Hey guys, I am going to get into PROM burning ASAP. I have the money for equipment, etc. but I'm trying to convince a friend to get into it with me. He's asking me some questions about it. Most of which I have the answers to but one he asked me has me wondering. He asked me what kinds of gains can be expected.

Does anyone have any before and after data from thier stock chip to thier custom ones without any other changes?

Stock or modified engine?

Dyno or track numbers would be most helpful.

Hodge

 

Its impossible to give an answer like that. there are way too many variables. If you build a motor like the one in my camaro and have a Speed Density system and run the stock chip then there might be 50 hp lost due to the chip. Another set-up might have 80hp another could be 10hp. There are way too many variables.

It all comes down to if you want to go fast with fuel injection you NEED to burn a chip. If you change a cam or heads or port heads. Or any of that you change the flow characteristic of the intake. And therefore could possibly run lean. There is no way to just say you will gain this set amount. It all comes down to teh application.

 

I wasn't asking anyone to tell me what my specific car would gain. I know that is impossible. I was just asking if anyone who has done it to thier car had any numbers on thier own car and if so what mods they had besides thier custom prom.

for example if someone out there did mods to thier car, enough to change the airflow characteristics of the engine anyway(i.e. cam headers etc).
THEN they got into prom burning.
What did THEY gain from prom burning.

Just wondering if anyone had any hard numbers about thier own personal gains.



My personal guess is that PROM burning would yield about a 10-20% gain on any TPI engine. But that's just my guess as I haven't seen any numbers or even started doing it myself.

Hodge

 

From one day at the track, I gained around a tenth tuning PE variables.

On the street, my fuel mileage is a lot better. This is after tuning the injector constant and VE tables and disabling EGR. I might have a little more throttle response down low, but I could be hallucinating.

The only relevant mods I have are SLP headers/dual catco cats/3" Flowmaster catback, ported plenum, 24" Accel injectors, and K&N filters.

 

There is more to be gained from prom burning then just
going faster. Changes I have made to a stock PFI 3.1L:

Reduced fan turn on/off temperatures

Increased vehicle speed limit

Enabled lean cruise mode, 12% increase in MPG

Changed startup choke timing to eliminate knocking
after a warm start

Reduced SA timing at 3000 to 3200 RPM 100 KPa to
eliminate WOT knock retard

Enabled the park/neutral anti-abuse RPM limiter

I have also made some code changes that have improved
driveability. Rewrote the TCC routine as it was quite
buggy. Changed how the integrator value is handled at
WOT to prevent a varying excessive rich AFR.

HTH's

RBob.

 

I've never heard of this. Can you elaborate a little?

 

Sure. There is code that adds a secondary RPM limiter. This
limiter is only in effect with the transmission in park or neutral
(automatic).

There are a couple of additional qualifiers that can be changed.
One is a MPH threshold. If over this threshold then the RPM
limiter is disabled. Then there is a delay once the trans is put
into drive to disable the RPM limiter.

I set it just to see how it would work. Set the parameters
to limit RPM @ 2100/2200. Then set 40 MPH as the disable
threshold. Set a 1 second delay for a prk/neut to drive disable.

At a stop can floor the go pedal and the engine just bounces
off the upper 2200 RPM limit. If moving over 40 can slid the
trans into neutral and rev it up.

The one second delay should prevent a neutral slam into
drive. I don't do this and haven't tried it. Might make an
interesting method of launching from a stand still.

RBob.

 

anyone else have any comments about thier experiences with gains from PROM burning.

Hodge

 

That's kinda like asking what gains you get when you buy a set of wrenches...or a 100 piece socket set.

PROM burning equipment is a tool. You are no longer confined to just turning the distributer and raising the fuel pressure...which is a band-aid fix at most.

Once you get into it you'll see that the best "gains" from burning your own PROMs are not neccessarily the things that make you "go faster". The best thing is being able to adjust ANYTHING. Smooth out the idle...get rid of the spark knock...make it start quicker...tune it for best throttle respone. I could go on all day

 

I cant tell you how much HP ive picked up so far if any at wot.
In just a weeks time i have made my drivability so much better i cant even describe it,and that is drivability over my stage 6 TPIS
$600 dollar rip off chip..
I can only imagine what can be gained at the track.

