Revhead Kev
Date Registered: 10-2006
Location: Mona Vale, Sydney, AUSTRALIA
TOTAL POSTS: 6355
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Upgraded Compression - 11:1 Pistons
Hi all,
Just saw this while trolling around the net and wondered, especially from RedDragon, what this upgrade kit might do for our Xtrails.
11:1 Pistons QR25DE
--- Kev X450(c) T30 Guru
03 Titanium Ti T30 Series 1 **MODIFIED**
My Blog
My CarPC Worklog
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30/Mar/2008, 8:17 am
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Eggins
X-TRAIL ENTHUSIAST
Date Registered: 08-2004
Location: Brisbane
TOTAL POSTS: 184
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Re: Upgraded Compression - 11:1 Pistons
It'd be good if you want to run 110 octane fuel all the time, or the engine would be running with the timing so retarded there'd be no advantage. And in fact it'd probably drive you nuts trying to find fuel that works.
I know I have enough trouble now getting consistant fuel quality...
Definitly the way to go for racing though!
--- Shawn and Belinda Eggins
2003 STR, K&N, Strut brace, Ground wires, Dunlop LM702's, Tint, Mud flaps, Tow, Nudge, Spots, Mats, Rear scuff plate
http://eggins.synthasite.com/
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30/Mar/2008, 8:43 am
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Revhead Kev
Date Registered: 10-2006
Location: Mona Vale, Sydney, AUSTRALIA
TOTAL POSTS: 6355
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Re: Upgraded Compression - 11:1 Pistons
So, for a person like me who knows what increased compression does for an engine, but not the relationship between octane rating and compression, what would be the effects of running higher compression without increasing the octane ?
--- Kev X450(c) T30 Guru
03 Titanium Ti T30 Series 1 **MODIFIED**
My Blog
My CarPC Worklog
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30/Mar/2008, 7:49 pm
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basshead
X-TRAIL HOLIC
Date Registered: 02-2004
Location: Panania, Sydney
TOTAL POSTS: 2852
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Re: Upgraded Compression - 11:1 Pistons
Kev, it would be likely that an aftermarket ECU would also be required as I don't imagine the stock ECU would be able to cope with the increase in compression. Our recently joined member (Kevin) from the US might be able to confirm this.
As Shawn mentioned, without upping the octane rating, the ECU would be trying to retard the timing (with input from the knock-sensor) to eliminate "pinging" or "pre-detonation", which if left to continue (say the factory ECU can't retard the timing enough) would damage the engine internals (the term "piston slap" comes to mind) - essentially when the explosion in the cylinder occurs, the piston is still on it's way up, or not quite ready for the downward stroke, thus it would be fighting against the explosion during the combustion process.
I also had a shaved head (which results in increased compression) in my previous car; the more you do to the engine, the more critical it is that it's tuned properly, and always requires higher octane fuel. I ran regular unleaded occasionally (when there was no premium available when I had to fill up) and only ever put $10 in unless I was on a long trip and didn't have a choice, and I noticed the difference in performance immediately. My aftermarket ECU was already programmed to run "rich", so it prevented damage occurring. In an ideal world, I'd have had it tuned to run more "lean" and performance would've increased, but with our petrol quality, it wasn't worth the risk of damaging the engine.
--- Rich. X-013(c)
'04 S2 ST Auto. Nudge_roofracks_tow_tints_Lightforce_GME_YokoGeoA/T-S_TBS_bashplate_50mm-spacer-lift
Click here to see >300MB of photos and videos All For His Glory.
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30/Mar/2008, 8:57 pm
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waky53
X-TRAIL ENTHUSIAST
Date Registered: 06-2005
Location: Barossa Valley
TOTAL POSTS: 286
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Re: Upgraded Compression - 11:1 Pistons
High compression is OK for racing, but not suitable for 4WD driving where you mostly need torque at lower speeds.
11-1 compression would lead to burnt pistons without better fuel & timing changes
--- Regards Dave, X162 Oct 04 Series 2 ST
Mods Strut bar_Fuel cap holder_earth wires_No door beep_Bonnet Struts_TBS_bash plate_16" Alloys_Rear sway bar_ F&R fogs
High Range 4WD Club
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31/Mar/2008, 11:28 pm
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