Blow-off valves test

1|ltID(:
Ct|MPRESStlR
varve
BYPASS
BL0W0UT-ry:,ffi':l,*t,l*-?,'
Inturbocharged
andcentrifugalty
supercharged
engines,
thecompressor
often
(or
triesto flowmoreairthantheengine
closed
throttteplate)will accept.
Every
time
youshifta turbocar,forexampte,
theturbo
ptate.
hasto pumpagainst
a closed
throttle
pitesupinthepipeandpushes
Pressure
backward
through
thecompressor.
This
causes
atlsortsof badstuffto happen;
compressor
wheelblades
resonate,
thrust
bearings
fail.
Settting
intomyzeroperiod
mathclass,
Ball-bearing
turboscanhandle
this
oftendemands
moreairthana [aggy
turbo
"What's
thevoluptuous
Virginia
asked,
surge,
butconventionaI
pumping,
bearing
turboscan
is
making
thecompressor
littte
wrongwithyourcar?lt sounds
likeyou
bekittedquickly.
ThereaIbummer
with
morethana restriction.
yourgears
ground
coming
intotheparking
eitherkindof turboisthisbackoressure
Compressor
bypass
vatves
canatteviate
[ot."Asmyprideevaporated,
I tried
slowstheturbo,increasing
lagthenext
bothprobtems.
Blow-off
vatves
ventthe
desperately
to explainthatit wasactuatly
timepoweris demanded.
pressure
totheatmosphere,
whilediverter
thesound
of myshinynewHKScompressor Centrifugatly
supercharged
carshave
valves
recircutate
theairbackinfrontofthe
"hybrid"
problems,
bypass
valve,
which...
Theblankstaretotd
simitar
butsince
thecompressors compressor.
5o-ca[[ed
vatves
are
just
menotto bother.
always
spinwiththecrank,
evenhigh-rpm
a mixofthetwo,recirculating
airat
I reatized
twothingsthatday.Virginia
cruisecanmakethecompressor
fightthe
tighttoad,
andventing
someat hightoad.
doesn't
careaboutbypass
valves,
andmany throttle.
Sincesuperchargers
won'tslow
Selecting
thecorrect
valvetypeis key.
ofthosewhododon'tunderstand
them.
theywaste[argeamounts
of horsepower
lf yourengine
management
isspeedCompressor
bypass
vatves,
commonly
fighting
thepressure
buitdup.
densitybased,
bothstylesof valvewil[work.
probtem
knownasblow-off
valves(BOV]
or diverter
Theopposite
atsooccurs.
At low
Massairftow(MAF)
vehictes
require
a DV
valves(DV),area solution
to a reaIproblem. rpmandhighthrottte
angles,
theengine
setupto ensure
correct
fueling,
otherwise
I first became
awareof the
problemnearlya decade
ago.
Thatday,[ikemost,I triedto
finishmydriveto schoolwith a
glorious,
ass-out
stideintothe
parkinglot.Deepdown,I
alwayshopedto impress
the
chicks.
lt neverseemed
to work.
| 1229
-
turbotech
I COTIPRESSOR
BYPASSBU'W{ruT
>{--
compromise
a[[ows
somesurge,
but
according
to itsdatagathering,
maintaining
about4 psiin thepipeduring
a shiftmakes
themfaster.
Thisshould
onlybeconsidered
witha ballbearing
turbo,
of course.
3
E
TEST
I1{
G
Always
theinquisitive
bunch,
we
gathered
everycompressor
bypass
valvein
arm'sreach
for a littlereal-world
testing.
=
Ourgoatwasto geta feelingfor how
6
different
valves
wouldoerform
under
simi[ar
conditions,
on
a
relatively
E
common
vehicle.
of Diamond
Star
Ilrylcallayoutof Intercooler
andplumblng
In a FWDtu6o appllcatlon,
lasonGardner
NoUce
thecomprcssor
bypass
valve
locatlon,
anddlrcctplumblng
backto thetulboInlet.
