darwin_evo

What is the highest rpm recommended for this engine?? should rev more than a 2.3 because of the long rod no?

Tks

JohnBradley

iTrader: (30)

8200 or so on average and it seems that the math would allow somewhere around 8700. That equates around 9500 for a 2.0L for reference.

BLKCarbonEVO

iTrader: (2)

Just to expand on what Aaron said. The 8200 limit is the point that reliablity is still high based on piston speeds and load. Sure you can rev higher but remember that stress, over time, will destroy a well built motor. So the goal is to find a well rounded rev limit that is fun and safe at the same time. It looks as if 8200 is about right. 8700 on the other hand is in the load 3 cat with the highest stress levels that I for one, don't ever want to put my LR2.4 through. I'll have my daily limit at 8200 and my track limit max of 8500 (but if I get 4.11 gears I will trap below 8500). A lot of that depending on the turbo and if it even makes power up that high... I don't have a HTA3586 like some people... cough cough

Darwin_evo, Here is the load chart that R/TErnie posted in another thread so you can look at the load cat per the different stokes. Load 2 is all I would personally ever run the below strokes to daily on the street, however at the track I would push closer to Load 3 Just because I want my LR2.4 to last, I'll prob rev to 8000 most of the time.

Stroke - Load 1 - Load 2 - Load 3
100mm - 7892 RPM - 8285 RPM -8746 RPM
94mm - 8219 RPM - 8629 RPM - 9108 RPM
88mm - 8573 RPM - 9000 RPM - 9500 RPM

Mikey

darwin_evo

Tks for all the info. It seems though that above calculations only took into account the piston speed, what abt rod/crank ratio?? the higher it is the more you can rev your engine, but that's not been part of the equations you referenced.

BLKCarbonEVO

iTrader: (2)

ok, what does having a better rod/stroke ratio really do? Do you have lower piston speeds at the same given rpm when comparing a 150mm rod to a 156mm rod? Also what about the long rod allows you to rev higher? Do you understand what benifit a long rod gives you? It is late and I'm tired

Mikey

JohnBradley

iTrader: (30)

Acura/Honda B18C1 (GSR) hasa 1.58 R/s and revs to 10,500 with supporting mods. Reciprocating weight is the danger zone on revs, the R/s is how fast the cylinder walls wear because of sideloading.

Since max piston speed is achieved earlier with a shorter rod, you can make a bad head work better or use the long rod to really make a good head work.

s.e.a.n.

iTrader: (10)

Nice numbers.

darwin_evo

That's what i meant... since you have a longer r/s (than with a 4g63 block), this will decrease the side load on the cylinder wall and thus allow you to rev higher than if you were running a 150mm rod no?


Tks

BLKCarbonEVO

iTrader: (2)

Correct, kinda, but the lower piston speeds are more so the reason we can rev higher, the reduced side load is just an added "comfort and Longevity benifit" if you will. The longer rod does reduce side load so that you are not tearing up the cylinder wall as bad as a 4G63 motor with a 150mm rod (moving the wrist pin further up in the piston resulting in a 1.13CH). The nice benefit of the longer rod is that the piston speeds at any given rpm are lower than a 150mm rod motor. So based on piston speeds alone increasing the rod from a 150mm to a 156mm allows for 200-300 more rpms. The other thing to look at is your rotational mass. The long rod has more rotational mass, not by much, but we kinda burn at both ends. Together, both the lower piston speeds and the reduced side load are what make the LR2.4 more reliable and safer to rev.

Mikey

R/TErnie

iTrader: (32)

The equation I used to come up with those numbers takes into account R/S ratio piston weight, PE rod weight, etc.

I set the maximum piston force equal on all three engines and this is resulting RPM you can rev to.

JohnBradley

iTrader: (30)

Good to know

tscompusa2

iTrader: (22)

aaron ygpm ignore the others i sent and read the remote one. nice numbers btw

n2oiroc

iTrader: (33)

doesnt a longer rod decrease piston speed at the top of the stroke and increase it at the bottom?

BLKCarbonEVO

iTrader: (2)

Yes you are correct. With a long rod the piston travels from BDC to 90-o BTDC faster than a short rod and travels slower from 90-o BTDC to TDC. A longer rod tends to have better combustion in the high rpms than a shorter rod

You need to remember that the "mean or average" piston speed is not just the speed of the piston at the TDC/BDC of the bore, but the piston's full motion of travel from TDC to BDC and back to TDC... Mean piston speed will remain the same between the different rod lengths as long as the stroke remains the same. Peak piston speed on the other hand is the fastest that the piston travels (fpm) within a given stroke, and the longer rod will lower the peak piston speeds.

For example: Center line @ 90o 7500 rpm

Stroke / Rod Length / Rod Angle / Peak piston speed
88mm / 144mm / 17.07 / 2728
88mm / 156mm / 15.76 / 2100

Notice the difference in peak piston speed by just changing the rod length. The longer rod the lower peak piston speed at the same given rpm vs. a shorter rod with all values being equal. At the same time while reducing the peak piston speed which is equal to the level of mechanical stress exerted on the piston and wrist pin, the rod angle centerline angle is reduced as well, resulting in less side loading on the cylinder walls. The longer rod will have less centerline angle for the same crank angle than the shorter rod and therefore has lower side loadings

Mikey.

n2oiroc

iTrader: (33)

shouldnt we worry about peak though? it seems as if peak will be the same no matter the rod length.