26.5 m/s is kind of low as an arbitrary limit (maybe for a 150mm rod). I would up that a touch for the higher R/s or shorter stroke motors. I look at from the aspect of a 100mm 2.3 going to 8500 pretty regularly with a light piston. The 2.4 is swinging more weight and has the historic 8k rev limit. A long rod 2.4 would be more in the 85-8600 range which happens to be the traditional K24 (1.54) limit.

A street 2.0 has little problem revving to 9500-9600, my 2.2 seems to just keep going and going so I have it limited the same amount. Remember Marco's rev limits are based on experience not just math or a guess.

 

I think what TedB is getting at Aaron is there are mechanical limits... and then there are VE limits to a cylinder head. Rod to stroke ratio's help your mechanical limits, but you're still attempting to fill x volume through y valves.... you're going to reach peak efficiency at lower engine speeds as you increase the volume that needs to make it through the valves.

I guess that the big limiting factor to getting a 2300cc engine to make power at 9k is getting the head to meet the requirements. If we increase the displacement we start pushing the peak ve to the left and limiting the amount of power we can produce for the given cylinder head.

bah... I guess the climax of my mental masturbation has led me to the conclusion that my increase in stroke (and ultimately displacement) will be limited by the flow of my cylinder head. So I should first optimize the flow of my cylinder head...and then figure out what stroke/displacement will best use that air flow prior to 9k RPMS.

 

Gotcha...like in my car despite a ported head the power peak dropped about 5-600rpm to the left.

 

Ok, Marco's rev limits are configured around what he defines as acceptable, but for what type of usage and rebuild interval? Remember that 200 dragstrip passes is only 50 miles. Likewise, when a motor breaks, it's nothing Marco hasn't addressed multiple times previously, and he isn't buying parts at retail. I'm just trying to illustrate that there cannot be one rev limit that 'fits all' for any given combination.

In the road car world, the ~25 m/s region is noted as a practical limit across the board, from OEMs to F1. It's largely a function of rates of wear and the chance of catastrophic failure, and what is deemed as acceptable risk vs. reward. It doesn't mean it cannot be exceeded, but statistically speaking, one's pockets should be sufficiently deep. I make this point for the benefit of many here who ogle over things beyond the scope of their budgets.

Again, the intended application of this exercise hasn't yet been made clear, and that should be considered. There's a substantial difference between a vendor sponsored drag motor that is refreshed after every season for peanuts and beer vs. a road car engine that is expected to go 50k miles (or more) between rebuilds at retail cost.


The problem with an EVO head is that even when ported to the physical limit, it cannot be made to flow well enough to match even a bone stock F20C head, and that is just a reality for which the only workaround is larger turbos and/or more boost pressure. Not to mention, the relatively short rod stroke ratios of increased displacement 4G63s favor better low speed VE, and that has things going in the opposite direction. For these reasons, a 4G63 is a better street engine than an F20C, but it's never going to do some of the things an F20C can do.

It's just a world of compromises, but I think agonizing over certain minor details more or less results in agony. LOL

 

The other way to go about it would be to build a big disp lower revving motor which suites the head and the transmission and all parts life span and just change either the final drive with larger tires or use a different final drive gear ratio. For a street car more useable torque and the same HP up top with a wider powerband will always drive nicer and at the track it doesnt matter what you are revving to if the power and the speeds are the same. Take the load off the engine parts and increase reliability. It isnt like we are limited by stock gearing and tires sizes for some sort of class racing.

 

LR 2.4 with 156mm rods and a rev limit of 8-8.5K would be a great street motor. This approach is also a LOT cheaper and much more readily available and repeatable.

 

Great thread. I have been thinking about the same thing recently and why I started this thread about adding deck height to the 4G63/64.

I do agree with TedB on his comments about reliable engine RPM with the different rod ratios. It really matters what you are going to be using the car for. Those quoted RPM limits may be fine for a tracked car that will have it's engine rebuilt on a certain interval, but what about people who daily drive their cars and just want a powerful engine for the occasional track visit or people that road race, etc? You have to look at the wear factor and harmonics of the engine then. And the rod ratio is a major player there.

This link has been posted in a few threads on EvoM and is a great read:
link to paper - to stroke or not.pdf

I found this particular quote and graph very interesting and it shows exactly why rod ratio and RPM limits are so important:

The rest of the paper has some invaluable info. It definitely shows the point that TedB is making about reliable RPM and I completely agree with him. I wouldn't want the piston speeds and accelerations at the limits as proposed by the RPM limits that you have posted previously. The beating the bearings will be taking and increased side load of the pistions with the rod ratios just point to an engine that will not last that long. Of course this is relative to your goals for the car, but I always think about a reliable daily driver first, and a powerful car second.


