[Supras] blowoff valve recommendation

Tue Nov 13 23:04:35 CST 2007

Jordan:

    I have only one piece of blue silicone line and that is between the 
FPR and the VSV which controls it for hot starts.  It seems rigid at 
temperature and is there only because it was handy and was the right 
length.  All of the other hose is black rubber.

    Vacuum plumbing to the Bosch blowoff valve is stock, meaning that it 
goes through the small bore tube next to the 3000 pipe.  Since there is 
more volume to be exhausted in the Bosch diaphragm chamber than in the 
stock valve, I could understand the surging to continue for a fraction 
of a second.  But it lasts almost a second if I suddenly close the 
throttle and disengage the clutch at the top end of any gear and let the 
engine come to idle.  It is possible but doubtful that the Bosch valve 
is not getting any vacuum since everything is plumbed like stock.   Yet, 
it is one thing to check.  One  other thing I'm thinking about doing is 
putting a tee in the vacuum line at the front of the intake plenum and 
running 1/4" fuel hose right to the BOV diaphragm.  Since the fitting is 
large, I can alternatively remove it, drill and tap it for either a hose 
barb or for a 1/4" flare fitting, and run 1/4" aluminum tubing to the 
BOV.  The aluminum could be tucked out of sight and tie wrapped to the 
frontmost tubing bundle (in front of the 3000 pipe). 

Bernie (now looking for more power, dammit). 

Jordan Weaver wrote:
> Bernie,
> What is the condition of your vacuum lines? A year ago, I installed some
> brightly colored silicon vacuum lines (bought off eBay) to go with my new
> 60trim CT26, and almost immediately noticed compressor surge - even at low
> boost. My setup is all custom, and my BOV is more than adequate. A friend
> cautioned me about using those silicon vacuum lines saying they will
> collapse when hot. Switched to some generic black vacuum line bought at
> Autozone and haven't had any problems since.
>
> Jordan
>
> -----Original Message-----
> From: supras-bounces at supras.com [mailto:supras-bounces at supras.com] On Behalf
> Of Jeff Mohler
> Sent: Tuesday, November 13, 2007 10:09 PM
> To: berniek at technicaldevelop.com
> Cc: Supras at supras.com
> Subject: Re: [Supras] blowoff valve recommendation
>
> Well..good luck with that.
>
> On Nov 13, 2007 6:59 PM, berniek at technicaldevelop.com <
> berniek at technicaldevelop.com> wrote:
>
>   
>> Jeff:
>>
>>    Huh???
>>
>>
>>    From all I could gather, the stock blowoff valve was said to be WAY
>> to small for a 57 trim turbo.  The Bosch unit is much larger
>> internally.  Right now I have a spare piece of head to crankcase vent
>> hose (same as the hose behind the alternator) connected from the 3000
>> pipe to the inlet of the Bosch valve, maybe 6" long.  The Bosch valve
>> outlet is connected to the accordion hose in the stock location with
>> almost a zero length piece of thin wall copper tubing, a tight fit in
>> the Bosch outlet, held with high temperature epoxy.  The other end of
>> the tubing is forced into the rubber bung on the accordion hose, secured
>> with a hose clamp.  Of course the vacuum diaphragm hose is hooked up
>> too.  It should be very free flowing.
>>
>>
>>    Bernie
>>
>>
>>
>> Jeff Mohler wrote:
>>     
>>> OEM works.
>>>
>>> I hear it bolts right up.
>>>
>>> On Nov 13, 2007 5:43 PM, berniek at technicaldevelop.com
>>> <mailto:berniek at technicaldevelop.com> < berniek at technicaldevelop.com
>>> <mailto:berniek at technicaldevelop.com>> wrote:
>>>
>>>     For the last two weeks I've been getting my jollies by driving my
>>>       
>> '91
>>     
>>>     with 550cc injectors, 57 trim turbo, Walbro, Lexus, 3" exhaust from
>>>     turbo back, etc.  However, a disturbing boing-oing-oing sound has
>>>     persisted from the air intake when closing the throttle under 15 PSI
>>>     boost.  Spoke to James at Performance Techniques about this, and
>>>     he says
>>>     it is compressor surge, which I suspected.  From all I have read,
>>>     using
>>>     the Bosch Porsche right angle blowoff valve should have been
>>>     sufficient,
>>>     but it is not.  I get the sound even at low boost.
>>>
>>>
>>>     So I'm looking for recommendations as to which BOV to use.  I
>>>     would like
>>>     to recirculate to the accordion hose, even if I need to cut a hole
>>>     in it
>>>     and use curved, clamped large washer-like pieces on the inside and
>>>     outside to provide a large bung for the BOV discharge.
>>>
>>>
>>>     Any and all suggestions would be appreciated.  Thanks.
>>>
>>>
>>>     BernieK.  PS:  Arlene and others were right.  There is never enough
>>>     power even if you can "walk" the tires in second gear.  Starting to
>>>     wonder what to do next for more HP.
>>>
>>>     _______________________________________________
>>>     Supras mailing list
>>>     Supras at supras.com <mailto:Supras at supras.com>
>>>     http://supras.com/mailman/listinfo/supras_supras.com
>>>
>>>
>>>       
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