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Dyno HP vs. Tq -- The Real Deal

 
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Old 20 Aug 2003, 12:37 pm
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Default Dyno HP vs. Tq -- The Real Deal

I'm still amazed at everyone's fixation on peak Hpvs. Tq -- with regard to our engines, not diesels, et al. To me, I look at the Tq under the curve (basically the average)thru a given rpm range to determine which car should be quicker thru the 1/4 mile (top-end speed is another issue and trap speeds --an indication of Hp-- don't win races), assuming competing vehicle variables being equal. My point is not one of contention, but hopefully of edification, to the forum members who buy performance parts based on dyno Hp numbers. Even with advertised Hp no.s, there's peak Hp gains and Hp gains at a given rpm, which the mfr's., most times, fail to delineate. And then there's the old, "You may see up to a "x" Hp gain," with this part; again, buyers beware!
Since obviously the PT's aren't exactly built for top speeds, I'm discussing short-distance acceleration modifications and what the more important info to be gleaned from a dyno-curve is, IMHO, of course.
There's at least 3 types of racing: bench,dyno-curve Hp, and dragstrip; again, IMHO, there's only 1 of the 3 that's a true measure of a car's performance.
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Old 20 Aug 2003, 12:58 pm
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GT Turbo peak horsepower and torque according to...

[u]Road and Track</u>, June 2003, reported that after a dynamometer test of the Mitsubishi TD04LR turbocharged engine in the Dodge SRT-4 (same engine as used in the 2003 PT Cruiser GT) the output at the crankshaft was 238 bhp which is 23 bhp more than than claimed by the manufacturer. The findings, after subtracting 16 bhp for drivetrain loss, showed the turbocharged engine sends 222 bhp and 246 pound feet of torque to its front wheels. When Chrysler was asked about this because they rate the GT Turbo at 215 bhp they indicated that "It's always better to be a little conservative on your power ratings."
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Old 20 Aug 2003, 01:12 pm
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Only THREE kinds of racing???? "bench,dyno-curve Hp, and dragstrip." Boy, you have never been in an Autocross or a road race, have you. Anybody can drive in a straight line, it takes a driver to turn right and left. I have done all FIVE types of racing, have enjoyed all FIVE, but speeding thru the twisties is way more fun than going fast in a straight line.

Mike
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Old 20 Aug 2003, 04:40 pm
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I think he meant that "3 kinds of racing" ironically. IOW the first two don't count.

On the horse power to torque question, keep in mind that torque is a measure of twisting force, while horsepower is a measure of twisting force over time.

That's why an engine making 200 ft lbs of torque at 5000 RPM won't be as fast as an engine making 200 ft lbs of torque at 9000 RPM. (read Honda)
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Old 20 Aug 2003, 09:19 pm
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I wrote a paper on this subject as it is always topic of controversy.

Basically, torque is that kick in the back that you feel when accelerating. Also, torque makes HP (torque x RPM / 5252 = HP) Torque across the rev range is good, provided you are starting from xxx RPM.

Peak HP is important to everyone because it is the energy used to keep the vehicle moving. HP is used up in wind resistance, drivetrain loss and friction to the road. When racing, you are usually shifting at the higher RPMs around where the peak HP is so the entire torque curve is not needed. For example, you are drag racing and are now accelerating in 2nd gear to redline, say 6300RPM, you shift in 3rd and the revs drop back to say 4300RPM. We now don't care about the torque below 4300RPM because we'll never see it again! Peak HP is important because it tells us where to shift so we stay in that powerband. That is why torque at high RPMs is desireable, which co-incidentally is the equation for HP.

edit: Sorry, I forgot to mention that I do agree that parts advertising + X HP is misleading. I know that a lot of those fart sounding exhaust systems for the imports add peak HP, but at the cost of low end torque.
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Old 20 Aug 2003, 10:06 pm
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Quote:
quote:Originally posted by GLH_TC 16V

I wrote a paper on this subject as it is always topic of controversy.

Basically, torque is that kick in the back that you feel when accelerating. Also, torque makes HP (torque x RPM / 5252 = HP) Torque across the rev range is good, provided you are starting from xxx RPM.

