Downshifting LS3

[Norm Peterson]

Originally Posted by Spec

Higher RPM burns more fuel than lower RPM. Your engine goes through more cycles in a minute obviously at higher RPM than at lower RPM... thus burning more fuel measure on a timeline... even if you don't press on the pedal, its still needs to spray more fuel into the cylinders to maintain the higher rpm... I think, lol... I'm no mechanical engineer either...

Not necessarily (I haven't read the whole thread yet).

EFI can have "fuel cut on deceleration" logic built into it, where if you're decelerating (typically closed throttle) and the revs are above a certain threshhold, the signal for the injectors to open is not sent. Below whatever that rpm is, you'll get fueling as usual (though they may be able to lean it out some since there is no power demand beyond not letting the engine stall).

If you kick the throttle to rev-match (as you should), you'll use a little extra fuel during that part of the process.


Norm

[Norm Peterson]

Originally Posted by xinfamousxi

New to driving stick. What I have been doing is throwing it in N and coasting to the stop

Not a good idea.

You're throwing away one of your vehicle control options by not having acceleration instantly available. Keep in mind that the time you'd most urgently need to cram it back into gear - any gear - will be the time you're most likely to screw it up under the pressure of the moment and end up wasting still more time fumbling around until you do get it into some gear. Which probably won't be the right one, just better than nothing (neutral).


Norm

[ytown87]

Originally Posted by gajagfan

I think the amount of fuel saved here over a year of engine breaking vs. using the clutch / brakes is about enough to buy one Happy Meal from McDonalds. Hardly worth the discussion is it? To me, using the opportunity to practice your rev matching down shifts is much more valuable.

.....so you're saying I can save enough for a Happy Meal!?!?! TOTALY WORTH IT! And if Wendy's holds onto this 4 for $4 deal I can plan on getting one with all my money saved next year!

[drew peacock]

i always take a dump before i take mine out...less weight means i save money...

[gajagfan]

Originally Posted by ytown87

.....so you're saying I can save enough for a Happy Meal!?!?! TOTALY WORTH IT! And if Wendy's holds onto this 4 for $4 deal I can plan on getting one with all my money saved next year!

That Wendy's deal is pretty amazing!

[GMfan454]

Originally Posted by paul84043

But he's not revving it.. he's downshifting.. Different animal..

When you down shift, your engine revs higher which yes, uses more gas.

[ytown87]

Originally Posted by GMfan454

When you down shift, your engine revs higher which yes, uses more gas.

[GVA 45TH 2SS]

Originally Posted by GMfan454

When you down shift, your engine revs higher which yes, uses more gas.

Only if you push the accelerator pedal

[Spec]

If you're going to hold at that rev and rev higher - YES

If you're going to just downshift and allow the car to break with its motor - NO

[762SPR]

Originally Posted by Nate76

That all makes sense to me. The only part where I'm confused is where is all the sound coming from? When you downshift, it sounds wonderful and loud similar to when you're accelerating. So if the sound isn't from gas being combusted in the cylinders, then what's making it? Is it just the car inertia causing the cylinders to move and that makes the noise? I assumed the beautiful growl of the v8 was made by the explosions of gas in the cylinders.

Depending on the conditions you will hear a mix of regular combustion (if there is fuel being injected), also even without combustion there will still be noise from the engine running and probably the biggest contributor will be the release of the charge in the cylinder when the exhaust valve opens. If there is unburned fuel in the exhaust that will also cause backfiring. Different, but also common when coming off the gas.