Dyno Question

[BobK898]

Got 1250 miles on my RT 10, followed break-in for first 1000 miles. Only mods are smooth tubes and S&B Air Filters. Had it dynoed on a 248C DJ, best pull was 369, was expecting 400. Spoke to the Viper Tech at the dealer and he put in a call to Dodge. Any input, thanks.

 

[SoCal Rebell]

I think that's pretty low. Was it SAE corrected, did you get the air/fuel ratio? My 2000 with the same mods & 5,000 miles turned 400.3 RWHP & 434 RWTQ. Also I find it is good to let the motor cool before running, were they using a high output fan?

 

[Jason Heffner]

That is definitely not enough horsepower. I have several friends who have dynoed their stock Vipers and all of them made between 398 and 409. I have never dynoed my 00 GTS but I do know that when the car had low miles (1000) the car was espacially slow in the quarter mile. As soon as the car got around 2000 miles the engine must have severely loosened up and the car is now way faster. I would contact DC and see what insight they may have to offer. Good luck.

 

[treynor]

Actually, I've had many dyno pulls where my readings were 20-40 HP below where they should be. In the most recent example, I ran 475 HP, let the car cool for 5 minutes, and then ran 511 HP. This typically happens when the engine gets heat-soaked and the coolant temp gets up to 200+ degrees. Per the service manual the ECU watches coolant temp, and from my dyno experience it seems to pull timing and add fuel once the engine gets hot. If you have an air/fuel meter on the car, you can see this - the mixture will go down to 11.5:1 (or even richer!) and power will fall off a cliff.

The easiest way to solve this is to get a high-speed fan pointed at the front of the car and leave it sitting on the dyno, but turned off, for a few minutes to let the coolant in the radiator cool down. Start it back up, idle for 30 seconds to get coolant & oil circulating, then do your pull.

obVendorPlug: For those of you who drag race, Sean Roe's fan kit is an excellent cheap hop-up because it'll pull heat out of the coolant between runs. Mine works like a charm.

 

[BobK898]

It was SAE corrected, there was a big fan in front of the car. I read some old posts about dynos and saw one from another guy in STL who had low readings - it turns out it was at the same place. He went somewhere else that had a Dynojet and got satisfactory readings.

FWIW, Sean Roe told me to always take out the mats before doing the dyno as it may inhibit WOT. He also suggested doing them at tire pressures of 36, and prior to the dyno to WOT several times in 4th gear for several seconds so the PCM senses WOT.

Anyway I'm going to try all of the above and do it somewhere else.

 

[RickV2K]

first dyno pull of 398 with just tubes & k&n's. did a pull a couple weeks ago after the other mods..including removing the rain baffle...402 hp ...446 torque. don't think the alum. flywheel & 3.55 added any extra hp. the extra 4+ may have been from removing the rain baffle. at the first dyno pull there were about 20 cars and of all the cars with roughly the same mods as me i had the highest reading due to the 30,000 miles on the car. others with little mileage were a little disappointed at their readings. i think there were a couple acr's in the 380's. i do remember there were some dejected looks there. i hear as a rule there's about a 13 to 18% loss to the wheels and two identical cars can vary anywheres from 10 to 20 hp. word has it that the engine is capable of cranking out 500 horses...as is, if tweeked properly.

 

[JonB]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by dgeviper1:
....the people in the KNOW, say that you will show about 20 less RWHP with a 3.54 than a 3.07! The reason is due to the fact that it takes a much shorter time to do the dyno pass.... and that the dynojet has a problem doing a proper reading. It requires a certain amount of seconds to do an accurate reading. The 3.54 and above dont allow for that <HR></BLOCKQUOTE>

If this were true, an Alum flywheel would do the same thing. Time-To-Peak-Rev is much less. 3.55 vs 3.07 is 16% less time.
If so, an innacurate DYNO is the reason.....not 3.55 gears.

Driveline loss is probably less than 1% greater loss with a 3.55 vs. 3.07. We had a friendly yet intense debate at UniTrax a few months ago on just this point. We came to the --mediated-- conclusion that it was .5-.8% greater loss(.005 -.008). Some say NO DIFFERENCE. I believe Ben "Dyno-****" Treynor!

 

[Mike Brunton]

Who are these people "in the know"? Are they the same people who might be making excuses for why engine packages they sell don't perform on the dyno? Not naming any names, just curious...

I talked to an engineer who did some work for Dynojet a while back, and his explanation was simple.

The dynamometer knows how big the drum is that the tires are on. It also knows your vehicle's RPM. That is ALL it needs to know. Gearing does NOT MATTER AT ALL. Neither does inflating/deflating your tires (unless you are spinning), neither does changing your gear ratio or anything else in your driveline. It's not like the operator has to key in the gearing you have - they just plug in the RPM reader and make sure you are on the drums and that's it!

Regarding the reason being a shorter pull, this was refuted by the engineer I talked to, and ALSO REFUTED BY DYNOJET! Call them and ask, and they will tell you the same thing. There are Supras that put down over 1000RWHP that spin the dyno in a fraction of what a stock Viper does it in, and they get Ok readings.

I wonder where this rumor came from.... oh, wait, I know where it came from.

 

[LTHL VPR]

We have done dozens (over 100) dyno passes with varying years of Vipers at APEX Motorsports. There are a number of things that can cause higher and lower numbers on a dyno and it is important to keep the conditions consistent. We have found that dynos results can vary between Dynojets, so it may not behoove you to compare your results to others from different dynos. Air fuel ratio is also important. We believe that a 13% driveline loss seems accurate with our dyno.

Most GENII stock Vipers are making around 400rwhp and 445 ft.lbs. Depending on the year/cam they make slightly more or less in the low-mid range. We have found that 2000-2001 Vipers do not seem to respond as well as earlier GENIIs with basic mods like headers and exhaust and make about 5% less hp and about 2% less torque.

We have recently tested the Belanger and CDI/Archer headers on an otherwise stock 2001 as well. Will post results tomorrow. We will also compare these headers on our LETHAL 600 package in the next couple weeks.
Happy Dyno'ing!!
-Wayne

 

[Bill/APEX Motorsports]

Bob, there's a difference between a _big_ fan and a _high-speed_ fan. We have a huge fan that pushes a large volume of air and also a pretty compact fan that pushes the air at a tremendous velocity. We use the smaller fan on the dyno because it really concentrates the air into the radiator. The larger fans really aren't good enough to control the Viper's hot-hot-hot tendencies.
Also, we've found that dynos do differ in the numbers they spit out. Your best bet is to find a shop that produces "admirable" numbers (!!), sticking with the same dyno upon which to base all future upgrades.

 

[BobK898]

Bill, funny how the better numbers are more believable than the lower numbers.

 

[Gary Lashinsky]

Recent dyno test on my stock 2001 GTS with 1200 miles showed 415 HP on the first pull and 409HP on the second pull. This was done a Vinci's High Performance in Orlando on a Dynojet 248.