(DSS)
Specialties
in SanLuis0bispo,
Catif.,
thesuckerthat
heis,offered
uphis1993
paralte[,
theair blownouttheblow-off
valvewitl be
thenetlossis lowerthaneither
Mitsubishi
Eclipse
GSXfortesting.
measured
bytheMAF,
andfuelwitlbe
individuaI
avenue.
Throttle
response
at
Modifications
to theEclipse
wereminor;
delivered,
butthatair wit[neverreach
the
theselowloadsimproves,
asdoesturbo
anAFC-MASC
withconefilterreolaced
the
cylinders.
Thiscanprofoundty
affect
spoolandeconomy.
stock
airboxandMAFassembly,
2.5-inch
driveabitity.
Diverter
valves
canbeusedas
Howimportant
is it thatMAFcarshave
D55upperintercooler
pipe,ported
zG(or
blow-off
valvesbysimptynotrecirculating recirculating
diverter
valves
ratherthan
generation)
second
exhaust
manifold,
t6G
thedischarge,
butbesureto puta filteron
open-air
blow-offvalves?
Tomakea BOV
turbo,ported
0, housing,
andWalbro
fuel
theendif thevalveopens
undervacuum.
worksuccessfully
involves
pump.Thewastegate
a [ongstringof
wasptumbed
directly
Bypass
valves
shouldbeplaced
asclose
compromises.
TokeeptheBOVfromleaking to manifold
pressure
to eliminate
any
to thethrottlebodyaspossible.
Since
at idte,whichwouldintroduce
unmeasured variation
induced
byanaftermarket
boost
pressure
surges
beginhere,it'sthebest
air,thespringhasto beexcessively
tight.
controller.
0urtestswererunat a relatively
placeto stopthem.Theexception
to therule
Thisslowsthevalve's
response,
anda[[ows
mitd9 psiof boost.
Someof thevalves
witl
isthatanyadditional
fue[injectors
or
briefperiods
of surge.
Inaddition,
anytime
respond
differently
at higherpressures.
nitrousoxidenozzles
shouldbeplaced
after
thevalveopens,
airislostandthevehicle
Atlthebypass
valves
weremounted
to a
thevalves.
Theroutingof air backfroma DV
runstoorich.Thisusually
shows
asa
plateonthesamesection
common
adaptor
to thecompressor
inletis important,
too.Try
hesitation
orflatspotin throttleresponse. of intercooler
pipe,andusedthesame
to keepthepathsmooth
andstraight,
but
Recirculating
thedischarged
airdoesn't
pressure
dedicated
manifold
hose.
mostof all,besureto directtheair backinto
necessarily
eliminate
all thecoolblow-off
Adiustabte
valves
weresetto thelightest
thecompressor.
Sending
airbackwards
out
valvesounds,
either.
Anyopen-element
air
setting.
A[[thediverter
valves
were
theMAFwittgiveit a falsesignal
and
filterwittletyouhearit lustaswellasif it
ptumbed
to recirculate,
withtheexception
justasmuchasventing vented
degrade
driveability
to theopenair.
of theSubaru
andVortech.
These
twohave
theair.A bonus
forrecirculating
theairisan
It should
bestated
thatcompressor
goofy
passages
somewhat discharge
that
increase
justweren't
in pumping
efficiency,
asthe
bypass
valves
arenotdesigned
to timit
goingto workwithoursetup.
compressor
doesn't
needto drawadditionat boostundernormal
conditions.
Pop-off
Fora baseline,
andto seewhat
airthrough
thefilter.Thiskeeps
compressor vatves,
[ikethoseusedin CARILeMans,
compressor
surge
isrea[[y
a[[about,
the
speedup,furtherreducing
[ag.
andprofessional
motorsports,
area
stockbypass
valvedischarge
wasplugged,
Vehicles
withlong,complex
inletand
separate
animalentirely.
These
valves
are
rendering
it useless.
Using
an Edelbrock
plumbing
intercooler
witlbenefit
fromDVs
designed
to [imitboost
andpower,
as
datalogger,
we
Quickdata
logged
throttle
thatooenundervacuum
(TPS)
conditions.