 

RBob, can you elaborate on the code changes a little also? Is this anything like rewriting the source code Grumpy is talking about?

Steve

 

Yes it is. The ECM is nothing more then a digital computer. Changing
the code changes the functionality.

The performance of this particular vehicle was always inconsistent. I
never knew why until I started to datalog the ALDL data (8192 baud).
Once I started looking at the data I noticed two items that stood out.

One was that the integrator would be locked if adding fuel as PE mode
was entered. The other was that after a period of time the PE mode
commanded AFR would drop by another 1 AFR. In other words the PE AFR
would suddenly go from 12.2:1 to 11.2:1, for no apparent reason.

This is the first mask ($88) that I have ever seen lock the INT to
something other then 128 whenever in PE. The reason this affected the
PE AFR is due to the weak AE (pump shot). As the throttle is rolled
on the INT would skyrocket to make up for the lean AFR. The INT
would typically reach the 160 to 170 range. Then as PE mode was entered
the INT would lock at that value. That is 20 to 25% additional fuel.

If the throttle was opened quickly the INT never had time to increase
before it was locked due to PE mode. The result being inconsistent
PE final AFR and performance.

My fix was to change an instruction. There is a test that will reset
the INT to 128 if it is removing fuel. I changed it to reset the INT
to 128 whenever in PE mode (adding or removing fuel).

The change looks like this:

;*----------------------------------------------------
;
; Force INT reset whenever in PE mode
;
;*----------------------------------------------------

ORG $CB82

BRA $CBB9


Here is the original code:

;*----------------------------------------------------
;
; if in PE and INT removing fuel, reset INT
;
;*----------------------------------------------------

LCB7C: BRCLR L0040;$20,LCB84 ; bra if PE not active
CMPA #128 ; compare INT to 128
BCS LCBB9 ; bra if INT < 128 (reset)


The BCS (branch if carry set) instruction was changed to
always branch (BRA). Now the INT was locked to 128 whenever
in PE mode.



The action of the PE AFR suddenly dropping by 1 AFR is a catcon
protection feature. Unfortunately it is not implemented correctly.
It works by counting the amount of time in PE mode. Once in
PE mode for more then 20 seconds the commanded AFR is lowered.

Problem is, this mode is never reset. And, the time in PE is
cumulative. See the problem? An additional time check needs to be
added so that after say 5 or 10 minutes w/o PE mode the 1 AFR
drop PE timer is reset. For now I just changed the AFR drop to 0.

Once the code has been mastered there is no limit to what can
be done. Not only can functionality changes be made it is easier
to understand the calibration parameters.

(little long, HTH's)

RBob.

 

My personal toy is an 87GN. Twice now I've gotten over 30 MPG. That is will using 55#/hr injectors (on a mere 231 CID v6). I can routinely run 25 PSI of boost on PUMP gas. Around town she has all the manners of a proper lady, actually much better then stock even thought of. I have a lean cruise patch, anti-theft, and launch assist. I can stage and bring the revs up and spool the turbo with only making a limited amount of boost, then when I release the brake and the car moves, instant boost. And this is with the stock ecm.

I have a modified GM ecm, with my own source code for it (based on the GM code), that I can do some other things with.

You can start with just improving the manners of your car, and go to full blown crazy on what you want to do (learn).

 

It's easy to understand why every beginner wants to know this. Most think it's just another hp mod with some pirks. It would be nice if we could get some more answers from everyone's experiences. Thanks.

 

I would also like to see some real 1/4 mile(hp) gains from just burning a chip. I already own the equipement(can't spell), just haven't had the time/motivation to do anything with it. (spun bearing in my car with mods(cam/siamesed base/supercharger collecting dust)

Out of 13 responses this guy only really got 1 good answer .1 sec.

I know there's power to be made with chip burning b/c one of my cars had over .5 sec and 5mph difference in 1/4 between a stock chip and a SLP chip(same night), cam/porting etc. mods .

I doubt I can do the same to my TBI car as SLP did for my 5 speed TPI car.(I believe .3 sec and 3 mph w/ only bolt-ons at the time)

I'd like to see what some people are gaining besides gas milage and drivability on bolt on cars.