Ideal Compression SOHC

[Sedition]

What is "ideal" compression, in PSI, for the SOHC engine?

 

[deweyville65]

In my opinion, there is no "ideal" compression figure. There are just too many variables, the main thing is, the difference between cylinders. I would say, if the compression is, say, 80PSI, then that would be low. I like to see around 120 minimum, at 5000 feet elevation.

 

[Sedition]

these were my figures when I did my compression test:

1) 160 psi
2) 105 psi
3) 160 psi
4) 165 psi
5) 167 psi
6) 171 psi

So I'm guessing 160-170psi is good then, Except for cylinder 2. I removed the head and found the piston on #2 sits 5mm from the top of the block when at it's TDC position. I must have a bent connecting rod from when I hydrolocked my motor 10,000 miles ago.

 

[deweyville65]

You're one lucky man, if thats all it did.

 

[colintrax]

Sounds like you got pretty good compression, how many miles are on that engine? Even 80 psi will = a running engine, just a poor running one.

 

[deweyville65]

80 PSI was just an illustrative number. Not ment to reference anything.

 

[Sedition]

88,000 Miles, I don't think I'll worry about the re-ring kit then.

 

[colintrax]

I understand you were just throwing 80 out there, I was saying that it's even good enough for running.
And that's why you got good compression check it again around 300,000 and let me know

 

[2000StreetRod]

compression test

Although I've never seen it specified, good compression on the SOHC V6 would be 180 to 185 psi for a warm engine with the throttle plate wide open.

 

[FordGalaxie1963]

these were my figures when I did my compression test:

1) 160 psi
2) 105 psi
3) 160 psi
4) 165 psi
5) 167 psi
6) 171 psi

So I'm guessing 160-170psi is good then, Except for cylinder 2. I removed the head and found the piston on #2 sits 5mm from the top of the block when at it's TDC position. I must have a bent connecting rod from when I hydrolocked my motor 10,000 miles ago.

How did you hydrolock the cylinder? Was it a stuck injector? Also how well did the motor run with that compression variation?

 

[imp]

How did you hydrolock the cylinder? Was it a stuck injector? Also how well did the motor run with that compression variation?

A "stuck" injector would load it's cylinder with lots of fuel, but nowhere near enough to cause hydrostatic lock, because the fuel evaporates very quickly in a hot cylinder. A leaking head gasket can cause a cylinder to fill with coolant, then cranking the engine can lock-up the crankshaft and bend a connecting rod. Out-of-time valves can hit pistons, causing bent rods, broken pistons, bent/broken valves, etc. Mayhem.

 

[Mbrooks420]

A "stuck" injector would load it's cylinder with lots of fuel, but nowhere near enough to cause hydrostatic lock, because the fuel evaporates very quickly in a hot cylinder. A leaking head gasket can cause a cylinder to fill with coolant, then cranking the engine can lock-up the crankshaft and bend a connecting rod. Out-of-time valves can hit pistons, causing bent rods, broken pistons, bent/broken valves, etc. Mayhem.

You can hydrolock a motor with an injector that leaks after shutdown. Doesn’t take much liquid at all if the valves are shut.

Of course, I’d bet it was water intrusion.

 

[imp]

You can hydrolock a motor with an injector that leaks after shutdown. Doesn’t take much liquid at all if the valves are shut.

Of course, I’d bet it was water intrusion.

Very interesting thought. After shutdown, pressure in fuel rail and fuel line will "spurt" out a few ccs of fuel, then pretty much stop. Given combustion chamber volume of 40-50 cc, I don't imagine filling of the cylinder to cause lockup. Do not most EFI applications position the injector above the intake valve, where the atomized spray mixes quickly with the airstream? No airstream, spurt directly into cylinder? The valve would have to happen to be open. Likelihood of leaky injector "seeing" an open valve after shutdown? 1 in 6, 1 in 8, would happen only now and then, unless I'm missing something.

 

[Mbrooks420]

I’m not saying it’s common, but I have seen a bad injector put an amazing amount of fuel into the crank during troubleshooting.

 

[donalds]

the ford manual

 

[imp]

the ford manual



View attachment 325040

View attachment 325041

Yer a lifesaver!!

 

[donalds]

Yer a lifesaver!!

I'm just a standard American SOB

 

[imp]

I'm just a standard American SOB

Ahhh,,,, selling yourself short knowing ya know more than 90% of us!