Why do some engines rev quicker than others?

[acf8181]

Just a random wondering I had the other day, some engines seem to rev up quicker than others, why?!

Like for like example that i've owned both of....

Pug 306 gti6/Xsara vts 2.0 16v = very good vs mk2 toyota mr2 n/a 2.0 16v = not good (slow and sluggish). Both similar weights of cars, and similar bhp output.

Other one i've owned that was good was a VAG 1.8T, obviously turbo in that case may help.

[Krikkit]

The lower friction/lighter the rotating components of the engine, generally the quicker it'll spin up on its own.

So an engine without too many accessories and a nice, light flighwheel will have easy revving characteristics, but a diesel with AC, PAS, Alt, water pump etc all going and a heavy DMF in the way it will be harder to spin it up.

[Benbay001]

acf8181 said:

Just a random wondering I had the other day, some engines seem to rev up quicker than others, why?!

Like for like example that i've owned both of....

Pug 306 gti6/Xsara vts 2.0 16v = very good vs mk2 toyota mr2 n/a 2.0 16v = not good (slow and sluggish). Both similar weights of cars, and similar bhp output.

Other one i've owned that was good was a VAG 1.8T, obviously turbo in that case may help.

My MR2 revs very quick imho.

[HemiCommander]

Ratio of rotational inertia (including rotating engine mass, cylinder/conrod weights and flywheel) to torque. Torque is not constant over the rev range either so the instantaneous rate of rotational acceleration will be proportional to instantaneous torque over the rotational inertia.

[bicycleshorts]

acf8181 said:

mk2 toyota mr2 n/a 2.0 16v = not good (slow and sluggish)..

The MR2 has a long 2nd gear so that it hits 60mph without needing a 2nd gear change. At least mine did in NA form. [Assuming you're talking while moving (rather than sitting in neutral/with clutch in - see replies above if that's the case)]

I certainly wouldn't call it "slow and sluggish" though.

[PhillipM]

Add in transitional mapping/fuelling, throttle body size/opening rates, etc. And in most stuff with electronic throttles these days, that godawful half-second lag they use to smooth inputs from Numpties out.

[peterbredde]

Good question. I once had a V6 galant that seemed to rev very quickly. That, and the beautiful engine tone made for very addictive playing with the throttle whilst tinkering.

[Baryonyx]

Benbay001 said:

My MR2 revs very quick imho.

My MR2 Turbo had a really sharp throttle for a turbocharged car. It was utterly fantastic, it was practically at N/A levels of response. My 106 Rallye takes it a step further, with an extremely light flywheel, a freer flowing exhaust, and a small engine driving few ancilliaries; it's a crazy little thing on cam.

[Oilchange]

fresh oil will help too, especially if it hasn't had it in a while, reduction of internal friction

[rohrl]

Oilchange said:

fresh oil will help too, especially if it hasn't had it in a while, reduction of internal friction

Appropriate username.

[Superliminal]

No idea why, but these are the best and worst in my ownership - both 1.4 petrols.

Worst - Lupo 1.4 16v. Felt reasonable when in gear but when out of gear it seemed to take an age to build the revs.

Best - Citroen AX GT. If I didn't know any better I'd swear it didn't have a flywheel. It revved like a motorbike.

[brillomaster]

might have something to do with drive by wire throttle mapping - some cars have a slow throttle response in lower gears, so older cars with an actual cable connecting the pedal to the throttle might seem to rev up faster.