Outer Limits 4x4 Board

Couple of questions.
Turbo Patrol TB42
How hard is it to change the bushes on a dizzy shaft and would they be causeing a miss/lumpy acceleration.
Its got a adjustable B.O.V. Whats the advantage of this and why?

No advantage really but sound and you can adjust the bov release to your liking and car, tighter it only releases at higher psi and will cause compreser surge, softer it will release at low psi and you won't get compreser surge but get sound all the time. I had one on my Subaru for abit full boost was 12psi I had it set to go off over 8 psi ended up just removing it and running nothing.

And then some people think a bov is Just part of the sound system of the car, have it soft when the feel like being a mad prick so people know they have a turbo then tight if they want no sound really defeats the real function of fitting one.

The purpose of a BOV is to prevent compression surge thus reducing wear and tear on your engine and turbo system.

http://en.wikipedia.org/wiki/Blowoff_valve

Check this for more info.

I've always understood that BOV's are sensitive to vacuum and boost spike - they aren't set to operate a given psi as danny has stated.

coxy321 wrote:I've always understood that BOV's are sensitive to vacuum and boost spike - they aren't set to operate a given psi as danny has stated.

yes they are as the have a spring in them the harder/tension the spring the more presure it takes to open and opisite if softer spring, so you adjust it to what psi you want it to open. it's all on the turbosmart web site if you want a read?

coxy321 wrote:I've always understood that BOV's are sensitive to vacuum and boost spike - they aren't set to operate a given psi as danny has stated.

While you are right for normal BOVs, adjustable ones can be used as a pop off valve by reducing the spring pressure required to open. ie: with the BOV adjusted tight, it will increase spring pressure and rely on neg pressure (vac) to pull it open like a normal BOV. The more tension on the spring, the more vac needed to operate the BOV so you can even fine tune it to have it fully open or only partially open on activation.

With the BOV adjustment backed off, spring pressure can be reduced to the point that a required boost pressure is enough to push the BOV open. So if you were running 10psi you could set the BOV adjustment to open at say 12/14psi or so under boost while still operating normally under vac. Basic overboost protection. Most don't use them for this application though, more commonly used to vary the amount of PSSSH for attention seekers.

danny40 wrote:

coxy321 wrote:I've always understood that BOV's are sensitive to vacuum and boost spike - they aren't set to operate a given psi as danny has stated.

yes they are as the have a spring in them the harder/tension the spring the more presure it takes to open and opisite if softer spring, so you adjust it to what psi you want it to open. it's all on the turbosmart web site if you want a read?

I've just had a read through their site, and while it doesn't refer tothe use of BOV's as boost control devices, i can see how it could work as one. The only issue i can see here is that to truly get it working as you describe (for boost control), you would have to buy the correct spring to suit your boost level, as while under boost both the feed and piston are under equal pressure.

Turbosmart wrote:Blow-Off Valves eliminate compressor surge when changing gears. Excessive back pressure is created when the throttle is closed during gear changes or deceleration, causing turbo cavitation. This is detrimental to the life of the turbocharger. Fitting a BOV will substantially improve this problem....

HKS USA wrote:....The primary function of any blow-off or by-pass valve is to prevent compressor surge by relieving the compressed airflow that reverses direction as the throttle is closed. HKS blowoff and bypass valves reroute the pressurized air, that is normally forced backwards into the turbo compressor, into the intake stream or by venting it to the atmosphere.....

Who mentioned boost control? I didn't. That's what the wastegate does. The reason bov's are fitted is to prevent compreser surge or keep it to a minimum(low boost). All these adjustable ones do Is allow you to adjust the tension of the spring which then determins how much presure is needed for it to open.

From your original post, wouldn't having your BOV set at 8psi be controlling the boost pressure in your intake?

coxy321 wrote:From your original post, wouldn't having your BOV set at 8psi be controlling the boost pressure in your intake?

no because it only releases over 8psi once you get off the gas( throtle body closes) not while under exceleration(throtle body open) its just like any other bov, these are no different you just have the option of adjusting the spring tension.

The wiki link posted above explains how they work if your having trouble

danny40 wrote:

coxy321 wrote:From your original post, wouldn't having your BOV set at 8psi be controlling the boost pressure in your intake?

no because it only releases over 8psi once you get off the gas( throtle body closes) not while under exceleration(throtle body open) its just like any other bov, these are no different you just have the option of adjusting the spring tension.

The wiki link posted above explains how they work if your having trouble

Its ok - i know exactly how they work. Maybe i just misunderstood what you were trying to say - which is that you had it set to trigger on pressure over 8psi. I read that as "the piston opens at 8psi" rather than boost spikes over 8psi will trigger the piston.

All clear now.

mmmm. Ok.
Thanks.

Only test driven it so far. Pick it up in a couple of weeks

The car has a miss, although it feels like a timing issue to me. Apparantly has newish leads and plugs . He has been told the dizzy needs rebushing. Would this cause the rough acceleration/miss etc.?

Not a great shot of the BOV

coxy321 wrote:

danny40 wrote:

coxy321 wrote:From your original post, wouldn't having your BOV set at 8psi be controlling the boost pressure in your intake?

no because it only releases over 8psi once you get off the gas( throtle body closes) not while under exceleration(throtle body open) its just like any other bov, these are no different you just have the option of adjusting the spring tension.

The wiki link posted above explains how they work if your having trouble

Its ok - i know exactly how they work. Maybe i just misunderstood what you were trying to say - which is that you had it set to trigger on pressure over 8psi. I read that as "the piston opens at 8psi" rather than boost spikes over 8psi will trigger the

All clear now.

no worries, you will find some factory bov's are designed to work for boost spikes aswell as comp surge but aftermarket ones only comp surge as they are designed to run unlimited psi, this is so you can run more boost and not have the valve open.

http://www.gfb.com.au/technical-information

To answer orig question without going off track to much...........

If the dizzy has electronic sensor it should be ok . At idle it may vary timing a little bit.

Performance ignition (scorcher??) in Nunawading can fit new bushes etc.

Bazzle