Tractorsport Flowbench Forum Archive

Posted: **Mon Aug 04, 2008 3:06 pm**

[color=#000000]This is a site I go to often as these guy's are way into making the HD (John Deer of motorcycle) make big power

Posted: **Fri Aug 08, 2008 6:34 pm**

Hi Rick, Being a retired engineer, I played with these numbers some myself. (I can hear Bruce laughing in the background now!) Using the calculator on the link to calc Lovell Factor and working with the results vs inputs it appears that the Lovell factor equation is:

L=K*(B^2*S*Nv*RPM)/Dvi^2

where Nv is the number of intake valves and Dvi is the diameter of the intake valve. B, S, and RPM are the usual. Working from answers back to equation also provides the K value as 3.33*10^-5 for L in M/sec. I don't know what good it is, but it was interesting!

By the way, my 100cc Honda pushrod has a Lovell factor of 55.20 for the baseline engine (as I run it). The calcs I used are on the linked spreadsheet. -- Doug

Posted: **Thu Aug 28, 2008 6:30 pm**

Doug,

This is awsome and remindes me of when my Dad would do Calculas problems over his morning coffee.

But i am still not sure "What a Lovell Factor is, or means?"

Rick

Posted: **Thu Aug 28, 2008 10:34 pm**

Rick, Something has been bothering me since I did this and looking at again today, I found it! The equation is wrong as the Lovell Factor goes down as the number of valves goes up. The right form is:

L=K*(B^2*S*RPM)/(Nv*Dvi^2)

This is Disp per cylinder per minute divided by the flow area of the valve(s).

I think that it is like Reynolds number or Prandtl number in aerodynamics. The numbers themselves have little meaning, but provide a way of comparing lots of variables on a common basis. I have no idea which way is good, but Formula 1 numbers are very large and Harley numbers are small so big must be better!

-- Doug

Posted: **Sat Aug 30, 2008 9:50 am**

If you're working with your pitot.....you're already targeting that....sort of anyway

77MPS = 252.62FPS [probably about ideal for HD drag motors]
70MPS = 229.65FPS [bit on the slow side]

Here's the thing with those numbers Rick.

Head flows xxxCFM. Probed with pitot it's right on your target......Carb and manifold killed off 20CFM....you just got bit...

Another detail you can watch out for is the port velocity may appear to be very balanced when probed with a tapered port opening manifold. Then when you insall everything else and reach through the carb, you may find the air isn't grabbing one of the walls the same way it did with your nice tapered flow bench test manifold.......Result = varied air speeds from one side of the port to the other.....You just discovered you needed to shape things differently...

Those calculators estimate what the engine wants. What the engine gets consists of the full system. Don't measure only half the system if you can measure with all of it.

Simplified way to look at it:

You travel 3 roads going to work. 2 back roads for 20 miles and then the Interstate for 20 miles. Boss is angry because you're late all the time. He calculates it should take you XXX Minutes to get there..BUT he's only including the interstate miles in his calculations.....

JMO
Larry C

Edited By larrycavan on 1220105028

Posted: **Sat Aug 30, 2008 10:33 am**

Posted: **Sat Aug 30, 2008 11:53 am**

John,

That's exactly what I mean. It's possible for the head to look too fast until you mount everything else up. Also, with PipeMax. If you use 100%Ve and look at your piston demand you get xxx requirement. Pretty good place to start.

Never set require CSA aside totally while aproaching an FPS too fast issue either. Remember we're talking "mean" vs "local"....

I had a head this past week where bare port testing looked great. Mounted up the rest of the system and discovered the manifold shape caused the air to favor one side of the port. Velocity profile changed completely.....

Edited By larrycavan on 1220111668

Posted: **Sat Aug 30, 2008 12:55 pm**

John, My Honda is a multivalve only if you count 1 intake and 1 exhaust.

The attached pic is my model, but NOT my bike. This is the original 1964 Honda Touring 90 OHV (aka CA200), not OHC Super 90. You DO meet the nicest people on a Honda!

Larry, I hope that head wasn't mine! My question is how do you probe for velocity profile with a carb and manifold on the head? The passages on my little engines are so small to start with I have trouble getting a probe in there, without other obstructions. BTW, did my stock head get there? (And how does it look?)

If I read you right, the Lovell factor is a REQUIRED value for the engine to make max power and, therefore a target to shoot for when working on the head. I'll have to look at some of the other equations and see if I can figure out how to convert the mean speed to flow and compare to the other values for required flow. HMMMM! -- Doug

Posted: **Sat Aug 30, 2008 1:45 pm**

Posted: **Sat Aug 30, 2008 9:38 pm**

Posted: **Sun Aug 31, 2008 2:18 am**

This is what we ran around on in high school. I think they had 27 hp and were 305cc Honda CB77 Super Hawk

John

Posted: **Sun Aug 31, 2008 11:26 am**

This is what I started out with. Suzuki T125 2 stroke / twin

Edited By larrycavan on 1220196456

Posted: **Sun Aug 31, 2008 11:52 am**

John, You really have to go to Bonneville. I inspected a 305 like yours, but it was BLOWN. The blower was an air pump from the emissions control system for a Porsche 928. It was an OPEN record so the guy just had to make 2 passes, but it was a really nice installation. The rest of the motor was stock and the owner was a little surprised to find out he had to tear it down to be measured for record certification. He said he had never had had it for a long time, but it had never been that far apart before.

Larry, Is that a recent pic and you still have it? BTW, how is the streetfighter project coming along? Last pics looked good!

Doug

PS - Unless you count a month in 1963 using a friend's Honda 50 step through with auto clutch and 3 speed a motorcycle, I never rode a bike until I was 50! Come to think of it, maybe that 50 was the reason I went to the 90 pushrod: old memories? Hmmmmm!

Posted: **Mon Sep 01, 2008 2:24 am**

hey now my first motorcylce was a honda c110 the 50cc pushrod manual clutch version with the up pipe got my first speeding ticket on that thing

Posted: **Mon Sep 01, 2008 6:31 am**

This is one of my current bike collection (I think I might have about 14 at the moment).

125cc and 30bhp in stock tune.

Tractorsport Flowbench Forum Archive

Lovell Factor - Port & Valve curtain air speed