Hey guys I just bought an s5 and wanted to know what numbers would be considered good compression for an s5 Fc3s? I poked around for some info but after awhile I figured someone here could help or direct me to a link lol. Thanks

 

Minimum spec is in the FSM: 83 psi. But ideally you want 90-120 psi per pulse.

 

I consider 90 on the low side, 100 - 120 is what I would like my engine to be at. Good luck!

-93FD3s500r

 

damn.. the car i bought came with a new s5 motor and i havnt done a compression test till now cause the battery was dead. my mechanic told me it read high 80s - low 90s but since the battery wasnt strong it had week pulses... would it be wishful thinking to think that it would pulse higher in maybe the 100s if it was on a fresh battery?

i took the previous owners word when he said it read 105 when he did it.... =(

 

More than likely. Compression specs are at 250 RPM (cranking speed), so a weak battery will lower the values. A warm engine and open throttle plates will also ensure more accurate numbers.

 

i assume ur saying it would likely be higher on a charged battery? i hope so. hopefully its right around the 105 the previous owner said lol cause im already investing a lot in it... would a warm engine typically give a higher reading or lower? thanks rocket

 

A warm engine and faster cranking will yield higher numbers.

 

THANKS!!! made my day

 

try this page(link):http://www.rotaryresurrection.com/2n...ion_check.html

 

^ The only thing I don't like about that writeup is where it talks about 30-35 psi per pulse being good. That assumes you leave the schraeder valve in the end of the tester, and it also assumes all schraeder valve springs are created equal; they're not. A stiff spring won't even allow the needle to move at all, which is why it's suggested that you remove it.

Ditch the valve, and look for numbers (per pulse) above the factory spec.

 

"1) note battery strength. A weak battery will yield low compression results. "

YES!!! lets hope its in or near the 100s lol =)

"let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment."
How Accurate Is The Statement above??