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Discussion Starter #1
I remember years ago some debate on here about running a skyline without BOVs (and the delicious noises it would likely make). A few may have even done it without issue.

Has anyone done this on the R35, be it stock turbo or modified.

And if not, what are peoples thoughts on the theory - detrimental action to be avoided? Or an option to be considered (looking for considered pros and cons really)

Cheers
Mart
 

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Depends on the turbos you have fitted I guess..... or indeed how strong the standard turbos are. A lot of turbos will not like the shock of the air coming ramming back down through the induction system and will soon break them. Not sure what it will do to fuelling either
 

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Running without BOVs fitted will theoretically help response as it will hold boost pressure on the shifts, however if it holds pressure too much it will stall the compressor wheel as the excess boost escapes back past the wheel in the opposite direction. That shock loads the wheels spinning at 150,000 rpm to zero and back up again which isn't great for longevity of the wheels or the bearings.
On other platforms such as rally cars who change their turbos a few times a day, it's fine :)
A well designed aftermarket BOV setup will help response yet will protect turbos.
Please note... OEM valves are designed with engine and turbo protection from a stall and overboost point of view i.e. they are designed to be open and stay shut if needed. Aftermarket performance ones are designed to stay shut and open if needed, subtle but big difference.
Avoid full atmo on the gtr due to the MAFs being the main input for engine load calculation that is also used for the primary input for clutch control, The only ones we would recommend would be the latest version of the GFB response valves, however the HKS sqv 4 also does a good job of performing well.
 

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Discussion Starter #4
Running without BOVs fitted will theoretically help response as it will hold boost pressure on the shifts, however if it holds pressure too much it will stall the compressor wheel as the excess boost escapes back past the wheel in the opposite direction. That shock loads the wheels spinning at 150,000 rpm to zero and back up again which isn't great for longevity of the wheels or the bearings.
On other platforms such as rally cars who change their turbos a few times a day, it's fine :)
A well designed aftermarket BOV setup will help response yet will protect turbos.
Please note... OEM valves are designed with engine and turbo protection from a stall and overboost point of view i.e. they are designed to be open and stay shut if needed. Aftermarket performance ones are designed to stay shut and open if needed, subtle but big difference.
Avoid full atmo on the gtr due to the MAFs being the main input for engine load calculation that is also used for the primary input for clutch control, The only ones we would recommend would be the latest version of the GFB response valves, however the HKS sqv 4 also does a good job of performing well.

Thanks for that Andy. It was the GFB recirc I was interested in actually - or if I SD tune maybe the atmos ones. Didn't realise the stock ones were like that. Interesting

What sort of HP do we think the stock BOVs are good to (or is it PSI based?)
 

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Thanks for that Andy. It was the GFB recirc I was interested in actually - or if I SD tune maybe the atmos ones. Didn't realise the stock ones were like that. Interesting

What sort of HP do we think the stock BOVs are good to (or is it PSI based?)
They get a bit 'floaty' about 1.8 bar, but an improvement at all boost levels is noticeable with the GFB response ones, they hold boost much better and respond much faster. Met their chief designer a few weeks ago while he was over and had chance to talk through a few points. There's a minor tweak to assist the low throttle manners and torque calculation side of things coming now. That will assist them to operate correctly when running them dual port.
 

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Sort of... Compressor surge is when there's a mechanical mismatch front to rear on the turbo and the turbo produces boost that the engine isn't consuming. If you run a lot of VVT angle on a gtr with low mileage turbos you can get them to surge so need to dial it out in the tune.
 

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Running without BOVs fitted will theoretically help response as it will hold boost pressure on the shifts, however if it holds pressure too much it will stall the compressor wheel as the excess boost escapes back past the wheel in the opposite direction. That shock loads the wheels spinning at 150,000 rpm to zero and back up again which isn't great for longevity of the wheels or the bearings.
On other platforms such as rally cars who change their turbos a few times a day, it's fine :)
A well designed aftermarket BOV setup will help response yet will protect turbos.
Please note... OEM valves are designed with engine and turbo protection from a stall and overboost point of view i.e. they are designed to be open and stay shut if needed. Aftermarket performance ones are designed to stay shut and open if needed, subtle but big difference.
Avoid full atmo on the gtr due to the MAFs being the main input for engine load calculation that is also used for the primary input for clutch control, The only ones we would recommend would be the latest version of the GFB response valves, however the HKS sqv 4 also does a good job of performing well.
Nice bit of info there.

Andy, what do you think of the Tial BOV's which is pretty much what the boys run exclusively in the US on the high power GTR's?
 

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Nice bit of info there.

Andy, what do you think of the Tial BOV's which is pretty much what the boys run exclusively in the US on the high power GTR's?
The Tial ones do work well, I've run them on many many cars over the years at high boost levels (up to 55-60 psi boost, and that's relative not absolute ;) ) But on the GTR as we've mentioned, it's the low speed and part throttle manners that we're questioning.
If you spring them properly they won't open at light throttle or idle so thats fine, on forged motors we generate enough vacuum at idle to pull them both wide open so need spring changes.
If you're running on your MAFs, when they dump air at light/low throttle openings or on overrun, the ECU does need fine control to operate the clutches/choose gears/run fuelling which has just (literally) gone out the window. So do expect poor control and wavy idles coming up to a stop even if they're sprung correctly.
If you are running FULL SD, and it's mapped correctly... It'll be fine :)

AC
 

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Everytime I read a post by AC, I feel like spending my money with him.

This is in stark contrast to another well known tuner, who makes me feel like saving it.
 
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