grinchy

You are all going to laugh at me, but in the spirit of 'there is no such thing as a stupid question', here goes.

I have owned 3 manual transmission cars. I have the current priviledge of owning a 90 n/a rx-7 convertible, and the gods blessed me with an automatic (yes, I hate it, but that isn't the point). It is the first non-rental automatic I have ever driven.

Is the correct launching method to:
a) stand on the brake, stand on the gas, and just drop the brake when at a good rpm, while in first gear with the hold button on
b) shift into neutral, stand on the gas, and drop it into drive when at a good rpm
c) shift into first, stand on the brake, take your foot off the brake, and floor it (in hold mode, of course)
d) something else?

Thanks.


Thanks.

grinchy

All I need is one reply! I just don't want to do the wrong thing and blow up that damn tranny. Or maybe I do, so I can put in a TII manual and lsd diff.

10sec rx7

but your foot on the brakes, flatter the throttle when stalls up to good revs let foot off brake. dont rev it and drop into first gear it will blow the box.

grinchy

thanks.
sounds like option a).

I'll experiment with that tonight.
I will avoid option b) at all costs.

peejay

Neutral drops are illegal in NHRA...

Try different stuff! Sometimes you even launch quicker by NOT brake-torquing it.

grinchy

I did some experiments tonight. Not promising.

in first, with the hold on, with the brake depressed with left foot, and flooring it with right foot, the rpm's would not exceed 2000. some sort of rev limiter or safety is engaged. pita!

even when dumping the brake from 2000, it seemed to launch slower than just flooring it from a standstill, kind of coughed, like it was gagging on extra fuel.

times were not impressive - upper 8's and some 9's.

is there a way to disable the rev safety thing? it must cut something whenever the brake is depressed.

Happy to hear opinions. I'd love to squeal the tires, just once.

I went out and started my didn't pass smog so can't drive it 1986 bmw 325es today. Man I miss that straight 6. It would squeal in 1 and 2 no problem. But it handled like a boat compared to the 7. And no top end (redline is 4500 or somthing). But the torque.

peejay

What you are experiencing is the stall speed of the torque converter. The stall speed is the maximum amount of "slip" that the torque converter can have when you're brake-torquing it.

As the engine (and torque converter) spins faster, it gets a lot harder to make it slip... the "stall speed" is the point where the engine can no longer make enough torque to overcome that. Because of this, stall speed is just as dependent on the engine's torque curve as it is on the converter's design.

Ideally, for max performance, the stall speed will be just below the peak torque of the engine. Not just because this gets the engine into is powerband without lugging it, but also because a torque converter mutiplies torque. Describing how would take a few more paragraphs but suffice to say multiplying peak torque will get you going a lot faster than mutiplying a fraction of it.

However, a higher stall speed converter has its downsides... it heats the trans fluid a lot more, for one thing. Transmission life is directly linked to fluid temperature, and it's far from linear. Also, if the stall speed is above the cruising RPM, the torque converter will always be slipping while cruising around, which is bad for fuel economy and bad for transmission life (heat). That's where lockup torque converters come in... but if you've ever driven a car with a high stall speed and a lockup converter, it gets very annoying to drive - when you accelerate the converter unlocks, and when you back off it locks up again, and it feels like the transmission is constantly hunting between gears. (Any GM with the 1.8/2.0 OHC four is a very, very "good" example of this)

What can you do? You can modify the engine to make more low-RPM torque (basically, forced induction or a bigger engine). You can also go for a higher stall speed converter, but I don't know if anybody makes one for the transmission in the RX-7. I know they make 'em for Civics but they are very expen$$ive. Or, you can take the common route and spring for a manual transmission.

grinchy

That's a great explanation. Thanks. f*(&(&#$ automatic transmissions. I'm headed to MBA school this fall, so I won't be getting a new tranny, or a supercharger, though I'd like to have both. Guess I'll keep my eyes open for a project TII though, one never knows when the skies will open.

I love every single thing about the 'vert except the auto. I think I could even deal with the n/a engine if I had a manual. Reading all the cooing from Turbo owners has me itchy, though.

85rx7blue

crazy

sbrx7

Upper 8's and low 9's in a car that onlry is supposed to run 17's in the 1/4? I'll assume those are 1/8 mile times, and that's pretty quick. Is there something about this car you aren't telling us????


Steve Bertok
94 MB touring
88 'Vert
85 GSL-SE

all manuals

FC3AZ

that is what I was thinking. An 8.1 is like 13.5 in the 1/4 or somewhere around that, I think............... you runnin turbo or nitrous or somethin man?

jr

I think he's reffering to 0-60 times...

grinchy

jr is right, those were the horrible 0-60 times. Counting thousands, no less.

I'll check that launching technique brake.

Thanks. This weekend I'm going to verify that my 5 and 6 ports are opening.