Peak HP is important to everyone because it is the energy used to keep the vehicle moving. HP is used up in wind resistance, drivetrain loss and friction to the road. When racing, you are usually shifting at the higher RPMs around where the peak HP is so the entire torque curve is not needed. For example, you are drag racing and are now accelerating in 2nd gear to redline, say 6300RPM, you shift in 3rd and the revs drop back to say 4300RPM. We now don't care about the torque below 4300RPM because we'll never see it again! Peak HP is important because it tells us where to shift so we stay in that powerband. That is why torque at high RPMs is desireable, which co-incidentally is the equation for HP.

edit: Sorry, I forgot to mention that I do agree that parts advertising + X HP is misleading. I know that a lot of those fart sounding exhaust systems for the imports add peak HP, but at the cost of low end torque.
I've always believed the Tq "area under the curve" is important in straight line performance because of the initial acceleration advantage. My Vette (supercharged) Tq curve jumps (near vertical) to over 400 lb-ft from 2400 to 2600 rpms and stays horizontal to 6600 rpm (rev limiter setting); whereas, most naturally aspirated Tq curves climb at a 45^ angle. The area under my Tq curve is &gt; that of my friend's modified '02 Viper, although his peak Tq is &gt; than mine. My premise has been based on me spanking his Viper one night for about an 1/8 mile on the street by about 1.5 car lengths before having to shut down due to road conditions. I'm not disagreeing with your post, just telling what happened in my particular situation, to which I attributed to my Tq curve advantage.
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Old 20 Aug 2003, 11:15 pm
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I would have to agree with you if you are talking about a standing start as you are going to pass through the majority of the rev range, it helps give you the 'hole shot' advantage. Let's not forget that a flat torque curve with lots of area underneath it also makes for a very responsive driving car.
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Old 22 Aug 2003, 10:56 am
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Quote:
quote:Originally posted by GLH_TC 16V

I would have to agree with you if you are talking about a standing start as you are going to pass through the majority of the rev range, it helps give you the 'hole shot' advantage. Let's not forget that a flat torque curve with lots of area underneath it also makes for a very responsive driving car.
Yeaaaah, Babeeeee...[^]
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Old 22 Aug 2003, 01:05 pm
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I can confirm the response that Steve's 'Vette has from:

1. riding in it,
2. looking at the various dyno plots taken at each step of the way from stock to current state.
and
3. from the rep of the tuner that has done the work. You don't get in the car mags year in and year out by turning out bad installs.

The name MTI of Houston, TX should ring some bells.

I am new to the performance game. I have had some "performance" cars in the past, but was always content to stay with the factory configuration. Having said that, there are some constants in the GT that I have noticed that should go far in obtaining predictable results.

1. The stock turbo has small volume and spools fast. It begins building boost at 2300 RPM.

2. The 2.4L engine has a natural powerband that starts at 3500 and continues to 5500 (the 5500 figure is from N/A models; I cannot swear that it still applies to the turbo). The top end figures are a toss up between engine capabilities and PCM programming.

3. Torque should be high from 2300 to near redline on a stock configuration.

4. Increasing the flow of the intake air or the exhaust path MAY decrease low end torque.

5. In order to have the highest torque available at the earliest time, the design parameters of the system should be followed; until new "calibration" is offered by the PCM to offset flow modifications in a positive manner.

Number 5 will probably cause some comments of dispute, and possibly comments of support.

There are more and more indications from both the GT and SRT-4 members that the various intake options have had negative effect when used in conjunction with the Stage I programming.

Stage II is projected to include additional programming to handle a 3" exhaust system. The upstream O2 sensor housing chokes the exhaust path down to 2 1/4" leading up to a 2 1/2" exhaust system. This may lead the way for a progressive increase system to be developed that will allow smooth transition to a larger diameter exhaust system that uses stepped increases from the smallest (2 1/4" O2 sensor housing) to the larger (3" exhaust system), and will preserve the low end torque characteristics of the small turbo. It would seem that a sudden transition from small to large would give the exhaust gasses a chance to cool and become more dense. This would lead to restricted extraction. On the other hand, the larger volume of the 3" system would allow more exhaust gasses to be extracted once they became dense enough to recreate the flow that was present before the increase size; thus retaining the low end torque inherit in the smaller turbo. If this is possible, the net result would be higher volume extraction without any deterrent to low end torque. This would seem a desirable goal, and with proper flow design, I would think it would be attainable.

