a MAF too small

[Patrick G. Moore]

Dave Zug wrote:
> 
> Heres a brief intro to my project, for those new:
> 
> I have an 89 5.7l Iroc, 165 ECM, ARAP (vette) binary. I have put a
> supercharger on it and the computer has no idea what airflow is
> coming in after about 3000 rpm cause the MAF reads 255 right about
> there.
> 
> The definite solution is to go to a MAP system. I dont want to hack
> the wiring apart and have to use a binary that I'm not skilled enough
> at to tune from scratch.
> 
> Heres my thoughts as to a solution to the MAF max problem:
> 
> If I drill holes PAST the maf sensor, effectively forcing it to
> read 75% of the actual air entering the engine.. I can alter the MAF
> tables to re-compensate. If it works, I can wrap foam around the
> holes and lube with K&N oil for now.. until I can get a pipe made.
> 
> Voila.. don't have to buy a twin MAF, dont have to use a translator,
> don't have to go to a MAP system. only trouble is at idle, the
> resolution might make idle quality suffer. If (there should be)
> there is a fairly linear relationship between volume thru the
> sensor and unmeasured volume into the "post sensor holes" or larger
> single  "post sensor hole", it should work.  one snag is the
> difference between the filter restrictions but it may be neglidgable
> enough to tweak the MAF values at WOT manually using an EGT or O2..
> 
> Am I missing an easier solution? Do I even really care what's going
> on at WOT above 3000 rpm?  I MAY max the MAF at 70% TPS and 3500 rpm
> so my thinking is I DO care.
> 
> I have a few more days and I'll have the alum heads, 28#
> Buick GN injectors (12.7 ohms (??)) and new fuel pump on so the
> problem is about to get worse.  PS I blew the head gasket probably
> from being lean so my mission is that much more critical now with
> 1200$ heads to warp 8-(
> 
> Dave Z. www.delanet.com/~tgp

Hi Dave,

That idea has a fatal flaw, I bet you thought of it already. Doh..
Under boost, air will flow out, not in - Hence 2 and 3 bar MAPs.
I remember as a youth, pulling I think 35"hg manifold pressure on a 
turbocharged Cessna 320.  We called it pulling anyway, it's really
pushing.

I was thinking about putting the MAF in a larger pipe, so air could
flow around it.  I am afraid to do this before an initial tune and
cut at a modified chip however, because I ported my heads and stuff
and I'm afraid it will be way too lean until it learns in. And on
initial start, I want to run it up to about 1800 for 10 minutes for
break in.  It might REALLY break in if it's way too lean.  I think
with the MAF in a pipe, with the screens in place the low velocity
readings may still be fairly stable.  The only thing to do is try
I guess.  Maybe you could streamline the outside of the MAF with
the ol' Dremel and help reduce the turbulence out there.

I have an 87 Buick Century 3.8 and don't want to spend money for an
LT1 MAF and translator for less intake restriction.  I don't think
I will run out of MAF range with this NA setup (but there's always
hope).

Another option might be to plumb your post-MAF hole(s) to pre-MAF
hole(s).  Then you maintain the pressure while reducing the flow
through the MAF.  If I got out my old fluid mechanics books, given
the pressure drop across the MAF vs flow (or if you could estimate
it) it might not be hard to figure out the size of bypass for
a given amount of range adjustment.  Or you could watch the MAF
reading, if it maxes out, increase the hole/pipe size.  Don't forget
to make the bypass connections able to take some pressure without
popping out.

Just some thoughts...

See Ya
Pat