@ least it did in my automatic tibby when cruising but now since ive gotten my ground effects put on, which is the only change i can think of ive made to the car, besides it being colder out, my car cruises @ 3500 RPM @ 80mph hmmmmm....

 

Absolutely positively "placebo effect"

I gaurantee 100% that it is physically impossible to change the MPH you travel versus RPM if your ONLY mod is ground effects. Wanna know why?

Ever play with gears?

There is a solid link between how fast your engine is turning and how fast your wheels are turning -- it's the gears in your transmission.

Unless you CHANGED the gears in your transmission (nope, sorry) then your engine goes the exact same speed it did before the ground effects.

Thank you, drive through

-Red-

 

No, sorry.

You are thinking about a torque converter that is always "slipping", and if you did such a thing to a transmission, the torque converter would die within just a few thousand miles. The torque converter never "slips" when you keep the car at constant speed, be it 35mph or 75mph.

After a very brief period of slipping to engage the gears smoothly, the torque converter locks. When the torque converter is locked (ie constant highway speed) it's just like a manual transmission with the clutch fully engaged.

The engine cannot spin any slower or faster to maintain the same vehichle linear speed just because of mods.

You take an automatic Tibby that runs 3300 RPM's at 55mph as an example. Rip out the stock engine, drop in a 500HP turbocharged BETA engine and take it for a spin. The engine will still do 3300 RPM's at 55mph.

This is simply a case of placebo effect combined with "allowed error" in the manufacturer gauges. His engine speed at 70mph cruise did not change.

-Red-

 

Sorta true sorta not, the gearing is fixed, you can't change it, now I can see the drag causing him to cruise at higher rpm but only 50 rpm more due to the torque converter, never less than the gearing. A 10 mph change could be wheels, tire pressure but not a kit. Now if he has new rims or changed tire pressure significantly yes.

 

No, even drag wouldn't cause the engine RPM to change.

You can load the car with 1000 extra pounds and it will still do the exact same engine RPM for 80mph. You could strap on a 100 foot mast with a 5000 square-foot main sail to the top of your Tiburon and it would STILL go the same RPM for 80mph (saying you could even get that fast)

The ONLY WAY to change how fast the engine revs versus how fast your speedometer goes at constant speed is by changing the gearing in the transmission or changing the circumference of the tire tread (bigger wheels or tires).

That's it. Period. End of argument.

There is no magical slipping torque converter, there's no difference for weight or drag or parasitic loss or horsepower or whatever else.

-Red-

 

Okay, not to start a pissin' contest but trying to openly discuss this issue.

Given this unwritten Red's rule we'll call it when you are driving down the highway on a level road let's say for argument purposes you are going 65 MPH at 3200 RPM. If the road then inclines to a 15% pitch you would have to increase the accelerator pedal to maintain the 65 MPH. So far so good. While driving up this incline the tach would be greater than our theoretical 3200 RPM's, let's again say for argumanet purposes it's now at 3450 RPM but we are still traveling at the same speed. Let's say that this incline is 15 miles long. When we finally get to the top after maintaining 65 MPH, would the RPM's be at 3200?

Applying Red's rule, after a short amount of time the RPM's would return to 3200. Er... I know for a fact this doesn't happen.

Anyone care to explain...

If this were completely true, then why doesn't an Automatic get better gas mileage? They still have higher gearing than manual tranny's don't they? If this lock-up occurs then once I'm at crusing speed with an Automatic my RPM's would be lower and my fuel economy would be greater... er wait that doesn't happen either... must be some sort of torque loss.

 

Alright just a little check, when cruising down the road, with your foot still on the gas, lightly depress the brake, do you see the RPM rise, then fall. What I just told you to do is disengage the lock up in the converter, then as soon as your is off the brake the converter will lock up again. I have to disagree about the idea that the tranny will burn up or the converter, if it is not in lock up, It won't! Have you noticed any drop in MPG. Another comment, when your car is shifting through the gears, count how many times it shifts, make sure your getting four gear changes and a slight bump when it goes into lockup. As for converters slipping, before the days of lockup and the CAFE standards, converters did slip going down the highway, which lead to poor fuel economy, that is why they created lockup. Yes converters will slip greater dependent on the amount of torque input. There are two forms of stall, the one is what is called flash stall, thats when the braks is depressed and the accelerator is depressed and when the brake is released, when the engine flairs that is the flash stall. Then there is the just plain old converter stall which is what it stalls at under driving condictions. Lets just say we have a small block chevy that puts out 350hp with a 2500 stall, the guy throws in ZZ430, 430hp, and the stall RPM would increase due to the higher engine output. When radical came say 265 duration at .050, may require a stall of 3500rpm, because of the added duration of the cam. If the stall was too low, the engine will suffer poor drivability problems and engine stall problems, because the engine has to be at or above the recommended cruise RPM for that cam.

[ January 14, 2002: Message edited by: HRD_Tiburon ]

[ January 14, 2002: Message edited by: HRD_Tiburon ]

 

Ok ok..get this. And this is purely hypothetical.. you're going oh 65mph at 3200rpm down a 2 degree incline. It curves up ahead and you lose control and fly off the edge of a cliff. The car now is not under any load except for the 3 foot super-rice spoiler at the rear of the car. Assuming your downward acceleration is 9.8 meters per second per second, how big is the crater you make in the earth's surface?

 

well i just had my rear tires changed back to stock while the front ones are my euro T/A's which are 205/50/R15