Dyno Numbers...need opinions.!!

[ASASN]

Hello all.!!

My name is Mike P., I live in South Ga.! I bought a 14 GTS about a month ago and decided to stick it on the dyno last Friday. First, let me say I love the car.!! Isn't my first Viper, but haven't been in one since the Gen 3....oh man, what a difference.!! I love the refinement of the car but yet, when you're driving it, you still know you're in a Viper....just really an amazing car.!! now if I can just git it to make power....here's the deal....

The car had just over 500 miles on the dyno, these were the first full throttle/redline pulls done with the car...my intake temp was showing 64, water 177, oil 173...the air outside was in the 30'S....hood was down (not shut), fan blowing into induction...here's what I got...

493.32rh/473.75rt SAE was the best number....this was run 3. Run 4 was 485.61/477.15......DynoJet 248...

At 5K rpms, the car begins to act goofy....tq falls off like you threw it off a cliff. Car continue's to pull, just ain't goin anywhere.!! HP graph is smooth as glass til 5k the it begins to roll, as in up and down...choppy.!!

Needless to say I was looking for quite a bit more, but it cars..I'm just thinking something is going on with the pcm or there's a bad censor or something...any advice would be great.!!

Thanks in advance...

Mike P.

[ICPREY]

What was the A/F ratios throughout the pull? I would check the easy stuff like plug/plug wire connections first.

[FLATOUT]

1. I know from a convo with the SRT guys that the ring packs are indeed tight and do loosen up a little as you get some more miles on the car.

2. The factory ECU starts to pull timing as the IAT's hit 86 degree and higher. I can assure you that if the airbox was not sealed (hood closed) that you will start pulling in hot air as the rpms rise. We did multiple back to back pulls studying this effect between the K&N and Factory air box. The non sealed K&N's show a rising IAT throughout the pull where as the Stock sealed box actually decreases it's IAT's as the rpms rise. So that could have had something to do with it.

3. What does a stock Gen IV or V Viper typically put down on this particular dyno SAE?

[ASASN]

ICPREY.....well, I didn't check the AFR.!! It being stock, I knew it was gonna be rich, so I didn't bother...that's my bad.!!

[1.8t]

My car made 535whp/480wtq SAE on a Dynojet 248C. See my thread about the Arrow PCM to see my stock dyno curve and compare to yours.

[ASASN]

1. I know from a convo with the SRT guys that the ring packs are indeed tight and do loosen up a little as you get some more miles on the car.

2. The factory ECU starts to pull timing as the IAT's hit 86 degree and higher. I can assure you that if the airbox was not sealed (hood closed) that you will start pulling in hot air as the rpms rise. We did multiple back to back pulls studying this effect between the K&N and Factory air box. The non sealed K&N's show a rising IAT throughout the pull where as the Stock sealed box actually decreases it's IAT's as the rpms rise. So that could have had something to do with it.

3. What does a stock Gen IV or V Viper typically put down on this particular dyno SAE?


Hey FLATOUT...I was kinda thinking the same thing after the fact, was I pulling in hot air.!! There hasn't been a Gen IV and I'm the first V....a Corvette shop mostly.!!

Thanks guys...

[ASASN]

My car made 535whp/480wtq SAE on a Dynojet 248C. See my thread about the Arrow PCM to see my stock dyno curve and compare to yours.

1.8t.....been following your thread, considering doing the same thing, don't want to do it....just to get it where I think it should be stock tho...dyno curve looks similiar til 5k...

[1.8t]

You can always go pull your car on the same dyno and see how your stock numbers compare to my stock numbers. It is in Marietta. www.dynolab.net

[Jack B]

1 I would wait for the rings to seal.

2. You want to watch iat, it did not stay at 64.

3. If they shifted quickly before entering 4th, the cat protect could have enriched the af, that is a stretch, but, the af would gave shown the issue.

4. Not tied down correctly, tires slipping.

[FLATOUT]

Hey FLATOUT...I was kinda thinking the same thing after the fact, was I pulling in hot air.!! There hasn't been a Gen IV and I'm the first V....a Corvette shop mostly.!!

Thanks guys...

Ok well if there is no point of reference on that particular dyno then there isn't really anything to discuss here. Every dyno I have been on has varied wildly, as much as 50rwhp SAE. I have dyno'd on a Land & Sea, Mustang, Dynojet, and a Dynopak (whichever one bolts directly to the hubs. I just base my numbers off of what other cars do on the same dyno.

[ICPREY]

I would hope that doing pulls in 30 degree weather with a fan going would not cause the PCM to pull timing due to high IAT temps.

[ASASN]

Thanks for the input guys...

