09 HP questions

[ferraritoviper]

The round number of a 600HP rating seems to be a marketing dept idea. Is it actual, and if not what is it really? I've seen references here to 'rear wheel HP'...what is the difference if any, to the factory HP rating? What is the 'cubic inch' displacement? I have the Corsa exhaust system on my Viper, no headers and no other mods...does this add any HP, if so approx how much?

Thanks.

 

[01sapphirebob]

"Rear wheel H.P." is what the car is actually putting down to the the ground at the rear wheels. There is about a 15% drop off in power from the motor to the rear wheels. So if did the math right the GEN IV motor makes 600 hp and puts down about 510 hp at the rear wheels. The new motor is really rated at 600 h.p.

The round number of a 600HP rating seems to be a marketing dept idea. Is it actual, and if not what is it really? I've seen references here to 'rear wheel HP'...what is the difference if any, to the factory HP rating? What is the 'cubic inch' displacement? I have the Corsa exhaust system on my Viper, no headers and no other mods...does this add any HP, if so approx how much?

Thanks.

 

[CitySnake]

The typical "factory" HP rating is called Brake HP, which is actually the HP generated by the motor at the crank (not the rear wheels). HP is used and therefore reduced as it goes thru the drive train to the rear wheels where, when measured again, is measured as Rear Wheel HP. Once the car is built, you can no longer measure at the crank (without a lot of effort) so most typical dyno measurements are made at the rear wheels.

The drive train loss varies from car to car (4 wheel drive requiring more energy and more loss). The typical industry standard is a 15% loss in HP from the crank to the rear wheels. Many have suggested that the Viper is more efficient that the standard and use a 12% loss factor. Others who are more familiar can comment on the appropriate loss for a Viper (which probably even varies a slight bit from gen to gen).

Remember that every motor and every dyno (as well as the influence of temperature, altitude, humidity, etc) has it's own personality, so RWHP numbers are difficult to accurately compare.

 

[mjorgensen Woodhouse]

The Corsa will not add a significant amount of HP to the Gen IV Viper because the stock mufflers are very efficient already. It will change the looks and sounds though for the better!

 

[99FRC]

The round number of a 600HP rating seems to be a marketing dept idea. Is it actual, and if not what is it really? I've seen references here to 'rear wheel HP'...what is the difference if any, to the factory HP rating? What is the 'cubic inch' displacement? I have the Corsa exhaust system on my Viper, no headers and no other mods...does this add any HP, if so approx how much?

Thanks.

I think the Geb IV are under rated. Most of the cars I've seen dyno between 525-545rwhp and some ringers have been above 550rwhp...that puts them closer to 615-625hp!!!

Either way the Gen IV's are beast 100% stock, but add headers,exhaust,intake, and mopar race computer and they get nasty. I can't wait until some more R and D for cams, tune, and bolt-on mods is done to the new viper. I think 650-670rwhp is possible when it's all said and done.

 

[ViperGTS]

According to the papers/documents I have it is 450 kW for the 2008, which is 612 hp.

 

[Tom Shapiro]

My stock baseline on my ACR with 1500 miles on the car was 543 HP and 503 ft-lbs of torque . With Belanger headers & exhaust, 3000 miles on the car and 200 miles on the Mopar cpu , the best pull was 583 HP and 554 ft-lbs of torque. Weather conditions were similar and we used the same dyno.

 

[Viper X]

RCK,

Most Viper Clubs have an annual dyno day. I'd suggest you attend one and see how the car's rwhp / rwtq vary. It can be a fun day.

Dan

 

[SilveRT8]

My stock baseline on my ACR with 1500 miles on the car was 543 HP and 503 ft-lbs of torque . With Belanger headers & exhaust, 3000 miles on the car and 200 miles on the Mopar cpu , the best pull was 583 HP and 554 ft-lbs of torque. Weather conditions were similar and we used the same dyno.

Stock baseline on my 08 was pretty close to yours at 545 HP and 505.8 TQ. With Mopar pcm and Roe High Flow cats I got 563.4 HP and 533.9 TQ. Headers will come in the Spring.

 

[FastestBusaAround]

Only a 7% average drivetrain loss on the Gen IV's? That's pretty low considering. Very impressive...either that, or these things are making much more than 600 at the crank. My Z has a much higher drivetrain loss than 7%; more like 13-15%.

 

[ferraritoviper]

RCK,

Most Viper Clubs have an annual dyno day. I'd suggest you attend one and see how the car's rwhp / rwtq vary. It can be a fun day.

Dan

Thanks Dan. BTW, anybody able to answer my question regarding the cubic inch displacement for the 8.4L engine?

 

[01sapphirebob]

That would put the 8.4L Gen IV motor up to 640 HP!!!!

My stock baseline on my ACR with 1500 miles on the car was 543 HP and 503 ft-lbs of torque . With Belanger headers & exhaust, 3000 miles on the car and 200 miles on the Mopar cpu , the best pull was 583 HP and 554 ft-lbs of torque. Weather conditions were similar and we used the same dyno.

 

[SilveRT8]

Thanks Dan. BTW, anybody able to answer my question regarding the cubic inch displacement for the 8.4L engine?[/QUOTE

512 CUBIC.INCHES (8.4 X 61)
Should be pretty close.

 

[Johnbennett]

Ask.com: how many cubic inches is 8.4L. Answer: 512.5995 cubic inches

 

[Viper X]

Our club's average stock "baseline" numbers at DC performance on a Dynojet are all about 510 rwhp.

