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Old 12-06-2007, 09:06 PM   #1
skyline31
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Default Is low speed in high gear (5th) causing knock easily??

If driving in low speed with high gear (5th), will it cause knock easily??
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Old 12-06-2007, 09:26 PM   #2
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I've picked up alot of false knock in the lower rpms in any gear. Usually between 2-3.5k.
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Old 12-07-2007, 02:11 AM   #3
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If you floor it at low RPMs, yeah, easiest way to knock.
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Old 12-07-2007, 10:19 AM   #4
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Hmmm i tend to try to get through my gears as quickly as possible to get to 5th or 6th and usually im cruising in 5th or 6th at 2k rpms or so. So would it be better for me to cruise around in 4th at 3-4k rpms or so instead (I have a lot of 40mph speed limits around me) ?
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Old 12-07-2007, 10:40 AM   #5
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just don't accelerate too hard and you'll be fine.
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Old 12-07-2007, 12:46 PM   #6
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Originally Posted by Dynasty336 View Post
So would it be better for me to cruise around in 4th at 3-4k rpms or so instead (I have a lot of 40mph speed limits around me) ?
I have to do the same, 40mph in 4th . I generally don't like to be in 5th or 6th at <2700 rpms. Boggy and a lot of engine load when accelerating.
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Old 12-07-2007, 12:57 PM   #7
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Quote:
Originally Posted by Dynasty336 View Post
Hmmm i tend to try to get through my gears as quickly as possible to get to 5th or 6th and usually im cruising in 5th or 6th at 2k rpms or so. So would it be better for me to cruise around in 4th at 3-4k rpms or so instead (I have a lot of 40mph speed limits around me) ?
going to 2.5rpm will be fine.. jus dont go any lower.. its hard on the engine.. If you start hearing bogging noise jus step on the gas a little and youll be fine.
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Old 12-07-2007, 12:58 PM   #8
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Originally Posted by WRXJAY03 View Post
If you start hearing bogging noise jus step on the gas a little and youll be fine.
No, that is the problem. Downshift.
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Old 12-07-2007, 01:22 PM   #9
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Quote:
Originally Posted by aaronmsadler View Post
If you floor it at low RPMs, yeah, easiest way to knock.
Maybe I should search, but why is this? Also, define "low" rpms...

Quote:
Originally Posted by WRXJAY03 View Post
going to 2.5rpm will be fine.. jus dont go any lower.. its hard on the engine.. If you start hearing bogging noise jus step on the gas a little and youll be fine.
Are you saying that cruising in 5th or 6th gear at less than 2500rpm is bad for the engine? I may be way off base, but that sounds absurd... I cruise on the freeway at ~2000rpm all the time, and when I put the pedal down to pass someone, there's hesitation, but I've never noticed detonation... I was under the impression that it was just turbo lag?
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Old 12-07-2007, 01:36 PM   #10
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Originally Posted by Menik View Post
Are you saying that cruising in 5th or 6th gear at less than 2500rpm is bad for the engine?
No, but when you floor it to speed up it is putting an amazing amount of stress on your engine.
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Old 12-07-2007, 02:31 PM   #11
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I see. That makes sense. I don't think I've ever floored it in that situation; mainly because it just makes more sense to downshift if you need to get moving fast very quickly. Still, though, would that strain on the engine really cause detonation? I would think it would be more likely to lead to mechanical problems, no? Just curious...
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Old 12-07-2007, 02:36 PM   #12
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This has been asked, answered, and discussed several times. Do a search for false knock or low rpm knock.
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Old 12-07-2007, 04:44 PM   #13
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Originally Posted by Menik View Post
Still, though, would that strain on the engine really cause detonation? I would think it would be more likely to lead to mechanical problems, no?
Detonation = Mechanical problems.
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Old 12-07-2007, 05:08 PM   #14
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Originally Posted by aaronmsadler View Post
Detonation = Mechanical problems.
I always thought that detonation lead to mechanical problems. (eg: things melting, breaking under extra stress, etc.) Not arguing, just trying to learn.
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Old 12-07-2007, 11:00 PM   #15
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Originally Posted by Menik View Post
I always thought that detonation lead to mechanical problems. (eg: things melting, breaking under extra stress, etc.) Not arguing, just trying to learn.
Correct
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Old 12-08-2007, 03:38 AM   #16
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Just tune the car correctly. It should be set up to handle a WOT load in any gear at any RPM. The problem is 90% of professional tunes only tune for WOT pulls from around 2000rpm to redline in one gear, with (if you are lucky) a little bit of road tuning for drivability.

