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05-11-2018, 04:48 PM | #1 |
Scooby Specialist
Member#: 468393
Join Date: May 2017
Location: PDX OREGON
Vehicle:2017 STI |
Removing cylinder 4 timing comp
I read about removing the 4th gear cylinder compensation, but the discussions are years old, and there never seemed to be any concrete answer.
Is there a definitive answer on whether or not it's a bad idea to remove this compensation? I have all the bolt on stuff, and forged pistons. MY 17, and the map is adding .70 of timing in 4th.
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05-12-2018, 04:38 PM | #2 |
Scooby Specialist
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Join Date: May 2017
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No one?
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05-13-2018, 02:42 PM | #3 |
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NWIC
Location: Portland, OR
Vehicle:2006 Impreza WRX STI WR Blue |
I generally leave the #4 compensation alone on EJ257 and the #2 compensation alone on the EJ207. A knock sensor will not save you on this one as these are just the hotter running cylinders - the comps are designed to have them run a little cooler.
This is something of an assumption on the EJ257 - I've seen rally cars remove the comp. and burn the #2 piston (EJ207) and the #4 comps on the 2.5 are set up almost exactly like Subaru set-up the comps. on the 2.0... so call it an educated guess? |
05-13-2018, 02:45 PM | #4 | |
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Quote:
Last edited by PDXREALTOR; 05-13-2018 at 03:04 PM. |
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05-13-2018, 03:18 PM | #5 | |
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Quote:
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05-14-2018, 01:59 AM | #6 |
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I don't really subscribe to the belief that the manifold is the cause of this issue so I'm probably not the best one to answer that. Without logging 4 EGT channels at the same time, it's pretty tough for anyone to prove anything with this one.
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05-14-2018, 03:37 AM | #7 | |
Scooby Specialist
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Join Date: May 2017
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Quote:
IF I was seeing knock counts on cylinder four only I would remove it, but, in reality I rarely see knock counts on cylinder four. I plan to leave it. I was wondering if perhaps the ECU does not display knock count up to the timing amount added in that cylinder. Interesting thought I think . |
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05-14-2018, 01:18 PM | #8 |
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Knock is not the reason for the compensation on the EJ207 - under hard running, the cylinder overheats in a way that basically just fails without knock. It's not detonation so much as it is the piston just melting (for a quick a dirty explanation). I'll try to dig up some pictures of a rally motor I've got where a guy kept burning the cylinder walls without the comp.; once added back in, his problems went away.
I imagine the 2.5 motor is similar, just on a different cylinder. My own take is that the intake geometry (throttle to valve) has much more to do with this than the exhaust manifold. It would be interesting to see what happened on a EJ207 if you flipped the intake manifold and ran the motor hard (endurance or rally) - not a common modification for the rally guys as they usually avoid front-mounts for obvious reasons. |
05-15-2018, 03:55 PM | #9 | |
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I wonder what a cosworth or PW would do ? |
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05-15-2018, 07:13 PM | #10 |
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It's not very expensive if you have aerospace fuel lines and are running speed density - you just flip the manifold and plug everything back in. Some wires might need to be extended for the throttle.
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05-15-2018, 07:16 PM | #11 |
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I'm certainly not going to try it on my car. I like the flipped look, but not a chance I'm going to flip it to see if cylinder four burns up.
I have Perrin rails with their rubber fuel lines. I routed them away from the engine to keep clutter to a minimum (around the battery and along the top of the radiator) and I'm thinking I may want to re-think that route due to safety. I have a new FPR with sensor for AP monitoring I need to install. Just finding the time has been a challenge lately. |
05-17-2018, 11:47 AM | #12 |
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05-23-2018, 02:27 PM | #13 |
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Really I'm not liking the rubber fuel lines Perrin uses. But, ya, you're absolutely correct. No idea how what I was thinking over-rode the complete idiot thought I got to route them that way!
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07-19-2018, 01:19 PM | #14 |
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So.... Ignore my words above about flipping the manifold. It's flipped. Lol. I got bored.
I need to decide what to do with cylinder 4 additional timing . Input welcome.... Leave it or remove it? |
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