Engine compression numbers

i think it's less important what the actual PSI number is, as long as it's not absurdly low like <100PSI, and more about the variance between all the cylinders since each gauge used for the test could be calibrated differently.

From your numbers, it looks like a 2.3% variance (178-170)/(170+178) which would be a healthy engine.

 

Does look good from a variance standpoint but how many miles are on the car? Interesting that these numbers are about 25-30 psi less than my 360 when it had 5,600 miles on it. Different engine design but interesting to note. Yours makes more HP with 4 valves per cylinder compared to the 360 with 5. Another interesting observation that I made is that my car still felt like it was breaking in up till about 12K miles! It's times like this that we need some experienced wrenches to participate and extract the most value from a thread like this.

 

What elevation were these measured at?

 

Compression gauges are not accurate. They contain a Schrader valve which will sometimes mask a problem. To get a real accurate compression reading, you need to take it to someone who knows how to use an In-cylinder Pressure Transducer. You don't need to go to an "Exotic" Shop, just find a Tech who has the ability to use a Pressure Transducer.

 

Very good results

 

Said the guy at 5300' elevation

 

First, the percentage difference between cylinders tells a lot. The high value comes from the number of cranks. It's also important to watch the rise per crank. A high rise is strong compression. So, just posting the final numbers is just not enough information to properly assess.

 

Engine compression numbers can vary greatly from car to car depending on: gauge type and the method of the test. Some mechanics have a very specific method of performing a compression test without taking into account the many variables that can cause different readings: gauge type/construction, engine temperature, cranking speed (battery and starter motor condition), engine size, compression ratio, cam profiles/overlap.

I know mechanics that will only crank an engine over 7 rotations, because that is what they were taught. I crank the engine for peak compression reading on the first cylinder and count the number of rotations that it takes to get to that figure. I then crank the engine over for the same number of rotations for the rest of the cylinder. This is with the engine at/near operating temperature, battery at 100% charge (or with a jumper battery connected), and throttle pedal at full throttle.

Your numbers are roughly 30PSI lower than what I normally see in a 430 motor. I would not worry about it, all the numbers are very close to each other, the engines in these cars are pretty bulletproof, and the mileage of the car is very low.

 

Brian, I don't disagree but I will post my experience with a 355:

1) Open throttle vs closed, I have not seen any difference

2) If I did a CC on a 355 at operating temp, I would have 3rd degree burns



But, we are talking 430 here and I have no 430 experience.

 

Dave,
That is just my standard operating procedure for a compression test, and comes from working on a variety of older cars. On the newer cars it is virtually impossible to get the spark plugs out with the engine hot. Cars like 599 or a California take hours just to change the spark plugs.

Generally for the most part newer Ferrari's have engines that are virtually bullet-proof. With the exception of the crankshaft recall on 458/California the dealership that I work for has never had to do any engine work on a newer car. The only time there has been major engine issues is when a customer runs over something, rupturing part of the cooling system or engine lubrication system and then keeps on driving the car to engine failure.

Certainly there are engine issues like soft valve guides on 355/456/550, or engine damage from driving a car with broken headers/catalysts that should be considered, But for the most part there are other standard problems that each model should be checked for that are more prevalent.

On the newer cars, Ferrari has you perform a compression test by using a PicoScope with a pressure transducer that is screwed into just one cylinder. The engine is cranked and a computer program calculates the compression electronically. It works ok, but is a little bit of a pain in the ass, in trying to get the information out of the PicoScope and transferred onto a regular computer, as I am somewhat of a troglodyte.

https://www.picoauto.com/library/automotive-guided-tests/WPS500X-In-Cylinder-Compression-petrol-cranking