If you need to know how much compression you sould have - Max RPM - look here

[mthieme]

I see the questions to these answers come up a lot.
Specifications are from my 1989 OMC manual. Good for generic use though.

2.3 4 cylinder with 8.5:1 compression - 130 psi - 4200-4600 WOT
4.3 V6 - 160-175 psi - 4200-4600 WOT
5.7 V8 - 155-175 psi - 4200-4600 WOT

 

[HT32BSX115]

Re: If you need to know how much compression you sould have - Max RPM - look here

I see the questions to these answers come up a lot.
Specifications are from my 1989 OMC manual. Good for generic use though.

2.3 4 cylinder with 8.5:1 compression - 130 psi - 4200-4600 WOT
4.3 V6 - 160-175 psi - 4200-4600 WOT
5.7 V8 - 155-175 psi - 4200-4600 WOT

And you left out those lucky people with the 7.5L engines

7.5L V8 - 165 psi, 4400-4800 WOT, 600-650 idle, Timing: 86AKI fuel, 10* BTDC, 89AKI 15* BTDC

 

[mthieme]

Re: If you need to know how much compression you sould have - Max RPM - look here

Actually, the manual has Ford 302, 351 and 460 motors but oddly don't list the specs. No Chevy big blocks. Go figure.
I just posted what I found, not a complete go-to source....sorry.
Hopefully this should still cover a lot of territory for the crew though.

 

[a70eliminator]

Re: If you need to know how much compression you sould have - Max RPM - look here

Cool, anything on the 5.8L ?

 

[mthieme]

Re: If you need to know how much compression you sould have - Max RPM - look here

Full specs are in here for the 302, 351 (5.8) and 460 Fords...just not the compression or rpms.
They give complete instructions on how to do a compression test but only state "The compression pressures are considered normal if the lowest reading cylinder is within 75% of the highest".

Can't explain why they have them for Chevy and not Ford.

 

[mthieme]

Re: If you need to know how much compression you sould have - Max RPM - look here

I found the Fords specs in another area....
5.0 and 5.8:
compression 145-155 psi, 4000-4400 WOT
for the 460:
compression 155-165 psi, 4400-4800 WOT

 

[chiefalen]

Re: If you need to know how much compression you sould have - Max RPM - look here

I don't know about that 75 Percent thingie.

If compression is more than 10 psi different i would think there is a problem.

Anything under 100 psi is unacceptable. And must be addressed.

In my humble, inexpert opinion.

And the compression test should be performed on a warm engine, one that has had the oil flowing freely.

Other wise the test won't be accurate.

 

[rodbolt]

Re: If you need to know how much compression you sould have - Max RPM - look here

the only thing the manuals leave out is where to by the calibrated certified compression tester and where to get it periodically tested.
thats why if the numbers vary more than 20% highest to lowest I then use a leakdown tester to get an accurate indication of what is going on with the cylinders ability to seal.
they also failed to mention the throttles need to be at the wide open position and if EFI the fuel pump needs to be diasbled and the spark disabled.
thats why I dont do much generic as the correct procedure is stated for each engine model. case in point, how many marinized versions of the GM 5.7L and the ford 5.8L engines are avalible?
compression will vary widly between the models as do the correct procedure to test compression on how to disable fuel systems and ign systems.

 

[chiefalen]

Re: If you need to know how much compression you sould have - Max RPM - look here

rodbolt is right on the money.

 

[mthieme]

Re: If you need to know how much compression you sould have - Max RPM - look here

Doubtful the average Joe has a calibrated certified compression tester (never seen one of those) or leak down apparatus. Most don't even have a manual.
For the supreme mariners, you already know what you're doing.