Northstar Engines and System Technical Discussion Discussion, DeVille vs DTS in Cadillac Engine Technical Discussion; Thanks for the clarification between the two engines, seems like they are close to being the same. Why would Cadillac ...
There are a few reasons the 300 hp version is offered.
1) Marketing is a big reason. You need to have that high horsepower number for "brochure racing". The numbers mean a lot to some people, even though they may be meaningless in the real world.
2) The STS/ETC/DTS engine, the L37 engine...even though it makes less power and torque across the band than the LD8, it still performs better in the upper rpm range -- and because of the 3.71:1 final drive, should ultimately win in a drag race.
The LD8 engine makes more torque and power down low than the L37 does -- making it a perfect match for a large luxury car...and it returns great mileage. The LD8 is in fact the original design Northstar. Cadillac felt the need for the L37 to get that magic 295/300 horsepower figure...when paired to the 3.71:1 transaxle, it's a good drag racer.
I think that Jason needs to check his figures. The L37 engine does NOT make less power and torque across the band. It makes MORE power and LESS torque. Plus the power band is only 400rpm higher. The comment about the L37 being "a good drag racer" is a little off-base as well. Horsepower may sell cars but torque wins the races. If it weren't for the rather substantial boost in gearing, the STS/ETC would be getting SMOKED by that base models with their "less powerful" engines.
I think your first comment was MOST accurate, it's about marketing.
Look at the power curves and then analyze them. What really counts is not peak power, but the area under the curve. If you have a CAD program (like AutoCAD), digitize those power curves and find the area under the curve. You'll find out that the LD8 engine makes more total power and more total torque across the entire RPM range. I didn't say that the L37 makes less peak power or torque, I said that it makes less OVER THE RANGE of engine speeds. This is, in effect, a good measure of the engine's capability and responsiveness.
The L37 makes more peak horsepower, and it does so at a higher rpm. The hp peak is only 400 rpm higher, but at those speeds, the L37 exceeds the LD8 in horsepower AND torque. Combine that with the torque multiplication of the final drive (3.71:1 vs. 3.11:1), and it's apparent that the L37 makes a slightly better drag racer than an LD8 car does. I'm not making a case for either engine here, just stating the facts.
You're right -- torque wins races. Now it's time for speculation: if you put an L37 engine in front of the LD8's 3.11 gears, the L37 would lose. It's the combination of the engine and final drive that spells out the performance of the car, not just the engine. Your last comment was my point exactly -- the L37 is a result of demanding marketing types. And it works good because it's paired with the right gearset. You have to have the right gears with the right engine, or the results will be disappointing. Performance is lacking if you mis-match either engine with the wrong final drive.
Here's a discussion from the caddyinfo.com board. I brought up this very issue with one of the engineers and this is what we talked about:
Jason, I've got data from some of the newer engines that we are working on that I need analyzed....can you help..?? LOL Seriously, nice approach, that is exactly where we start out when designing an engine and tailoring it for a specific application.
Your conclusions illustrate why it is important to look at the car/powertrain as a "package" rather than just the engine and the HP rating.
Understand that there is a severe pressure from
"marketing" to have a big HP number. The public in general does no analysis like you did and just sees "horsepower" as a measure of performance and technology. I think they judge a manufacturer's capability or technological expertise by the "horsepower" of the engines they produce. As you see in your analysis, to get a high "horsepower" number involves certain trade-offs.
The horsepower rating is a good way to generally compare engines but it is not the overriding indicator of performance. Your analysis is a good example of the "next step " in analysing the true performance potential.
If the engines can be operated at their peak power points then the higher horsepower engine will be faster. That is why in racing the engines are tuned to make a lot of power at a specific RPM and then the gearing of the car is adjusted to keep the engine in that range all the time.
The original Northstar design was to optimize the practical performance of the engine , hence the 275 version. The 300 HP version is more performance driven so the torque curve was moverd up the RPM scale to make more HP and the gearing of the car was changed (to the 3.71) to make use of it.
I've stated before that the SLS and the STS in general are very close in performance....but remember that the STS has bigger, stickier tires for cornering performance. Those bigger tires are a sink for power. If you put the same tires on the SLS and the STS the STS powertrain is clearly quicker in acceleration because the gearing gets the engine up into the range that the HP can used. So, in effect, just like a race car, the engine power is traded off for cornering performance to overcome the big tires. Race cars trade off HUNDREDS of horsepower in aero drag to get downforce to corner faster....same type deal.
