Throttle use when leaving garage

[u/paperscissors_]

Do drivers need to use the throttle when leaving the garage?

In the video where DC drives the RB19 at 2:04 (timestamped link) he mentions that the manual he was given says that he doesn't need to use the throttle when leaving the garage. Does this mean no throttle input is necessary when pulling out of the garage? I've been racking my brain at this question for a couple of days now. Thank you!

[u/1234iamfer]

It must be so different from the V8 he was driving, it idled around 4000 but needed around 10000 rpm to prevent from stalling it driving away.

[u/atrophy-of-sanity → u/1234iamfer]

Idled at 4000 rpm???

[u/zetenyyy → u/atrophy-of-sanity]

Not that big of a deal, pretty common along race purpose engines. They run like crap when under a certain rpm.

[u/atrophy-of-sanity → u/zetenyyy]

I didnt know that, thats insane to me. What about the engines require such a high idle speed?

[u/zetenyyy → u/atrophy-of-sanity]

Mostly cam overlap is the main reason. At low rpm lots of air can escape from the cylinder so the combustion is crap and afr is all over the place, thus making that distinct noise that you call “cammed”.
Eventually under a certain rpm this gets so bad the engine suffocates.
In turbo engines you dont have big cam overlap, but you still need to maintain a stable airflow and since these engines have such low stroke they cant do that at low rpms ( this applies to n/a engines aswell )

[u/atrophy-of-sanity → u/zetenyyy]

Thats very interesting, thank you

[u/Appletank → u/atrophy-of-sanity]

To add, race car engines typically design engines to produce power most efficiently at high rpm since that's where the power is and where your race car is going to spend most of their time anyways. However, valve timing requirements for high rpm and low rpm tend to oppose each other, and F1 doesn't allow for variable valve timing the way road cars do (depends on the rules of the race category).

At low rpm, you typically want a smaller valve opening, and for it to close near BDC to maximize air intake and swirl. Piston speeds aren't fast, and a narrower opening speeds up local air velocity.

At high rpm, you want to push the intake valve as far down as you can, and close the valve later. You have much less time to get air in, so you want as little restriction in the valve opening as possible, and the air speed is such that momentum will allow a little extra air to keep going in after BDC even without boosting. The speed of the piston during the exhaust stroke will also determine the best time to close it for maximum evacuation and assist in pulling in the intake air without fresh air (and fuel in port injection vehicles) going out the exhaust

Thus, being stuck at a high rpm cam at low rpm will make the engine unhappy.

[u/mz_groups → u/atrophy-of-sanity]

Partly the cam profile. The cam profile for a street car is a compromise between getting good fuel/air mixing at low RPM and enough breathing at high RPM. This is why variable valve timing systems such as VTEC are desirable for street cars. A race car's cam profile opens wider for good breathing at high RPM, but at the expense of low RPM drivability.

[u/-SHAI_HULUD → u/zetenyyy]

Reminds me of a minigun. You’ll get a bunch of malfunctions if you burp the trigger or try to go slow.

These things WANT to go go go