Your rwhp will vary by dyno's, software programs, weather, correction factors, etc.

For some reason, all the big stock HP cars seem to get delivered to the Midwest and the East coast.

 

[Darbgnik]

Only a 7% average drivetrain loss on the Gen IV's? That's pretty low considering. Very impressive...either that, or these things are making much more than 600 at the crank. My Z has a much higher drivetrain loss than 7%; more like 13-15%.

I would think that some are making a little more power than advertised, unlike the Gen 3's which seems to make a little lower than advertised.

Last dyno day we did, the only Gen 4 (with 2000 miles on it) did almost 540 (537?) at the wheels, whereas the Gen 3's like mine only made 430ish.

I would estimate the drivetrain loss percentage to be similar, as the drivetrains are similar.

 

[Martin]

Our club's average stock "baseline" numbers at DC performance on a Dynojet are all about 510 rwhp.

Your rwhp will vary by dyno's, software programs, weather, correction factors, etc.

For some reason, all the big stock HP cars seem to get delivered to the Midwest and the East coast.

The power produced is going to be affected by the energy content of the gas going into the engine, and the CA reformulated gas has the lowest energy content of all the blends. Depending on the season, the reformulated gas in CA can be as much as 5% lower energy content than the 'good' gasolines available elsewhere. For example, CA reformulated gas has about 111,000 Btu/gallon, and 'good' summer standard gas can have an energy content of 117,000 Btu/gallon. Surprisingly, the energy content can vary quite a bit between brand formulations, and it always varies a lot season-to-season.

So, if cars in CA are showing lower dyno numbers than in other areas of the country, I'm personally convinced the energy content has a lot to do with it.

What someone should try (if they have no cats on the car) is to do a back to back dyno run with premium reformulated gas, and then 100LL AvGas. The AvGas is blended to have a rather high energy content - it averages around 124,000 Btu/gallon. I think you'll see numbers in the range of areas in the country that have 'better' gas.

By the way, I pulled these numbers from a few EPA studies on fuel economy. They showed lower fuel economy in direct proportion to lower energy content in gas - across different gas producers, across different seasons, and between normal and reformulated gas. That same linear proportion should also apply to maximum horsepower since, at stoichiometric mixture, there's only so much gas you can stuff in a cylinder and have it completely combust.

 

[ViperGTS]

>>>as the drivetrains are similar<<<

no.

different clutch.
different tranny.
different rear differential....

 

[Tom F&L GoR]

By the way, I pulled these numbers from a few EPA studies on fuel economy. They showed lower fuel economy in direct proportion to lower energy content in gas - across different gas producers, across different seasons, and between normal and reformulated gas. That same linear proportion should also apply to maximum horsepower since, at stoichiometric mixture, there's only so much gas you can stuff in a cylinder and have it completely combust.

There is another way to interpret the EPA data.

The fuel economy is reported in miles per gallon, not miles per BTU. So if the gallon of fuel has fewer BTUs, the vehicle will travel less distance. It says nothing about miles per BTU, which I think until you get to the tiniest details, would be the same. This phenomena is even more obvious with summer vs. winter (kerosene) diesel fuel.

At WOT, the engine is an air pump and power output depends on air consumption. The fuel system "should" run a little rich and deliver "more than enough" fuel. If it is too lean, it would allow engine knock. The volatility characteristics of all fuels are close enough, since they are also EPA regulated.

Gaseous fuels (LPG, CNG) produce less power because they enter the combustion chamber as a gas and displace air (oxygen.) But since gasoline enters as both vapor and droplets, you can tell by my comments, I'm stumbling over the idea that the BTU content of the vapor+droplets reduces power output. So it would be a good experiment.

Or you could leave a few gallons in an open container, allow the volatile components to evaporate, then go to the dyno. The PCM would have to quickly learn the new fuel, but you'd get the same effect. Conceptually.

 

[Martin]

Hi Tom,
I hear what you're saying, and I was scratching my head about the relationship between MPG and max power. After a lot of thought, what it came down to is at partial throttle, there is enough 'air room' to add fuel to achieve the amount of power the car needs to do what the driver asks of it. Since the fuel has a lower energy content, the fuel system is adding more fuel - hence the lower MPG.

When you get to WOT conditions, you're 100% correct that a naturally aspirated engine is essentially an air pump. Under those conditions, the engine can only supply so much air for combustion, so the amount of fuel burned is limited by the amount of air available.

So, let's say that we're running at a 12:1 A/F ratio at WOT and, for the sake of discussion, let's assume the efficiency of combustion is equal for both fuels. Assuming we have the same 12 parts of air available to burn that one part of fuel, the same amount of fuel will burn in each case, and the lower energy content fuel is going to produce less power.

If my reasoning is flawed, please feel free to point it out.

 

[Darbgnik]

>>>as the drivetrains are similar<<<

no.

different clutch.
different tranny.
different rear differential....

Similar, although not the same.
Different clutches, yet the loss at the clutch is negligible anyway

Different transmissions, yet the losses should be close as they are based largely on the same design.

Different LSD unit once again with the same housing and same gear ratio.

I'm no expert but I'd call them similar, and say the losses would be close.

..................but I've been wrong before. Also my english is not so good.