Your analysis is correct for just the engine but it can't stop there. You have to take the whole vehicle into account. Your analysis needs to use vehicle speed on the x axis. Convert vehicle speed to engine RPM by using the final drive ratio and trans gear ratio for each of the gears. You'll end up with 4 hump shaped curves that will obviously be different between the STS and the SLS. NOW, plot the HP/torque for the individual powertrains per this graph by converting or sustituting the HP/torque for each RPM point to show the "area under the curve" for the VEHICLE as it accelerates. You'll see that the STS has more area under the power curve due to the effect of the gear ratio.
Another thing to consider is at top speed the engine should just peak at its peak HP to maximize the top speed. With the STS and the 3.71 the engine is turning higher RPM at top speed and can use the higher peak power number to run faster.
Your analysis is a perfect example of how everything in a car is a compromise. When racers say they "eliminate the compromises" that the manufacturers build into the car , in effect they really add MORE compromise by making the engine make more peak HP but loosing more low end torque. The car might be less compromised for one specific purpose but it is more compromised for all the other uses. The auto engineer's job is to provide the vehicle with the fewest compromises or to optimize the compromises so that the vehicle is compromised the least in the area of the greatest desired performance.
Remember, " PEOPLE BUY HP BUT DRIVE TORQUE" Your analysis shows this. A great example is the Honda S2000. 100 HP/liter out of a normally aspirated engine!!! Definitely the benchmark in performance, correct? Drive one. Unless you keep the engine above 8000 RPM all the time the car is a dog. Not to bad mouth it, but it is a serious performance car. On a race track it is a riot...on the street you are constantly shifting to keep the engine in it's power band. For normal driving your type of analyis comes into play and the high HP engine looks weak....except at peak power. A Corvette doesn't have the most stellar power numbers but drive one....it has the most punch at just about any speed in practical driving because of the low end torque.
The other thing to do is repeat the analysis described above using the two different gear ratios but the same torque curves....just like if the LD8 was in the STS. Having driven an LD8 with a 3.71 final drive many times I can tell you it doesn't drive as good as it might sound. The LD8 seems to "short winded" and does not have the high RPM capability to "carry" the deeper gear. It seems to hang at the top of each gear and cannot "over rev" past the power peak to pick up the next gear at the best point. We are exploring putting the LD8 with the 3.71 in the Limosine chassis due to the excessive mass of the stretched limos....but now you are into "truck" analysis, not performance.
Anyway, sorry to get long winded about this but it is a complicated subject/concept to explain...at least for me. This only scratches the surface believe it or not. But it does illustrate the marketing problem of why one would want a high HP number.....it is the first thing people want to know. If you don't have a high HP number then you are into a long explaination like this and people write you off. They figure you are hosing them...that you are making excuses for not making much power.!!!
The premium V-6 was a perfect example of this. The Olds Intrigue was one of the best performing vehicles in it's class...with the lowest horsepower rating!! In effect, that car had the "LD8" type of engine...even more so. It worked and Ward's Auto World recognized the engine as a "10 Best" for two years in a row...but they are engineers. The press brutalized the engine in the "buff books" due to the low specific output. As a result, the engine was viewed as a low performance engine when in reality it was perfectly tailored for the vehicle....it just didn't have that majic HP number. The Olds Intrigue would out accelerate cars with engines with 60 more HP but now we are explaining.......
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I did this today while I was bored. Wife and I are both kinda sick...didn't go to church...news is drowning me out on sniper coverage -- gotta find something constructive to do until the race comes on. :-)
I used AutoCAD to digitize the image of the torque/power curves I downloaded from gmpowertrain.com. I then had AutoCAD calculate the area under the curves. I wanted to verify to myself that the 275 hp version indeed made more torque across the board than the 300 hp version did. What surprised me is that it also made more horsepower! Across the entire operating range indicated by the red tick marks in the image, the area under the LD8's hp curve is greater than the area under the L37's hp curve, even though the L37 peaks higher.
(LD8 in green, L37 in red)
'bill', and/or other engineers, why did Cadillac use the L37 engine at all? It makes less hp and torque across the board. It's been mentioned here that it can have a slightly rougher idle because of the cams. The cams probably have more overlap (maybe increased emissions and decreased mileage). The only reason the 'T'ouring models perform better than the "base" models is because of the final drive ratio.
Why didn't Caddy use the 275 hp version in all their cars, changing final drive ratios for the Touring cars? It seems that based on what I've read on the board and what the numbers show, the LD8 is a superior engine in all indicated respects (more hp/tq, smoother idle, etc.). Is marketing the only reason the L37 variant was invented, so they could sell a "300 horsepower" car than a "275 horsepower" car?
I used to have a 1985 Ford LTD (Fairmont-sized one) with the 3.8L V6. The engine was rated at 135HP, but the magic number was the 250 lb-ft of torque at 1500-1600 RPM - way down low where you can use it. 2 BBL carb, Non-OD transmission and 2.73:1 final gearing. It was really "power"ful and responsive in everyday driving & just plain fun to drive. I could easily pull ahead of most vehicles across an intersection. But it just ran out of steam at about 75 mph.
