why is the vaccum resitrictor needed in the sfmu setup? im currently not running with one in line.

thanx
James

im not sure. i ran mine w/out it for awhile.then i put it in, noticed no difference

i noticed a big difference. with the vacuum restrictor in there, my fuel pressures felt "laggy"... for example, if i tried to rev the engine it would cough and pause until the fuel pressure caught up to where it was suppose to be with the given manifold pressure. kind of hard to explain.

if i took the vacuum restrictor out, i'd run very rich in boost. no matter how many turns i took out of the bleed valve on the S-FMU i would still run rich. i'm betting this is because the bleed valve is simply incapiable of bleeding off that much air.

so, i made the hole in the vacuum restrictor a little bigger. everything is happy now.

2016 WRX STi Limited (current)
2001 A4 1.8tqms (donated)
1991 GVR4 #1933 (sold)
old.dsmregistry.com/detail.php?carid=218 (dismantled)

interesting.. i feel a little laggy now as it is but have plenty of fuel under high boost.

James

It "smooths out" the vacuum signal... so your fuel pressure is more of an average, than a slam-spike like when the BOV goes off.