fuel pump.
Thats correct isn't it??

HardYota wrote:Just a question since you guys are talking about this on this thread

I have a 1kz surf, iv disconnected the egr and, plated up, and cleaned the manifolds ect, but left both butterflies hooked up because i was under the impression thats where i get my throttle from because i dont have a manual fuel pump.
Thats correct isn't it??

the TPS is on the butterfly shaft controlled by the throttle cable, so you can't rip out the whole unit. i'm rusty on the setup but usually they disable the small butterfly so its open all the time, or remove the butterflies off the shafts.

bov works well on diesels that have intake butterflies.

tweake wrote:

HardYota wrote:Just a question since you guys are talking about this on this thread

I have a 1kz surf, iv disconnected the egr and, plated up, and cleaned the manifolds ect, but left both butterflies hooked up because i was under the impression thats where i get my throttle from because i dont have a manual fuel pump.
Thats correct isn't it??

the TPS is on the butterfly shaft controlled by the throttle cable, so you can't rip out the whole unit. i'm rusty on the setup but usually they disable the small butterfly so its open all the time, or remove the butterflies off the shafts.

bov works well on diesels that have intake butterflies.

The 1KZTE use the TPS to control the throttle settings for the ECU / Electronic pump. (Fly by wire)
You can completely remove and relocate the throttle body...Or just remove the butterflys....Remove the screws and slide out butterfly....The shaft still stays in place....Note the screws will have had the threaded end hammered over to stop them unscrewing.
Some of us have done this as part of putting in inter-coolers.
If you have an auto you will also have a second cable to the auto.....This controls line pressure in the auto. (some models use a solenoid and don't have this cable again uses the TPS for info)