When I tune I spend a lot of time tuning low RPM load sites at various throttle angles for this very reason. I do a 5th gear pull starting from like 1200rpm and I just floor it while datalogging, and I let it pull till about 4000RPM or so just so I can hit the load sites in that range. (obviously that isnt the only pull and gear I use, but I do it so I can get those load sites. I want a good solid tune everywhere.)


As far as detonation=mechanical problems, it doesnt always cause problems. All it takes is one det event to blow a motor, but it doesnt have to be the first event. It could knock for years and never blow, or it could knock once and lose a piston. If detonation blew motors every time, then every early 04 STI and every 06+ STI and most 06+ WRX's would have blown motors the first time someone floored it. Luckily that isnt the case.
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Old 12-08-2007, 07:07 AM   #17
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Quote:
Hmmm i tend to try to get through my gears as quickly as possible to get to 5th or 6th and usually im cruising in 5th or 6th at 2k rpms or so. So would it be better for me to cruise around in 4th at 3-4k rpms or so instead (I have a lot of 40mph speed limits around me) ?
It depends on the engine load! If you are on a slight down hill you can cruise at light throttle 5th gear at 1500 rpm. There is almost no load in that situation. If on the other hand you are pulling a long gentle up hill you would not want to pull the engine down below about 2000 - 2200 rpm (depends on which engine too, 2.0L will not pull as low an RPM as the 2.5L). The engine will tell you when you are working it too hard at low rpm if you will just pay attention to it. If you feel a vibration or surging sensation as you increase throttle, that is the engine struggling to pull the load, down shift. If it readily accepts additional throttle you are probably okay.

Have you ever ridden a multispeed bicycle and accidently shifted up to a gear that is too high where you can barely push the peddles down? That is what you are doing in a car when you are in too high a gear for the load. Like on the bicycle if you are on level terrain or a slight down hill you can peddle a long gear, as soon as you hit a small up hill you suddenly cannot create enough pressure on the peddle. Inside the engine you push cylinder pressures and bearing loads through the roof when you over load the engine in a high gear, and you are setting up ideal conditions for severe detonation since engines are much more prone to detonation and damage due to detonation under those conditions.

Larry
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Old 12-08-2007, 08:59 AM   #18
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Quote:
Originally Posted by Freon View Post
This has been asked, answered, and discussed several times. Do a search for false knock or low rpm knock.
Yep, its in the tuning forums.

I had this problem as well, here was my resolution:
http://forums.nasioc.com/forums/show....php?t=1327893
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Old 12-08-2007, 10:52 AM   #19
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Hasn't anyone heard of downshifting? lol.

I do agree with what Defiant Autospeed just said. Most tuners will not test the car from a low-RPM WOT pull in 5th gear ON THE ROAD. This is an absolute must if you want to be able to use 5th/6th for accelerating on the highway without downshifting.

t
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Old 12-08-2007, 11:07 AM   #20
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Originally Posted by Menik View Post
I always thought that detonation lead to mechanical problems. (eg: things melting, breaking under extra stress, etc.) Not arguing, just trying to learn.
Yeah, I guess that was little vague. But still pretty true.
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Old 12-08-2007, 12:48 PM   #21
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I think that downshifting rather than bogging is pretty much common sense, here.

I suggest an automatic to those opposed to downshifting a manual.
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Old 12-08-2007, 01:02 PM   #22
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Originally Posted by reddoak View Post
I think that downshifting rather than bogging is pretty much common sense, here.

I suggest an automatic to those opposed to downshifting a manual.

Agreed, but it should still be tuned in that area.
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Old 12-08-2007, 01:17 PM   #23
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Originally Posted by Defiant Autospeed View Post
Agreed, but it should still be tuned in that area.
Well, yeah, but even if he's tuned correctly, it's poor driving, and pretty straining on the car. Accelerating that is, not cruising.
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Old 12-08-2007, 02:56 PM   #24
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true


I dont downshift to pass in 5th gear. But I have an FXT which has 4.44 final drive, and a 20G setup, which I have spent a LOT of time tuning low throttle angle load sites. But at 65ishmph, I am well past 2000rpm anyway so I guess its kinda irrelevant.

Even so, a ported/polished exh manifold, larger up pipe, catless TBE, TurboXS tmic (easier breathing by a longshot) and the large exh housing on my turbo all contribute to a LOT better "off boost" throttle response and power, which makes low RPM work a lot less strain.

Still, its a turbo car, not an NA car. sub 2k rpm isnt going to be good for power.
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Old 12-08-2007, 02:59 PM   #25
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Quote:
Originally Posted by STIBungy View Post
I've picked up alot of false knock in the lower rpms in any gear. Usually between 2-3.5k.

false knock is almost always real knock. Especially at low rpm/high load.

true story.
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