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-   -   Sportster Crankcase Pressure / Engine Breathing / Wetsumping and Mods (

bustert 13th August 2019 14:51

actually, the readings will not be like a intake charge where you have an abrupt flow stop and some reversion.
the c/c pressure should remain fairly stable since you have a valve controlling it. remove the valve, then you will see fluctuations.
i used a valve on the first reading because it did not know what to expect. i did not use it afterwards. your orifice size is based off piston diameter. on the oil tank test, did not use one since the vent size was the restriction and basically i am closed ended.
what helps as you brought out is the size/range of the slack tube. the reading were well within the 15" model i have but it would pull the fluid out of it.

bustert 13th August 2019 14:57

i wouldn't put much stock into moco figures.
in the past, mfg's manipulated numbers to satisfy laws. case in point is chevy and notably chrysler understating hp. i often wondered why big brother taxed us on speed/power. i remember the suzuki b100p had a brake hp of 8 but the machine produced around 15.

shanneba 13th August 2019 15:16

Here is what I found in the Owner's Manual Specs (2003, 2004. 2007), Sportster Pedia (cam changes) and Hammer (head changes)


|      |        | compression | torque  |      |        |                          |                  |
|      |        | ratio      | Ft / Lbs | rpm  |        |                          |                  |
| 2003 | 883    | 9.0        | 49.0    | 4500 |  D cams |                          |                  |
|      | 1200  | 9.0        | 68.0    | 4000 |  D cams |                          |                  |
|      | 1200 S | 10.0        | 72.0    | 4000 | W cams  |                          |                  |
|      |        |            |          |      |        |                          |                  |
| 2004 | 883    | 8.9        | 51.0    | 4300 |  D cams |                          |                  |
|      | 1200  | 9.1        | 79.0    | 3500 | W cams  | Head change 62 cc chamber | larger 7mm valves |
|      |        |            |          |      |        |                          |                  |
| 2007 | 883    | 8.9        | 55.0    | 3500 | W cams  |                          |                  |
|      | 1200  | 9.7        | 79.1    | 4000 | W cams  |                          |                  |

Hippysmack 13th August 2019 15:41

Thank you!
I'm working on bringing in bustert's testing into the pedia.
If you guys who have the info in your owners manuals for the different years, please post it as I have parts books up to 2016 but only FSMs up to 04.
And even fewer owners manuals.

bustert 13th August 2019 18:12

personal library?
i might have a couple

Hippysmack 13th August 2019 18:41


Originally Posted by bustert (Post 5769951)
personal library?
i might have a couple

Yes Sir.
I need to create a space for a chart and I'm not sure how much criteria is needed to include but that determines the chart.

We've got some specs already in the history (individual) sections of the pedia already but it's not complete yet.
Click on a year model.

I moved things around and have the slack tube testing side by side now.
It's a lot better than having them separate.

dieselvette 13th August 2019 20:42


Originally Posted by Hippysmack (Post 5769833)
Scavenge oil drain?

I've been thinking there is higher or lower pressure depending on parts installed.
Whether higher or lower, they both pulse at respective pressure levels back and forth between pos and neg.
For argument sake,
One engine with a pulsating 5psi (5 pos-5 negative)
as opposed to the next with a pulsating 2 psi (2 pos-2 neg).
In a lab with one engine in a perfect environment, it may pulsate with a slight vacuum.
Different engines in the real world will have many different results based on the conditions at the time.
Results from higher vacuum or pos at various conditions.
Bustert's testing reveals the balance of pos and neg on his engine at varying RPM.
What's the actual flow rate though?

It's obvious from bustert's testing that pressures can be different within one machine.
Incorporate 2 machines with different parts and you should get 2 different results.
This takes testing to prove or disprove.

The balance tube is simply another form of pressure gauge. Anyone can make one with just a length of clear tubing and a ruler, and it is very repeatable. Using water, 28" is about 1 PSI. So busterts readings of just a few inches is a relatively insignificant amount of pressure in his cc (on average).

The pressure in the cc rises/falls with piston displacement of course. Omitting any blowby, this can easily be calculated if the volume of the crankcase is known (and we already know the displacement).

Let's just hazard a guess that the CC volume is 2400cc, witht he pistons at halfway. And let's assume it's connected directly to the breathers, and not to the rest of the engine. Bustert came up with avg pressure very close to atmosphere.

When the pistons go down, the volume reduces to 2400-600 = 1800. So pressure goes up by a factor of 1/3. Atmosphere is at 14.7 PSI x1.3 = 19 PSI. Minus 14.7, a gauge would read 5.3 psi

Pistons UP, volume is 2400+600 so 3000cc. 14.7/1.25 = 11.6 psi. Minus 14.7, a gauge would read 3.1 to the negative (about 55" water).

Im not sure that my formula is perfect, but it's close. I have no idea what the actual cc volume is either. Any bike with the same cc volume and displacement would go up/down by the same factor.

Now oncve that's understood, we can throw in the cam chest etc and relevant restrictions between the different cavities and how they affect the volume/pressure changes.

bustert 14th August 2019 01:14

in moons past, they used to kill cylinders by solenoid and lock out on the intake to make the 4/6/8 engines. the cylinders pretty much followed manifold pressure even though the pistons were changing volume, if it did not then the manifold would pressurize and kill live cylinder fill.
now days, they use lifter hydraulics to kill cylinders by taking out the stroke so the cylinder is closed. the gas is compressed and expanded as long as the lifter is out of service. testing show there is a negligible energy loss because as mr. hippy brought out earlier the compressed gas just returns the energy.
although there is varying volume, it averages out, the final pressure determined by the umbrella open/closing points.
while there is probably pulsation going on, it is the blowby volume which under normal healthy engine would be little.
one test can be done like the diesel engine wear test and that is to block all escape of c/c vapor and record highest reading developed. as the engine wears, the pressure will rise.
there is a test you can do on the volume out the breather ports and that is to use flow tube like you use to set gas flow rate when mig or tig welding.

Hippysmack 14th August 2019 01:18


Originally Posted by shanneba (Post 5769897)
Here is what I found

This is the conundrum:
The FSMs do not necessarily show consistent data with each other.
It appears at some point they tried to get dead bang on the numbers where in previous years they just rounded or nominalized them.
I have a 98 owners manual that is slightly different than the FSM but close enough.

Here is where I'm at so far.
Due to formatting, it's not possible to bring the chart into a post.
You can create a PDF off that page if you like though.
I haven't brought your info in yet but I will shortly.
But it appears somewhere between 2000-2004 they stopped releasing BHP (horse power)
Between 2010 and 2013, they stopped releasing torque data also.
04 torque for a 883, you've got 51 @ 4300, the FSM has 51 @ 4000.
Both figures come from HD.

60Gunner 14th August 2019 01:35

Not sure where the 9.1:1 compression ratio on an 04 1200 comes from. It was 9.7:1 on my 05.

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