kendogg

iTrader: (2)

Looking at the LQ4/LQ9 FSM, I'm seeing there is a different spec for piston to wall clearance between the 2:

LQ4: 0.0008-0.0022 in
LQ9: 0.00094-0.00098 in


Could this be part of why the LQ9's 'made more power', or since the LQ9 was a fairly limited motor, there's a better chance the pistons simply fit better, and have a low chance of becoming piston slappers? Just an (uneducated) guess, but could the excessive piston to wall tolerance in the LQ4, which might be for allowance of piston size variences across the line, to cause some engines to become piston slappers??

96capricemgr

iTrader: (1)

I wouldn't read that much into it. The LQ9 was higher compression and I believe tuned for 91 octane fuel as opposed to 87 octane.

The tune is probably the vast majority of the power difference.

(edited had written LQ4 accidentally)

kendogg

iTrader: (2)

No, it still ran on 87. And Perhaps I shouldn't have mentioned the power difference, but could this take into account an engine built to slightly more stringent standards? Have many LQ9's developed piston slap? Perhaps rebuilding an LQ4 with the tighter LQ9 piston/wall clearances would yield an engine more likely to live a quiet, happy live, with less bore & skirt wear, which should also lead to less oil consumption over time?

baronsmith98

iTrader: (2)

I believe the lq9 piston skirts were coated but don't quote me on this

kendogg

iTrader: (2)

Actally, now that you mention it, the FSM is listing a spec with a skirt coating for both the LQ4 & the LQ9, but not a service limit for the LQ9 with or without coating (unless it's a typo, since it's the last line under LQ9 Production, and where it says LQ4 with coating it SHOULD say LQ9??:


Piston
Piston Diameter - LQ4 Measured at Size Point 101.58-101.598 mm 3.9992-3.9999 in
Piston Diameter - LQ9 Measured Over Skirt Coating 101.611-101.642 mm 4.000-4.001 in
Piston-to-Bore Clearance - LQ4 Production 0.02-0.056 mm 0.0008-0.0022 in
Piston-to-Bore Clearance - LQ4 Service Limit 0.02-0.081 mm 0.0008-0.0032 in
Piston-to-Bore Clearance - LQ9 Production 0.024-0.025 mm 0.00094-0.00098 in
Piston-to-Bore Clearance - LQ4 Service Limit With Skirt Coating Worn Off 0.024-0.080 mm 0.00094-0.0031 in

2000PewterT/A

The LQ9 is higher compression, 10.1:1 for the LQ9 vs 9.4:1 for the LQ4. Also the LQ9 had coated skirts and the LQ4 did not, there are other differences but I don't remember them all.

kendogg

iTrader: (2)

OK, that makes more sense then. It's a typo in the FSM I'm reading. Interesting though. Thanks for that!!

kendogg

iTrader: (2)

FWIW, this si the FSM I'm referencing:

http://www.pleasurecraft.com/manuals/L510016.pdf

96capricemgr

iTrader: (1)

That was just a typo on my part I know the LQ9 is the higher compression. I will edit just so someone skimming the thread doesn't pickup the wrong info.

Now that you say it the coated piston sounds familiar too.

Far as octane requirements "ran on 87 octane" is meaningless the tuning was different and it came with a 91 octane recommendation, if you put 87 octane in, the pcm would pull any timing neccessary to stop detonation but it wont make the rated hp with the timing pulled.

1FastBrick

iTrader: (16)

FWIW The later LQ4's did have coated skirts. I believe it started in 03 on all the Iron block truck motors. I know for sure the 05's with the floating rods had coated skirts for sure.

I believe the difference in spec is just whom ever original measured the OEM parts when creating the spec for the manual. The coating thickness can vary along with the piston size.

The size can also change depending on the ambient temperature.

The cam is different between the LQ4 and the LQ9. That along with the added bump in compression and a slightly more aggressive tune are what make the power difference.

2000PewterT/A

I knew the earlier ones didn't have a coating, wasn't sure about the later ones.