Why is it a lot of older carbed engines seem to be able to redline in an instant. Even the larger V8s have no problem doing it. I could understand a four banger, but a V8? The newer FI engines don't seem as able to do it, though I can't imagine there being that much of a delay on the injectors, is there?

Thanks for having fun with my curiosity.

 

the newest v8 i have owned is a 1995 460, i never really noticed much difference.

but when i think, my 1971 chevy has a 454 in it, it did rev up alot quicker, but of course it was modified to do so.

 

Most engines today have a lighter rotating assembly, plus if they are automatic, they are swinging less weight around than a manual with a heavy clutch and flywheel.
The delay on new generation engines is due to the fly-by-wire throttles used on most engines. The computer looks at how hard and fast you hit the pedal, then opens the throttle to how much it thinks you want.

 

Hmm good points. I was also thinking maybe since carbs are usually (always?) mechanically pumped, they would instantaneously be able to draw in as much fuel as they wanted.

Both of my family's ex 454s would rev fast compared to my 4.0L and mom's 5.3L. My dad's 350 will out-rev them both, but it redlines at like 4K lol.

 

Do you mean in neutral or in gear? In gear it's going to depend on not only the fuel inj. system, but gear and power to weight ratios. It seems many older trucks came with not only lower gears, but also shorter tires. Both add up. In neutral it still depends on power/weight (of the internals) to a point, but a lot is w/ the computer.

I've noticed some newer engines don't seem to like it if you just stab the throttle. Not really a bog, more of a hesitation to make sure that's what you actually wanted (maybe?). You can actually get a better/harder launch by rolling into the throttle with some it seems.

Some also take redline to mean where it will upshift (in an auto). If I remember correctly my 4.6 revs about another 1K RPM before it shifts at WOT compared to a FI 5.0 truck. That's ~20% give or take.

I've driven a Hennessy 650R Viper (actually had more work done after that package) that idled at just under 2K to stay running. It would rev up in neutral like mad compared to a stock Viper, you could barely get your foot to the floor before it hit. It was also a completely different engine at that point though, maybe not the best example. Pretty sure it had been whittled on and changed up down to the crank and block at that point.

BTW I got to drive it to get an alignment after the owner ran it over a curb and thru a fence. You DON'T want to have to buy a hood for a Viper. I don't remember exacty, but it was pretty close to the price of my new V8 Dakota at the time. Well over $15K retail...paid out of pocket.

/rambling
//a bit tipsy, sorry

 

Good points. Ford_Six is right on about the 'fly-by-wire' throttle. I'm still not really used to it on my truck. My 94 Bronco (5.8) had no delay in revving, my wifes 97 Mustang GT (4.6) did rev a little more slowly than the Broncos 351.

I also feel the throttle system on my Super Duty affects the cruise control, it's not as precise as vehicles I've owned in the past. Maybe a fly-by-wire issue as well?

Interesting thread Ranger Pilot.

 

Everything else being the same, a modern computer-controlled SEFI engine w/electronic ignition will get to the redline smoother and faster than a carbed/distributor-equipped 70's powerplant.

However, when you start getting into performance mods (and, conversely, wear-and-tear issues) then you're essentially changing around the whole equation, and so the general rule doesn't always apply.

 

I'm referring to neutral revving with no load of the vehicle, just the engine itself.

Now I know a four banger would beat a V8 probably. But I've got a sound clip on my computer of a 77 truck that seems to happily bounce from idle to redline almost instantaneously.

And let's take for example a common engine, say the 302. One old school carbed one, and one of the later FI ones. Which one would rev faster? I know the FI would rev smoother because of the fuel injection for obvious reasons, but would the carb hit the line faster?

 

Add something new:

Through a fun mishap today with my truck (new gauges requires new tools sometimes), I drove our GMC a couple of times. It's got a 350, old school, throttle-body injection. Now does TBI function just like a carb, only the fuel is shot into the carb rather than the pump pushing it in? I notice that 350 revs faster than my 4.0L, but I expect it to rev faster based on it's history.

 

On the newer motors (post OBDII) the engine management has some say in how fast- and how high- yu can rev that motor in neutral. Quite a bit of say, actually.

 

With the older engines (non fly by wire, less computer controls) the big bore, short stroke is a major factor. The SB ford and chevy was well known for quick revving. This is know as over-square, bigger bore than stroke. Most big blocks have a stroke in the 3.75~4.25 range, where as some of the small blocks have strokes in the 2.75 range.

These quick revving engine will usually rev higher and make much less torque down low. They work great in a light weight car and were very popular in trans-am racing.

I have a 700cc motorcycle that has a 2.5 bore and a 1.9 or so stroke, it revs to 10,000 rpm real quick. Not a lot of torque down low