Miata Mailing List: February 1999, Message #156

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Herb,

It sounds like you have a pretty well optimized system and the question is,
what do you want to do?

Going from 11 to 12 psi is only (14.7 + 12)/(14.7 + 11) = 1.04 or a 4%
torque or HP increase - not real noticeable. How high do you want to go?

11 psi is good power as you noted.  To get more fuel you either need to
increase the injector pulse width, or the fuel pressure, or the injector
size itself.  You may be able to adjust your existing VFPR to put out more
pressure at high boost, or possibly buy a new one from BEGI or get a used
one from someone who's upgraded to an FM ECU.  These hit well over 100 psi
with the pierburg booster pump which can supply plenty of fuel at that
pressure.  This won't affect your idle and drivability.  Asking if Ken can
increase the duty cycle for your injectors is another approach.  New
injectors may well unbalance the optimum setup you now have and force you to
buy lots of new toys :-)

Good luck
Mike Marzalek
mikem@sr.hp.com
'96 red aerodyne
Sonoma County, Ca.

-----Original Message-----
From: samueh01@MCRCR6.MED.NYU.EDU [mailto:samueh01@MCRCR6.MED.NYU.EDU]
Sent: Monday, February 01, 1999 4:13 PM
To: Mike Marzalek
Cc: miatapower@rampage.net; miata@realbig.com
Subject: RE: Injector size (was RE: Interceptlink)



Mike and the list: I don't post to the list much but I have a BBR with an
auxillary ECU which is programable.  It plugs into the stock 1.6 ECU and
controls virtually all engine functions except for idle which is
controlled by the stock ECU. It was programmed by Ken Brittain at BBR.
I've checked it with a Link A/F meter that I got from Bill and it never
runs lean on boost until you hit 11 lbs which is probably due to a
limitation in the flow of the stock 1.6 injectors.  Yesterday it was about
35 deg in the New York City area and it did 50-70 mph in 4th gear in about
3.2 sec which is getting up there.  However, I'm a little nervous to push
it when it get close to 11 lbs because the A/F mixture can suddenly go
lean.  I could replace the injectors with 1.8 230 cc injectors or RC's 250
cc injectors.  Is the increase in boost that I would be able to run safely
before the A/F mix would become lean just of functon of the ratio of the
230 or 250 cc injectors to the stock 1.6 injectors or a more complicated
function.  I've heard that the 1.6 injectors are either 195 cc or 205 cc
and am not sure which is correct in my Sept 89 Miata. If the larger 230 or
250 cc injectors are used is it possible to adjust for the idle by
adjusting the the A/F meter without re-programing the ECU?  The auxillary
ECU controls pulse width and is programable (it was programmed by BBR) but
I'm not sure how to do it.

Thanks,  Herb Samuels