[Shotimes] Interesting...porting the intake

[Bruce Malachuk]

one of the things I'm really trying to avoid is changing any of the actual
ID's of the runners, just matching them up for a smoothed out airflow into
the engine. From everything I have read relating to EFI cars and thier air
induction, that smooth airflow and velocity are essential to making the
power. Removing the mismatch is oly going to further enhance the resonance
effect that Yamaha designed into this engine. I'm betting that the original
"fabled" 300hp SHO enging prolly had all it ports matches exactly, prolly a
little higher compression, and a better cam profile. If it is true that the
long tubes are "tuned" for 2950, then cleaning up the mismatch may only
enhance this as it will see a faster movement of the air at this RPM level.

It lends to the the idea that EH throws more towards the high end of the RPM
scale when the engine cares less about the resonance, and more about gulping
air. The enlarged runners allow that. But by keeping the runners stock ID
I'm hoping that I can maintain what the "normal" look of a nearly stock SHO
HP&TQ band, just a little higher numbers.

It's my hope that with this is that the airflow is smoothed out, nothing
more. If I see HP and TQ especially what I can feel by the sometimes
unreliable butt dyno, thats just a welcome side effect :-) At least it'll
give me one more thing to add to my signature on the shoforum making my car
look all the faster to all the youngins. LOL wow do I feel old now after
that statement.

Bruce
94 Opal Frost MTX
93 Black ATX - winter beater then parts car :-)


----- Original Message ----- 
From: "Mark Nunnally" <manunnal@netheaven.com>
To: <shotimes@autox.team.net>
Sent: Tuesday, August 05, 2003 7:14 AM
Subject: Re: [Shotimes] Interesting...porting the intake


> The more I read, and talk to folks a lot smarter than me, and tinker with
> these things, it's more apparent in an n/a motor, the cams/intake runners
> are a paired team.  Basically the stock SHO runners are designed (through
> shape/size/length) to create the best resonance (ram air effect) where the
> stock cams want to make the most torque.  When you shorten the length of
the
> runner, or enlarge the ID, you are changing the resonance rpm tune on that
> runner.  You'd be moving it up higher in the rpm range.  I also think the
> shape of the runner is important as well.
>
> I think EH is probably the best (yeah it's $$$) method to "cleaning up"
the
> runners.  What I would be interested in is having somebody measure up some
> EH runners and figure up the math to determine what rpm resonance that
they
> are "tuned" for.  Then build a cam profile to suit.  And of course
> gasket/port match the runners to the heads.
>
> One of these days I'll get around to port matching the intake/head runners
> on the 3.2L (mine have a terrible mis-match, one of the worst I've ever
> seen).  I borrowed an EH intake once and lost significant low end torque
> (above 3k it would regain itself).  Never ran it at the track to see what
> top end gains might have been there, but it seemed to pull hard.
>
> Realize going much higher hp that what you can get out of a BOS 3.2L is
> probably going to be maxing out the stock injectors.  I'm getting 90% duty
> cycle on my stockers on my 3.2L now (at 216 FWHP).  If you are shooting
for
> 300 hp some 30 or 36 lb'ers probably would be needed.
>
> I think for open track work the stock cams/runners do pretty decent, as
they
> make a lot of torque over a broad range of rpm.  Personally I'd rather
build
> power through more cubes (3.4L anyone? <g>) and compression.  Ie, things
> that will pick up the whole torque curve, and not just from 6000 rpm on.
>
> I think if you EH'd a set of runners, had a cam profile built to match, on
a
> John H. type 3.4L stroker motor using about 10.75:1 (or 11:1) compression
> (running on 94 pump gas) with a little more injector, I think you could
make
> an honest 300 hp with a GOOD torque curve.  Hmm, sounds like what I want
to
> build for the track 89 :)
>
> mark
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