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Old 07-11-2010, 12:19 PM   #1
Bluefoton
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Default lugging, or minimum RPM for WOT

Recently it came in a discussion on how allegedly lugging is bad for an engine. I haven't heard actual arguments or specifics though, however I started wondering if I the way I drive is detrimental to the engine. Basically, my lower limit for WOTing is 1500rpm - so when not in a hurry, and wanting to enjoy a bit of the rumble, I sometimes shift so that the rpm lands at 1.5k, and WOT at that rpm. No "pinging" or knocking of any sort, but still. Too low? Risky? excessive wear?
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Old 07-11-2010, 01:38 PM   #2
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Lugging and bogging promote knock, so I wouldn't do it.
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Old 07-11-2010, 06:48 PM   #3
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Lugging is not "allegedly" bad, it is unquestionably hard on an engine. Going WOT from 1500rpm isn't going to cause the world to end, but doing it repeatedly just for fun is not doing your engine any favors.

Think about trying to accelerate from a slow speed on a 10-speed bike. What puts more load on your legs - doing it in 3rd gear, or shifting all the way up to 10th? In 10th you're pushing with all your might just to barely accelerate. In 3rd you lessen the stress on your legs, take advantage of the proper gearing, and accelerate more quickly. Same thing goes for the engine - being in the wrong gear puts more load on the rotating assembly for little to no gain.

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Old 07-12-2010, 06:23 PM   #4
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Good point, thanks. However, isn't the stress on internals simply due to applied torque ? If such, there should be no difference whether the said torque overcomes resistance (i.e WOT, and your engine's RPM changes), or not (i.e. WOT, insufficient torque to accelerate).

Or does the low RPM, and long intervals in between each cylinder fireing have an impact as well?
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Old 07-12-2010, 10:20 PM   #5
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I wouldn't worry about anything. I've done +100 <1500rpm pulls to redline just datalogging my car through various engine mods. What breaks engines is knocking. This happens when just pushing tunes too hard. It's not what really happens just by running a stock engine. The knock sensor is there to keep the engine from doing something bad anyways. If you have concerns, I can suggest that you do certain preventative actions. You could run a higher octane. You could run a higher rated oil (going from 5w30 to 5w40). These help prevent knock and prevent wear if it does happen. Are these things you need to do? No, not really. Can you do them anyways? Sure, if you are really concerned. I'll tell you I'm running double the timing you do running my I-Speed SRS-20 tune, but I'm also running 91 octane, and I run more viscous oil, although I do these things because I use my car for sport. I do auto-x and rally-x, so I've done things to make it go faster. My stock internal are getting pushed more than yours. I just doubt you're doing enough with your engine to really care. You may think about downshifting though if you do want to romp on the car some. It's just that a lower gear and higher rpm gives you more power to the ground. While there might be some fun playing with low end grunt, there's just a little more fun blipping the throttle, dropping down a gear or two, and getting on it hard.

By the way, if you're looking to gain some bottom end power, I have a few suggestions. One cheap one is Grimmspeed's phenolic intake manifold spacers. While they don't technically do much for their thermal intent (intake manifold still gets hot from radiant engine bay heat), the do oddly add a bit of low end torque for some not really known reason. I could guess, but that's all it is. It seems to have something to do with air flow, offsetting the injectors, or something along those lines. All I can say is the low end gain is noticeable and proven with data logging. It's just a cheap plop on item that gives you some more low end. I personally have been curious what more than one spacer would do, but I've never attempted adding a second and seeing what happens.

If you seek more torque, I-Speed's SRS reflashes do work and add power across the board. The SRS-10 is a stock engine upgrade and does add 5-10 ft-lb across the board. The next major upgrade is a full exhaust, and you'll be spending a good $1k plus for a quality setup. Gains are again sizable with 10 ft-lb across the board easy plus noticeably improved throttle response. This would let you step to the SRS-20 tune instead which adds more timing and torque across the board. Beyond this, you have cams. There are a couple low-midrange torque geared cams from delta that act much like stock but just make more torque overall. You could upgrade the fuel pump and injectors and step to E85 and make a sizable gain in torque. Lastly, you could redo the internals and up compression and again gain torque.

These are the sort of things you're going to do when shooting for more torque, at least outside of forced induction.
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Old 07-13-2010, 12:12 AM   #6
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What are you spending $1000 on for an exhaust?
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Old 07-13-2010, 01:16 AM   #7
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TWE header (which is what you should be using) alone is almost that much. Cheap catback will put you at the 1k mark.


