99 ACR w/ exhaust dyno results

[racegate]

Hey guys, dyno'd my car today at a dyno day.

The car is a 99 ACR with cat-back.

Below is the dyno:

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Seems like it is down about 20hp. There was another Viper there with similar mods that did 425hp.

What I noticed on his dyno chart is that his AF was a bit leaner than mine (looked like a full point).

Does the AF on my dyno look a bit too rich? Wondering why if thats why it only put down 404.

Thanks.

 

[KNG SNKE]

I have a vec 3 for sale that you can throw on your car to tune it. Are you sure the other one didn't have a tune? 425 sounds about right with a tune.

 

[Greg 99ACR Red and Silver]

There were lots of discussions years ago regarding these dyno numbers, and whether just a cat back system would produce much gain. The answer is generally no. It varies of course but look at it like this, 404 hp divided by .88 (typical parasitic losses from flywheel hp as delivered) gives 460 hp. I know you don't like it but it means your engine is delivering the average horsepower as designed and that your cat back system did not add power, only improved sound.

My Mopar cat back system delivered the same results when it was new, until more significant mods were added.

Hope this helps.

 

[CSXT802]

http://forums.viperclub.org/threads/647540-Back-from-the-dyno.............AIR-FUEL-ratio-NFG.

 

[FastMatt]

My 2001 GTS with just a cat-back did 399 rwhp on a dynojet

 

[klamathpro]

It seams a little low, at least on the HP side, but it's not terrible. Go here for Dynojet reference numbers: http://forums.viperclub.org/threads/603643-MCVO-Dyno-Day-June-23
There are two GTS's with your torque numbers spot on, but slightly more HP.
It's apples to oranges, but my GEN1 pulled 405/443 with a catback. My GEN2 pulled 419/458 with a catback, both on a dynojet with stock tune, 580ft above sea level.
Go on ebay, buy a brand new SCT tuner for $150, call up Sean Roe and get him to give you a 93 octane NA tune for a catback ($161), and you'll be amazed at the difference. I haven't dyno'd yet after my Roe tune, but I'm blown away by how strong my GEN2 feels now. It almost feels like my GEN1 with 100 shot of nitrous.

 

[DrumrBoy]

You do seem rich at lower rpm, but A/F is about 12 (if I'm reading it right) at the top end... which is where you make max HP. Its a safe tune - you could shoot for 11:1 but introducing a piggyback tune for 20HP doesn't seem like a worthwhile tradeoff to me.

 

[racegate]

Hey guys, here is a chart from member Viperguynick. He dyno'd at this dyno day as well. As you can see his car is quite a bit leaner than mine, and up about 20hp. I'm guessing the missing power in the AF? Similar mods on both cars.

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What do you guys think? Same dyno, same day, etc..so its directly comparable.

My thought is since the dyno was using the tail pipe wideband, the reported AF is leaner than it actually is -- I.E. my 12:1 at the top could be 11.5 or richer. Nick's would be right on target then.

The main thing I'm trying to figure out is if there is an issue I need to "address" (leaks, or something) or if its just a richer calibration on my car from the factory (variance). If its the later, it will just resolve itself as I mod the car and put a tune on it.

 

[Dan Cragin]

Your numbers are in the range they should be. Stock engines can vary about 5-7%. You could get some more power with a custom tune. If you run on 91 octane fuel then do not get a 93 tune. These engines are very knock sensitive. A tune with more timing may feel good down low but can damage the engine at higher rpm and heavier loads.

How many miles are on the car?

Hope this helps.

 

[Dom426h]

You do seem rich at lower rpm, but A/F is about 12 (if I'm reading it right) at the top end... which is where you make max HP. Its a safe tune - you could shoot for 11:1 but introducing a piggyback tune for 20HP doesn't seem like a worthwhile tradeoff to me.

Am i misreading your post or are you saying that he could gain power in going from 12.0 to a richer A/F of 11.0. That sounds wrong to me

Max power for an N/A motor should be around 12.5-13.0.

Keep in mind that most dynojet widebands read like .7 to lean. This means that if your reading areound 13.5 on your dynojet printout that you are actually running around 12.8 which would be good. (13.5-12.8 = .7)

 

[Dom426h]

Its hard to give advice based on that watered down dyno printout. Sure that is good enough for what most people are looking for (a pretty picture with a max hp reading) but to me that is amateur night. I'd like to see a graph with a Usefull scale to analize what is realy going on with torque(the actual measured power) & A/F ratio.

Get the .drf file from your dyno operator if he still has it and email to me. I'll do a screenshot of the important stuff at a better scale and post it here so people can give you advice based on more detailed info. Better yet, get me Viperguynick's as well and i will overlay them so we can do a direct comparison.

This is what i am talking about. The following is my 1997 with headers & 3"exhaust. All of the power is from 400-500 so there is no need to start the scale at 0, all that would do is compress the data taking away detail from the viewer. I started the scale at 300 to spread the data out and allow room to display the A/F at a larger scale on the lower part of the graph.

GREEN = Stock Tune
BLUE = DCPerformance Custom Tune

(If you want to see larger)

 

[racegate]

Its hard to give advice based on that watered down dyno printout. Sure that is good enough for what most people are looking for (a pretty picture with a max hp reading) but to me that is amateur night. I'd like to see a graph with a Usefull scale to analize what is realy going on with torque(the actual measured power) & A/F ratio.

Get the .drf file from your dyno operator if he still has it and email to me. I'll do a screenshot of the important stuff at a better scale and post it here so people can give you advice based on more detailed info. Better yet, get me Viperguynick's as well and i will overlay them so we can do a direct comparison.

LOL...you da man.

I will see if I can get the drf files.

 

[DrumrBoy]

Am i misreading your post or are you saying that he could gain power in going from 12.0 to a richer A/F of 11.0. That sounds wrong to me

Max power for an N/A motor should be around 12.5-13.0.

Keep in mind that most dynojet widebands read like .7 to lean. This means that if your reading areound 13.5 on your dynojet printout that you are actually running around 12.8 which would be good. (13.5-12.8 = .7)

Yep, I'm an idiot. Meant to go up 1 (to 13) rather than down 1 (to 11). Doh.