1.8t....I know Dynolab, been with a few friends in the Vettes...I may consider that in a few more miles.! Btw, forgot to mention in previous post...your car is impressive.!!

Jack B...Think I will take your advice and put a few more miles on it. My iat's, according to the car, never went above 70. I was in the car, took it to around 3k to 4th, normal shifting. We were tied down pretty tight, same dyno has held my Heffner TT...but it was pretty cold, graph just doesn't look like wheel spin.

FLATOUT...I agree with you 100%, with no point of reference on this dyno, it hard to compare numbers. However, my concern isn't the overall numbers, it's the way the graph looks and what happens at 5k rpms...if it's not to much to ask, I'll be more than happy to send you a picture of the graph, so you can see what I'm talking about. PM me a email or a number to text you and I'll send it to you. Please for give my ignorance, when it come to computer and posting pick skills...

ICPREY...was probably warmer in the building, probably closer to 50..

Thanks again for the help guys....I appreciate it.!!

[triblk6spd]

Email the graphs. I'll post them for you.
justin@wrapdynamics.com

[ASASN]

Email the graphs. I'll post them for you.
justin@wrapdynamics.com

Thanks triblk6spd...sent it your way a minute ago.!! Again, I appreciate the help.....

[triblk6spd]

Hope this helps!

http://i1383.photobucket.com/albums/ah287/justin51/Mobile%20Uploads/2008-09/IMG_0034-2_zpswxgn8hwi.jpg (http://s1383.photobucket.com/user/justin51/media/Mobile%20Uploads/2008-09/IMG_0034-2_zpswxgn8hwi.jpg.html)
http://i1383.photobucket.com/albums/ah287/justin51/Mobile%20Uploads/2008-09/IMG_0034_zps3kwfefz1.jpg (http://s1383.photobucket.com/user/justin51/media/Mobile%20Uploads/2008-09/IMG_0034_zps3kwfefz1.jpg.html)

[99RT10]

ICPREY.....well, I didn't check the AFR.!! It being stock, I knew it was gonna be rich, so I didn't bother...that's my bad.!!

Hey Mike, long time, no see. Did you dyno at Aaron Scott's place?

Edit: yep, ya did. The A/F looks way lean.

[slowhatch]

Yeah AFR looks bad, however, it all depends on probe placement, maybe it wasn't properly in the exhaust flow.

You should be a 12.5-12.8:1 AFR across the board. Getting over 13.2:1 and I'd start raising an eyebrow. You're at 15+ in some spots!!

Also in reference to the curve being "jumpy", set the smoothing to '5' next time and it'll smooth out. They all look like that without a smoothing factor.

[ASASN]

Thanks again triblk6spd....

Hey Mike...damn, it has been a long time.! What are you up too these days...thinking I may need some T&D's for this thing..LOL.!!!!

You and slowhatch don't pay attention to the afr....it's a dummy....didn't have the probe in.!!

The "actual" number, with no correction, was 526rh...can't remember the tq. On the way home, a F350 blew exhaust smoke on me and then tapped his hood...couldn't resist...went down to third at 60, hammered it up to around 135...car felt like it was pulling good.!!

Thanks guys..!!

[mjorgensen]

No way they were taking A/F readings.... at that power level I would suspect 10.5's or 11.0's for WOT numbers.

[Jack B]

I don't want to compound the numbers issue, but, you should move to at least a 3 smoothing (as already was stated), however, when you do that you will probably lose another 5 hp. that does not mean much, you already know that the hp under curve wins the race, not the peak number.

[triblk6spd]

Trust me...I'm no expert but ya'll are saying it's normal for the torque curve to take big ol' dive at 5k and the, otherwise glass smooth power curve to go stupid at the same RPM? Shit just seems odd...especially given the low numbers.

[v10tt]

Mike, you might have to give it a pass in the 1/4 mile or try out another dyno to make sure.
Aaron's dyno might have gotten used to slow ZR1s.

[ASASN]

Thanks for the help guys....next time I'm down there I'll move the smoothing from 3 to 5 and see what happens.!! I agree with triblk, just seems odd that things start to bust up around 5k...I'll keep driving it and see what happens.!! Could be a combination of things....break-in, plus not having my hood shut. After looking at the way I had the hood laid down, I can see where I could've been pulling in hot air from the engine bay....

v10tt.....you may have a point....hey, but they were fast in the day.!! Man, have we come a long way since then....talk to you soon.!!

[mnc2886]

I am certainly no expert, but maybe the dealer can reflash your pcm with the factory tune. Might be a fix....if something there somehow got messed up when SRT loaded the flash. Good luck.

[Jack B]

Another stretch - your trace goes erratic at peak cylinder pressure. The two mechanical variables are valves and piston/ring mating, it is doubfult it is the valves, what is left?