To the OP, you can hear when the engine is happy or not, the tone changes. On a stock engine, 1.5kRPM is definitely too low.
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Old 07-13-2010, 10:38 AM   #8
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Sorry for thread jacking but - are there any ECU tuning options for the 05 RS? I looked and the SRS maps say that they're only used up to the 2004 impreza, and there is nothing for 2005.
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Old 07-13-2010, 12:20 PM   #9
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I can't see paying 4x as much for the TWE header as I paid for my OBX. The TWE may provide somewhat better performance, and I could easily afford the TWE header (or a few dozen of them) if I so desired, but I just don't see any way that the price can be justified. Of course, I say that having never seen any dyno results posted (other than the 300hp race motor build) that showed how awesome the TWE headers were compared to anything else.
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Old 07-13-2010, 02:17 PM   #10
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Quote:
Originally Posted by lemons View Post
Sorry for thread jacking but - are there any ECU tuning options for the 05 RS? I looked and the SRS maps say that they're only used up to the 2004 impreza, and there is nothing for 2005.
2005 can be tuned using the opensource tools. I've an 05 and have tuned mine extensively.

Quote:
Originally Posted by Patrick Olsen View Post
I can't see paying 4x as much for the TWE header as I paid for my OBX. The TWE may provide somewhat better performance, and I could easily afford the TWE header (or a few dozen of them) if I so desired, but I just don't see any way that the price can be justified. Of course, I say that having never seen any dyno results posted (other than the 300hp race motor build) that showed how awesome the TWE headers were compared to anything else.
My car, 20 horse at the wheels, 800RPM extra power band, between the OBX and the TWE. It just plain drives better with the TWE's as well, especially in traffic. I honestly wasn't expecting the TWE to be any better than the OBX but it absolutely justified its price tag.
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Old 07-13-2010, 03:49 PM   #11
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Quote:
Originally Posted by williaty View Post
My car, 20 horse at the wheels, 800RPM extra power band, between the OBX and the TWE. It just plain drives better with the TWE's as well, especially in traffic. I honestly wasn't expecting the TWE to be any better than the OBX but it absolutely justified its price tag.
Huh, I'll be damned. Too bad someone's been playing "I've got a secret!" and didn't share the results with the rest of us. I don't plan to have the EJ25 too much longer, so it's not worth it to change over at this point, but it certainly would've been interesting to play with the TWE header back when I had the ported heads and reground cams on the engine.

Last edited by Patrick Olsen; 07-13-2010 at 04:07 PM.
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Old 07-13-2010, 07:30 PM   #12
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Well, not so much "I've got a secret" as "I didn't collect the data well enough to make charts and a write up because that wasn't what I was on the dyno to study that day". However, I have been mentioning it at every opportunity.
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Old 07-14-2010, 06:56 PM   #13
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another bad part about "lugging", or whatever dumb adjective is used for high load low rpm conditions, is the relatively low oil pressure for the relatively high bearing loads. Low rpm's means the oil pump's pumping gears are also spinning slowly.
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Old 07-14-2010, 11:18 PM   #14
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^ Good point, thanks! Didn't think about that.
BackRoadRunner, any data on the spacers? I looked into threads about them a while ago, and opinions seemed to have been divided. From what you say, it basically shifts the TQ curve to the low RPM range... would be nice to se it on a dyno though. I didn't post the thread for any "performance" reason. The thought just came to me while driving, enjoying the sound, and not being rushed anywhere, and I figured I'd put it on the NASIOC grill
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Old 07-14-2010, 11:21 PM   #15
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FWIW, I measured no shift in anything at all using the 8mm spacers. I think it's going to be highly dependent on the specific intake manifold design. The cast metal manifold that showed up on the 05 RS and was used until 07 (I believe) seems to be the best flowing stock manifold and seems to be less affected by outside changes.
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Old 07-15-2010, 11:43 AM   #16
Patrick Olsen
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Quote:
Originally Posted by RaceFaceXC View Post
another bad part about "lugging", or whatever dumb adjective is used for high load low rpm conditions...
It's not a "dumb adjective", it's a defined industry term.

Last edited by Patrick Olsen; 07-15-2010 at 01:30 PM. Reason: speeling
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