Ford also offered this engine in the Mustang during that era, but discontinued it after 1986. I heard that one of the big reasons it was dropped was that it was too close in "everyday" performance to the 5.0L
Many give the 80s a bad rap, especially concerning cars, but I think that some of the coolest cars produced came from the 80s. I had an '84 Cutlass with a weird powertrain combination. It had a 4-bbl 5.0L V8 (Olds 307), a 3-sp automatic (TH-200-C) and a 2.14:1 rear axle (yes, you read that right, 2.14). That engine made 150 hp at 3800 rpm and 250 lb*ft of torque at 2000 rpm. For what it was, it was a really good performer, exceeding the average car for that time, considering most had 100hp 4-cylinders. The Hurst/Olds, the performance offering at the time, had a 180hp version of the 307, with less torque than the regular version.
Are we repeating a pattern here? How ironic, the low-hp/hi-torque 307 had a VIN code of Y, just like the low-ho/hi-torque Northstar. What was the hi-horse 307 VINed? Code 9, just like the L37 NS.
The whole exercise of plotting out the graphics on a CAD program (BTW, I use Turbo-CAD) was rather un-necessary. It doesn't take a graphic arts degree to know that the LD8's more conservative cam profile would provide a flatter power curve. Any highschool gear-head knows that.
The point was that Yes, I agree with your point about the "marketing" but that's where the true story of the STS/ETC/L37 combination lies.
The engine was increased to 300HP via a "push" from marketing, THEN engineering had to dump 3.71 gears into the car to give it some actual performance increase. That's the truth of the genisis of these cars.
The LD8 engine DOES have more USEABLE power across the RPM range but that does NOT translate into being able to say it has more or less power across the band than the L37. You MUST qualify the statement by adding the "usable" power. And you must also remember that one persons "usable" will not be the same as anothers. It's a rather subjective statement really.
And as for the statements you quoted from someone else, I would tend to disagree with his points concerning drag racing, and the tire sizes of the two cars, and how they would effect the car's ET's. I'm not sure he's taking into account the cars being FWD, and the fact that due to lower bottom-end torque, the L37 would have a rather hard time with the extra tire's traction off the line. You would most likely need to slip the tires quite a bit off the line in order to not bog the engine.
Again, I think what we're seeing here is someone who is talking out of BOOK knowledge and not practical application from actual track time.
Katshot, I agree that usable power is a subjective measure. That's why I tried as much as possible to OBJECTIFY all quantities involved here. But...like the FWD/RWD discussion, I can see that this isn't going to lead to anything but flame-throwing, so I'm going to stop.
Me and KC have MUCH more spirited exchanges and we get along great. But you're right to walk away if don't think you can discuss the point further without getting pissed-off.
I just hope you're not taking exception to my last comment about "book knowledge" vs. "practical experience".
It's just that I see this happen a lot in these forums. I've had many conversations with people that had college degrees out their butt, and I respect them for that. But, quite often, these very intelligent people incorrectly assume that their degrees, and possibly even experience in THEIR respective fields also makes them an expert in the automotive field. I'm here to tell you that this assumption is not neccessarily correct. There are also some very intelligent people that even have some actual automotive experience but lack the required SPECIFIC knowledge for the conversation they join into. This would commonly be called "talking out your butt". This, unfortunately happens a lot in automotive forums. Why? I'm not sure, it just does.
I myself try VERY hard not to "talk out my butt". In the end it only makes you look stupid, insecure, or both. This is why you won't see me posting in EVERY forum, just ones that I know enough about that I feel sure that I'm giving correct information. If I think someone is giving incorrect information on this forum (or any other), I WILL point it out. The reason is that this type of information source (internet forums etc.) is all too often filled with mis-information. Mis-information can be both costly AND even dangerous to people who take it as gospel.
So please don't be offended by me if I call you on any of the information you present here. If I believe it to be incorrect, I feel it is my responsibility to try to clarify the issue. I would expect the same of you or anyone else as well if you felt information I had presented was incorrect. Lord knows, I've been proved wrong a few times here before. Don't worry, you won't hurt my feelings.
God where's KC when I need him?!
I'm not offended at all. The truth is, many of these issues are subjective. You have your opinions and I have mine. And both of us obviously have reasons why we think we're right. I don't have any automotive college degrees -- I'm basing my knowledge from what I've found in the real world, coupled with what I trust from automotive engineers. They almost always coincide.
But my opinions are mine and yours are yours and we keep going back and forth, trying to further fortify our own opinions, and the discussion pertaining to the original question doesn't really go anywhere.