Coyote gen 3

[Stangludde]

Hi guys! New to the forum. I wonder what compression values a gen 3 engine should have? Looking to buy a 2000 mile old second hand engine. The owner did tests for me and sent videos of pressure up to about 250 psi. Is this normal? I heard it should be around 200 but like I said, I am new at this

 

[Hoytster]

I've seen quite a few compression tests on the Gen 3 coyote being in the 230-250 range, though I haven't seen a definitive reason why they read that high sometimes. I wouldn't be concerned about the 250 psi reading, I would pay closer attention to the readings between all the cylinders. They should all be within 10% of each other.

 

[Stangludde]

Thanks for your reply. The seller tested all 8 and they where all around 245-255 psi. So within margin. Should i go for it then in your opinion?

 

[I Bleed Ford Blue]

The gen 3's have a static compression of 12:1, that's the biggest reason for the high numbers on a compression test.

Just for reference, the gen 1 and 2's are only 11:1

 

[Stangludde]

The gen 3's have a static compression of 12:1, that's the biggest reason for the high numbers on a compression test.

Just for reference, the gen 1 and 2's are only 11:1

Yes I know. But 12 times atmosphere should only be around 180-190 psi if I calculated correctly. That’s why I am a bit concearned. But I guess since all 8 cylinders have the same compression it should be fine anyway?

 

[I Bleed Ford Blue]

Cam timing will also affect the readings. Lobe separation angles and valve overlap plays a big part. Engine masters did an episode where they explained it and how it worked, but I don't remember the specifics.
Also the weather plays a part, if the barometric pressure is high, it will give higher than normal readings.

In the end I think it's a healthy engine, the readings are within 10 psi of each other, whereas 10% is allowable. That engine is around 250 psi so a 25 psi range is acceptable, you got 10, so you're golden. Buy it and enjoy your car.