9 replies to this topic

[cpdenis]

I performed a compression and leak down test on my 111k mile 99' motor.

Compression Test
I brought the engine to operating temperature.
Removed all spark plugs and disconnected coil pack.
Did not open throttle body
From front of car to rear. Please correct me if I have it wrong.
Cyl#1-185 / Cyl#2-175 / Cyl#3-180 /Cyl#4-185

Leakdown Test
Set Gauge to 0, turned engine to DTC, connected gauge to engine spark plug adapter.
LeakDown came out as follows.
Cyl#1-85% / Cyl#2-55% / Cyl#3-35% /Cyl#4-35%.

Are these numbers possible? Big disparity between compression and leakdown results?
What would good pro numbers look like?
Thanks
CP

[Austin Robison]

With leak down numbers that high you may have been at TDC for the exhaust stroke (exhaust valves open), otherwise I'd be suspicious of your gauge. For my ~100k motor when it was cold I was around 15% for all of the cylinders. A warm, tighter engine should be far less. I'd be curious what kind of leak down numbers pro motors put down as well.

[cpdenis]

Austin, I suspect operator error as well on the leakdown test. I'll try it again but it will have to be cold. You posted compression numbers in the 200s for your motor or I think I read something like that.
That being said I also wonder what the Hp gain is between my 180s and a pro motor if all else is equal.
I look forward to all answers, suggestions, tips in rebuilding the lower end.
CP

[Glenn]

With leak down numbers that high you may have been at TDC for the exhaust stroke (exhaust valves open), otherwise I'd be suspicious of your gauge. For my ~100k motor when it was cold I was around 15% for all of the cylinders. A warm, tighter engine should be far less. I'd be curious what kind of leak down numbers pro motors put down as well.

> than 7% it time to consider freshining up!

[James York]

With leak down numbers that high you may have been at TDC for the exhaust stroke (exhaust valves open), otherwise I'd be suspicious of your gauge. For my ~100k motor when it was cold I was around 15% for all of the cylinders. A warm, tighter engine should be far less. I'd be curious what kind of leak down numbers pro motors put down as well.

I had less than 3% across the board on a Sunbelt that had over a year of racing...

[Jim Drago]

In my experience, some of the more inexpensive leak down testers can give crazy results as well, no idea what type you used.

[Danny Steyn]

Compression is low for a '99 but the leakdown numbers are not real - your compression numbers support much lower leakdown percentages

[ChrisA]

I performed a compression and leak down test on my 111k mile 99' motor.

Compression Test
I brought the engine to operating temperature.
Removed all spark plugs and disconnected coil pack.
Did not open throttle body
From front of car to rear. Please correct me if I have it wrong.
Cyl#1-185 / Cyl#2-175 / Cyl#3-180 /Cyl#4-185

Leakdown Test
Set Gauge to 0, turned engine to DTC, connected gauge to engine spark plug adapter.
LeakDown came out as follows.
Cyl#1-85% / Cyl#2-55% / Cyl#3-35% /Cyl#4-35%.

Are these numbers possible? Big disparity between compression and leakdown results?
What would good pro numbers look like?
Thanks
CP

CP, you should have done the compression check with the throttle open. You should re-do the test. The engine should be at operating temp, disconnect the fuel pump relay and run the car till it dies. Then disconnect the coils, pull all plugs and open the throttle and check away. I like to hook up the battery charger to keep the cranking consistant.

[cpdenis]

Thank you all for the help. I will give it a try again. Unfortunately, I've already taken the radiator off and some other peripherals so I won't be able to test it at operating temp.
CP

[FastM3]

+ 1 on Throttle full Open. Remember the engine is just an air pump. If it can't get air you wont get compression.