hausherrs

I am trying to estimate how many seconds the car was in the ranges below based on ignition #.


Range 4
Ignitions - 3445 Hour 581.9 (7400 - 8200RPM)
Range 5
Ignitions - 763 Hour 567 (8200 - 9000 RPM)

Thanks in advance,

Steven

boolala

Isn't it one ignition per RPM?

If so 581 ignitions/ 7400 RPM = 0.08 min = 4.8 sec

567 ignitions/ 8200 RPM = 0.07 min = 4.2 sec.

dD/dt

Three ignitions per revolution (not RPM). There are six cylinders, and each cylinder fires on every other revolution.

Range 4-5 overrevs are usually due to a missed downshift. The printout only shows the most recent occurrence. Considering that these happened at different times, it looks like the car was owned by someone who was unconcerned or unskilled regarding shifts.

No HTwo O

hausherrs, I hope you are not going to buy that car. Porsche would not even warranty that car, due to the over revs in range #4 and #5.

boolala

I'm not sure an "ignition" refers to the "ignition" of each cylinder individually. I.e., they may count an ignition each revolution not for each cylinder. Anyway doing it the other way:

So that would be 582 / 3 = 194 rev / 7400 RPM * 60 sec = 1.6 sec and

4.2 / 3 = 1.4 sec respectively.

No HTwo O

dD/dt, your are not 100% correct. The ignitions are stored cumulatively.

For example in the OP report:

Range 4
Ignitions - 3445 Hour 581.9 (7400 - 8200RPM)
Range 5
Ignitions - 763 Hour 567 (8200 - 9000 RPM)


There are 763 total ignitions in range #5 and the most recent one happened at the 567th operating hour.

Fin Fever

I may not be fully understanding your question, the answer is different if you want to know ignitions for one cylinder or ignitions for the entire engine (6 cylinders)

for any four stroke engine, 1 cylinder ignition would result in 4 piston strokes and therefore 4 revolutions
1 ignition = 4 revolutions

for a 6 cylinder engine, 6 ignitions occur during those 4 revolutions
6 ignitions = 4 revolutions

boolala

The question is not what "he" wants to know but how Porsche defines an "ignition."

RonCT

Looks bad to me, especially because Range 4 over-revs that aren't the same timing as Range 5. Often I'll see some Range 1, 2, and 3 that all happened at the same time, so there was one time when the owner bounced off the rev limiter hard (it happens and Range 3 can be hit even without a bad shift - I've seen them even in Auto / PDK car read outs).

dD/dt

You're absolutely right. I should have said that the printout shows only the *engine time* of the most recent occurrence. The number of ignitions is cumulative.

No.

Evidently none of us knows what Porsche defines as an "ignition," but let's assume it means the combustion stroke, just after the start of which the spark plug fires. Each stroke of a four stroke engine is one half of a revolution, not a full revolution. That means that one ignition is two revolutions. Since there are six cylinders, and each one fires 0.5 times per engine revolution, there are 3 ignitions per revolution. In two complete revolutions, each of the six cylinders will have fired once.

Back on topic, I agree with the others -- I'd walk away. This car wasn't well loved.

RonCT

Per Porsche in a boxer six engine there are 3 ignitions per revolution. So, 3445 ignitions at Range 4 is 1,148 revolutions or 0.14 minutes at 8199 RPM (assume the top of the range), which is 8.4 seconds. To me, that means a lot of time was spent there. Miss a shift and quickly push the clutch back in, maybe you'll spend a fraction of a second up there. But 8.4 seconds...

No HTwo O

Don't forget, the other condition that an over rev can happen is when the car has been spun and the engine gets spun in the opposite direction. Regardless, there are so many great Porsches for sale, there is no need to even consider this car.

boolala

Hey guys, this is the car that he already bought: https://rennlist.com/forums/7237980-post21.html

RonCT

Ahh, Option 1, return the car, get back the Cayman, and find another car without issues...

Edgy01

That you're even considering a car with so many overrevs is remarkable to me. This is the sort of information that one would use to determine whether to buy a car.

I have 1 ignition in Range 4, and my service rep says that can be in error--sometimes the machines throw an odd number.

Your engine sounds like it has been driven very hard and by someone who is clueless.

If this is now your car. Good luck. You will be living with a nightmare.