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Discussion Starter · #1 ·
Hi,

Had an interesting chat with a mechanic today (had done quite a bit of Evo prep work for Rallying) and he said to me that I should remove the dump valve completely. This would give much better performance. He said that all rally Evo's inc Tommy's do not have BOV's.

So, is he talking shite or is he spot on ?

Any comments ?
 
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Discussion Starter · #2 ·
Yup ! He is talking the truth......

Evo4-7 have a system which is like a form of antilag. It is called the Secondary Air Control system.

If you drive over 4000rpm with the throttle pedal depressed fully to the floor for over 3 seconds you activate it.
The air which would be wasted on throttle off(waste gated), is sent thru the turbo and keeps it spinning during gear changes.

the SAC system works in this manner for 3 mins unless the driving style continues in a WOT style when it is reintroduced.

BOV's just stop the system from working !

Remove it and see for yourself

Jonathan
 
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Discussion Starter · #3 ·
Jonathan,

Any down-sides you can think of before I remove it ?

Will I get that 'cool' fluttering noise between gear changes ?
 
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Discussion Starter · #4 ·
That cool fluttering nosie is your turbo blades stalling which is OK if your a rally driver as your engine is replaced after every race or round of the championship, depending on your racing. However the reason for the BOV on the road car is to maintain the life of the turbo.
Dont understand the secondary air system so may further comments will probably be shite but read on if you like. However if the secondary air system keeps the turbo spinning when you thrashing the engine then theirs no real need of for the BOV, however if it only comes on after 3sec, and your continually canning it around town the turbo will be continually stalling. Good bye turbo, hello expense.
Just remember turbo stalling bad, turbo spinning good.
Just see what HH6 says cause hes the daddyhttp://www.ltregister.f9.co.uk/graphics/happy1.gif border|EQU| 0 align|EQU| absmiddle >
Cheers
Al
 
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Discussion Starter · #5 ·
HH6 WHERE ARE YOU ?????? http://www.ltregister.f9.co.uk/graphics/happy1.gif border|EQU| 0 align|EQU| absmiddle >

Or has this one slipped past him ?

Nooooooo surely not.[img]http://www.ltregister.f9.co.uk/graphics/tonguewink1.gif border|EQU| 0 align|EQU| absmiddle >
 
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Discussion Starter · #6 ·
Could be hes had enough of discussing BOV as we had a major thread running a while back to the merits and disadvantages of BOV. Think he got feed up in the end with it.
Cheers
Al
 
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Discussion Starter · #7 ·
I've had a chat about this to Clive at RC, and if I remember correctly Porsche have been using Secondary air control for quite a few years on the 911 turbo's. However there is some debate as to whether it is for a form of anti lag, or to reduce emisions. As I see it there isn't enough air there, and no fuel to use as an anti lag system. All the anti lag systems I've seen keep the trottle partially open and alter the timing drasticaly so the mixture burns in the turbo not in the cylinders. Personally I'd keep the BOV and if you want anti lag (very short turbo life) buy a MOTEc (or similar) ECU. I would if I had the cash to spend but I haven't.........yet http://www.ltregister.f9.co.uk/graphics/happy1.gif border|EQU| 0 align|EQU| absmiddle >

These are just my thoughts on it so I'm open to criticism etc.

Adrian
 
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Discussion Starter · #8 ·
Have you considered removing the engine it will make the car a lot lighter, oh and dont forget to remove the plastic grommet thats good for a extra 100bhp.
 
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