Working with the Viper computer

[rcdice]

I recently added S&B filters, smooth tubes, RT 3" cats
and B&B catback to a previously stock car. The directions
for the catback said to disconnect the negative battery
terminal during installation. I'm sure this is supposed to
reset the computer so it can "learn" the new higher flow
rates. The Certified Viper Tech. that did the installation
did NOT disconnect the battery and told me that the car
will pickup on the flow difference and adjust itself
accordingly.

Who's right? Should the battery be disconnected or not? If
needed, should only the negative be disconnected or both
terminals? Thanks in advance for any insight into this.

 

[PhoenixGTS]

It is standard procedure from time immemorial (way before computers) to suggest that the negative terminal of the battery be disconnected before working on a car. My understanding is that this is to avoid the risk of sparks and fire (or possibly accidentally triggering the starter and squeezing a finger or rolling the car off a jack) and has nothing to due with resetting the computer. It is true that depowering the computer can reset it, but I have stood in the B&B R&D bay and watched them develop and test systems and would bet that they never even considered the computer learning anything about their cat back (if there even is a difference). Your tech sounds correct to me.

 

[viper spray]

Do the disconnect , then run her hard with the AC on for at least 40 miles for the best results. Put it to the floor at least 4 times.

 

[01sapphireGTS]

Even if cycleryan's advise is not acurate (I have no idea myself) , it will be FUN ! !

 

[rcdice]

I've driven the car about 125 miles since installation. Well over four WOT's at least in short bursts in various gears. No air though. As of now, the battery has not been disconnected. I had planned on getting the car dynoed next week. I think I'll leave the battery connected and see what the dyno reads over the bone stock results. Only changes are the filters, tubes, cats, catback. Should be about a 15-25 rwhp increase I'm guessing. If it's nil or very low, I'll try the disconnect route and re-dyno. Should be a fun experiment.

 

[99 R/T 10]

Make sure to post back to this thread with the results, will be very interesting!

 

[rcdice]

FYI, dyno is scheduled for Friday afternoon. I'll post the results here. If nothing else, the car certainly sounds different. A very good different.

 

[rcdice]

Ok, did the dyno. Not happy. Here are the results and several variables that could have affected results.

Bone stock high run about a month ago:

425 RWHP 455 RWTQ

Today's high run with S&B filters, smooth tubes, RT 3" cats, B&B 3" catback:

419 RWHP 438 RWTQ

Here are some variables that could have negatively affected the performance.

1. It was way hot in there today. 89 degrees and high humidity. Stock run was at 80 degrees but much lower humidity, didn't really feel hot. Today it did.

2. Their primary fan was broken. Ran two smaller fans that didn't seem to blow all that much air. Ran car with hood totally open, not just cracked open. Fans were directly in front of car.

3. I got stuck in traffic on way to the garage. Car was hot when I got there and ran hot the whole time. Pushing up to 225 range.

4. I DIDN'T disconnect the battery prior to any of this. Perhaps I should have. I did, however, run it somewhat aggressively for 150 miles or so after mods installation.

5. Gas. I filled up recently with Shell 93. They are making a big deal about it having like five times the engine cleaners in it as other brands. Does this affect performance?

Anyway, those are the numbers. Questions:

How much affect could the heat have had on results? 10%? 5%?

I want to go ahead and reset the computer by doing the battery disconnect. Can I do that at the junction under the hood or do I need to remove the rear wheel and get to the battery itself?

My personal take is to do the battery disconnect and wait for cooler weather and try again. I talked to the guy re: the accuracy of their machine. He said they had a guy come back a year later, simular conditions, no changes to his car and the machine read within 3 hp. Also, they have new high flow fans on order and software to read AF. Currently they do not measure AF.

ANY, insights, help, comments appreciated.

 

[Jack B]

Just to provoke some thought - there is too much "disconnect the battery" banter whenever a car does not dyno where it should be.

Think about it this way, the dyno pull is a WOT event which is open loop, therefore, there are no adaptives in place. The engine is running strictly off of a fixed matrix of a/f and timing cells. There should be little or no learning in this mode. If I am missing something, please give me some direction.

On the other hand, the SAE correction factors do not properly correct for extreme humidity and a dyno pull on a extremely humid day will show less power. Coolant temperature is not typically an issue, it is the temperature of the intake and heads which does not always correlate with the coolant temperature. These two will limit the hp.

