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downshifting vs braking, revmatching

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Saturday, June 25 2005, 02:31:18 #26833     downshifting vs braking, revmatching

so i been looking online for info on driving to save my precious synchros.
ive promised myself not to do any more hard shifting and i feel im doin a pretty good job. as far as slowing the car down i did some reading on downshifting and braking and this is what i gathered.
if youre slowing down and youll be accelerating soon (eg a turn or traffic ahead is accelerating) downshift. if your stopping maybe downshift on the higher gears but dont bother on the lower ones and rarely first. (brakes are cheaper than transmissions.) i downshift first if im crawling and see traffic is gonna move but thats it. i also read that all downshifting should be done with revmatching or tapping the gas rite before the downshift. this is especially good for skipping a gear on the downshift. rev matching seems like it would take some intricate timing (especially with a turbo) and it requires you to engage the brake and gas at the same time with rt foot. but if its the way its supposed to be done i wanna learn it
the ppl also mentioned some fancier stuff like brake boosting to wind up the turbo. anyone got any advice or input on any of this stuff? (*cough* marble *cough*) WTF
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Saturday, June 25 2005, 02:40:20 #26834     

this is why i drive an automatic. Very happy
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Saturday, June 25 2005, 11:39:32 #26836     

|DRC| Elusive wrote:
(brakes are cheaper than transmissions.)

Amen to that. Pretty much the only time I downshift is when I actually need some help slowing down, like going down a steep hill and there's a stopsign at the bottom. Riding out the hill in a low gear gives you more control if you need to do something in an emergency. In regular traffic (flat surfaces) and approaching a stoplight, put it in neutral and use the break to gradually come to a stop. the most common way to wear down breakpads and alignments AND waste gas is people that are hard on the gas and then hard on the break. Stabbing the gas 75% down at every takeoff only to run up to the next red light and break 1 car length from the stopped car in front of you is just stupid stupid stupid. Those people then complain when they get shitty gas mileage, are constantly changing breakpads, wearing out tires, burning up transmissions, in need of more frequent tuneups, burning extra fluids, etc. That is the treatment that sends cars to the shitter early in life.

As far as revmatching what you're describing is what some people call double-clutching. Speeding up the motor to better match the speed of the rear wheels (or in your case all the wheels) allowing the dog teeth to catch the next gear easier, because their speeds are "synched up". Basically when you do that you are doing the synchro's job for it. If you're really good at choosing engine RPM you can up-shift a car without ever touching the clutch, and there will be no grind noise. Thats how the big rig drivers shift. So think about that... in order to revmatch correctly, you'll need to be VERY comfortable with knowing EXACTLY what RPM the engine SHOULD be in if you were in your "desired" gear. So if you do it wrong you could be more destructive on your transmission by over-revving the engine, making the synchros work even harder. I'm not saying don't do it, I'm saying be very very careful.

basic do's and dont's:

Only touch the gearshift when you are changing gears. Do NOT use the gearshift as a arm or wrist rest. This damages the transmission by putting pressure on the dog-tooth gear I was talking about earlier.

Only touch the clutch when you are changing gears. This doesn't mean just don't ride around with it pressed to the floor (which stretches out the clutch-cable) but don't even lightly rest your foot on the clutch. Any pressure at all is causing extra friction between the clutch and flywheel.

Only downshift when you need to.

|DRC| SLIM wrote:
this is why i drive an automatic. Very happy

Bored zzzzzzzz
46 and 2

Last edited by HAL9000 on 18:20, Saturday Jun 25 2005; edited 1 time in total
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|DRC| Voodoo

Saturday, June 25 2005, 14:41:06 #26838     

Rev matching is simple, you've just gotta practice. Usually a quick tap of the gas to rev it about 1500 RPMs should do the trick, depending on your gear ratios. But if you're like me stuck behind a Buick LeSabre and going 10 under the speed limit in 5th gear at a nice calm 1400 RPMs and you drop 3 gears to pass, you're gonna have to rev it up about 4000 RPMs... ROFL

12.5 @ 111 mph
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|DRC| Voodoo

Saturday, June 25 2005, 14:43:51 #26839     

P.S. Brake boosting is for the fuckin race track... think about it... leaving your car in gear around a turn and applying the brake and the gas at the same time to slow the car down and spool the turbo at the same time... when would you ever have to do that on the streets? Well I suppose if you were running from the cops that might come in handy Evil grin
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|DRC| Marblecake

Saturday, June 25 2005, 20:43:22 #26851     

Ok heres the thing. Brake boosting doesnt work on dsm. Stage the car deep"farthest from tree you can be" This will set the stage lights off. NOW the trick with a dsm is riding then side step the piss out of it"clutch". Only ride it for about 3 seconds tops before dumping it.You will also notice the DSM 1 wheel lift. Seems like tranny side of car is lower at launch. This is the most powerful and safest way for a dsm to launch hard. If some fucking dsm noob tells you no then you know hes a fucktard. Also remember if you cant brake boost hard enough you wont get that much psi. THe motor needs a load in order to make a large amount of boost. Elusive do not launch that car higher then 3000. You will have fucked transfers or center diffs. Also watch out for clutch forks, they do like to bend easy on dsm's. Titanium forks ar elike 150 bucks with fork ball included.

