Dougal wrote: “On my bike I blip the throttle and downshift while braking before the turn (just like Keith Code says to), but its easy on a bike. Toe to heel isnt newbie material.”
Keith Code runs a RACING school and his advice is quite valid if your goal is to achieve minimun lap times on a race course.
If your goal is to maximize your fuel econony and engine/transmission life, you might want to ignore some of his advice.
When I drove a manual transmission car, I preferred to downshift while approaching the turn and then drive through the turn with the transmission engaged and my right foot off the brake. I felt like I had better control that way.
Dear dear Mr. Gift,
On most modern fuel injected engines, the fuel is shut off while coasting in gear, so I would like to know where this “sucking in more gas” theory comes from.
When you’re driving your Ford Expedition 100 MPH (at high RPM) and take your foot off the gas to coast, what part of the engine and drivetrain are receiving excessive wear? How is driving your Expedition 100 MPH any less harmful than downshifting to 2nd gear to make a turn, since either way, you will have to shift to 2nd gear?
Robert Gift, if you are talking to me, I just slow down in the gear I was using when I start to slow. If I’m cruising along at 35 on level road, I’d be in 5th, and I would simply slow down in that gear, which would take the engine from about 2000 RPM down to idle speed, when I’d go to 2nd. I’m not into down shifting through all the gears as I slow.
Also, what Whitey said above.
Using engine compression to slow the vehicle is turning the engine faster. If carburetor, more gas is sucked in.
In fuel injection if there is idle fuel, would that amount be increased because of higher engine rpm?
I’d place in neutral and use brake to slow, then into appropriate gear accelerating out of the turn. I would not want to put needless wear on the drive train by speeding everything up.
I dislike the wear and tear of high speeds, but during my latest emergency run the hospital called asking where their blood was.
Otherwise I am usually 50 to 55 mph in 55 to 60 mph zones to save fuel, pollution, wear and tear - always in the right lane. I am frequently passed by semi rigs.
In the days of carburettors, downshifting did indeed use more fuel and also with fuel injection that does not have deceleration fuel cutoff.
Many, if not most EFI systems employ deceleration fuel cutoff which completely shuts off fuel delivery during engine over-run. When you downshift many EFI cars, the engine just turns into an air pump. I’m pretty sure the throttle or the idle air bypass also shuts completely during overrun as well so the engine does not cool off the catylitic converter by blowing a whole bunch of fresh air through it.
Even so, if you have to downshift aggressively to slow down for a corner, that means you could have lifted your foot off the gas earlier saving the gas you burned going fast up to the last few seconds before having to brake. But if you decelerate in neutral, you can lift your foot off the gas even sooner because of the lack of engine braking. I’m not sure if the gas saved because of the earlier throttle lift offsets the idle fuel consumption during neutral coast down or not. It may depend on the exact situation, i.e, going uphill to a stop verses a level road.
Yet one more example of RG being unwilling to learn from the knowledge of others.
When your engine rotation speed changes, so does the speed of the oil pump. That oil protects your engine from damage, as long as you don’t push the RPMs past the red line on the tachometer, or past the activation of the rev limiter.
In addition to EFI fuel shut-off while coasting, modern cars have a rev limiter that prevents the engine from rotating fast enough to do the damage RG speaks of. If your tachometer red-lines at 8,000 RPMs, running your engine at 7,000 RPMs will do no harm. Preventing such damage is what the cooling system and lubrication system are for.
Robert, for Pete’s sake, coasting down in gear from 2000 RPM to idle speed isn’t gonna cause wear and tear. 2000 RPM isn’t even considered a high engine speed. As other posters have pointed out, modern fuel injection systems shut the fuel off during engine braking, so coasting down in neutral will just use more fuel than coasting down in gear will.
A rev limiter will not protect an engine from over-revving from aggresive downshifting, unless it also locks out the lower gears in an automatic transmission if shifting down into those gears results in engine over revving.
" If your tachometer red-lines at 8,000 RPMs, running your engine at 7,000 RPMs will do no harm."
I don’t completely agree with that and I stopped believing in “cinderella redlines” a long time ago. You know, in the Cinderella story, everything was fine until the stroke of midnight.
There actually is no well defined engine rpm where abuse “suddenly” begins. Defining the point where abuse starts is akin to defining the exact altitude where outer space suddenly begins. At 30,000 ft, a man needs oxygen to survive and 100 miles up, there is still enough residual atmosphere to slowly cause the orbits of satellites to slowly decay and re-enter.
The redline is higher to handle those “Oh S&^W-$#@@!” moments but going close to it regularly would, I think, cause more issues over time than not doing so. That doesn’t mean you can’t use the engine in a normal range, though!
Coasting down from 2,000 RPMs (heck, even 3,000 RPMs) isn’t really doing anything particularly harmful. I’d think that downshifting into an RPM range even close to the redline isn’t so good for things, however. Basically, so long as you’re in a normal operating range you should be fine.
I am referring to downshifting a manual transmission to stop or to make a turn.
The increased spinning of everything and reved engine (not even close to over-reving) is not worthe tiny bit more wear to brake pads.
You are also briefly adding fuel to rev thengine to downshift.
Thank you for informing thathe fuel is COMPLETELY shut off whengine speed is above whathe throttle calls for.
I had wondered about catalyticonverter cooling, especially descending long sections of I-70 in the mountains.
“Thank you for informing thathe fuel is COMPLETELY shut off whengine speed is above whathe throttle calls for.”
I think DFCO only comes into play when your foot is completely off the accelerator and the engine rpm is about two or three hundred rpm or higher above idle speed.
If you are coasting down a slight grade that takes zero horsepower to maintain the speed limit, in other words, you could coast down this grade in neutral, and you have the car in gear and the engine has to turn 2000 rpm to go this speed, you are essentially giving the engine the same amount of gas that it would take to rev the engine 2000 rpm in neutral, if you gave it less gas, the engine would brake the car and you would slow down. In this case, DFCO does not come into play and coasting in neutral with the engine idling at 800 rpm would definitely use less fuel than coasting in gear with the engine running at a 2000 rpm fast idle.