what gear for 7% grade
 

There's a 4 mile 7% grade where my civic gets down to 22 mph in 5th gear. This has only been an issue the last time when a truck was riding my bumper. This is a 2 lane road that only has 2 brief passing lanes going up. Previous trips I either had more momentum going up, and more space to anyone behind me, or else might have put the car briefly in 4th gear.

The car is probably fine getting up in 5th gear, but the low speed could be a hazard when there happens to be other vehicles going up quite a bit faster. The speed limit is 50mph in this part. Considering this, at what speed would you put the car in 4th gear?

I could probably get away with only using 4th gear for the worst parts.

I think you already answered your question. 4th gear unless you are not holding up traffic. 5th at 22MPH can't be good for the engine. Once had a 63 Valient that would not climb a 7% grade in high gear, 3 speed manual. Downshift to second at 35, up shift to third at 50, gradually loose speed, rinse and repeat until I got to the top.

regards
Mech

The main thing is to keep your peak bsfc in mind. I have to guesstimate, but I would guess keep it at about 2500rpm with 4/5s throttle, whatever gear gets you closest to that.

Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

Or install a mpg gauge and experiment with different gears and throttle settings.

I hate guys like you because when you bring me your engine to rebuild all the cylinders are oval. Many cases I end up sleeving the thing as you lugged the engine and scraped the oil film off the side of your cylinders.

If I had to go up a 7% grade I would select 3rd gear and about 3500 rpms,but thats me. :eek: This way you get adequate cooling and lubrication flowing through the engine. Lugging an engine like that also created harmonics throughout the derivation and extra undo stress to the system.

@ Old Mechanic, there are two places that I go down in 4th (from the other direction), probably the same good places to go up in 4th.

@ P-hack, I was using 4/5s throttle, but as you mentioned, the rpm's were too low. I will use 4th in those parts from now on.

@ Cobb, why would going up in 3rd gear at 3500 rpm make it cooler?

But they got a better MPG number readout on a gauge before a $5000 rebuild.

I'm not a mechanic, but my common sense tells me that running it like that puts the engine under tremendous stress, but only pumping enough fluid around to accommodate 2300rpm's (just as an example), but at a way higher engine load. I'm probably wrong but that would be my guess.

2500 rpm is hardly "lugging". Do you have any actual data on this? We DO know it is how you get the most efficiency out of an engine. Folks been driving like this for decades and 100s of thousands of miles so I'm not sure you have the cause and effect completely sorted yet.

My original 37 Ford, with no oil filter and a 6 volt system, with a starter that cranked at 100 RPM, produced 60 PSI of oil pressur in 5 seconds if you pushed the starter button with the ignition switch in the off position.

You can't put your car in gear fast enough to not have oil pressure after starting it up.
Lugging at 2500 is laughable. Why would a VX pull fine from 30 MPH at 1000 RPM and still have every valve lash in specs after 62k miles at the first adjustment.

regards
Mech

It's really simple. Pick your target speed, downshift until you can maintain that target speed. Use the highest gear that you can to maintain that speed.

That's it.

regards
Mech

well there IS such a thing as lugging, but it is down by idle speed. The journals need a certain rpm to distribute the oil all the way around them before it gets squished out. Also bsfc peak will fall either side from 2500 rpm, though most bsfc charts seem more sensitive to changes in load vs rpm. So too lightly loaded and too high rpm is a double efficiency whammy.

I watch the engine load on my scangauge, and will downshift on long grades if it's over 75% or so. Obviously I don't have as much rev range in the diesel, so I'd probably want 3rd for a hill that steep.

The original posted to this thread is doing 2500 rpms in 5th gear at 22 mph up a 7% grade? :eek: Yeah, hes more problems than lugging, oil psi and water circulation. :p

I missed that, He has to be doing a lot less than 2500rpm @ 22mph in 5th. folks report 65mph @3k(ish) in a civic, putting the rpm around 1015 with load

WARNING TOO LOW RPM FOR SUSTAINED LOAD!!!

The OP also mentioned driving 22 MPH in a 50 MPH speed limit. That sort of speed differential is downright dangerous, in addition to being rude.