For
mandated
byregulations,
position
andareof noreal
andpressure
inthe
manyyears,
0EMshavedesigned
these
usefor streetcars.
compressor
pipeduringa one-t,.r/o
discharge
vatves
to openunderlighttoad,allowing
the
lnterestingly,
wehaveseensomerally
gearchange.
engine
to drawairdirectly
through
them
cars,specificalty
Subaru's
ProDrive-prepped Fromthegraph,it'sclearto seethe
fromtheMAF/filter,
bypassing
anidting
Open-class
U.5.rallycars,running
very
compressor
pressure
discharge
riseasthe
turboandtherestricting
intercooler
smallvalvesin aneffortto keepsome
throttleisclosed.
Thisisto beexpected
and
ptumbing.
pressure
Muchliketworesistors
in
inthepipeduringshifts.
This
realtyisn'tatlthatbadsincethecompressor
e
turbotech
I COiIPRESSOR
BYPASSBU'WOUT
is designed
to compress
air.Astheflow
through
thecompressor
sta[[s
(remember
thethrottle
isclosed),
and
pressure
discharge
increases,
the
compressor
enterssurge.
Muchlikea
prop,
spinning
tireorcavitating
the
compressor
spinsbutnoairmoves,
thenit does,thenit doesn't,
overand
over.
Theeventisaudibte,
andhasa
warblingsound.
Not"Wooo,
wooo,"
rather"Wuh,wuh,wuh,wuh."lt'sthe
soundof badnews.
Moreidealthanthisdramatic
fluctuation
wouldbea smooth
reduction
in
pressure
asairisvented
fromthe
compressor.
Lotsoftimecouldbespent
analyzing
andspeculating
theslopeofthe
peakpressure
boostcurve,
rise,total
pressure
loss,
andmyinconsistent
shifting.
Having
drivena[[thevalves,
however,
thosewiththeleastsurge
andmost
gradual
pressure
lossdrove
thesmoothest
Maintaining
compressor
speed
and
pressure,
discharge
a seemingly
contradictory
endeavor,
isapparentty
the
keyto seamless
throttleresponse.
illT s u B r sDHvtrn 0 itl GD si l
It'snotallthatsurprising
thatMitsubishi
dida goodjobspecifying
theDVforthe
first-generation
D5M.lt'sbeendoingturbocarsforsometime,andhassomedeep
pockets.
A popetvalvedesignis used,whichisverysimilarto anexternal
wastegate.
These
valves
openunder
vacuum
andarecapabte
of hotding
significant
boost.
A common
modification
isto "crush"
thetopof
thecapassembly
downa few
millimeters
to raisetheinternal
springrate.Thisatlowshigherboost
to berunpriortoleakage.
lf you're
anxious
aboutcrushing
yourownvalve,Diamond
Star
Specialties
offersthesevalvesboth
stockandpre-crushed.
ilt T s u Bt sDHt F
|t n o il
2GD si l
The2GDSMbypass
valveis anexcetlent
performer
at towboost.Likeitsolder
brother,
it'sa popetvatvedesign,
though
it'smanufactured
in ptastic
ratherthan
aluminum.
Therubisthatit leaksbadly
beyond
15psiof boost,degrading
intoa
pop-offvalve.lf you'renevergoingto run
morethanr5 psi,chances
areyoucanpick
upa usedonefora song.
Mostpeople,
however,
wantmoreboost,andshould
juststayaway.
-i232 | :ulr zoosr wnrysporrcompacrcrffi.cou
I
gfflaH
FDd-rc-l
:E!]m
I
! "
o ;
3
turbotech
r COMPRESSORBYPASS BU'W{,UT
S U B I RIU
TRX
Dtl
The0EMsknowa goodthingwhen
theyseeit. Despite
thedifferent
intetflange
anddischarge
fitting,
theWRXDVappears
to bethe
sameoneusedbyMitsubishi
onits
lG DSM.
We'renotawareof
anybody
crushing
theirtopcaps
yet,buttheresurearea lotof DSM
purchasing
owners
WRXs...
Source:
Edelbrock
Quickdata
MAZDA
DUTR(IIII
FD
(3RD
G r i l .R
) X-7
It'stikethelittlevalvethatalmost
could.
Nearty
theentirevalvecould
fit in theGReddy
TypeRdischarge
passage.
