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Old 05-11-2018, 04:48 PM   #1
PDXREALTOR
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Default 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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Old 05-12-2018, 04:38 PM   #2
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No one?
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Old 05-13-2018, 02:42 PM   #3
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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?
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Old 05-13-2018, 02:45 PM   #4
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Originally Posted by mrsaturn7085 View Post
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?
Doesn't the elh header keep things cooler in that cylinder?

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Old 05-13-2018, 03:18 PM   #5
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Originally Posted by mrsaturn7085 View Post
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?
Educated case is good, and that's why I ask because there doesn't seem to be a definitive answer out there on the interweb.
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Old 05-14-2018, 01:59 AM   #6
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Originally Posted by PDXREALTOR View Post
Doesn't the elh header keep things cooler in that cylinder?
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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Old 05-14-2018, 03:37 AM   #7
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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.
Well, you're far more educated and experienced with this stuff than I am, and I've dug into this topic twice now with no concrete answer from anyone.

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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Old 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.
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Old 05-15-2018, 03:55 PM   #9
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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.
That would be interesting, and possibly expensive!

I wonder what a cosworth or PW would do ?
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Old 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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Old 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.
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Old 05-17-2018, 11:47 AM   #12
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I routed them ...(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.
Ummmm, yeah. Head on collision, even a minor fender bender, could see you barfing fuel all over the battery/exhaust.
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Old 05-23-2018, 02:27 PM   #13
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Ummmm, yeah. Head on collision, even a minor fender bender, could see you barfing fuel all over the battery/exhaust.
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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Old 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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