Mopar Performance dropped their CAI project due to not being able to predict noticable performance gains. The removal of the air box could have a negative effect on how efficiently the Charge Air Conditioning system can cool the compressed air entering the actual throttle body. Higher volume of air present at the input of the turbo's compressor may tend to reduce the efficiency of the turbo's ability to match the flow on the output side. In my estimation, the turbo has to be viewed from the tip of the input (size of the intake to the airbox) to the tip of the exhaust system (volume and density of the gas flow at the tip of the exhaust pipe. A change made in the intake volume and/or temp may result in a change in the predicted output volume and resulting power gains made by the turbo; same goes for the exhaust..

Any changes in these areas would require the proper broadening of acceptable data present to the PCU by it's sensors in order to change the "calibration" to reflect the possible gains.

A physical change without an available PCM reaction would only tend to reduce performance to the level that the PCM's incoming data would result in a programmed response. Another reason for followin
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Old 22 Aug 2003, 02:45 pm
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[quote]quote:Originally posted by Dalite

I can confirm the response that Steve's 'Vette has from:

1. riding in it,
2. looking at the various dyno plots taken at each step of the way from stock to current state.
and
3. from the rep of the tuner that has done the work. You don't get in the car mags year in and year out by turning out bad installs.

The name MTI of Houston, TX should ring some bells.

I am new to the performance game. I have had some "performance" cars in the past, but was always content to stay with the factory configuration. Having said that, there are some constants in the GT that I have noticed that should go far in obtaining predictable results.

1. The stock turbo has small volume and spools fast. It begins building boost at 2300 RPM.

2. The 2.4L engine has a natural powerband that starts at 3500 and continues to 5500 (the 5500 figure is from N/A models; I cannot swear that it still applies to the turbo). The top end figures are a toss up between engine capabilities and PCM programming.

3. Torque should be high from 2300 to near redline on a stock configuration.

4. Increasing the flow of the intake air or the exhaust path MAY decrease low end torque.

5. In order to have the highest torque available at the earliest time, the design parameters of the system should be followed; until new "calibration" is offered by the PCM to offset flow modifications in a positive manner.

Number 5 will probably cause some comments of dispute, and possibly comments of support.

There are more and more indications from both the GT and SRT-4 members that the various intake options have had negative effect when used in conjunction with the Stage I programming.

Stage II is projected to include additional programming to handle a 3" exhaust system. The upstream O2 sensor housing chokes the exhaust path down to 2 1/4" leading up to a 2 1/2" exhaust system. This may lead the way for a progressive increase system to be developed that will allow smooth transition to a larger diameter exhaust system that uses stepped increases from the smallest (2 1/4" O2 sensor housing) to the larger (3" exhaust system), and will preserve the low end torque characteristics of the small turbo. It would seem that a sudden transition from small to large would give the exhaust gasses a chance to cool and become more dense. This would lead to restricted extraction. On the other hand, the larger volume of the 3" system would allow more exhaust gasses to be extracted once they became dense enough to recreate the flow that was present before the increase size; thus retaining the low end torque inherit in the smaller turbo. If this is possible, the net result would be higher volume extraction without any deterrent to low end torque. This would seem a desirable goal, and with proper flow design, I would think it would be attainable.

Mopar Performance dropped their CAI project due to not being able to predict noticable performance gains. The removal of the air box could have a negative effect on how efficiently the Charge Air Conditioning system can cool the compressed air entering the actual throttle body. Higher volume of air present at the input of the turbo's compressor may tend to reduce the efficiency of the turbo's ability to match the flow on the output side. In my estimation, the turbo has to be viewed from the tip of the input (size of the intake to the airbox) to the tip of the exhaust system (volume and density of the gas flow at the tip of the exhaust pipe. A change made in the intake volume and/or temp may result in a change in the predicted output volume and resulting power gains made by the turbo; same goes for the exhaust..

Any changes in these areas would require the proper broadening of acceptable data present to the PCU by it's sensors in order to change the "calibration" to reflect the possible gains.

A physical change without an available
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