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just pull that engine , removing stuff "in the car" is possible, remounting it "prof" wise is another story.
I did it already outside, just a jack & hoist. Half day of fun . ( lift was occupied )
What concerns me at the moment is that you are not reporting excessive oil consumption or clouds of smoke billowing out of the exhaust that are typically commensurate with degraded compression due to mechanical wear.
I do no know what cranking compression pressures your model year should deliver and presume it should be in the region of 180 psig. The first point of note is that the pressures recorded are reasonably constant. Not sure whether those numbers were attained hot or cold not that it should make a great deal of difference. I would also note that if you had ring or piston issues I wonder if you would still achieve the "wet" numbers you report. Also note that it is more important to have consistent numbers - some test rigs read low. Do you have another engine you can test on to see if they also read "low" on that motor.
One thing that perhaps should be considered at this stage is to ensure that your timing belt has not skipped a tooth on the crank sprocket for whatever reason. If this happens cam timing will be retarded and this will drop the cranking compression pressure. I am not overly optimistic this is the case but for sure well worth ensuring such has not happened.
Carbon deposits can build up in the ring lands and that can also cost some compression loss. Giving the system a clean is not exactly over taxing considering the work involved in a total strip down.
You should also ensure that you are not looking for performance that simply does not exist. Have you checked 0 to 60 times against those specified for your model?
The tests result are from a hot engine and the timing belt was checked and found to be ok.
Will give the system a clean as you and others suggest.
On paper the 3-speed 4.7L 310hp Euro will do 0-60 in 7.2secs. Mine is at about 12secs so I'm sure it should be better and that those missing HPs are in there somewhere! - even 40 years later.
The tests result are from a hot engine and the timing belt was checked and found to be ok.
Will give the system a clean as you and others suggest.
On paper the 3-speed 4.7L 310hp Euro will do 0-60 in 7.2secs. Mine is at about 12secs so I'm sure it should be better and that those missing HPs are in there somewhere! - even 40 years later.
That sure is a heavy loss time wise. Did you get chance to check the cams are indexed correctly?
I very much doubt that kind of deficit is recoverable but...?
You also need to eliminate any other potential problems with the engine management system. Hopefully you will get some more "to check" suggestions.
On paper the 3-speed 4.7L 310hp Euro will do 0-60 in 7.2secs. Mine is at about 12secs so I'm sure it should be better and that those missing HPs are in there somewhere! - even 40 years later.
There's more wrong that a couple of stuck rings to loose that much acceleration....
There's more wrong that a couple of stuck rings to loose that much acceleration....
Most likely more than one cause for sure Greg.
Have the following items on my radar to check and eliminate/repair as needed.
Torque convertor - possible cause - too expensive to try anything yet and is deemed a long shot by many - yourself included.
A/T Bowden cable - tightened and gears are shifting as they should.
Compression - poor results - will engine flush and most likely pay somebody to pull the engine and replace rings and check valve etc.
Vacuum circuit - checked and no leaks found.
CIS - pressures were off - WUR rebuilt now and pressures set. Not tested yet as off the road while waiting on new power steering hoses but should improve the situation.
CIS - new check valve fitted at FP and seal kit on pressure regulator. Has made no difference to hard warm start but can live with that.
CIS - Currently fitting an A/F meter to monitor mixture while driving - this should shed some light and verify warm control pressures.
Timing - checked by a mechanic who found the timing off by 2 teeth on belt. Corrected now but no big difference in performance noted.
Ignition - new coil and plugs. HT leads tested for resistance - all ok now.
If adding oil to perform a wet compression test improves the dry test reading by 40psi, doesn't that indicate 100% that the rings/cylinder wall are the cause of the 40psi loss?
If adding oil to perform a wet compression test improves the dry test reading by 40psi, doesn't that indicate 100% that the rings/cylinder wall are the cause of the 40psi loss?
It does..but.."simple" cylinder issues are not 40psi loss, without a lot of visible evidence out the back end...
Most likely more than one cause for sure Greg.
Have the following items on my radar to check and eliminate/repair as needed.
Torque convertor - possible cause - too expensive to try anything yet and is deemed a long shot by many - yourself included.
A/T Bowden cable - tightened and gears are shifting as they should.
Compression - poor results - will engine flush and most likely pay somebody to pull the engine and replace rings and check valve etc.
Vacuum circuit - checked and no leaks found.
CIS - pressures were off - WUR rebuilt now and pressures set. Not tested yet as off the road while waiting on new power steering hoses but should improve the situation.
CIS - new check valve fitted at FP and seal kit on pressure regulator. Has made no difference to hard warm start but can live with that.
CIS - Currently fitting an A/F meter to monitor mixture while driving - this should shed some light and verify warm control pressures.
Timing - checked by a mechanic who found the timing off by 2 teeth on belt. Corrected now but no big difference in performance noted.
Ignition - new coil and plugs. HT leads tested for resistance - all ok now.
What else is there??????
Sorry, but....
Cam timing off two teeth from stock.
Moved back to factory settings....
Without any performance change is: Absolutely, completely, totally impossible.
Sorry, but....
Cam timing off two teeth from stock.
Moved back to factory settings....
Without any performance change is: Absolutely, completely, totally impossible.
You need to look there, again.
@GregBBRD
Below is a screenshot of a video the mechanic sent me before the timing was addressed.
He said the pointer should align with the line between the O & T.
To correct this he had to move the belt by "2 teeth on the camshaft side"
There was no performance difference, good or bad.
He was recommend by other Porsche owners so I had no reason to challenge him on this and I have been working on the basis that the timing is correct.
Are we talking about the same teeth?
Does the misalignment in the photo equate to 2 teeth in your eyes?
Either way there is doubt now so I have another job to do.
That is correct.
But the "correct difference" would be a night and day difference.
You need to pull the upper two plastic timing covers, turn the engine to the line between O and T and see if the cam timing marks now line up. (This only occurs every two revolutions, so you may have to turn the engine two times to find the cam timing marks.)
It does..but.."simple" cylinder issues are not 40psi loss, without a lot of visible evidence out the back end...
But...
Hi Speed toys - sorry I dont fully understand your point....
Do you mean ring wear could not cause 40psi of loss?
Or that 40psi loss via ring wear should result in a far more visible plume of smoke form the exhaust?
Hi Speed toys - sorry I dont fully understand your point....
Do you mean ring wear could not cause 40psi of loss?
Or that 40psi loss via ring wear should result in a far more visible plume of smoke form the exhaust?
It should result is yes, ,much more visible signs.
So where did the lost psi go? Why is the compression x.y% lower than new.
Bad rings, worn pistons and cylinders, leaking valves.
For the answers we use a leakdown test.
Not only do we collect the basic percentage of leakdown, we determine where the leaks are.
With this information you can make an intelligent decision of where to spend your money.
Last edited by Speedtoys; Nov 3, 2021 at 05:26 PM.