In West Virginia is common to see a line of Cavilers in the far right lane going 20 mph on most climbs. The middle lane has the big trucks. The left lane has me pushing 15 psi of boost doing 75 mph and 16 mpg. Most speed limits are 70. Most people go 80.

https://www.youtube.com/watch?v=A-rGPir8Zx8

Ever driven Route 50 through WV?

Many times. That route was the source of legislation that made it illegal to coast in neutral in Virginia, enacted in the 1930s when Plymouth came out with "freewheeling". Problem was you could not engage-disengage it unless you were stopped, which combined with the brakes of that era meant melted brakes and a trip over a cliff.

Ever seen the freeway to nowhere in West Va?

regards
Mech

I just follow my gps. If this is the road with a toll booth every few miles, then yes. Its well worth the toll for a nice stretch of road to travel and plenty of spots to do a 0-70 run.

SMH....If your 37 ford operated at room temperature this would be great. Unfortunately that is when you develop the highest oil psi and as the vehicle warms up the oil psi drops.

Low oil psi at idle can be fixed in a number of ways. Heavier oil, high volume oil pump, replacing engine bearings or just increase the idle speed. You need to check the engine out from the bottom end to get an idea why you have low oil psi so you dont do something stupid and let the spinning parts loose.

PSI is just one aspect, you also need volume and quantity. Its not uncommon for most V block engines to pump oil to the top faster than it can drain back to the sump. This causes oil and air to get pumped into the system and its easy to spot on bearing shells.

Its also not uncommon to turn faster rpms of the rods that you sling the oil out faster than it can be pumped in for proper lubrication.

These are reasons alone why Bubba can floor his v 8 auto and have it instantly throw a rod.

Many engines have a pressure relief valve. Its basically a spring with a ball bearing inserted into one of the oil gallery. It helps to regulate oil psi by bleeding off excess psi. This can get stuck in the open position and cause a lost of lubrication as the rpms climb.

Furthermore many oil filters contain a bypass valve so you do not blow your oil filter if the psi is too high or if the filter is too clogged.

You ever consider adding a relay inline with an oil psi sensor so the ignition is not powered til oil psi is sensed? I want to say thats how my riding mower is setup. I tried to start it a few weeks ago to move something. IT cranked for 10 seconds and nothing happened. After 10 seconds it seem to suddenly crank faster, then it fired up. Im assuming the faster cranking ment oil had started to be pumped into the system and the low oil shut down decided to let me start up.

No, where is that?

I do know Route 50 though :eek: Decided to take that instead of I-68 this past summer. I do remember one climb where I had to keep the car pretty much floored in 3rd gear for quite a while headed east. And then the curve from hell at the bottom. Don't know what the grade was, but my Corolla didn't like it. Surprisingly mileage for the trip was one of the best that summer???

West Virginia Turnpike - Wikipedia, the free encyclopedia

regards
Mech

What I hate are the addresses. I was headed to a Toyota dealer in Chapmansville for a truck show. Mike Ferrell Toyota? Their address was like corridor G, section 8, road 5. Not something easily to enter into a gps. I used the address of a kohls I had met some scion guys a year before, then drove an hour down that road to get there looking the whole time for a toy dealer on the right. :turtle:

Based on gearing in a 99 civic and 24" tall tires at 22 mph in 5th you are only turning 820 rpm. On a steep hill that is definitely lugging and I bet you have to floor the pedal to do it. Seems like a lower gear would be more efficient and 22 mph up a hill where nobody can pass seems like a hazard.

Someone being unable to NOT ram into slower traffic is the ONLY hazard. If you are saying we have a lot of idiots on the road, lets not encourage them to go fast. That would be really moronic on a grand scale, oh wait...

The hazard of lugging is largely obsolete in modern engines with knock sensors and ECU controlled injection/ignition systems. 800 RPM in a Civic is fine, the problem is that there is no power, so there is no way you are maintaining speed on a hill. The real hazard in your situation is going 22 in a 50 :eek:

The ecu will prevent you from wiping the oil film from the side o the cylinder during the compression stroke?

The ecu will prevent you from cooking your clutch? That maybe how he is doing 2200 rpms as its slipping.

For that to happen you would have to assume at 800 RPM the Civics oil pump couldn't supply enough oil for the demands of high load at low RPM. And the potential for this type of damage increases the longer you operate the engine in this situation. If you are at WOT under these conditions then yes, you will have some issues if it's a habit. I was referring to the pinging and knocking people associate with lugging.

