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Discussion Starter #1
On the next to last page of the 2007 Sky brochure are the engine specs. And they raise some questions.

Sky;
Engine: 2.4 liter, 16-valve, etc.
Horesepower: 177 @ 6600 rpm
Torque: 166 @ 4800 rpm
bore and stroke: 88 x 98 mm

Redline;
Engine: 2.0 liter, 16 valve, turbocharged, etc.
Horsepower: 260 @ 5300 rpm
Torque: 260 @ 2500-5200 rpm
bore and stroke: 88 x 86 mm

Do YOU see what is odd? Is GM sandbagging the power ratings like the days of muscle cars in the 60's and 70's? A bigger displacement, undersquare engine peaks at 6600 rpm while the undersquare, turbo powered engine peaks at only 5300 rpm. And look at the torque specs!! What did GM do with the rest of the rpm's on the turbo engine? What is the PEAK torque, and is there MORE peak hp at higher rpm on the Redline engine?:eek:

Hmmmmmmmmmmm.........................:confused: :crazy:
 

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Peak

The peak horsepower and or torque does not necessarily happen at the highest possible RPM. If you look at any of the dyno charts already published for the base model Sky - you will see that the horsepower actually reaches very nearly peak at something like 2500 rpm - then gradually climbs to the actual peak then gradullly trails off.

For some cars/engines the peak is reached in the 3000-4000 range then it drops off dramatically afterthe peak is reached.
 

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Discussion Starter #3
Lil GTO said:
The peak horsepower and or torque does not necessarily happen at the highest possible RPM. If you look at any of the dyno charts already published for the base model Sky - you will see that the horsepower actually reaches very nearly peak at something like 2500 rpm - then gradually climbs to the actual peak then gradullly trails off.

For some cars/engines the peak is reached in the 3000-4000 range then it drops off dramatically afterthe peak is reached.
I have seen/used/done dyno work. HORSEPOWER "gradually" climbs to its peak, after which the graph plot generally drops like a stone, and so does ones bank account balance if one goes too much further north!! I any event, the computer hits it's programmed rev limiter. TORQUE, however, plots a line much like you have described. The main point of my post is that the 2.4 shows a specific torque/rpm value, while the 2.0 shows a range. The other curious point is that the 2.4 peak hp is at 6600 rpm while the 2.0 is at 5300 rpm. In the "old days" of muscle cars all the manufactures understated their killer engines by simply stating horsepower at lower than peak rpm in order to "fool" the insurance companies. With a 10% shorter stroke than the 2.4, I can't imagine the 2.0's PEAK hp comes in 20% lower rpm. IMO, it's either a misprint or a sandbag.
 

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Due to the revised SAE J1349 specification that GM is adhering to, all new and future engines from GM will be "SAE certified" and provide a more accurate engine power rating. No sandbagging here, at least not by the numbers.

It is possible the ECU is holding back full power potential in order to have good mileage/reliability, as is indicated by the very flat torque curve and peak [email protected] rpm.
 

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Discussion Starter #5
arm1tage said:
Due to the revised SAE J1349 specification that GM is adhering to, all new and future engines from GM will be "SAE certified" and provide a more accurate engine power rating. No sandbagging here, at least not by the numbers.

It is possible the ECU is holding back full power potential in order to have good mileage/reliability, as is indicated by the very flat torque curve and peak [email protected] rpm.
Good point, BUT, why not rate the 2.4 that way? Hmm.
 

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<-- not an expert

snaponbob said:
I have seen/used/done dyno work. HORSEPOWER "gradually" climbs to its peak, after which the graph plot generally drops like a stone, and so does ones bank account balance if one goes too much further north!! I any event, the computer hits it's programmed rev limiter. TORQUE, however, plots a line much like you have described. The main point of my post is that the 2.4 shows a specific torque/rpm value, while the 2.0 shows a range. The other curious point is that the 2.4 peak hp is at 6600 rpm while the 2.0 is at 5300 rpm. In the "old days" of muscle cars all the manufactures understated their killer engines by simply stating horsepower at lower than peak rpm in order to "fool" the insurance companies. With a 10% shorter stroke than the 2.4, I can't imagine the 2.0's PEAK hp comes in 20% lower rpm. IMO, it's either a misprint or a sandbag.
Sound like you have way more experience with dynos than me - so no argument there.

I kinda doubt that insurance considerations are much of an issue considering that we are not talking about 500 or 600 hp or a 0-60 time in 3.0 seconds and that there are vehicles such as the Corvette and GTO etc with more hp. Not saying that this is not an issue at some times and with some makes and models etc - just doubting that for a 260 hp Saturn that there is any issue - besides which - if the engine really was able to make say 350 hp but the computer is programmed not to let you go there - unless some other part of the car is just unable to handle that or unsafe in that range why would GM/Saturn not want to use the higher number at least for marketing. I would think you'd want to go the other way around - claim 350 hp under specialized hghly controller circumstances even though the average consumer is not likely to actually see more than 315 under real world conditions. But then I have no knowledge of all the various legal and other issues that might raise.

Lets hope it is not ignorance on someone's part involved in the whole testing process etc. Kinda reminds me of the 3-Mile Island Nuclear Plant accident - one of the contributing factors was a temperature sensor that was only designed to function in the expected range of normal operating temperatures - the guage was not designed to report excessively high temperatures that would indicate a run-away reaction - so while the reactor core was melting the operators had no instrument to tell them that.
 

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Engine Power Curve

All

Engine power curves are not linier they curve and approch an upper limit (saturation). When somebody specifies a HP 260 at 6600 RPM, they are specifing the limits. When a range 2500 (excellent low end by the way) to 5000 is given that is more or less the linier range. The range between 5000 and 6600 is the saturation range - very little HP is gained in this range.

Also to those who are willing to void their warranties by removing the RPM limits on their engines, might give this some thought.

Happy adrenaline rushs on the Sky Redline,

PS I own a regular, normal, every day 177 HP Saturn Sky and love it as much or better than my classic 1966 TR4A roadster (140 HP ported with a D Rally cam - 3/4 race).
 
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