elnots

I heard from a fellow RX7 enthusiast that if I take off my emissions equipment on my turbo rotary engine that I should not downshift again. And that I need to stop downshifting as is because rotary engines weren't designed to do so.

I've downshifted in my car ever since I owned it. I hate using my brakes to brake the engine unless I'm coming to a quick stop. He said something about the afterburn being bad or something to that extent. Any truth to that?

mycarisolderthanme

None.

tjeter

hmm i have NEVER ever heard that before, but i have heard you put alot of strain on your drivetrain by downshifting to stop, i heard its much better for the components if you just actually use the brakes for what they were mean for which is stopping..

re.fc3s

Its all about technique, if you can rev match downshifting is not a bad thing..same with doing the double clutch, its a hard thing to master though. I cant see how it would effect your engine as it would be more of a drivline issue, unless you constantly pull a stupid and try to downshift gears, and make it go over the redline all the time.

WVRx7

This is a tragic load of mis-information.

Downshifting is not the proper way to slow your vehicle.

The manufacturer installed brakes because they are the only proper way to slow a vehicle. Using the engine to slow the vehicle is incorrect driving technique, it is extremely hard on the drivetrain and generally the procedure shows others that you don't know how to drive a car.

If you are slowing to a stop, you simply use your brakes and just before you stop, you engage the clutch and move the transmission to neutral and then 1st gear.

If you are slowing and need another gear, you simply slow the vehicle until another gear is appropriate and you engage that lower gear. If you do it properly, you don't need to do any fancy "rev match" ballet maneuvers.

re.fc3s

i agree with braking to slow you down. I didnt say brakes shouldnt be used; of course you should use your brakes. Anywho, rev matching, well many ppl use this technique when racing, if you lose momentun on a turn after using your brakes, you rev the engine, engage the clutch , and are trying to bring up the RPMs up to try to meet the most optimal shift. thats rev matching. "ballet moves?" ... Whenever a worldwide driving technique becomes a ballet move id like to know, it would be a pretty fucked up world.

WVRx7

rev matching, double clutching or whatever you want to call it is done in racing. It is also done in heavy equipment and trucks.

The procedure was invented to allow non-syncromesh transmissions to move from gear to gear. Even in the years of marginal syncronizers, it was recommended that the driver still make an effort to bring the revs back above idle in order to get the next gear to select without a crunch.

These days all street driven cars are equipped with robust syncronizers and the ballet is largely acedemic. Sure, there is a benefit in some situations, but largely the act is something that pseudo drivers believe makes them look like talented drivers.

My rationale assumes that everyone that is competitively or agressively driving on a race track already knows how to properly drive a manual transmission vehicle. Yes, they will be in situations where they may require a prod of the gas pedal in order to keep the vehicle balanced and get it in the proper gear for the next portion of the track.

On the street, none of this is necessary. You go up through the gears to accelerate and when you need to slow or stop, you use the brakes. When you are ready to accelerate again you select the proper gear for the speed you are going (if you are stopped, this is 1st gear) and if you chose wisely, you don't need any special footwork, maneuvers or math equations to get it in gear.

fc3sdrifter121

fk that,
I downshift and rev match all the time, I am sure it is hard on my driveline, but it is verry convinient to me, Say I am in 3rd coming up to a stop light I am at around 3.5k so I slow down by releasing the gas till bout 2.5k then down shift to 2cnd with a good rev match, and the light turns green.
I also do this b4 coners on a daily driving basis. so I am in the right gear when I exit.
I dunno everybody drives different, But I agree don't just depend on down shifting to slow you down.

fc3stech

Stop listening to retarded fellow rx7 owners, but yeah the breaks where designed for a reason and you should only really down shift in racing to keep the rev's up or to go to a lower gear because you have to slow down a little for traffic and dont need to be in a low gear, Rotary engines werent designed to be down shifted what the hell, the tranny gets downshifted and the engines goes up in rev's just like if you where accelerating, so maybe he's telling you RX7's can't be reved up or something, and downshifting is a lot of unecessary stress on the drivetrain

snowball

brakes are cheap drivetrain parts are not, ill stick to using my brakes for the job they were made to do.

Syonyk

Personally, I like to be in the proper gear *before* I'm around the corner - I enjoy accelerating out of corners.

For hard stops, I use my brakes. Otherwise, in normal driving, I'll tap my brakes a few times to let people know I'm slowing down, but otherwise I engine brake. The stresses on the drivetrain from WOT acceleration are significantly greater than those of engine braking, and when done properly, there's no wear on anything (other than a trivial bit of clutch wear).

*shrug* No, it's not proper race technique, and on the track, I use the brakes. I'm also slowing down a lot faster on the track. On the street, when I'm usually driving 2-3 blocks ahead of myself, and have plenty of space to change speed, it works wonderfully.

And I can't come up with a single way removing emissions would change how downshifting would affect an engine.

-=Russ=-

hIGGI

iTrader: (7)

proper downshifting and engine breaking does not tear your drivetrain more than is supposed to be wearing in normal use and its lowering brake wear

as well its good for weight balance (in some situations, driver will preffer more weight in back than in front and using only brakes, will always transfer more weight into front)

RotaryWeaponSE7EN

iTrader: (6)

And in some cases, like higgis avatar downshifting is needed.

