More Horsepower. More Torque!!

[Roger Heflin]

On Tue, 30 Mar 1999, Dave Hempstead wrote:

> Hi everyone,
>     A question.
> 
>    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??
> 
>    Now, I know there are alot of different assumptions that need to be
> made to answer this question, and that there are a number of companies
> already doing this, but let me change the assumptions somewhat.
> 
>    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.
>    I will NOT assume that I will give up engine reliability and, in
> general, longevity (I believe that the tuning companies are decreasing
> the reliability, in general, although that may be an old rumor).
> 
> 
>    OK, given my assumptions, how much more can I get?
> 
>    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.
> 
>    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?
> 
> Food for thought,
> Dave Hempstead
> dave_hempstead at hp.com
> 
> 

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.

One thing you can do is adjust the WOT lock speed for the A4 tranny,
this will improve the acceleration at higher speeds as it locks at too
low a speed in 3rd gear (95 in my car, unknown in a 95).  I changed
mine to lock about 5600 rpm in 3rd (unfortuneately I don't get there
in a 1/4 mile).  You can raise the rev limiter a bit, but the hp dies
pretty fast after redline (maybe 200-300 more rpm).

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.

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
the headers and exhaust, if not the best headers are probably Hooker
or Gro.... I cannot spell the name.  Both have clearance problems
(they hang really low) on a f-body, but somehow I don't think you will
be having this problem.   A torque convertor will improve how much hp
it feels like you have, I have a viligantie 2600 rpm convertor, and
that woke things up quite a bit.    If I was doing it again I would
get one with a higher stall speed (maybe 3000).  both are lockup
convertors.  If you car is heavier than the car your engine came from
the stall speed will be higher, if you car is ligheter it will be
lower.  I don't know what stall speed a 96 b-body came with.  The
f-bodies came with a stall speed of about 1700-1800.

Right now my car runs about 370 rwhp (dynoed on two different dynoes,
several months apart), with an A4 tranny.   Stock the car probably ran
about 235 rwhp with a A4.  I know a magazine dynoed a M6 and got
242rwhp, so I am guessing at the 235, so I have about 135 hp over
that, that is with better heads, cam, bigger tb, headers, exhaust,
a DIS ignition system, 1.6 rockers, a high flow cat convertor, and a
better intake. I have a few other things
but they don't really make a hp difference.   I could gain more hp
over what I have by replacing the exhaust system with a bigger system,
either a dual 2.5 or a single 3.5.   From others reports with a
modified vehicle with headers I may get up to 30-40 hp, but the
aftermarket 3.5 in exhaust are supposed to be really loud.

                        Roger