Aaron mentioned this is another thread and it kind of sparked some questions... Before I came to the evo side of the house I was a Honda nut and use to have a k24/k20 along with a H23/H22 hybrid. That being said, the k24/k20 hybrid is almost the same engine comparable to the 4G64.

However, most turbo k24/k20 revs to 10k all day everyday and seems to have no problems in doing so. Then the NA k24/k20s rev to 10.5k. What makes the k24/k20 able to rev so high?

K24 - 99mm stroke, 87mm bore, 152mm rod, 1.54 r/s ratio

4G64 (LR) - 100mm stroke, 87mm bore, 156mm rod, 1.56 r/s ratio

To my understanding what limits revs are the large strokes with the high piston speeds; clearly not hurting the K24s... Even with a 1mm smaller stoke, it only changes the piston speeds by less than 2 ft/sec per given max rpms, not really anything if you ask me.

When looking at the rod/piston/pin weights, they are almost identical to what the evos are. Obviously it depends on the brand, type, length, etc... But they seem to be very similar if you build both with steel H beams or I beams. I don't see the rotational engine weight affecting their revving capability either when compared to the 4G64. I know if someone decided to run light weight Ti rods and pistons that will help eliminate a total of over 1000 grams of rotational weight compared to a std steel I beam and piston motor but it doesn’t however lower the max piston speeds that really effects the revving capability...

The 4G64 does give us the extra 6mm deck height to add a 156mm rod over the std 150mm rod allowing the 4G64 to have a better r/s ratio than the K24 but that is more of a longevity/less side load benefit than a over all high revving capability. Also when comparing a 1.54r/s (K24) vs 1.56r/s (LR 4G64) that is a very mild difference and shouldn’t change that much in the characteristics of the two motors!

The only things I can think of that could ultimately be limiting the 4G64 to higher than 8.5k revs could be the valvtrain, flow capacity of our head, and possible oil problems above 9k.

However Kevin Kiggly seems to have proven he can rev a std 2.3 to 9100-9200 for the whole past season and is in the progress of taking it even higher!!! Not sure if Kevin has taken the motor apart to check bearing wear and/or look for oil starvation (I'm sure he checks oil pressure at 9k though)...

Kevin seems to have laid to rest that a proper valvetrain/head can rev to at least 9k on a 2.3 or 2.4... Kevin also says that there is not a problem with our pumps going over 9k, however, at what point will our oil pump cavitate and lose pressure? I know the K24/K20 pumps start to lose oil pressure above 9k and the Honda guys are now using a modified S2K pump that allows them to have proper oil pressure to 10.5k on the K24.

Sorry for a godly long post but I thought about brainstorming out loud and seeing what everyone's point of view is on this. What is really allowing the K24 to rev 1500 rpms higher than the 4G64?

Mikey

 

There is the stigma of the 2.3L/2.4L not being able to rev above ~8500 RPM because of the bottom end and it probably is incorrect. There are big blocks with 4.5" strokes that rev higher then that. I think it's kind of a moot point though as the strokers I've been in drop torque badly at higher revs.

I think head flow and camshaft selection is probably the main problem as the lack of top end power likely discourages people from pushing them higher into the 9k+ range.

 

I believe its the fact that Honda guys have generally no idea what theyre doing or why they do it, and if they blow their motors up they can simply go find a new block for $48.16 and have it built for $19.95.




Mikey, your knowledge and logic is situated much better over here in the Evo world

 

^^^ How is the 4G64 bottom end balanced compared to the K24? H22A's, for example, needed balance shafts to reliably rev to 8K in factory trim, so that might be an indicator as to the difference.

 

Based on 167 trap speed, I'd guess that Kevin is pushing his setup a good bit higher than 9000 rpm.

I've had to push the revs on my 2.3l AWD DSM out to 9200rpm so I can get across the traps before hitting the limiter. So far I haven't seen any apparent ill effects on bearing life.

There is a fix for our Oil pump issues:



http://magnusmotorsports.com/?page_i...&product_id=35

 

Thanks diesel. I do however, miss the days when a full engine build was 1k instead of 8k...

Both from the facotry seem to be on point in terms of balancing and to my knowledge a lot of honda/evo shops don't balance the 2.4s in the first place when doing an engine build. I can't intelligently speak on the balance shafts, however there are plenty of evos reving 9-10k that don't have balance shafts, however the 100mm crank does add more vibrations.

Mikey

 

Balance shafts have nothing to do with balancing the rotating assembly. They are there to simply hide the vibration inherent to an inline 4 cylinder. You cannot eliminate that vibration no matter how well balanced the rotating assembly is.

 

John, not a bad way to spend 5k... I just threw up in my mouth!

Mikey

 

Correct, that I know. As I stated above you have more vibrations with the 100mm stroke than the 88mm stroke. However, I don't know if the vibrations due to removing the balance shaft have any effects on the longivity of the motor and the revving ability of the motor.

Mikey

 

Yep, competently ported K-series heads flow ~330 cfm, and that makes a substantial difference in how the engine behaves at the speeds in question.

 

Whats a fully ported Evo head typically flow?

 

This is a great discussion...
And Honda K-series blocks are not cheap...cost just about the same as a Evo block...

 

thats a $5000 fix....

 

On the same bench, with a CNC port (e.g. Headway, AMS) that takes it to the absolute limit, ~295 cfm around 12mm lift. The more common hand-ported heads flow somewhat less.

 

This basically. Now Im from a muscle car background, I can build a 350 small block an have it turn 10k all day long and not have to worry about it for a second. The limiting factor there is valvetrain, which is why most people dont turn 10k.

When I built my motor my dad asked what I was going to rev it to, when I said 7.5-8k he said why dont you upgrade the springs and retainers so you can rev it to 9k. When I explained the whole rod/stroke ratio he just looked at me an said why the **** didnt you build another chevy.

Anyways I believe sbr revs their 2.3l an 2.4l to 9 or 9.5k.