when does high rpm become worthwhile

[vr41mpg]

ok so I am not sure where to begin my question... bare with me here

The whole point of this is to figure out an engine configuration that maximizes displacement without sacrificing RPM Limit with a given turbocharger lbs/min set in mind. We wouldn't want to build a 4g64 2.1L destroked with an 11,000 rpm limit if we were planning on using a 16g turbo.

I guess turbo size plays a determining factor, right? Like people say there is no reason to rev a 16g much over 7k on a 2.0, if even that much, correct? What about a 16g on a 2.3? When does that run out of breath, like 6500rpm or even lower?

So its based upon the displacement of the engine and the choke point of the turbo? And the cam profile just moves the powerband up or down within the set range that is determined by displacement and lbs/min of the turbo? Is this right?


Well lets say we were building a 4g64 block with a 97mm crank and 156mm rods putting us at a 2.3L with a 1.608 ratio... higher than 1.5 ratio 4g63 2.3L 8500rpm but not as high as the unnecessary 1.7 ratio 2.0 4g63 10,000rpm. This 1.6 ratio puts us just around 8800 rpm limit.


Well then, lets take two turbos such as the HTA82 70lbs/min and HTA86 75lbs/min. I am trying to figure out what combination makes the most sense. At what RPMs would 75lbs/min and 70lbs/min run out of room on a 2.3L engine? If the answer is 10,250 and 10,750 rpm, then I have nothing to worry about but if, coincidentally, the 70lbs/min runs out at 8500rpm where the 75lbs/min is good up to 8800rpm, then it makes it so that you could either run a 4g63 2.3L with 8500 rpm limit and a 70lb/min turbo OR a 4g64 destroked 2.3L with a 79lbs/min turbo. Phew... I hope this made sense.



Basically when it comes down to it I am trying to figure out at what RPM will a certain lbs/min turbocharger fall off on a 2.0, 2.2, or 2.3L engine. Is there some kind of formula or should I just look at other people's dynographs with similar setups, .

 

[delta448]

The formula you are asking for is a compressor map. You can calculate everything you need if you have the maps for the compressor wheels you are hoping to use. This page explains it all in detail.

I'm also wondering where you're getting the max engine speed values in your example from? Are you interpreting solely based on the rod ratio? Also, where are you getting pistons for a 97mm crank in a 2.4 block?

 

[vr41mpg]

The max RPM i came up with was based on recommendations from various experienced vendors who offer different combinations.

This is the GSC 2.2L kit with a 94mm stroke and 156 mm rods, recommended with a 9k RPM limit
GSC Power-Division 2.2L XR-1.7 4G63T Stroker kit for the for the Evo 4-9 :: DSM/EVO 1-3 Stroker Kits :: Mitsubishi Lancer Evolution 1-3/ DSM (4G63) :: Mitsubishi :: GSC Power Division: Performance Camshafts, CNC Cylinder Heads, Race, Engines, Parts


This is magnus' chart of their options with the recommended RPM Limits
http://magnusmotorsports.com/wp-content/uploads/2010/02/DetailedEngineList.pdf

And here is R/TErnie's thread where he did some awesome work already
4G64 w/ 96mm Crankshaft? Great idea? - evolutionm.net




As for the pistons,

I figured magnus could have a set of Ross made or Jackson auto Machine could have a set of Venolias made, or someone else could have a set of Wiseco HDs made. I am pretty sure there has to be some out there since K1 makes a 97 mm crank.



You are right that compression maps I need to learn.

This will tell me whether a turbo at 30 or 35 psi is better for a 2.1L revving to 11,000 or a 2.3L revving to 9,000? Maybe the same turbo can get both jobs done but to me it seems like there would be a different ideal turbo for these two setups.

 

[yhype]

a 2.1L at 11,00rpm with probably be making the same amount of exhuast flow of a 2.3L at 9,000rpm. So its more of would you rather have a 2.1L 11,000rpm engine to make the same amount of power or a 2.3L 9,000rpm engine. Are looking to just to find and turbo that you use to its absolutely fullest potential? Most people have certain power goals for their cars and then select a turbo based from that.

 

[vr41mpg]

"2.1L at 11,00rpm with probably be making the same amount of exhuast flow of a 2.3L at 9,000rpm"

this is what I am trying to figure out. how do you know this? and if this is the case, its a no brainer to me. the 2.3L will have more power down low and create the same power at a lower RPM up top, saving strain on drivetrain parts since you are 2k rpm lower. On the other hand, if the 2.1 at 11,000 actually were to flow more then the 2.3L at 9,000, then that would be a different story.

