which would rev faster (Page 1/2)
BingB DEC 19, 03:09 PM
I know there are many factors that determine how fast an engine will rev, but all things being as equal as possible would a 2.4 liter four cylinder engine rev faster than a 2.4 liter in line 6?
Patrick DEC 19, 05:15 PM

quote
Originally posted by BingB:

I know there are many factors that determine how fast an engine will rev, but all things being as equal as possible would a 2.4 liter four cylinder engine rev faster than a 2.4 liter in line 6?



I suspect the lighter, shorter crankshaft and two less reciprocating pistons/con rods of the 4-banger would allow it to rev faster than an inline 6.
BingB DEC 19, 07:10 PM
This is way above my tech level, but I also figure the 4.

The individual pistons would be smaller and weigh less in the 6, but overall there is more mass with the longer crank and more moving parts.
82-T/A [At Work] DEC 19, 07:40 PM

quote
Originally posted by BingB:

I know there are many factors that determine how fast an engine will rev, but all things being as equal as possible would a 2.4 liter four cylinder engine rev faster than a 2.4 liter in line 6?




Are we talking about the GM LD9 2.4 Twin Cam? Because that's an awesome engine... or at least, it can be made to be an awesome engine with some very light modifications using stock parts.
MarkS DEC 19, 08:18 PM
Maybe ask a BMW guy. They have both inline 4 & 6's. We have 2 BMW 6 cyl turbos in our stable but no BMW 4cyl. Rotating balance may play into it if only from a vibration standpoint. We've had the BMW 4 cyl in loaner vehicles but were pretty much unimpressed.

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1965 Tempest 400 CID
2018 Chevy Colorado Z71 3.6
2017 BMW X3 3.0 T
2015 BMW 535iX M Sport
2008 G6 GT "Street" Coupe 220K miles
2005 Buick 3.6 Rendezvous 235K miles

82-T/A [At Work] DEC 20, 08:00 AM

quote
Originally posted by BingB:

I know there are many factors that determine how fast an engine will rev, but all things being as equal as possible would a 2.4 liter four cylinder engine rev faster than a 2.4 liter in line 6?




I'd like to add to my original post... just want to better quantify what we mean by rev faster.

Do you mean:

A - The ability for the motor to get up to it's redline more quickly?
B - The ability for the engine to have a higher maximum redline?


For A... to achieve engine rpm more quickly, it largely has to do with reciprocal weight... the less weight of the rotating mass (which includes everything from the flywheel to balancer assembly) allows it to get up to maximum speed more quickly. In this case... it doesn't really matter if the engine is a 4 cyl or a 6 cyl... so long as both rotating assemblies are the same weight (in which case, if they're both 2.4L, then it's probably insignificant).

For B... to achieve a higher engine top speed (redline), it largely has to do with engine balance. An inline 6 cyl engine... all things being the same as the 4 cyl, will have a better balance due to the mass being more equally distributed across the crank. In an L configuration, generally pistons are matched in pairs of 2. That means two go up, two go down. In a 6 cyl engine, you have two up, two down, and two in the middle... which helps distribute the load across the crank.


But again... what it really comes down to is what 2.4 L4 you're talking about, and what 2.4 L6 you're talking about ... as they both may not be built and designed the same.
Hank is Here DEC 20, 10:20 AM
There are too many variables undefined

The largest factor (assuming all others being equal) is....

What is the bore and stroke of both engines? Are these motors square, over square, or undersquare. There are many different ways to get to 2.4L which will have very different effects on rev'ing.
maryjane DEC 20, 04:54 PM
More interested in which will blow up first...
Patrick DEC 20, 06:09 PM
maryjane DEC 20, 10:45 PM
the crankshaft kept turnin long after the thrill of runnin was gone....

I've seen a couple of diesels run away and come from together, one lots bigger than that little popcorn engine.

The worst tho, was a USN 6-71. Small engine room space, with 4 of those N90 injector nozzled 2100rpm screaming Detroits (a pair each on the starboard and Port propellor shaft) and, a 4-71 running a ship's service generator all in the same little low overhead crammed full machinery space. It was noisy even when everything ran right, and HOT.

For whatever reason, one day one half of one of the paired 6-71s took off, dragging the other one's rpm up via the shared gear box.I felt the craft lurch forward too. Closed the air box on the unaffected engine but about that time, the skipper shifted the gear box into N and the bad engine took off over 3200 rpm, gave up the ghost and most of it's internals. There just was no where to hide. Pieces (and HOT Oil) flew everywhere.
I ain't never forgot that one.