SRT 10s DYNO Charts

[RC Viper]

Recently I had the opportunity to attend a Dyno day with the Carolina's
VCA. We had 3 2003 SRT 10s in attendance. All of the cars had minimal modifications so we had a good opportunity to compare the dyno results stock car to stock car. My SRT was one of the valve recall cars so I was anxious to
dyno the car after the fix. It had dynoed at only 424 HP last year prior to the valve replacement and I was really looking for some improvement.

The good news is that all three cars dynoed within around 10 horsepower of each other (one car had a muffler and cat removed and got high 430's) and had similar HP, Torque, and Air to fuel curves. From this you would assume that they were running according to factory specs.

The bad news is that this was not that impressive. Perhaps we are all spoiled by the under-rated Gen II cars. My car dynoed at 430.56 HP and 478.15 torque. If you use a 12% loss value this is only 482.22 HP and even using a 15% factor it is still only 495 HP. While I would like to have seen higher numbers, the purpose of this thread is not to complain. Instead I am concerned about the Air to fuel ratios that we all saw. They were extremely RICH. The Dyno operator immediately picked up on this. The curve passed over "ideal" at about 3700 RPMs and went down hill from there. By 5000 RPM's it was down to around 10.5. This is barely on the scale of the Dyno chart.

Are other owners seeing the same type of A/F ratios on the car? I'm sure that if the car ran a bit leaner it would improve the Hp and Torque ratings. Does anyone know if this if the SRT 10 was designed to run this rich? It is MUCH richer than my Gen II car.

 

[Frank Parise]

A couple of comments regarding your dyno results.

First, with a 12% driveline loss, your horsepower at the flywheel would be 489.27, not 482.22. Your torque would be 543.35.

With a 15% driveline loss, your horsepower would be 506.54 and your torque would be 562.52.

My guess is that the 12% driveline loss is probably closer to reality. Either result is impressive. Your car is producing alot of power, especially considering that different dyno machines produce different results, even when "corrected".

As an example, a couple of years ago I had my highly modified 96 GTS dyno with RWHP of 497. A month later I had the same car dyno at 452 during a Viper Racing League dyno test. Both dyno runs were "corrected".

If you take your car out on a track, I bet you will find that your car is nearly identical to all the other SRT-10s. By the way, 10 horsepower is not something you will ever feel in the seat of your pants unless you have a very vivid imagination.

 

[vipah]

I am a bit confused by drive line loss as a percentage of HP. Why isn't the loss a constant based on the configuration of the drivetrain components?

For example if I had a dyno reading of 400hp, then did some engine mods to bring it to 600hp why would my driveline loss increase and take more HP to overcome?

 

[RC Viper]

Frank

Thanks for your response. I am not really complaining about HP as much as I am wondering about the air fuel ratio. All three SRT 10's were running very rich. I just wonder if the HP numbers might be higher if the cars were leaned out a bit. Since it was the same for all three cars I have to think that the engine management system is correct to factory spec. The A/F ratios of Gen II cars we have tested are much leaner. After an SRT finished three runs you could literally smell the excess gas in the room! Reminded me of my 440 Six Pack at WOT.

 

[Torquemonster]

Frank

Thanks for your response. I am not really complaining about HP as much as I am wondering about the air fuel ratio. All three SRT 10's were running very rich. I just wonder if the HP numbers might be higher if the cars were leaned out a bit. Since it was the same for all three cars I have to think that the engine management system is correct to factory spec. The A/F ratios of Gen II cars we have tested are much leaner. After an SRT finished three runs you could literally smell the excess gas in the room! Reminded me of my 440 Six Pack at WOT.

1 - the closest formula we have found for calculating flywheel hp from rwhp is to add 10hp then divide by 0.88 for a RWD manual. At 430rwhp that is exactly 500hp at flywheel (430 + 10)/0.88 = 500. This means your cars are making excatly what the factory claim.

2 - yes they are way too rich and leaning them out will add power, but sometimes a car will give a different reading on the track or road than on a dyno - for this reason I'd run an A/F meter on the car out on a track somewhere to validate readings. If you are still getting 10.5:1 on the open road at WOT then I'd be looking for a fix

3 - did you notice the dyno graph was spikey - like jagged? Most Gen 3 engines seem to have jagged graphs. I suspect a valvetrain issue that could be springs or lifters - but any upgrade I did would upgrade both those to be sure.

 

[RedEnuf93]

This makes me feel good about my 410HP/477TQ with my 1993 Gen 1....

I was explained that different dyno's will also give different readings? (Some too optimistic, some "not so optimistic")

 

[SnakeEye]

This makes me feel good about my 410HP/477TQ with my 1993 Gen 1....
I was explained that different dyno's will also give different readings? (Some too optimistic, some "not so optimistic")

Here's an interesting read on the subject...Fine Dyno'ing: All Chassis Dynos Are Not Created Equal.
Click For Details

 

[Kai SRT10]

I recently dyno'd my (stock) 2004 srt-10.

