Silly question...

[Phantom440]

...I've tried to search on Google but only get answers about cars with computers, so I figured I'd go to the experts!
Why do some engines take longer to fall back to idle speed after you give it some revs?
For instance, with race engines, you hit the gas and it falls back to idle almost immediately, but other cars, it takes a couple of seconds to go back down to idle. Is this a cam thing? Rotational mass? Lightened vs a heavy flywheel?
Thanks for any info!

 

[super-bee_ski]

I would say it was (is) fuel flow specific in conventional engines...something with the fuel delivery system?

Why?
Hmm, that's a silly question...LOL

No, but RACE specific engines need to REV quickly..
They need to RPM real quickly and that would be CAM specifics...

More "HELP" needed on this one....

 

[67 coronet]

it has to do with rotational mass.a true"race"motor has much lighter parts allowing it to spin up faster.also has to do with the cooling fan set up a lot as well.you would be amazed to compare eng rev speed changes with and without a mechanical cooling fan attached.

 

[shorty64]

meesa tinkin it might also have to do with emission controls vs regulations, etc.

have an okie day!

 

[Rick@Laysons]

Higher compression in a race engine will slow the light weight rotating mass quicker compared to a street engine with a lower compression and a heavier rotating mass.

 

[69Runner]

All of the above, plus with a carburetor when you let off the gas the throttle plate closes, whereas in newer cars the fuel flow and throttle are controlled by computers based on engine maps and feedback from sensors.

 

[Phantom440]

Thank you!!
So, if I wanted to build a big block that had that sound, unlike, say, my old 318, I'd need a carb (was going that route anyway), aluminum forged pistons/con rods, high-ish compression (want to run street gas) and an electric fan set up?

 

[roadrunner69440]

Higher compression in a race engine will slow the light weight rotating mass quicker compared to a street engine with a lower compression and a heavier rotating mass.

Absolutely correct, you can also get the similar affect with Efi but the iac valve won't let it just fall to idle immediately , it will stay up a couple hundred rpm then fall to idle . The bigger the mass, the longer to slow down, simple physics