Compression Test - Any Good?

sly · 01-09-2007, 05:11 PM

Just wondering if anyone has typical compression test figures for their I6. Tested mine today, all cylinders test between 1500 and 1550 kPa (roughly 220 to 225 PSI in the old money). The manual says it should be 1010 kPA minimum and all within 100 kPa. Are mine a bit high?

howesy · 01-09-2007, 10:55 PM

compression is fine stop worrying

sly · 01-09-2007, 11:38 PM

Thanks, but I always worry a bit about forking out large chunks of cash. I'm planning to add forced induction to this engine soon and was moved to comp test it after a mechanic mate queried the wisdom of boosting a unit with nearly 320,000k's up. I think I'll just do it...

FGII-XR6 · 02-09-2007, 03:54 AM

Quote:

Originally Posted by sly

Thanks, but I always worry a bit about forking out large chunks of cash. I'm planning to add forced induction to this engine soon and was moved to comp test it after a mechanic mate queried the wisdom of boosting a unit with nearly 320,000k's up. I think I'll just do it...

The falcon I6 is a good strong motor but I too would question the wisdom of FI on an enging with this many Ks on it. if you are going down that track do yourself a favour and rebuild the bottom end. if you don't you may end up with electrical problems ( where the conrod comes through the block and hits the alternator

)

sly · 02-09-2007, 09:33 AM

Quote:

Originally Posted by au3xr6

The falcon I6 is a good strong motor but I too would question the wisdom of FI on an enging with this many Ks on it. if you are going down that track do yourself a favour and rebuild the bottom end. if you don't you may end up with electrical problems ( where the conrod comes through the block and hits the alternator

)

From what I've dug up so far the rods don't seem to be a problem at the sort of boost levels I'm looking at. Worn rings seem to cause problems with pressure leakage into the sump (hence the compression test). Failure to retard timing causes some rather fetching holes in pistons. Check out the "Nuts & Guts" panel on http://www.snortperformance.com/ for their opinion of the relative strengths of the I6 pistons & rods.

If I go with a 6 PSI turbo, the Ford flash tuner bloke in Thornton will be doing the job so the timing will be safe before it turns a wheel. If I go with the CAPA Powerdyne kit the car can be safely driven to him for tuning either limiting the revs to 2500 or just by disconnecting the belt.

howesy · 02-09-2007, 10:15 AM

That being the case with that many Km's did you check for leak down? comp. may show fine but you have to keep watching it for 30secs to see if there is any leak down. You will always get a tiny bit but if it is at a reasonable rate then this will be multiplied by more cylinder pressure.

sly · 02-09-2007, 10:36 AM

OK will check that out. Does leak-down indicate worn rings or valves? Head is only 65,000 km old so valves and seats should still be OK.

ratter · 02-09-2007, 10:48 AM

A leak down test will show whether you have leaking inlet valve or exhaust valve or leakage past the rings

howesy · 02-09-2007, 12:29 PM

Quote:

Originally Posted by sly

OK will check that out. Does leak-down indicate worn rings or valves? Head is only 65,000 km old so valves and seats should still be OK.

When you do the leak down do a second test after squirting a liberal amount of 50W oil into the pot on to the top of the piston and redo it. If it slows it considerably then you can hunch that its mainly rings if not then there may be a bit of both but dont go looking for problems that aren't there just take it step by step. With compression readings like you had I can't see any problems but be aware that the increased pressure on the old motor may accellerate the wear out factor.

sly · 02-09-2007, 12:49 PM

Quote:

Originally Posted by howesy

When you do the leak down do a second test after squirting a liberal amount of 50W oil into the pot on to the top of the piston and redo it. If it slows it considerably then you can hunch that its mainly rings if not then there may be a bit of both but dont go looking for problems that aren't there just take it step by step. With compression readings like you had I can't see any problems but be aware that the increased pressure on the old motor may accellerate the wear out factor.

Fair 'nuff. If it starts to show signs of increased wear, I can always get a complete 120,000k donk for $770 from my friendly wrecker and build it with an ACL Race Series kit, perhaps swap the heads as mine is LPG-spec and only has 65,000k's up, then swap the engines. I suspect I might have to do the tranny before the engine though...