More Horsepower. More Torque!!

[Roger Heflin]

On Wed, 31 Mar 1999, Marc Randolph wrote:

> 
> >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.
>
I think the problem  is that with a real custom chip (only for your
car) the company is not going to go to the effort to approve it.  It
costs more than a chip costs to make to get it carb approved.  The
only chips I saw listed as onroad where the cookie cutter (ie the ones
hypertech or TPIS sold for all LT1's). 

 > 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?

Leaning things tends to increase temperature.  My understanding is
that rich kills cats.

> 
> 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.
> 
So far I seem to be getting the impression that you need both EGT and
O2 to get a good number.  I have been told that EGT is mostly useless
by itself (different engines EGT vary too much based on how it was
build), and the O2's vary based on the O2 temp, so the claim is that
if you have O2 temp (EGT), and the O2 reading you can get a pretty
good idea where to tune things.

 > [...]
> > 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.
> 

If you are careful there are CARB approved headers AS&M and RK sport
and several others are approved.  The original hooker design does not
have air fittings and O2 fittings, though there is someplace else that
adds on both of those parts to make things at least possibly legal (if
someone did the paperwork).

I don't thing any reasonably cam is CARB approved, and are probably
not approvable since they do change emissions (at least without a
major amount of computer adjustment, which very few (maybe none)
outside of the big automakers have the equipment and ability to do.

			Roger