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Anyway, to summarize the answers to the original question: (At least in regards to GM products.)
[list=1]
[*]Vettes have lots of torque in the lower rev range and can run an extremely tall 6th gear that helps with highway mileage tremendously. S2000s have a good bit less toque at slower engine speeds than higher, so possibly wouldn't be able to properly do this. There's currently no way to test this, however.
[*]Vetts also have a skip-shift feature that forces the driver to go from 1st to 4th under certain circumstances. (Thanks, KeithD. I'd forgotten about that one.) Again with the lack of low-end torque, this most likely wouldn't be practical on an S2000. This can easily be tested by anybody. Try it and see how the engine likes it, if it doesn't seem to cause problems do it for a tank of gas and see what effect it has on gas mileage.
[*]So far, we have no idea what Mustangs do to get their particular gas mileage readings.[/list=1]
A dyno run of my car:
I don't have any runs that go below 3000rpm. Anyway, at 3000rpm it makes 120lb-ft at the wheels, peak at 6500rpm is 136lb-ft, and just before redline it drops to 122lb-ft or thereabouts. So if we could do 2500rpm at 70mph, we'd definitely have less wheel torque available to us (both because of the engine characteristics and the gearing change) than if we were at 4000rpm at 70mph. (I thought it was closer to 3500? I'll have to remember to check today.) So a larger throttle opening would be required. The cool thing is, however, that engines are more efficient at larger throttle openings. Don't ask me why, but apparently they make better use of the air and fuel given to them. R&T did a gas mileage study with a car under four different conditions - small throttle opening with 2000rpm shifts, large throttle opening with 2000rpm shifts, and the same with 5000 shifts. By far the best gas mileage was achieved with large throttle openings and 2000rpm shifts.
Also like CoralDoc has reported, I get a lot better gas mileage than the EPA reports - during 32 fillups between August 1st and Nov 23 last year, I averaged 24.64mph. Highest recorded was 31.30mpg over a 331 mile trip, lowest was 9.53 over 112 miles. Hehe, obviously a track day. The lowest full-tank was 21.02mp over 241.2 miles. Four of those fillups were for over 30mpg. Possibly the EPA numbers are in error, and we have a good bit better gas mileage than they're saying.
Originally posted by KeithD You need to remember a Vettes MPG rating is achieved with Skip Shift, which forced a 1-4 shift unless your at WOT.
This happenes under a very strict set of circumstances. Speed, RPM, temperature, and throttle percentage all have to be within a certain limit for the CAGS to shift from 1st to 4th. If one of those variables doesn't fall into the correct range, it wont skip. It's not just WOT or not.
Blake, you got it right from chris's mouth. He didn't miss the point and several of us got what he was saying. If Elistan can pipe in about something 100% theoretical, it's just as valid for chris to pipe in and say why and how it would and wouldn't work. It's YOU that missed chris's point.
It's just how you come across. You only show up in the post to tell somebody they're wrong without adding anything to the post, and the point is, they weren't wrong in the first place. That's what I consider rude.
I appreciate cdelena's input on a great many threads.
there is more to fuel economy than tall gears. The car should be geared so that at freeway speed it is producing the minimun amount of power to overcome the cars weight, the friction on the road, and the amount of drag the car encounters at that speed......
I've driven MANY vettes. I've only been able to get it not skip shift with a SIGNIFICANT (nearly WOT) amount of throttle.
Personally I think its the stupidest thing in the world. Only could GM manage to come up with something to screw up a perfectly good manual transmission. I'm sure the read enthusiants buy the skip shift defeat box from one of the LS1 tuners.
No, see, you can do a higher 6th gear, it just would be useless for acceleration, like I said. You can cruise in 6th gear at 3500 rpms with no problems. Hell, increase the gearing so that at 70 you're at 3000 rpm's. You'd probably see a little improvement in gas mileage, and you'd just have to use 5th gear a little bit more to get to the point you want to cruise at.
Under cruising conditions, again, as I said, with taller gearing would probably not increase the work required of the engine much. If you accelerate in the higher gear, yes, that would cause much more work. If you're cruising though, it would not require much more.
And I never said Chris was wrong. I repeated AGAIN, TWICE, that he quoted elistans entire post, and the main point of the post was not what he was talking about.
Yes a taller 6th gear would require more torque, assuming you want to accelerate in it.
The hell do you think a C5 owner does? You think he uses 6th gear for acceleration...not when 5th will get you to a higher speed. You use the lower gears (You know, 4th, 5th, etc.) to get you up to the speed you want, then you use 6th to cruise in. Then when you want to accelerate, you DOWNSHIFT, use the lower gear for its intended purpose, then shift to 6th again. Once you get to the speed you want and don't have to accelerate, torque plays a MUCH smaller role.
Originally posted by infinitebass No, see, you can do a higher 6th gear, it just would be useless for acceleration, like I said. You can cruise in 6th gear at 3500 rpms with no problems. Hell, increase the gearing so that at 70 you're at 3000 rpm's. You'd probably see a little improvement in gas mileage, and you'd just have to use 5th gear a little bit more to get to the point you want to cruise at.
Stock at 3500 rpm in 6th is 65mph. Estimate that the minimum rpm for general cruising in 6th is 2800 (accounting for the need to handle grades, wind, etc.) so if you raised 6th enough to obtain 70 at 3000, the minimum speed for using 6th would then be 62 mph. Not only would alot of people be lugging the engine during slow highway runs, but 6th gear would feel piggy under 70 mph (with, like I mentioned before, more criticism as a toqueless wonder). This is a high price to pay for a couple of mpg. I think Honda got it right the first time.
I agree...I don't think it should be done, and I wouldn't approve of it, but I really don't think it would be as bad as you say....Maybe I'll run some tests....assuming I get a seat...
For what it's worth, on my car 70mph in 6th gear equates to 3750rpm.
I also tend to drive in 6th a lot - it's quite common for me to use it at speeds as slow as 45mph, sometimes even 40.
Originally posted by cdelena I think Honda got it right the first time.
Exactly! Believe me, I'm totally pleased that 6th gear is designed strictly for performance. I would have been very disapointed in Honda if they did anything else.
Yeah, blake, I was talking like 1800 rpm not 3500 rpm. Cruise around under 2000 rpm and see what it gets you. That's the difference between a vette and a s2000. try driving the s2000 around under 2000 and see how hard it is to accelerate, or even keep from decelerating.
I agree Honda got it right the first time. What we need is a 7th gear. I just got home, drove over a hundred miles on the freeway, and I don't think this car will pull at all at 1800. It won't keep it's speed, it'll slow down..... The engine has to turn as high as you mentioned (3500 + ) just to keep itself going. Anythin less, like you said, it would feel piggy. Hell it would just stop.
I like how you say that - 6th gear is useless for accleration "like I said". Funny, when chris said it all you had to say was "you missed the point", now you're claiming it for your own. Whatever....
I'd like correct a bit of factual innacuracy in your last post, wicky. Like I said above, I do a lot of 6th gear driving on regular city streets and the car behaves perfectly well. 45mph is 2400 rpm.
03-16-2003, 08:28 AM
