Miata Mailing List: June 1996, Message #40
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   From: brian goodwin 
Subject: blower lag
   Date: Sun, 2 Jun 1996 18:12:01 -0400

Hi Everyone,

        Birdmeister writes that his turbo spools up faster than his old
roots supercharger did.  That old roots blower was just not very good.
Corky did a writeup a few years back comparing lag and efficiency, etc.,
between the various forms of forced induction.  I seem to remember that on
the subject of lag he rated the Lysholm screw supercharger as best at
avoiding lag with the variable vane turbo a close second and the traditional
turbocharger way down on the list.  This matches my experience.  I have the
autorotor and the beauty of this kit is that the boost is just there as soon
as you blip the throttle.  There is no turbo rush--it really just feels--as
Bill Cardrell was saying recently--like a larger engine.  None of the
turbocharged miatas I have driven, with the exception of the aerodyne units,
has come close to matching the responsiveness of the whipple.  You don't
even have to mash the throttle.  Even a 1/2 inch downward push on the gas
will get your boost needle INSTANTLY jumping to about 5 pounds of boost.  As
someone pointed out already, the boost is not linear in the sense that max
is reached only in high rpms.  From 2000 rpms my boost need jumps to 5 or 6
psi and then quickly climbs to max boost.  Max boost well before 4000 rpms
is easy.  

        There are certainly advantages to a turbo system but lag resistence
is not one of them.  One of the great things about turbos is that you can
adjust the boost level SO easily.  I think Birdmeister was talking about 12
psi last week.  He could even add an electronic boost controller like the
units from HKS or Greddy and do it all from the comfort of inside the car.
Another nice aspect of turbocharging is that he gets the same amount of
maximum boost regardless of the temperature outside because he has a
wastegate as part of the kit.  On the Whipple unit I have noticed quite a
discrepancy between cold and warm days.  On really hot days I get as low as
7.5 or 8 psi max.  On really cold nights I can get over 9 psi. 

        It is definately true that modern turbo systems run far less lag
than old ones did.  Corky's own variable vane Aerodyne is a great example.
As far as the non-variable vane units, however, there is still detectable
lag.  For most users the lag may be so little as to be insignificant.
However, if you like to autocross like I do, even that little bit of lag is
too much because it can upset the car at critical moments and send you
spinning through the cones.  I eat enough cones as it is without turbo lag's
help.  (Yesterday I was out autocrossing my car with a new tire and
suspension setup at Jack Murphy stadium. Met and talked with Rainer (sp?)
who was out there as well.  Great guy, great day of fun).

        I should note that even non-variable vane turbos do not have to
suffer lag.  On one of my previous turbo race cars I used Spearco's lag
eliminator kit.  This is a fill the gap nitrous system.  As soon as the
pedal goes down the nitrous comes on and turns off once the boost is up.  I
put in a variable control on the thing such that the nitrous eased on and
then eased off in proportion to the rising boost (such that even the nitrous
was not instant full on--in a sense, too little lag can be a bad thing too).
With such a system the nitrous is only on for a second here and there so the
bottle lasts a good long time.  Using a dump valve to keep the turbo speed
up between shifts can also go along way toward making a turbo feel lag free.


Brian Goodwin