Thevalvehasa Nippon
partnumber,
Denso
whichwethink
isverysimitar
to theunitusedon
thetwin-turbo
Supra.
Since
RX-7
andSupra
owners
tendto makea
goodbit morepowerthanourtest
Source:
Edelbrock
Quickdata
car,at significantly
higherboost
tevets,
it'sprobabty
a goodideato upgrade.
In addition
to a[[theaftermarket
offerings,
running
twoofthesestockunitsin parallel
wouldbea validoption.
iltssAlt
R32
st(Yil1{t
Dt,
GT-R
Wehadit,sowe
testedit.Nissan
used
twoofthesein
parallel
onitstwinturboterror.
Two
generations
later,on
theR34,
Nissan
began
usin5
surprise,
surprise-a
valvemuch[ikethe
16DsM.
ttr.o strt&taE2 W
,I
I
/\
/
I
n
2
\
rcF
/
Y_____J\/
Source:
Edelbrcck
Quickdata
turbotech
I COMPRESSORBYPASSBU'WOUT
Grutchfield's
B ( ) S CD
l | t ,F R ( I M
A U D [I 4 I . 8 T
Variations
onthisbasic
Bosch
valveareusedin a[[manner
ofAudi,Porsche
andVW.The
design
usesa simple
diaphragm
pressure.
to control
Whitethedesign
istightandfast-acting,
thediaphragms
areknown
to tear,causing
boostleaks
andperformance
[oss.
These
valves
do
openundervacuum
andarequiteinexpensive.
TheA4r.8Tmodel
wastested
here,
though
it
seems
theunitfromtheTTis more
desirable.
Available
through
A
Audi/VW
dealers,
theTTpart
number
iso6A-145-no-N.
s@h
rydd
Mg
lffl
JA^
""-1y\
& *
I
\
/
Y
/
ttt
Soume
Edelbrcck
Quickdata
A'PEXt
TtilltCItAMBtR
B[0lY-0tt
uAtllt
APEX|
delivers
a greatunit,atbeitit'sa somewhat
largepackage.
Thepopet-style
BOVoffers
preload
adiustable
anddischarge
flow.Restricting
thedischarge
flowcouldachieve
theraltystylesemi-surge
wementioned
earlier.
lt alsochanges
theaudible
tone,whichisprobabty
why
it'sthere.lt'stheontyvalveinthetestto comesetupto usea push-putt-styte
actuation
where
(BoththeGReddy
bothmanifotd
vacuum
andboostpressure
areusedforactuation.
valves
can
beconfigured
thisway,butweren't
forthetest.)Application-specific
installkitsandinstructions
areavaitable
formanylapanese
vehicles.
Btanksteelftanges
are
available
forcustom
insta[[s.
Listprice,
APEX
$219.
Integration,
Inc.
l7t4l 685-5700,
wwwapexr-usa.c0m.
Slammin'tracks
r Hlgh-energy
muslc
tracks
youraudio
showcase
system's
caoabilities.
r Theuailegof stylesgives
your
system
a workout
across
the
your
sonic
spectrum,
helping
system
sound
itsbest.
. Deep
basstonesprove
how
lowyoursubwoofers
canplay.
GalltodayforyourFREE
CD!
Sourcer
Edelbrock
Quickdata
B A I T E iYI ( ) T ( l R S P ( l RATtS
I . ( l YD l ,
Bailey
Motorsports
devetoped
thisdirectreplacement
fortheBosch-style
valves
common
to
European
vehicles.
A high-temperature
pistonis usedto control
composite
airftow.
Thisalternate
to hetpit respond
fasterandholdmoreboostthantheOEMpart.Bothstraight
0rvisitwww.crutchfl
eld.com/basscddesignisclaimed
pressure
andangled
manifold
fittings
Hurry,
supplies
arelimited.
areavaitable.
Thecomoact
sizeand
lifetime
warranty
arereaIpluses,
asare
thedetaited
instructions
forVWand
thebestselectlon
andservlce
fol 29 yean
Audiowners.
Avaitabte
in potished
silveror anodized
btack.
Listprice,
$tlg.gS.
(888)
AWETuning,
www.awe565-22j7,
tuning.com.
