I removed this from another thread and thought it should have it's own Beginning. It's a little long but it's the only way I know to explain what I think I read.. I'm looking at optimizing my current 96" evo.. AM I on the right path. I truly value your opinions. Thanx

We are always hearing "I want more Power" and what really really forget to look at is where we want more and how to increase the maximum efficiency of the motor at that rpm where we want more.

I believe that we cannot improve performance without improving efficiency.... As we all know it takes many components and lots of calculations to improve on both of these area's, "Power and Efficiency" But without a doubt we all know it's in the heads........

So I have been messing with both of these calculators that show actual flow coefficients and where they come into play.
"Lovell Factor, Inlet Valve Mean Gas Speed" and
"Inlet Valve Mach Index Calculator"

What I am going to show is how they are used to calculate what components in the cylinder heads (valves) i will need, matched to camshaft that I am using to produce the best power and efficiency I can muster out of the motor at a given rpm range. Naturally we know that we need a certain amount of compression necessary to match the cam we chose based on the range we want our best power. Based on what I've read, mean gas speed is the actual speed the air and fuel mixture will flow past the valve and into the cylinder and to produce the most efficient power or burn. I will be looking at a range of speed from 70 to 77 m/ps. Keep in mind that the higher the gas speed the more restriction there is in the port and at the valve..

The Mach index I will use for this scenario will be a coefficient of .6
"The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off." quoted from RB racing calculator.... where that index actually comes from I'm not sure. I am using the information that i read. I am not an engineer......

So here's the scenario of my current 96" Evo.

In the this first calculation my 96"er with 1.90" intake valve at various rpm ranges (where I want my power). All the following calculation are done with RB Racing's calculators... starting with the
"Inlet Valve Mach Index Calculator" www.rbracing-rsr.com/machcalc.html

bore size is 3.625 inches with a stroke of 4.625 inches and has 1 inlet valves with a diameter of 1.90 inches. Running a Mean Valve Flow Coefficient of .336 inches at 5200 RPM, the inlet valve mach index is 0.603 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off.

Now if I was to run in the 6000 rpm range for peak numbers without changing the valve size you will see how it will increase the co-efficient but will actually decrease the efficiency.

bore size is 3.625 inches with a stroke of 4.625 inches and has 1 inlet valves with a diameter of 1.90 inches. Running a Mean Valve Flow Coefficient of .336 inches at 6000 RPM, the inlet valve mach index is 0.696 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off.

To be able to get back to the maximum volumetric efficiency of .6 @6000rpm I would need to increase the valve size to 2.02"

bore size is 3.625 inches with a stroke of 4.625 inches and has 1 inlet valves with a diameter of 2.02 inches. Running a Mean Valve Flow Coefficient of .336 inches at 6000 RPM, the inlet valve mach index is 0.616 . The mach index for maximum volumetric efficiency is .6 . Beyond .6 the volumetric efficiency falls off.

So based on these calculations it is safe to say the if I wanted to run my motor for peak efficiency at 5000 rpm a 1.90"valve would work perfect for my bore and stroke.... If I wanted the motor to run up to 6000 rpm and retain the same amount of efficiency I would need to go to a bigger valve, a 2.02" But don't forget it's the cam grind that decides my rpm range...

Now for the "Mean Gas Inlet Valve Speed" dubbed the "Lovell Factor" as used here www.rbracing-rsr.com/lovellgascalc.html
The speed I am basing my info on is 70-77 m/ps is in the scenario of the Formula 1 engine. Again I am using my motor and am trying to configure max power and efficiency.

Inlet Valve mean gas speed is defined by five variables which are defined as:
Bore-- 3.625"
Stroke-- 4.625"
Valve Diameter-- 1.90"
Number of Inlet Valves per cylinder: 1.
Peak RPM: 5000
With the "lovell factor" calculator, these numbers produce a gas speed of 71.27 m/ps. and will work very well. Now if I pushed my max rpm to 6000 rpm my gas speed will increase dramatically to 85.52 m/ps but that would change the way that the fuel would atomize with the air and will not burn as efficiently as it would at 71 m/ps and create less power.
Now if I want to keep my m/ps at or around 71-77 @6000 rpm I would need to increase my valve size or match a proper sized valve to my application and rpm range. In this scenario a 2.02" valve will work very well in maintaining the desired speed. which would be 75.66.

Remember all these calculations are used to determine what we want our motor to do and at what rpm range. This is why we need to match parts because a matched system will out perform one that is not. And of course a good port job is necessary but I'll leave that to the pro's

Now this is the way I understand what I have read and believe it to be true. If not please let me know... This is a forum and it is where we learn... Looking Forward....

 

Seems to me there are two ways to approach this conundrum, the scientific and the empirical. While your study of those various websites etc will undoubtedly make fascinating reading and improve knowledge, we have access to a few expert tuning shops who can precisely predict engine performance, based on their extensive experience of getting results. It is routine around HDF to read of members with highly tuned and much bigger engines getting great fuel consumption, comparable to stock bikes, which indicates they are also getting improved efficiency. We'll ignore the effects of EPA regulations!

So while it only costs time to study the subject and to better understand it, I'm old enough to have learned to bypass that and contact a lifetime expert! Although we own 'Evos' which have been on the planet for a lifetime, we also have access to the very latest technology in camshaft design and other top expertise. The likes of Scott at Hillside can probably turn around your engine for you, at modest cost, with some head work, high CR pistons and a Woods cam, transforming your performance, putting an idiotic wide grin on your distinguished visage and achieving improved efficiency at the same time.

Today we can have performance not available to the engineers at the time our engines were originally designed. A win-win.

Just a thought!

 

I read a book years ago when messing around with my old Camaro called "Performance With Economy" I believe it was one of David Vizard's (hope I got that right). Changed my whole outlook on building engines. Everyone loves numbers, especially bigger numbers on the dyno sheet, but what good is 140hp at 6500 rpm if you never ride at 6500 rpm. I agree with the point you are getting at, if you achieve maximum efficiency where you use your engine then you are making all the power you can at that point. I find what you have posted very interesting because its puts mathematical formulas to the ideas I have running around in my head. There is actual proof to what should work and what may not for the goal you're trying to accomplish, instead of "this guy who used to live across the street from my ex girlfriend's grandma knew a guy that worked with this dude that hung out at this biker bar and one of the guys that went there used to race bikes and he said you should always........"