 

[malcoll]

When performing modifications, you should take your baseline and subsequent dyno runs on the same dynomometer. That way you do not get variations in the dyno.

Also, the dyno run should be under fairly similar conditions.

Where are you getting this done, cause I would like to get a new baseline now that I am in Columbus? Maybe we could set up a "dyno day" and get a group rate?

Lance

 

[rcdice]

Dyno machine was the same. Conditions were definitely different. Humidity was stifling. Standing there in shorts and a t-shirt, in the shade and still sweating, hot. Also, I feel the lack of a significant fan had something to do with it as well.

I'm going to wait for slightly cooler weather, for them to get their two new high velocity fans in and for the software upgrade which will allow AF readings. We'll give it another shot then.

I'm going to go ahead and do the battery disconnect just for the heck of it. The Viper Tech swears it's not necessary but what the heck. Can't hurt anything.

Lance, I'm sure they might be open to a multi car discount. Would depend on how many I guess. There is a fair amount of time spent just getting it strapped down and such, but I'm sure they would be willing to negotiate. If not, I know of another place that also has a dynoJet. The second place, Auto Assets, has been a lot less flexible in scheduling time so I've steered away from them. They are primarily a porsche race shop but told me that they have dynoed a few Vipers in the past.

 

[joe117]

I'm with JackB.
I think that under WOT the computer isn't doing anything. The disconnect to reset probably won't do anything for your dyno run.

I also agree with him that the correction adjustments the dyno operator makes, will probably not track exactly.

In other words, if you tested the same car on multiple days on the same dyno, with only atmospheric changes and other correction factors plugged in for each day's conditions,
you wouldn't get the same results.

I believe the note telling you to disconnect the battery was to avoid the possibility of shorting a tool to some 12v+ point on the engine.

Was the car strapped down exactly the same way?

 

[joe117]

Why the dyno didn't see an improvement is question #1.

The #2 question would be,
Can you feel the improvement?

 

[Buckeye Viper]

When performing modifications, you should take your baseline and subsequent dyno runs on the same dynomometer. That way you do not get variations in the dyno.

Also, the dyno run should be under fairly similar conditions.

Where are you getting this done, cause I would like to get a new baseline now that I am in Columbus? Maybe we could set up a "dyno day" and get a group rate?

Lance

I still have to tune the Vec1. If you want a dyno day, I'm definitely in.

Saw another 96 black/silver RT/10 today on Lane Avenue. License plate was VVVIPER. I actually saw the driver my sophomore year in college (think it used to be a 94 black though, must have traded). Have been wondering about him for awhile. Cool to have closure.

Anyways, let me know about the dyno day, and I'm totally in.

 

[rcdice]

Joe, as far as I remember, it was strapped down the same. Four straps on the back, one on the front, blocks on both sides of the front wheels. My questions are:

How much of a factor can heat, humidity and lack of air flow be? 10hp? 20hp? 30hp? I was thinking I should see about a 25-30 hp gain with the mods. Instead I got a 6 hp decrease. Could those factors alone cause that much of a shift? In my work I deal with money and tend to think of things in percentages. On a 400+ hp engine, 10% is 40 hp. Can the above factors affect it that much on a Dyno?

Next question, with the discussed mods, should I definitely see a hp increase? I purposefully left the stock exhaust manifolds/headers in place to give some back pressure. I wanted the after market cats to reduce heat and catback for sound and "hopefully" performance. Could opening up the airflow on both the front and backend of an otherwise stock car actually reduce hp?

I'm leaning towards both your and Jack B's assertions that the disconnect theory is not necessary. Seems to be a lot of data pointing that way.

Can I actually feel any difference? Well, I'll tell you this: I haven't driven the car all that much since the changes, maybe 150 miles. If someone really pinned my down I'd say there is perhaps, a slight decrease in performance of the very low end, say at 2,000 rpms and a slight increase in the upper end, say 3,500 and above. I could be nuts, maybe it's just the increased note from the exhaust but that's what it feels like to me. The only other mod I had wanted to do this year was a rear gear swap. Not sure which one, 3.33, 3.45 or 3.55. If there really is a slight decrease in low end performance due to the increased air flow, the gear should help that. Or at least keep the rpms's higher into the powerband.

All in all, I feel the humidity, etc. lowered my numbers. I love the new sound and the car is still a blast to drive.