ORIGINAL: 1971Chall
RLSH700 I just enjoy the conversation. Just to make it clear I am not pitching for any one thing in particular. I agree with you on most points except usually with the supercharger or turbo you are using less gearing due to the big torque increase under boost. My old 1987 Grand National used a 3.42 axle ratio and it performed the best with it. I had a vortech supercharged 1993 Mustang with a 302 and it was geared at a 3.55. My Cobra is also a 3.55 gear. Looking at the physics of it, 400hp is 400hp. It will take the same amount of fuel to produce it no matter how many cylinders you have. This being said a 4cyl turbo and a V8 NA both making the same power will use the same amount of fuel at full throttle. The difference is when you are at cruising speed the smaller engine will then show an advantage in fuel economy as it will be out of boost. I've been highlighting the boost thing but let's look at NA. The advantages I like about big inch NA is you don't stress the engine as much and it usually has a more linear curve. What you stated about gearing on this type of set up is true, you won't need as much compared to a smaller NA engine which will help in the fuel economy dept. I will give GM credit as far as fuel economy goes, the LS engines do get excellent fuel economy for their displacement and power. Again, your statements about the Corvette are very true. The LS-7 makes 505hp and is rated at 24-25mpg on the highway out of 427 inches. The 3100pd weight helps though. I have driven a modified 5.7 here in a Magnum and that car performed outstanding. I don't see any Challenger fan being disappointed with the performance of these cars. Thanks for your view points also.
Another thing that is important to remember is that GM generally sets up their engines and transmissions to use taller gearing than most other manufacturers so this isn't too surprising. Although you may be correct about when they are just cruising it will yield an advantage, the issue at hand is that will do very little to help them with the CAFE standards from what I understand. The CAFE standards are based significantly off of the "official" EPA sticker ratings. If those ratings say it does no better than a V8, it's not going to help them. Will it help the customers who drive them? If what your saying is correct, then yes. The other thing is under current use of technology the forced air-induction systems are not being paired up with a multi-displacement systems, and that has the same basic effect of when not being used at full power it really can yield some significant advantages. Our administrator has mentioned many times about how his in-laws were able to get 30mpg with a 300C, but that does little to help Chrysler with the Government because their system says 25 (or 23 by the new standards). Also I have talked to many owners of the last F-body cars (Firebird and Camaro owners) and many of them have claimed that the old ratings they had up to 28mpg was accurate, so I don't know how much better off a person would be with the forced air induction route anyways. I don't know any one who owns the current Vettes or any other models so I can't testify about those per say. I will admit I don't know enough results of forced air inducted cars to make a judgment call about what mileage they get so someone else will have to add that one.
I believe part of the reason why the LS engines do so well in fuel efficiency besides weight and gearing is the compression ratios. The LS2 had a 10.9 to 1 compression, the LS7 has about a 11.1 to 1 or 11.0 to 1 (depending on the source). The 5.7L Hemi currently has a 9.6 to 1, the 6.1L has a 10.3 to 1 in comparison. The Viper's V10 improved significantly from 19 to 22 (using the new standards) thanks to the VCT, the increased compression (from 9.6 to 1 to 10.2), and the updated TR-6060 from the old T-56 transmission, despite the slight displacemen