Max horsepower was 438.7
Max torque was 479.6

This was at 5000 feet above sea level, with no SAE correction factor applied.

Graph here:

http://www.larsonweb.com/dyno.JPG

 

[Paul Hawker]

I find it interesting that people tend to wish to post their highest possible Dyno results (Dyno racing). There is no interest in averaging the results. If a lower # is seen, it simply falls to the dyno facility floor, and is ignored. Kind of like the track results, where the fastest time is memoralized forever, and slower laps are quickly forgotten.
(I am also guilty of this ego stroking).

 

[Snakester]

I know that the GenII Vipers had a factory fuel delivery mix that needed to be tweaked to optimize the power output.

Sean Roe made a VEC-1 box that smoothed out the A/F mix so that the car stumbled less at low revs, and made more power across the rev range. He has a VECII now with much more tuning control, but I'm not sure if it works with the Gen III Vipers.

Adding the VECI didn't raise my dyno numbers a whole lot, but it smoothed out the power curve (especially mid range) and the difference was immediatly felt in improved drivability.

-Dean.

 

[kenvw]

Yes, we found my car to have a very rich mixture (Heffner did the research) and when this problem was adjusted it did make about a 10-12 hp difference. I was told by a reliable source that the cars are sent out with a richer mixture to keep things on the cooler side. Keeping that in mind the tolerances are + or - 5 off of 55 psi. Ths swing if your are closer to the 60 mark is rich and about a 12 hp difference than your viper mate who might be closer to the 50 side. The difference % wise is high when talking psi from 50 to 60 but DC says this falls within their specs. I have found the best solution for too much noise and lower than desired hp ratings was to let Heffy put on a TT system.

 

[RC Viper]

Torquemonster:

Yes the graph was jagged, although it was better than when I dynoed the car prior to the valves being swapped.

Kenvw:

I would love to go with a TT set-up. Think he takes charity cases?

 

[Torquemonster]

I made some enquiries and Jason Heffner has a cure for the jagged dyno graph readings - it is an inherent weakness in the stock SRT10 engine that the factory is apparently happy to leave as it is, but I wouldn't. It's a simple fix.

Ken - the only man I know that bought a twin turbo package as a MUFFLER....

 

[Y2K5SRT]

I am curious about both the jagged peaks and the air/fuel mix. Is this something that can be adjusted manually or is it a computer reflash? Sorry for my mechanical ignorance, but I am genuinely curious as to how this works. Here is my long-ago dyno when the car had 540 miles on it:

http://www.kansascityvca.com/srt/dynosheet.jpg

I will get it dyno'ed again very soon after the bog reflash and with 5600 miles on the clock. Should be interesting!

Chris

 

[Torquemonster]

Hey Chris - sent you a pm as I don't want to start a war re factory issues. For the curious - call Jason Heffner - he has the fix for this jagged engine performance problem. Not sure how it will affect warranty but if you ever plan on engine upgrades - the problem will likely get worse so this fix is a must in my opinion.

 

[RC Viper]

Torquemonster

May I have a copy of that PM?

Randy

 

[Torquemonster]

sent pm - hope it helps.

 

[Skip White]

I wish Sean Roe would come up with a VEC for the SRT. I had them on every GTS I had. What a difference. These cars are to rich in certain areas. As Ken said, this could be for cooling. You could control the heat a little bit, but not A/F ratio. Lets find a simple solution for this.

Skip

 

[Viperfreak2]

Sean said they were going to have the supercharged SRT-10 ready by summer (I think) which would include a VEC2. Should be available as a stand alone too.

 

[Torquemonster]

Sean said they were going to have the supercharged SRT-10 ready by summer (I think) which would include a VEC2. Should be available as a stand alone too.

I doubt it will be stand alone - the SRT10 computer controls a lot of non engine things - if you cut it to run a stand alone engine management then a lot of things will not work. Sean will find a way to run the two side by side with the VEC2 over-riding factory settings. The stock computer will have to stay.

 

[Kai SRT10]

I am curious about both the jagged peaks and the air/fuel mix. Is this something that can be adjusted manually or is it a computer reflash? Sorry for my mechanical ignorance, but I am genuinely curious as to how this works. Here is my long-ago dyno when the car had 540 miles on it:

http://www.kansascityvca.com/srt/dynosheet.jpg

I will get it dyno'ed again very soon after the bog reflash and with 5600 miles on the clock. Should be interesting!

Chris

Do you know what the SAE factor was for your test?

Kai

 

[Dyno Dave]

It's that rich to cool the catalysts. It would make more power if leaned out but the cats would fail if run at high loads for an extended period and we all know the EPA and CARB wouldn't like that.

 

[Torquemonster]

It's that rich to cool the catalysts. It would make more power if leaned out but the cats would fail if run at high loads for an extended period and we all know the EPA and CARB wouldn't like that.

Am I other only one who sees an irony here?

The cats are there to help make our planet greener and cleaner, but if we run them too hot, they don't work - so the simple fix is to pour raw fuel into them to keep them cool.