Syonyk

It's not the same. It's similar, it accomplishes the same end result, but rev matching is different from double clutching.

Rev matching is using the throttle to accelerate the engine's RPM to match the transmission input shaft RPM for a smooth shift. The synchros are used to match the transmission input shaft speed to the output shaft speed, through the proper gear ratio.

Rev matching:
1. Press the clutch in
2. Shift to a lower gear, letting the synchros speed the transmission input shaft up
3. Blip the throttle to match the engine speed to the new transmission shaft input speed
4. Release the clutch

When done properly, it should be a perfectly smooth engagement, with no dragging of the clutch needed. If you do it perfectly, you can let the clutch out very quickly, since the flywheel and clutch plate are already at the same speed.

Double clutching is used on vehicles without synchros, on vehicles with worn synchros, or to allow you to make a larger RPM jump than the synchros will let you do otherwise (shifting into 1st at 25mph on an RX-7, for example).

Double clutching:
1. Press the clutch in
2. Shift to neutral
3. Release the clutch
4. Blip the throttle to bring the engine and transmission input shaft to the correct speed for the next gear
5. Press the clutch in
6. Shift to the appropriate gear
7. Release the clutch

Actually, when done properly, you don't even need to use the clutch at all. RX-7 transmissions, in my experience, are too tight for this to work very well, but other vehicles I've driven are perfectly happy to let you do this (and it was required for a while on my old Subaru to get home when the clutch cable broke ~50mi away).

Yes, newer cars have robust synchros. I've been amazed with the power of the synchros on some newer vehicles I've test driven. My transmissions, in both my daily drivers, are 20 years old. They're street driven, and rev matching/double clutching is needed to keep shifting smoothly. I know I'm not the only person here with weak synchros. And, I'll stand by the statement that to drive a stickshift smoothly, you MUST be able to at least rev match.

To get from point A to point B, I'll agree with you. It's posible to not rev match or downshift, and get to your destination. I'll also say that it's absolutely no fun at all, and involves a lot of synchro & clutch wear if done as you describe.

*shrug* Opinions differ. I have yet to see any convincing evidence that engine braking, rev matching, and downshifting do anything bad to the drivetrain if done smoothly and properly. Yes, you can abuse the drivetrain and damage something, but there's no reason to do so when it's easy to do it smoothly.

-=Russ=-

NZConvertible

Why is it that every discission on downshifting brings out the idiots? Using a combination of wheel braking and enigne braking is a normal part of driving and every car was designed to do it. Anybody who thinks rotaries is different in this regard is an idiot. Anybody who thinks it should only be done on racecars is an idiot. And all of this has nothing to do with emissions - that's a whole different level of idiocy.

GregW

We are all soooooo impressed! Your really smart.

elnots

Well his arguement was pretty flawed and based on," rotors are a total different design so it's not the same because the engine load being used to slow the car down rather than speed up hurts the dynamics of the engine, causing backfire's, excessive vibration, quicker wear on engine parts. And with no air injection into the exhaust stream at the manifold on an N/A engine would cause even worse backfiring while downshifting for deceleration."

Now that aside. I went to a technician school and they told me that downshifting is a NECESSITY! Just like not resting your foot on the clutch pedel or resting your hand on the shifter. The manual transmission gets lubricated by the countershaft (might have been main) throwing fluid around the transmission case lubricating the other shaft, and slowing the car down in nuetral gear causes the transmission to not get lubed and wear quickly.

Is that a case in RX's?

janm

Oh no I accidentally took my foot off the gas in traffic today I think I need a rebuild now

snowball

read some of the older downshift threads smarter members said that the lub theory is BS

1SWEET7

iTrader: (1)

Like NZ said, using both techniques is a NORMAL part of driving. If you use both ways of stopping in their own situations that is the greatest benefit.

MaczPayne

iTrader: (5)

Shift Technique

I personally rarely ever downshift when I'm on the streets.

fc3cNyC

whats engine braking ... i kno of engine breaking ...

you can use one of these to do the latter, but regarding the former i am clueless ... this notion of using your engine to brake. HA ... what a silly idea to drag it on the floor to produce enough friction to stop ur car ...


(note on the sarcasm: the more we as a group perpetuate this ignorance, the more this ludicrousness will keep continuing ... now that's not nearly as hard to believe as ... NO EMISSIONS = NO ENGINE BRAKING )

TurboFB

I agree RED1990GTU. Engine braking combined with braking is 'in my opinion' a great way of additional breaking. It gives you the extra force to slow down quicker when exiting freeways etc. When you brake...what other form of slowing down is there besides your emergency break? Ehh...hehehe....yeaaaah...

Lucky13

i completely agree with you and i dont think i couldve said it better haha

slow_2ed_gen

i see alot of people saying "its bad for the drivetrain!!!" but can anyone tell me why? like mechanicaly what does downshifting to slow down hurt/put excessive ware on?


i guess if you think of the engine as a heart: there are only a set number of beats your heart is ever going to beat so you make it beat more efficently so it lasts longer. so in the engine the less you have to rev it is better, like wasting rev's on your engine downshifting.

btw this is just something i was thinking i dont know if it holds any truth about the engine at all

ps: i downshift all the time to slow down