[mkiv] Overboost with rps manifold and 42mm racegate

[Axoman]

Original RPS headers are known to boost creep when going to a 3.5" or larger
exhaust.  A larger wastegate may help, but the header itself is going to
continue to cause problems with a 4" exhaust.

John

-----Original Message-----
From: mkiv-bounces at mkiv.com [mailto:mkiv-bounces at mkiv.com] On Behalf Of Ted
Volkman
Sent: Tuesday, April 15, 2008 9:49 PM
To: The MKIV.com National Mailing List
Subject: [mkiv] Overboost with rps manifold and 42mm racegate

my setup is as follows:
rps header (original)
42mm turbonetics racegate (routed back in to the dp)
67mm w/ .68 hot side and 3" vband discharge

i had been running a 3" dp/mp with cat and a trd gen2 exhaust.  last
time i was at the track, my traps were down and increasing the boost
did not increase the trap speeds.  i assumed the cat was finally done
and decided to finally step up the exhaust to 4" from the turbo back.

on a baseline pull the car made ~420rwhp at ~12.5psi.

after fabbing the 4" dp/mp and installing the 4" catback, the car
raced to 20psi and 625+ rwhp (not even a full pull).  this was with no
change to any settings on the aem.

another pull was made with no boost control (other than a line
directly to the wastegate) and the boost quickly passed 15 psi with no
signs of slowing down.  he then tested the wastegate to determine
whether or not it was even opening.  it started to open at 9 psi and
was fully open by 11 psi.

we hypothesized that a combination of wastegate size and placement
were to blame.  i think the placement is more to blame than the size.
shouldnt a 42mm wastegate be able to bypass enough exhaust (given
there is sufficient exhaust flow to the gate) at this power level?

has anyone else experienced this phenomenon with a small/moderately
sized turbo and 4" exhaust?

might stepping the exhaust housing up to a .96 slow the spool enough
to gain some control?

any other thoughts?

thanks
-- 
ted
02 is300 L-tuned, 5 speed
94t supra 6 speed, 67mm, aem
93t mr2 gen3, t3/t4, 264s, aem
89na mr2
88sc mr2
98 honda vfr800
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