Partial success

[Walter Sherwin]

If really bent on keeping the blow-thru config, then what about a couple (or
more) BOV's between the S/C and the TB in order to gain adequate flow and
response?  Pilot them all via manifold vac from beneath the TB.  Smallish
Turbo BOV's may have a short life span because they just weren't designed to
be open/stressed all the time in that manner.  Vortech make a Mondo Race BOV
that may prove successful, as do Cartech/BEGI.  Magnuson/Eaton have a
universal flapper style BOV/bypass that may offer even better life.

Locating the TB downstream of a S/C does have it's merits if worried about
things like  1) the TB area unduly restricting the inlet flow capacity of
the S/C, or  2) exposing the S/C end lube seals to substantial vacuum and in
turn causing lube entrainment, or  3) you wish to retain a wet engine inlet
manifold setup, but wish to keep the S/C and intercooler dry.

Most any S/C type can be made to work in this config, but some will impose
considerable heat and parasitic power loss issues no matter how much BOV
flow you have (ie: S/C's  with internal compression).  The BO discharge will
be noisy but a length of tubing, with a filter on the end, directed to a
remote spot, can help.  Excess air can be dumped from pretty much any point,
but closer to the S/C is better.  Be careful about your dump point if
running MAF as opposed to MAP fuel.

In all other cases, the best bet is most likely to locate the TB upstream of
the S/C, and install a vac operated bypass loop around the S/C that would
connect the underside of the TB to the S/C outlet under high engine vac
conditions.  Magnuson/Eaton have a number of different styles and sizes for
this purpose.  Response and control are almost instant from a driver's
perspective, and the resultant cruise input shaft parasitic losses are
miniscule (eliminating the need for an expensive clutch with controls).


Walt.



>
>dzorde at erggroup.com wrote:
>>
>> Hooray, I've finally got my Fiat 850 sport running on fuel injection,
>> however I'm now in need of some suggestions for the next part.  I have a
>> Toyota MR2 s/c connected in a blow through configuration with the
throttle
>> body (it should be geared for 120kPa full boost, 17psi), my problem as it
>> stands:
>>
>> At idle the ecu reads a vacuum (-21kPa to be exact) while the s/c side is
>> seeing 90kPa (throttle blade shut).  At higher revs (no load) the boost
>> will build up even more (over 250kPa) as the throttle is only just
opening.
>> Obviously if I keep going like this the s/c is likely to blow a seal
>> somewhere.
>> Now here's my question, do I just fit a blow off valve and let it bleed
of
>> any excess boost above say 140kPa ?
>> And what sort of blow off valve would I use, the ones I have seen on
turbo
>> cars are very small and the s/c has like a 62mm outlet, so that is a lot
of
>> air to remove ?
>> I have looked at a few available blow off valves (greddy, hks, etc), but
>> they are all specced as turbo applications, isn't there anything for s/c
>> applications ?
>>
>> I'd appreciate any light people can shed on this unknown area I've
ventured
>> into.
>>
>> Dan  dzorde at erggroup.com
>>
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