Never weld your center diff. Also use a more stickie and soft compound for the rear say like this

Front NItto nt555 then rear nitto nt 555"R"<---- drag radial and handle fairly well in the rain.
You dont have to worry about front wheel lift with those your not making high HP so they will grip and rip like a bastid.

If you have money to play with and want to get rid of some weight. I know there is a full not cat back titanium exhaust for that car. Heres the downside, it costs 2000 for all parts needed. I would also recommend a clutch upgrade. Say a act 2600 or 2100. Always get the clutches sprung or you wont feel the clutch engage. Springless will cause it to catch as soon as it is lifted with no feeling in the pedal.

If you need more help advise with your new car just let me know.
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|DRC| Marblecake

Saturday, June 25 2005, 21:44:44 #26858     

Remember. Never ever ever ever ever ever shift fast and slam gears. DSM no likey.
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Sunday, June 26 2005, 23:45:42 #26909     

Hmmm.. let's see. I got so adept at shifting by matching motor RPM to forward speed that I didn't use the clutch if I wanted to impress someone. It takes an 'ear' to learn that "sweet spot"... but the principal is simple.

The best use for this was travelling the main street in town... right by Dickinson College. When I 'goosed' the throttle on that 427 big block '66 Vette, I could almost see coeds' nipples stand up. Cool When the engine rpm matched, the Vette would 'drop' into second and the sound of that big block with sidepipes winding down... my, my... still gives me goosebumps! Very happy

For any given speed, the engine rpm is higher for each lower gear. The ratio difference is greatest between first and second gear. Therefore, the difference in engine rpm is also greatest! Clutchless downshifting from second (or higher) to first requires a MUCH higher engine rpm increase than, say, third to second.

Use a speed that will be comfortable for 2nd gear to try clutchless downshifting from 3rd to 2nd.

You can try this if you do it carefully...

Find obstacle-clear road with no traffic. Go to 40 mph and maintain that speed for a short distance. You can push the gearshift FROM 3RD into neutral without the clutch. Don't slam it... just firm pressure to neutral position! With car now in neutral, bring engine rpm up. (Experience will teach you how far!) Begin a GRADUAL decrease in engine rpm. Simultaneously, put GENTLE pressure on gearshift towards the 2nd gear position. When the engine rpm matches the rpm needed by the tranny, the gearshift will literally 'drop' into 2nd gear position.

You just shifted without the clutch. Remember: be patient. It takes practice. You can use a similar procedure to UPshift... but remember: the rpm sequence is reversed! It's also harder to do!

I had one of the original '93 Mazda RX-7 twin turbos... Because of the turbos, clutchless shifting was harder. Over the years I've had many 'toys'... '60 Metropolitan (learned on this car), 82 "Z" (Datsun 240Z), '65 Vette LS-6 460hp, '66 BB Vette coupe, '98 BWM 'M Roadster'... I was able to shift without the clutch on all of them. Of course, I still haven't figured out what this is good for! Laughing
|DRC| Marblecake

Monday, June 27 2005, 00:28:33 #26910     

OMG the wise one has spoken. Where have you been. I have only had one half of the dynamic duo around.
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Thursday, September 29 2005, 03:26:45 #29040     

I thought I was gonna be the only car nerd on this site, guess not Smile should be fun!
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|DRC| Marblecake

Thursday, September 29 2005, 19:52:30 #29060     

My car geekness over rules all. I build, drive, have plenty of cars. My new project is a friends car. A SER with a bluebird motor. I just put a sc50 and 150 shot on that pig. DRAG radials are a plus hehehehehehe. As for my car its moving along. It always love to go sideways. I have just completed a sr20 for my firends s14. It makes 378 to the wheels. STOCK bottom end. WOOT!!!
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Thursday, September 29 2005, 20:42:00 #29065     

Thats good power outta the s14. What gen sr20, is it an s14? What kinda car do you have that goes sideways a lot? Mine is an 88 rx-7 Smile pushin somewhere around 240 to the wheels@16 psi
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|DRC| Marblecake

Sunday, October 9 2005, 13:09:14 #29216     

Its s14 with a s13 black top. I shgould be able to get around 430+ after the tune this weekend. I will also have video from the roll cage and motor install on my friends 1st gen rx7 race car. New snap on welder OH YEAH!

Is your 88 a turbo 2 or a 6 port made into turbo. You should have more hp then that if its a t2. Take a dremel and open up your exhaust ports"race port" It helps a ton. I also make custom mani's for them aswell.
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Sunday, October 9 2005, 22:01:07 #29220     

It's a t2... Not sure if that's the exact number, never had it dyno'd, but that's what the previous owner estimated it to be. Next upgrade for me for that car will be a GT2871R Very happy Big bucks, but worth it. I think I may trade the car for an FD, lighter, not as great of an engine, but a hell of a lot more potential. Not to mention looks better too.
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Sunday, October 9 2005, 22:36:05 #29221     

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Monday, October 10 2005, 02:35:48 #29228     

Yeah we have strict rules about thread jacking. Only we're allowed to do it Flip off
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Monday, October 10 2005, 20:28:08 #29234     

Maybe i'm an idiot, but what's threadjacking?
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