Leakdown resuts question for the pros

Thermostats have a long history of being problematic right out of the box (all cars, not just Ferrari). It is recommended that they be tested before installation in a pan of water on the stove.

 

As well as the POS Ferrari pressure caps.

 

Wow! Radiator caps and T-stats are a long way from a leak down test. Such a convoluted path.

 

Yes thanks
I always use the exchange rate to my advantage

FOREX

 

I like using bars stop leak in all my cars as preventative maintience in the cooling system. You can get it at Walmart. It raises the temp of your cooling system since it clogs all the water jackets in the process. This way you are protected against the enrichment low temp fuel map.


I figure you would all benefit from some comic relief.... This is a joke.

 

With the 100psi numbers i would just drive the car and enjoy it. But just to be a PITA here is some stuff to discuss.

First which test do you believe and why?

I have never had a tester which could do meaningful low and high pressure tests. Pressure and Orifice size has everything to do with the readings. There is no standard I know of for low pressure tests. An FAA certified tester is very specific and can yield reproducible results which is why I use only that tool at the FAA higher pressure. Why us low pressure test? No one has ever articulated the reasons why but some famous people use only the low pressure test. I could guess that a rocking valve in a bad guide could be sealed by a high pressure test and thus fool you into thinking you got great leakdown. Well I can rock a valve by hand an feel a 0.001 play so that sort of negates that. A test is a great thing but never test the whole story. You still have to use your brain. It is also easier to do a low pressure test. Often you can put in 40psi and not have to lock or just hole the damper and get your readings. At 100psi you have to be pretty dead on TDC or the piston will move or you got to lock the crank near TDC. That is a lot more work and takes more time. Why use the FAA test protocol? Well first you got a certified tool with gauges that meet a specification and an orifice size that meets a specification and the device is certified. That means you have a tool that can give you meaningful results. If you are not using an FAA gauge there are no rules to orifice size. Leakdown is a "flow" problem. There are many things that effect flow results turbulence, pressure and orifice being 3 big ones.

For an additional headache you could start discussing the value of a "dynamic" compression test.

Oh and don't forget the effect of the lifters.

 

Yes so true

Bruce and I did a compression with a brand new snapon guage and I showed him how under exact conditions we got if I remember correct 20 psi variation on one cylinder

Human touch is such a huge part in this

Yes his numbers look decent I would drive it, give it an Italian tuneup and have a nice day

 

I couldn't justify taking that motor apart.

 

Rings are pressure activated. More leakage at them should be expected at a lower pressure. I always connect to a cylinder at 0 and slowly turn the pressure to 100 on the supply side while watching the holding side gauge. You can see rings unstick etc but if a cylinder has a problem I know it long before it gets to 100. I only turn it all the way up to be able to quantify it for the record.

Any measuring device can be used for outcome based results if you want to.

As to how the FAA does it? Well in many ways they are still stuck in 1942 especially when it comes to recips. Besides I don't know about you but an R2800 with 100 lbs in the cylinder is going to have a lethal surprise for someone when that 13 foot prop decides to whack someone and I don't want to be anywhere near it. 40 lbs is as much about safety as anything.

 

Were you still able to vary the leakage by side loading the one valve by hand or was it solid at 100psi?

 

FWIW, FAA specifies an 80 psi test, with minimum acceptable cylinder pressure of 60 psi which is 21 or 25% leakage depending on how you calculate it. Leakage would only be dependent on orifice size and the size of the leak, if there were no additional sealing due to pressure forces on the valves and rings, when actually calculated correctly. Unfortunately, most mechanics are not engineers and as a result, they are taught to read a gage and be done with it. This leads to different leakage numbers at lower pressure even if the size of the leak is fixed. Making the correct calculations leads to lower leakage percent. Higher test pressures leads to less error between correct and incorrect leakage calculations. However, since leakage percent is little more than an indicator of condition, the errors are not really of much significance.

 

Same motor as this one in post 1?
1- 4%
2- 22%
3- 11%
4- 6%
5- 3%
6- 9%
7- 10%
8- 5%

The second test must be after the Italian tuneup?

Should tests only be done by engineers? (giggle.....imagine that 3-hour report of results)

 

Mark, you have nothing to worry about. Do your major and enjoy your car. Your experience is exactly why scientist repeat experiments over and over again checking for consistency and deviation form the norm.

 

That is the conventional way, but if you want to removed pressure from the result you have to use absolute pressures. Absolute pressures are gage pressures + 14.7 psi. So convectional would be (100-95)/ 100 = 5%. Using absolute pressures you would have (114.7 - 109.7)/ 114.7 = 4.3%. Note that the addition of 14.7 in the numerator just cancels out since the pressure difference remains the same. But if you use absolute pressures when you test at different pressures the % leakage does not change with test pressure, all other things equal. I wrote a document about this last year. You can download it here: http://musicanddesign.com/Ferrari/Leak_Down_Testing.pdf

Again, all things equal, lower test pressure will yield higher leak down % if you use the conventional definition. But you may still see differences using absolute pressures if the cylinder/valves seal better at higher pressure. Not to mention that you can read the pressures more accurately at high test pressure since the same leakage would have a greater pressure difference between the gages.

 

We can only assume that Mark's ability to do the 1st test was equal to Mark's ability to do the last test. That said it is unwise to throw out data one does not like unless one is pretty darn sure they know where the errant data came from. A 4% leak on #2 but "play" I can feel with my hands while shaking the valve is a fail regardless of what the leak tester says. A test is not an end all be all. Passing a driver's test does not mean one can drive. I'm not trying to be debbie downer but you want to make sure the proper things have been considered so you can make an informed choice on how to proceed. In other words treatment is easy once the proper diagnosis is made.

 

The bent needle alone, on the very first test, makes me throw that tester and its results out.

 

Analysis paralysis.


Drive the car.