1-800,555.8307
CRUICHFIETD
Sourcei
Edelbroct
ouickdata
$
:.
turhotech
r GOMPRESSORBYPASS BLOWOUT
BIITZ
S U P ESR( ) U I I D
B r . 0 w - 0 tvtA t l l tD D
Btitzoffersitstrick,piston-style
Super
SoundBOVDD.Twodischarge
flanges
areincluded,
onewith a couoteof
whistle-[ike
featuresmachined
intothe
body,the otherwith a mini-integrated
air filter.Sincethe springtensionon the
modelwe testedwaslightenoughto
leakat idle,the filteredflangecould
workwe[[for some.0f course,
the
preloadadjustment
cankeepthe valve
sealed,
too.Whyit doesn't
offera
fittingto a[[owrecirculation
isa
mystery
to us,though
there's
no
youcan'tmakeyourown.
reason
Apptications-specific
instatI
kits
andinstructions
areavailable
for
mostJapanese
vehicles.
Blank
aluminum
andsteelftanges
are
availabte
forcustom
instalts,
asisa
heavy
spring
forthoserunning
big
boost.
Listprice,$235.
Btitz
(7141
NorthAmerica,
m -1508,
nrsesd@D
l:;Gdl
V\
I
)
So!rce:Edelbrock
0uickdala
wwwblitzna.com.
Hr(s
ssQll
80l/
(stJPtR
srQUEilTtAr
Bt0fy-0Ft
vArvr)
lf altwecared
aboutwerelooks,
HKS
woutdstealtheshowwithitsSuperSequentiaI
BOV(SSQV].
lt'sa darn
handsome
piece
of potished
bittet
aluminum.
A[as,
function
isthecruxofthis
study,
andonourtestcar,theadjustabte
valvewasa bitslowto respond.
Whenthe
valvedidopen,
it emitted
a souno
reminiscent
ofa seatbeingbeaten
to
death.
Fun,kindofexciting,
andbound
to
getyouthelooks.
0f a[tthevatves
tested,
thisoneisthecatca[t.
Other
inserts
areavaitable
to raiseor
lowerthetone,asisa fittingro
provide
forrecirculation.
TheHKS
SSQV
isavailable
asa universaI
3
unitwithatuminum
orsteelflanges
forcustom
apptications
andalsoas
vehicle-specific
kitsforbolt-on
applications.
Listprice,
$zlo.HKS
HsWS#EW
l-;iG
/\,t
v\n
/
"\/\
/
o ;
/
\_/
,/
\__/\/
USA(310)
763-9600,
www.hksusa.com.
Source:
Edelbrock
0uickdata
turbotech
T COMPRESSORBYPASS BLOWOUT
dT
BEST
U
L{HEEI
(lSPIIERE
STRAT]t|
I|YPERB(l(lST
Dtl
TheHyperboost
isdesigned
asa drop-in
E
( 3 O s ) 8 2 4- !
www,Bestwhe
7" w/Tires
8" w/Tires
17" w/TiresS59?
18" w/tires $849
7" w llies 5599 I 7" w/Tires
9" w/Tires
S129918" w/Tires
replacement
for Bosch-style
valves.
lt'sreally
unique
in thatthevalvecanbedisassembled
andserviced
without
tools.Simply
unscrew
the
cap,liftoutthe[arge
Teflon-coated
aluminum
piston,
cleanandregrease
the0-ring,
andslide
it backtogether.
Whitethevalveis apart,it's
curious
to notethefundamental
similarities
between
the
Stratmosphere
andForge
units.
Pretoad
adjustment
isanoption
thatcanbeupgraded
downthe
road.Finish
options
arenickelplated
sitver
oranodized
btack.
Lifetime
warranty.
Listprice,$139,
modet.
$t79fortheadjustable
Sratmosphere,
Inc.(888)Bj-1m,
www.stratmosphere.com.
7" w/Tires
U ( l R T ERCI C
]| E
BYPASS
UATtlE
17"w llire
8" w/Tires5849 l 8 " w / T i r e
l9"w/Tire
Source:
Edelbrocl
Quickdata
,49
,949
8" w/Tires51,34919" w/tiresSl
?" w/Tires51,94?