That is called taking 2 steps back to go one forward. I'd sure like to meet the row of bean counters that made the engineers make that concession - and fire them all!!!

This continual war between the beanies and the engineers is too stupid for words. Somebody needs to introduce vision and lateral thinking strategies into accounting colleges and make them mandatory.

Sometimes I'm ashamed of my profession (accounting) - we would collectively be the most tunnel visioned, uncreative, strain at gnats/swallow camels, small picture group of geek professionals there are - yet we get to drive most big businesses. It is frightening, and thank goodness a good strong leader with some common sense can often over-ride....

but too often they just are not aware, as they are not involved in the minute details that make up the whole

back to the cats - WATER would do the same thing and be friendly to the environment, enable a lean and clean mix - have no down side other than something else to top up and a slight cost to develop... very little as everything is ready to roll - just adapt for the car and dial in.

I can't believe DC bosses allow this crap knowingly. Judging by some of the excellent engineering within the DC group (look at their fabulous ME 4-12) I have confidence that in time the beanies will be made to fall on their swords - and frankly there's no time like the present.

On the positive side - it is things like this that make factory cars SO EASY to improve in every way. Some more so than others...

 

[Dyno Dave]

This is not an unusual practice. It is done industry wide.

 

[Torquemonster]

Dave - I'm sure you are right on that once again... but I'd think it was industry wide in the USA.

You won't find that problem in the top Japanese or European engines where they produce engines that get great gas mileage even at very high outputs/cubic inch and under heavy throttle. That's my point.

America COULD match them, but is yet to find the commitment to do so, because they rely on cubic inchs to make up for it. Great as it is - the 500 cubic inch V10 could be even better is what I'm saying - both meaner and greener. The engineers know how - we just need to find some friendly beanies

 

[Dyno Dave]

I see the issue as the ability of a large catalyst that could take the high exhaust flows of a large displacement engine would have too much mass to light off quickly. These days the largest portion of emissions occurs in the first 30 seconds the engine runs. After that you're home free.

The reason cats keep getting closer to the engine is for faster light off times. The more material you have to warm up the longer it will take. Some of the European cars have double-wall steel exhaust manifolds where the inner material is very thin to reduce mass for cat light-off and the air gap to the outer wall helps insulate to keep the heat inside. After looking at an SRT10, I don't think there is much room to do that. The expense might be considerable because of the small production volumes and the engine is only used in the PVO products. This is probably not the case for many of the Japanese and European manufacturers but I am just speculating here.

An engine as large as the Viper might need multiple cats with a small one for initial light-off and some type of mechanism to switch to the larger one after warmup. The difficulty would be making such a mechanism to last 100,000 miles which is a requirement and also the space to package it. It could probably be done but it might be difficult considering the size of the team PVO designs/builds the Viper with.

 

[Torquemonster]

Granted a hi flow cat will take longer to reach operating temp - but assuming that is the trade off for high performance, the problem seems to be stopping them from getting so hot they then stop working if under heavy load too long and the mixture is correct.

Rather than waste fuel by making it rich - if sophisticated water injection was not wanted (the best solution IMHO) - then a simple fix would be to run an EGT sensor on each cat wired to a simple box that switched on when the temps reached a certain point and switched off when the temp dropped below a certain point. The switch would activate the most basic water injection (washer bottle and pump) that fed 2 injectors - 1 for each exhaust - right in front of the cats in a spray to cool it back to operating range. Under $200 should do it.

Do you think that would work? I'd rather that than go rich.

 

[Dyno Dave]

A water injection system might work but I'm sure the Feds would not consider that because the water tank could run dry without user intervention and no guarantee could be made that the cats would last 100k miles. Upgrades in materials could help push temperature limits such as the ceramic exhaust port liners used in some Porshes. Exhaust backpressure also plays a big part in driving high air/fuel ratios to keep temperatures down. The heat simply cannot escape quickly enough. A set of tubular exhaust manifolds with no cats will dramatically lower exhaust temperatures and allow a more reasonable and probably optimum air/fuel ratio.

 

[Viper Ram]

I had my Ram SRT-10 down at Seans shop at the beginning of the week and he "grafted" a harness and VEC2 to my truck. He removed the harness so he could produce a vehicle specific harness and should have it ready shortly. I was pleased with the initial results. My stock HP was 416 and 438 foot pounds of torque. With a dozen + pulls I'm now seeing 434 HP and 480 foot pounds of torque. I'm confident that we should easily see 450 HP and 500 foot pounds of torque with more "tweaking and with intake and exhaust upgrade. From 4000 rpm and above it was pegged at an a/f ration of 10:1. Very rich! The difference in torque down low and performance was noticable. It's amazing what taking fuel out of the engine will do for performance. I'm sure Sean will post something as soon as he has a product ready. (I can't figure out how to import the .bmp file into this post but the numbers are a great start)
Mark

 

[Gary C (GaryCSilver04)]

The NASCAR guys with a straight cut gears in the tranny say a 15% loss.