Why do 2.4L rev harder?

[HKSZ]

Looking thru different forums and sites alot of people feel the 2.4 is a harder reving motor than the 2.8 why is this so?

[240ZX]

I wouldn't have choosen the words "harder reving", but possibly quicker reving! Why, because of a shorter stroke.

[MikeW]

Not sure what you mean by harder. The two engines are basically the same except for the fact that the L28 is bored out more and has a greater stroke. The resulting extra displacement produces more power at the expense of more resistance to throttle response due to the extra inertia and friction.

[HKSZ]

Yeah I was going to say spins up quicker, its just i've never been that impressed with a 2.4 compared to a 2.8 in standard form. The torque I get from an unmodified 2.8 in a rally car always impresses me over say the quick reving, highly modified L18 that I and everyone else uses in a p510 rally car.

My researching is trying to help me on my next engine build -

triple Webers on

a) 2.4L n42 with head mods

2.7L a 2.4 with L28 crank, 2.4 rods, 85mm milled flat tops, STD N42 head

c) 2.8L STD bottom end, N42 welded & mods

I've already got the cams and light fly

[jmortensen]

The one with more hp should "spin up quicker". The one with a longer stroke might very well have a lower rpm limit or redline. If your L24 spins up quicker than your L28, it's most likely due to the L28 not being tuned correctly.

This subject used to come up all the time at hybridz, with people saying that a 327 revs faster than a 383. Built "the same" this is not true.

[240ZMan]

When I first had my 73 240z I had the impression that the 2.4l somehow would "rev better" than an L28. If someone had pressed me, I suppose I would have pointed to the shorter stroke.

If asked today which to choose, I would say L28 unless you a) you feel you want to keep the same block that came with the car, or you intend to compete and the rules require you to stay with the L24. Otherwise, if your desire is to make more power, then there's no reason to not switch to the L28 assuming you can get a block for a reasonable price, which is usually the case.

As for how fast it revs, the flywheel weight, choice of pistons, tuning of the fuel delivery system etc will all have a major impact on that as well. My sense without having done any side by side testing is that a well sorted L24 and L28 will both have the same responsiveness to throttle inputs and both can be made to rev to levels beyond what most of us could live with on the street.

With a streetable cam that doesn't run above 7k rpm I can't imagine that an L24 has any significant advantage over an L28.

I'd choose your option C, just watch the compression ratio if you plan to use flat top pistons. I'm running that combination with a reground cam (284/284 with .480" lift) and have to back the timing to no more than 24 degrees advance to avoid detonation, even with premium fuel. Perhaps you have better "premium" where you are, but I'm guessing you still won't be able to run full advance. If you don't already have the head you might look for a P90/P79 and shave it.

[HKSZ]

Thanks for your input guys,I do believe that a STD 2.8 is handicapped with a double or triple dampner and a heavier flywheel 10.5 kg vs 9.5kg STD 2.4L.

More and more I'm leaning towards rebuilding my F54 bottom end and spending the big money on the head.

Drove a 240z yesterday with the 2.7L I mentioned, similar diff ratio to mine but it runs the 240 SU's were as my standard 2.8 has triple 40 webers. After all the machining and money gone into the 2.7 I can't say the two are worlds apart, mine still has the torque, perhaps carbs the advantage.

Don't have the original block, so numbers aren't an issue and alot of the classes these days are simply 2lt and over

[Force Fed]

My F54 block/N47headed 2.8 w/ SU's revs like a banshee, even with stock needles in the carbs.

[sblake01]

Stock vs. stock, and I'm talking about an L24E vs. an L28E, the L24E doesn't pull harder or rev harder or whatever term you like to use. In the case of my two cars, the L24E seem to 'rev quicker' through the gears because the 810 has a 3.70 diff vs. the 3.54 in the Z, same 81-83 5 speed, but the Z will easily outrun the 810. Just my personal observation which may or may not be applicable to this discussion since the Z is lighter, has a larger engine and the 810 is basically a box.

[John Coffey]

I've actually had experience on a race track with almost identically prepared SCCA ITS spec L24 and L28 engines with SUs in the same car. The L24 had a higher rpm limit (7,200 rpm vs. 6,750 rpm) and made more horsepower as a result (190 vs. 180). On the race track the L28 had faster lap times because of a couple corners where the L28's better mid range torque got it out of the corner quicker. On the long front straight the L24 could match the top speed of the L28 but it couldn't make up the corner exit speed difference. With gearing better adapted to each engine the lap time difference would have been less, but the L28 would still have been faster around the race track.

[soundmasterg]

As the saying goes, there is no substitute for cubic inches!

Greg

[Force Fed]

While we're somewhat on the topic, what is the rev limit for a stock 2.8 bottom end?