Of course they don't, but they help "smooth" things out, which in turns makes things last longer, especially at higher rpm's. If they didn't, then I'm sure engine manufacturers wouldn't be incorporating them into the design of their engines. So...yeah, it's fine to run the engine without them, but for how long is the question. Most people that remove the balance shafts do so for a performance build, so I doubt they're looking or expecting to get 100k+ miles out of the engine like Honda and Mitsubishi design them for. I suppose I could be wrong about that though.

 

I dont trust balance shafts, they turn twice the speed of the crank so at 9k there spinning 18k. Thats FAST, whens the last time you heard of an engine failing because it didnt have balance shafts? But I can remember a few that had balance shaft failures and ruined the motor.

 

Ted, so a head like yours (Headway -295 cfm 12mm lift) at what given rpm on a 2.4L would the head begin to effect power? Those heads are usually good to 10,000 on a 2.0 so figure 8500 for a 2.4 before a significant lose in top end performance?

I would like to know what Kevin is doing to his head that he thinks he can rev to 9400+ however he is also running 14mm lift...

Mikey

 

2nd that

 

I wouldn't consider 14mm lift unless I had flow data to justify it.

As for where the very best flowing Evo heads will begin to choke with a 2.4 all depends on VE potential of the rest of the equation. The better it is, the sooner it happens.

 

Never, but you're also not going to have a catastrophic picture worthy engine fail with the balance shafts out like you would if the balance shafts themselves failed while in there. It'll just wear out the wear/friction surfaces in some form or fashion quicker than it would with the balance shafts in place. How much quicker I have no idea, but I bet the folks at Honda & Mitsubishi R&D know the answer to that.

Also.....you do raise a good point about the balance shafts spinning twice the crank. I'm sure if you're rev'ing the engine over 9K, then you're spinning the balance shafts beyond what Honda and Mitsu designed/engineered them for, so just like any other OEM component they have their limitations.

 

Balance shafts do not smooth out anything relative to the rotating assembly. The bearing loads seen by the crank and rod bearings are completely unaffected by balance shafts. B-shafts WILL NOT increase motor longativity.

They are strictly for NVH (Noise, Vibration, Harshness) improvements for driver comfort.

To me, B-shafts are a HUGE liability and I have pulled them on every car I have owned. You have two primary methods of failure, both of which will cause engine damage.
1. Bearing failure
This leads to oil contamination that will ruin the rest of the bearings in your motor and eventually lead to a seized B-shaft
2. Belt failure
This probably kills more T-belts then anything else and if you break a T-belt...yeah...

They don't belong in a 9k+ RPM motor at all.
Enough B-shaft talk.


While it's not really related to EVO, does anybody know what the max CFM you can get out of the 1G and 2G head respectively? I've always been a fan of the smaller ports of the 2G and EVO and I'd never build a 2.4L. However, I wonder if the 1G casting would allow a larger port that would better accommodate the 2.4L.

Port volume seems to be the biggest issue with the EVO on the 2.4L. You can only get so much volume out of the runner before you run into a water jacket. While bigger isn't always better, if you don't increase the volume in proportion to the increase in displacement, you will choke the motor and that is where the limit on the EVO port seems to be relative to the 2.4L.


Admittedly, I have not been in a lot of 2.4L Mitsu, but the ones I have been in all feel the same. Awesome torque that falls flat on it's face above 7k. 2.0L vs. 2.4L with similar setups, the 2.0L walks the 2.4L on the freeway every time. The 2.4L usually does better at the track though as most people have trouble with driving a car correctly and the added torque hides their inadequacies.

 

The difference is in the head.

 

Mikey,
I had this exact conversation with my Honda mate the other day.
He said the answer was "Metallurgy"

In the late 80's, Honda poured millions upon millions of dollars into their engine development. The scientists brewed up exotic metals and alloys for their whole engines that were better than the competition. They completely dominated in the following years.
Then look at the NSX that they released in '92. It completely dominated the european cars (ferrari etc), even though it was a "cheap" supercar.

When honda created the first vtec engine (89 honda civic?) it was producing the highest BHP/Litre.

From what i understand, the B18C engines (integra's) have similar rod/stroke ratios at the K20/24 engines. Stupidly high piston speeds.
But like you've said, they love it. and they do it all day, every day.

 

I wish my lawnmower had vtec...for those extra thick patches of grass of course. Sorry bad joke but couldn't resist poking fun (even though I own a Honda HA!)

Seems you bring up a good point Mikey...I have some friends in the K20/K24 scene and it's amazing how efficient they are and how much power they make. They all attribute this to how well their heads flow. I have had a very similar conversation before about this with them.

So what we need to do is figure out how to get an F20C head to bolt to a IX block. Now nobody has tried cross breeding before...that redefine the whole "frankenstein" term. I think it's well within your budget eh???

 

honda's give good head!

 

I'll just make a brand new head! F20C sounds great!

Mikey

 

Honda cylinder heads are better and always will be.

 

I don't think it's a case of not being able to safely rev to 9500 rpms, its been done already. I think it has more to do with it being to expensive. Because not only do you have to address the head plus add in aggressive cams which is probably some where around 3200.00. You also have to upgrade to a billet crankshaft and stronger rod bolts and head studs talying up to another extra 2000.00. So now your spending an etxra approx cost of 5000.00 to rev your engine 500-700 rpms. Thats why evo owners are so hated, a build for less than 7500.00 puts you in the tens on stroker motors and 9s on a 2.0 I can hear the haters yelling now what more do you want! Reving to 9000 - 9500 rpms will be by no means a budget build but it would be the best choice for the ultimate street/race car.

 

Great discussion!
have few questions:
1) Any idea what the stock evo head flows vs. the highly ported 295cfm head?
2) How many 2.4s have revved that high in the past?
3) How many of those 2.4s have failed due to high revving? and what were the guesstimated causes?
4) Any comparisons done between the honda and the mitsu bearings?

Hope Spyros from Extreme Tuners find this thread and comments. He seems to have alot of knowledge when it comes to building high revving engines.