8" w/Tires S84?18" w/Tires$2,
0" w/Tires51,69919" w/Tires$3,
Vortech
sentusits"smal["bypass
valvefortesting.
lt'sthesecond
largest
wereceived.
Coming
from
a company
witha history
primarily
i nvolving
supercharged
V8s,it makes
sense.
Thepopet
valvedesign
isverysimilar
to
GReddy's.
Spring
tension
is
adlustable
fromthe[id.Like
GReddy,
too,puttingpressure
to
thebottom
ofthediaphragm
can
bea chore.
Vortech
instatls
a
porous
metalfilterto keepdebris
out,though
reptacing
it witha
nippleshouldn't
betootough.
We'dfigureperformance
would
benefitsignificantly.
Theoval
discharge
isa bigoneandcanbe
toughto mateto commonly
avaitable
materia[s.
Mounting
is
prettysimple,
amazingly.
lt usesa
GReddy
compatibte
ftange.
Numerous
finishchoices
are
availabte,
asarealuminum
and
stee[-mounting
f langes.
Listprice,
Vortech
Engi
neering,
$2t0.55.
(805],
247-0226,
perchargers.com.
www.vortechsu
I
I
/ t f\
VIA
s 6
Sourcer
Edelbrock
Quickdata
:.i''; llfQQ[
r COMPRESSOR
BYPASSBLOWOUT
F ( ) R GM
E( ) T O R S P O
TR
AS
I T
R()AD
D l l & P I S T OR
I IA MB ( ) l /
Theterm"forge"
usually
implies
strength,
and,boy,isthatthecasehere.
These
vatves
arebeefy.
Forge
Motorsport
quitea fewdifferent
makes
bypass
vatves
for a
number
of applications.
Thetwoherearesuitabte
asdrop-in
replacements
forthe
2GDSM.
TheFastRoadDVusesa [arge
self-aligning
floating
piston
forpositive
closure.
Evenmoreinteresting
istheduat-piston
arrangement
onthePiston
Ram
pressure
BOV.
Manifotd
actsontheouterpiston,
eitheropening
or ctosing
it
d e p e n d ionngc o n d i t i oAns. m a li[n n epr i s t oinsi n d e p e n d e n
t lryu nagn do p p o s e d
sp
on[ybyboostpressure
piping.
intheintercooter
Thisdesign
guarantees
noidle
teakage
whitestil[allowing
theuseof a reasonab[y
softprimary
spring.
Al[Forge
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3
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products
areuserserviceable
and
covered
by its lifetimewarranty.
Listprice,$t35.Forge
(321)
Motorsport
689-0982,
l
www.forgemoto
rsport.com.
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So!rce:Edelbrock
Qurckdata
tech
r COMPRESSORBYPASSBTOWOUT
T Y PR
ED V S
G R T O IDYYP ES A I { O
product.
Both
atwaysseemsto comethroughwith a prettywe[[-engineered
GReddy
TheTypeS andTypeR altowfor
valvesusea popetdesignmuchlikeAPEXi's.
recircutation,
however,
anddespitethe hugediameterof theTypeR'sdischarge,
to adaptto neartyanyhosesize.Spring
areavai[ab[e
handythreadedreducers
.
f,
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1
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t e n s i o n i s a d j u s t a b t e o n b o t h , i n a d d i t i o n t o a s t i f f e r s p r i n g o p t i o n fA
ortheTypeR.
LikethatfromAPEXi,these
captive0-ringin the valvefaceensurespositiveclosure.
I
va[ves,
thoughneitheronewassetup to runthatway.lt seems
arebothpush-pult
thoughthe resulting
fromthe boostassist,
bothvalvescoutdhavebenefited
part-throttle
maynot beworthit. GReddy
offersinsta[[kitsfor most
boostleakage
turbocharged
vehicles,
as
lapanese
wel asflanges
forcustom
insta[[s.
List
price:TypeS,$zzZ.
TypeR,$254.55.
(949)
Products
GReddy
Performance
www.greddy.com.
588-8300,
F-Ps(i)
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Quckdata