Does shifting at low RPMs really hurt the engine?

[leevanf]

Originally Posted by mazeroni

Don't lug the engine.

Basically, you have a slow moving piston but a fast and power explosion. That force of combustion has to go somewhere. You want it going to the wheels, but lugging results in burning fuel to wear the engine.

Besides, the optimal operating range for our engine is somewhere in the 2,500~3,000 range, right? It sure seems that ways to me. If you're doing anything other than coasting on flat ground, I'd downshift and keep it over 2,000 until you want to coast again, then go to the highest gear.

Thanks Mazeroni! however, if i dont floor it, and go really gentle on the throttle, i dont feel the ''lug" at all, in fact its still quite smooth. Will that count as safe?

[Stang70Fastback]

Originally Posted by leevanf

Thanks Mazeroni! however, if i dont floor it, and go really gentle on the throttle, i dont feel the ''lug" at all, in fact its still quite smooth. Will that count as safe?

That's safe. You aren't automatically lugging the engine just because you're at a low RPM. What I said earlier is still true. Very light throttle application without bogging the engine is fine. Also keep in mind that modern engines are less prone to lugging as much as older engines. The wonders of Variable Valve Timing, etc...

This car makes a very unique (read: terrible) tractor noise below 2,000 RPM when you're lugging it. That's a good audible way to tell that you're being too aggressive with the throttle at low RPMs.

[mazeroni]

Originally Posted by leevanf

Thanks Mazeroni! however, if i dont floor it, and go really gentle on the throttle, i dont feel the ''lug" at all, in fact its still quite smooth. Will that count as safe?

I wish I knew more on the subject. I don't think anyone can tell you for sure. If you aren't feeling it, I'd guess it's not terrible. The engine is strong and can take a lot of abuse. Also the engine mounts are going to absorb some of the vibrations from the engine, and the firewall and other insulation could be dulling any sounds of "strain."

You say that manually controlling shifts gives you better fuel economy.

It could be that the ECU wants to keep you in lower gears for the sake of the engine, and thus you are seeing worse fuel economy. Or it could be it wants the car to feel sporty. But a lot of this is subjective. I don't really know what "gentle" throttle means and am not entirely familiar with you commute....

When crawling in traffic, I'm typically above 2,000 and use engine braking to slow to a near stop. I don't like the engine being under 2K because to my ears it sounds unpleasant.

[ermax]

I don't even let my car idle because I'm so afraid of it dropping below 3000rpm.....


leevanf, you are fine, keep doing what you are doing. If it doesn't sound like a tractor you are fine. I leave mine in second sometimes and just start in 2nd because I get sick of the 1-2-1-2-1-2 crap. Just be gentle. There is no mistaking the sound it makes when it's actually lugging. Don't ignore it if it is though because it really is hard on the engine.

[Tcoat]

Originally Posted by ermax

I don't even let my car idle because I'm so afraid of it dropping below 3000rpm.....


leevanf, you are fine, keep doing what you are doing. If it doesn't sound like a tractor you are fine. I leave mine in second sometimes and just start in 2nd because I get sick of the 1-2-1-2-1-2 crap. Just be gentle. There is no mistaking the sound it makes when it's actually lugging. Don't ignore it if it is though because it really is hard on the engine.

How is that engine rebuild going anyway?

[HKz]

yea I'm not sure why OP needs to go into manual mode during stop & go traffic especially considering how delayed & sluggish gear changes are at low RPMs, not sure what the point is with that. I would just keep it in D with Sport mode turned off so that it upshifts whenever possible if fuel consumption is really a concern and lugging the engine should never be an issue in auto mode, it'll downshift into 1st if it feels like it is required..

[norcalpb]

Lugging the engine can cause timing chain failure, and our boxer motors fire both cylinders on one bank before the other bank has a chance to fire. Great balance at high rpm, miserable balance at low rpm.

[8RZ]

Originally Posted by norcalpb

Lugging the engine can cause timing chain failure, and our boxer motors fire both cylinders on one bank before the other bank has a chance to fire. Great balance at high rpm, miserable balance at low rpm.

Is this the same effect on an inline 4?

[norcalpb]

Originally Posted by 8RZ

Is this the same effect on an inline 4?

Depends if the engine has a timing chain or timing cover.

An inline 4 will be more balanced at lower rpm but the consequence is an engine that is much bigger in length and typically much taller.

But I’m not sure why Subaru chose a boxer design over what porsche did with the flat(?) crankshaft.

Either way never lug your engines and they will never lug you.

[ermax]

Originally Posted by norcalpb

Depends if the engine has a timing chain or timing cover.



An inline 4 will be more balanced at lower rpm but the consequence is an engine that is much bigger in length and typically much taller.



But I’m not sure why Subaru chose a boxer design over what porsche did with the flat(?) crankshaft.



Either way never lug your engines and they will never lug you.

Flat, boxer opposing, all the same thing. Not really sure what you are referring to with regards to the crank being flat. The Porsche’s are laid out the same as ours. Both engines will have half the cylinders at TDC at the same time. Our firing order is 1324 just like the 718.

[fatoni]

Originally Posted by ermax

Flat, boxer opposing, all the same thing. Not really sure what you are referring to with regards to the crank being flat. The Porsche’s are laid out the same as ours. Both engines will have half the cylinders at TDC at the same time. Our firing order is 1324 just like the 718.

maybe hes talking about the crank plane?

[ermax]

Originally Posted by Tcoat

How is that engine rebuild going anyway?

I’ve got more time cleaning all the FIPG than pulling and disassembling. I got both pans cleaned, the timing cover cleaned and one head cleaned. Just need to clean the other head and then make a parts list and place an order. Toyota South East’s warehouse is right here in my home town so I should be able to get parts fast. I’ve got a hookup on pricing and the short block should cost me 1840. The problem is work has been nuts so I haven’t had the motivation to work on it on week nights so it’s been a slow project. I suspect I will have it back on the road this weekend or next.

I want to replace my DI seals but need that tool that is made out of pure gold. My seals actually don’t look bad but as cheap as they are I figure I may as well do them.

[Decep]

do the ATs really not force a downshift if you are lugging? Only time ive ever lugged an AT car is when i accidentally put it in 2nd instead of "D" (not all AT cars will even let you do that anyway)

never driven an AT twin though.

[HKz]

Originally Posted by Decep

do the ATs really not force a downshift if you are lugging? Only time ive ever lugged an AT car is when i accidentally put it in 2nd instead of "D" (not all AT cars will even let you do that anyway)

never driven an AT twin though.

it will but the OP goes into M (manual mode) instead of letting D do its thing to manage the proper gear...in that mode it will only automatically downshift when revs are very, very low, below 1k rpms..