 

[yhype]

I dont really know but any smaller engine will need to make more rpms to keep up with the power of a bigger engine as your trying to figure out. But I would call some of the known DSM engine builders and ask them as they would be the ones that know. But most people just build 2.3L engine for the little more torque and faster spool times. If each engine (2.1L vs 2.3L) were built identically i would imagine you could just multiply the 2.1 displacement times the 11k rpm and then multiply the 2.3 displacement times 9k rpm to get a basic comparison.

 

[vr41mpg]

that seems a little too simple but for what its worth....

2.1L or 2093cc X 11,000rpm = 23,023,000

2.3L (97mm crankshaft in a 4g64 block with 156mm rods) or 2307cc x 8994rpm = 20,749,158

2.2L (92mm crank in a 4g63 block with 150mm rods) or 2140cc x 9500 = 20,330,000

By these numbers, the 2.3L is flowing more at 9k limit then the 2.2 at 9.5k limit and would also benefit from more low end torque. Am I wrong about this?

idk wtf these numbers could possibly mean other than a 2.1 at 11k is outflowing a 2.3 at 9k which is the most you would run these motors respectively. the question that comes to mind is... is this extra flow significant enough to warrant building a longrod 2.1 if your only going to run a 79lbs/min turbo? what turbo size (lbs/min) would correlate with each maximum output of each engine? for example maybe the answer is 79lbs/min for the 2.3 setup and 90lbs/min for the 2.1 setup? or would you benefit more from the low end torque of the 2.3 spooling the turbo sooner?


keeping me up 2:45 am. ive caught the bug

 

[ed1380]

The difference between 2.3 and 2.1 is in the transmission. Do you want to snap parts from the torque? Or do you want to have a hard time shifting at 11k?

 

[TunaTalon]

Just spinning the crank faster does not necessarily mean more combustion air and more power. The intake valves in the 2.3l stroker are the same size and have the same flow limitations as the 2.1L. The following is from http://www.kidzuku.com/StrokeOrNot.pdf and the engines compared are from my first hot rod coupe and my current stroker Talon.

When air flow reaches mach one (equal to the local speed of sound) the flow is "choked" increasing the pressure drop across the valve just puts more energy in shock waves but the air flow does not increase. According to the Mechanical Engineers Handbook (19) engines have the best volumetric efficiency with a mach index of 0.45 to 0.5. While a mach index of 1 is a hard wall, the choking effect from high mach flow starts about 0.6. Above a mach index of 0.6 the volumetric efficiency of any engines falls off rapidly.

The state-of-the-art in car engines is now four valves per cylinder with overhead cams as in the 4G63 pent roof engine. See figure 2 at right and compare to the Hemi combustion chamber above. Notice how the two large valves in the hemispherical chamber leave much of the combustion chamber as "not valves". The pent roof design modifies the hemi just enough to fit two more valves in the combustion leaving little area that is not filled with valves.

A lot has changed. That 1951 hemi weighed in at 960 pounds and made 180 hp at 4000 RPM from its 331 cubic inches. With a few bolt on modifications the 122 cubic inch 4G63 easily makes 400 hp at 8000 RPM while weighing in at only 300 pounds. But the speed of sound is still the same as in1951. The hemi has an intake valve mach index of 0.51 at the 4000 RPM where max hp is developed. The 4G63 has the same .51 intake valve mach index at 8000 RPM. When the 4G63 reaches the mach index of .51 it's turning twice as fast as the hemi and with 15 pounds of boost is breathing more than twice as many pounds of air than the 331 hemi at 4000 RPM.

Boost is good. Aside from the history lesson, the message I get from this is that no matter how strong the main caps, or how well designed the pistons, there is a hard performance wall where the intake velocity approaches sonic flow through the valves. The 2.0L 4g63 with stock valves reaches 0.6 mach index at 9600 RPM. The 2.3L stroker reaches 0.6 mach index at 8400 RPM. Trying to spin the 2.3L stroker much past 8400 RPM will just hit the wall quicker as volumetric efficiency drops off.

The hemi powered 1948 coupe was a hoot to drive and that memory has influenced all mods to the 98 Talon.