Eric

 

In my experience and from what I've personally seen in the Oregon/Washington arena of built Supras, Evo's, SRT-4's, and Hondas.... a street driven built engine will last 20k miles. Usually not too much more and usually not much less.

I want to make clear that this isn't because the connecting rods failed, the piston collapsed, the bearings got beat, or the rings stopped sealing. Usually a built engine fails due to a vaccum reference line popped off, an injector failed, fuel pump failed, fuel was bad, and electrical issue (like cam synch), or the car was mis-shifted, over boosted w/out boost cut, the car was driven on a c16 map with pump in the tank, or the BC stroker crank wasn't machined correctly and the car looses oil pressure and junks the rest of the parts. Trust me I've seen and heard a lot of reasons why built engines get fubar'd. Rarely do they wear out. The list goes on and on. Usually it's not the hardware that gives up the ghost its the organic mass that pilots and maintains the engine that screws it up.

Eric,
An off the shelf wiseco with a standard length eagle rod (150mm) gives a compression height of 1.337" IIRC and weighs considerable more than a lightweight 1.012" CH piston. Not to mention a Carillo H beam is lighter than the eagle rod. As we all know F=MA.... we need to minimize any reciprocating weight to lower the over all force applied to the connecting rod fasteners and ultimately the rod bearings. I think the end sentence best sums up the information.. "Smooth transitions are much more important as RPM is increased and as piston/rod weight is increased. "

Judging by the R/S ratio graph that Eric posted from the to stroke or not to stroke thread... It seems 1.7 to 1.8 is more of a reasonable R/S target since I will be revving the crap out of it.

Using off the shelf components for the Long Rod 2.0L result in a pretty good r/s ratio. To follow my original thought of maximizing displacement while not limiting the engine speed to something below 9k... I think the 92mm setup has some notable worth.
OPINIONS?



Thank you guys for the great input/advice

Since people are asking for my intent...I daily drive a little green dodge neon. I'll drive the Evo when it's nice, when I want to go racing, or when I feel like driving chuckanut to work. I don't think any 700whp Evo can be considered as "reliable" when compared to a commuter civic or neon... so lets not get ahead of ourselves with this whole reliable term. In the same breath I also agree that theres no reason do design an engine with an inherent flaw.

 

This is practical ... for most applications anyway. F1 engines have R/S ratios north of 2.0 and the short strokes ensure they don't hit 25 m/s mean piston speed until somewhere above 16,000 rpm.


That's because something almost always breaks before they can wear out, and that is the fundamental weakness of casual engine building. Finding more power with a turbo engine is easy. Making the engine last while under power is not so easy.


Which is exactly why I paid a little more and went that route. Was it worth it? I don't know, but I feel that I did the right thing. I want my engine to last as long as possible.

 

I'm curious what I'm sacrificing as far as reliabilty for seeking a piston with a compression height of 1.012"? vs. the std 1.13" compression height stroker piston? I realize this will push the wrist pin up into the oiling ring (same as LS7)

Is the 1st ring landing thinner with the 1.012" CH piston? (From the top of the piston to the first ring)

Does anyone have any actual specs or pics of such a piston? JB?

 

I am with Ted on post number two. keep it simple with custom piston only.

Only custom engine I like is
94mm crank
2.4 block
156mm rod
custom piston with pin raised 3mm

 

Ring pack stays the same except for the oil ring which ends up having to have a support rail to make it all work. I'll send you some pix of what it looks like.

aaron

 

I'm going to Eindhoven, Colorado, and then Cabo San Lucas... so I won't be around until early March. Seems like a good time to order custom parts... waiting won't be a problem

 

why do that when you could run
4G64
94.00mm Crank
162.00mm Rods
Compression height 25.702mm or 1.012"
1.723 rod/stroke ratio
2235cc
8457RPM @ 26.5m/sec

 

Eric, I hope you get your motor build all figured out. I know this has been a topic of discussion for a long time. I'm sure you will have an awesome build and I'm excited to see what you actually decide to do! Keep me posted. I honestly like the setup that you listed in post #29, however I don't think you would be happy with that...

I'm in Fallon, NV right now and won't be home till the 29th... Call me tomorrow after work bro.

Mikey