More Horsepower. More Torque!!

[Marc Randolph]

I joined the list recently and have been waiting for the right time
to contribute.  This message is the perfect time for me to both answer
and ask some questions.

On Tue, Mar 30, 1999 at 10:38:26PM -0600, Roger Heflin wrote:
> On Tue, 30 Mar 1999, Dave Hempstead wrote:
> > 
> >    Given a stock GM engine (let's say, a '95  5.7 liter  LT-1, since
> > that's what I have :-), what kind of differences in torque and
> > horsepower can we get by modifying the computer??
[...]
> >    First, I'll assume I want more torque and HP, and I am willing to
> > give up gas economy and willing to give up meeting pollution standards.
> > I don't know if the tuning companies are able/willing to give up on the
> > pollution standards.
> > 
> >    Here is one way I'd implement it.  For me, I can take one of the
> > PCM's inputs, let's say the A/C input and wire it to a switch.  Then
> > let's assume I can modify the software.  I use the switch to select
> > either 'standard' operation or 'yee haw' operation.  I can switch modes
> > whenever I want.

Sounds like the valet switch in the ZR-1.

> >    OK, so what can be changed in the software?  Here I don't know enough
> > about tuning our engines.  Could it be as simple as telling the engine
> > it is running in WOT mode, going open-loop, richening up the injectors,
> > etc????  What do you experts think?
> 
> In general with a LT1 you want to lean it out at wot.  It will go open
> loop when you hit some throttle position, and you can set that lower
> if you want to.  The table is indexed rpm vs tps.  The tuning
> companies don't carb the custom chips, they are offroad only.

>From what I've seen, it depends.  Some custom chips are open-loop
(offroad) only, while others (especially Calloway and Lingenfelter)
actually attempt to make their calibrations 50 state legal (unless you
request an offroad chip).  Others just shoot for 49 state.

Speaking of the ZR-1, I'm looking for ideas on knowing how lean
to go when tuning a car with cats.  The optimal method is 
supposedly to drill a temp probe into the cats and measure the temp
of the cats to make sure they are running hot enough (hot enough to
protect the cats from being damaged).  Does anyone have any other
methods short of that?

I've heard the Buick GN guys shoot for something just under 800 mV 
reading on the O2 sensors for max performance, but I don't know of 
any data to back up that when the O2 sensor reads 800 mV, the cats
are hot enough.  Same for an Air/Fuel sensor - you can shoot for a 
certain ratio, but does anyone have any ideas if the cats are 
getting enough fuel to protect them?

Stock, the ZR-1 O2 sensors run about 900 mV at WOT.

[...]
> Generally without modifing the engine maybe 10 hp, and that is a
> custom tune job made just for your engine (manufacturing differences
> is what I believe causes the variation).    I don't think there is
> that much improvement that can be done.  GM makes a good general
> program to run their engines, some gain can be made for tuning it for
> exactly what (or how) your engine runs.    Other things that can hurt
> performance, the knock sensor can remove spark, the IAT (intake air
> temperatur sensor) seems to also use different spark tables.

I agree with Roger - GM does a pretty decent job of tuning their
engines.  Sure, it can be optimized a bit (for example, you can gain
a fair amount of torque in the mid-range on many V8 cars), but in terms
of peak torque or power, the gains will probably be minimal on a 
stock car.

> If you want more hp, replace the cam, put in ported heads, a ported
> intake, headers and a better exhauts (you probably have already done

Agreed.  On V8 cars sold today, headers are probably the easiest and 
biggest bang for the effort and dollar spent, but then you are no 
longer street legal.


   Marc

-- 
  Marc Randolph     -    mrand at pobox.com    -     PGP keyID: 0x4C95994D
   "During my service in the U.S. Congress, I took the initiative in
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