Under moderate loads around town, lower RPM's are fine. I do it everyday on the flat roads around town, anywhere up to 75% load. 60,000 miles and counting in the last 2 years with no issues. Generally I downshift when I can no longer gain any speed in a certain gear. Under the OP's situation there is no way a Civic is maintaining or gaining speed at around 1000 RPM's up a hill, so obviously it would be wise to downshift. I don't think I ever truly "lug" the engine.

I don't know what you mean about the clutch, where did 2200 RPMs come from?

Unless he has a modded or B series engine, I doubt he has the piston squirters inside the block. Those help to lub the pin, skirts to prevent seizing.

Otherwise most engines the pistons under side is lubed by splashing from the other parts. Kind of like how a typical lawn mower engine is. Thats why for those they have what seems like a high idle to allow sufficient splashing for lubrication and air circulation to keep it cool.

I'm pretty sure the OP didn't say 2500rpm, someone mentioned that was the best BSFC and then someone else got confused.

800rpm is definitely not good for the engine and 1000 probably isn't either. Most cars' owners manuals tell you explicitly to not put heavy load on the engine at low rpm (with manual transmission). Even if you had sufficient oil flow to protect the bearings (which is debatable, on a typical engine I would guess it's not entirely adequate), the cylinder walls are not under hydrodynamic lubrication even with piston squirters and high load at low engine speed will squeeze the oil film out.

How about a light load at 1000 RPM? Down to 1000 at times when in stop & crawl traffic with light pressure on the accelterator. The engine doesn't seem to mind. I can almost stop & still use 2nd gear as well, but not sure if this is OK either?

Thanks!!

Holy cow a 4 mile 7% grade. I guess I would approach it by as you said gain as much speed as possible and attempt to maintain 5th gear. But if you lose speed its time to admit defeat and downshift. We can't really win them all. 22mph in 5th gear is definately too low. I don't know what the speed limit in this section is but you can't just go over 10 mph below the speed limit and bottleneck traffic. Its not the right thing to do and you are not the only person on the road.

When your starting your car from a stop its just better to use the gears. First is for starting out. Second gear is good as long as your are still moving (rolling stop signs). I have been known to skip 3rd and 4th gears every now and then.

I feel I use more gas if I am trying to power up a hill in 5th gear with the accelerator floored and losing speed than to just shift to 4th and get over the hill quicker and not flooring it. I don't know for sure but I think I read that somewhere but don't remember where :P. Can someone prove me wrong please.

Cars maximum effeciency at 50-80% throttle? So if your flooring it to get up a hill would it make sense to downshift if your loosing too much speed?

I personally like to be going 10 mph over the limit at the top of the hill to give me a nice long coast. Doing so has netted me an improvement from 36mpg(constant 60mph speed) to 46mpg (pulse and glide (65mph - 55mph) on the hilly state road.

A 7% grade downhill coasting will get you way over the speed limit. Coming back from Va Tech there is a similar grade fro close to that distance. Behind a big rig, I was using 5th and DFCO to slow down from 85 MPH. The rig was sucking me into his rear end. I think I could have got close to 90 in clean air. Dropping 7 feet vertical at 65 MPH (100fet per second) at 75 (speed limit 70) you aredropping vertically about 9 feet a second, about 36-40 HP in energy to add to your speed.

Climbing a 7% grade in WVa my Scion XB wasrunning 4 k RPM and down shifted two gears.

regards
Mech

Perhaps I don't understand grades, having spent most of my life in Florida, but so long as I'm able to accelerate in a gear it should be safe to run in that gear?

I recently moved to Tallahassee and had to learn driving on hills, and found I could accelerate up some steep grades in 5th from as little as 15 or 20mph (850-1100rpm). I typically don't shift before 2000rpm, but I see my wife accelerating up some grades I'd eyeball at 30-40% in 5th below 25mph. Should I make sure she downshifts?

The owners manual for my Honda says drive in the highest gear that still allows the car to accelerate, which is the general rule I follow. If you can still accelerate then the motor is not being overworked, and you should be safe. If you are losing speed at high engine loads, it's time to downshift.

As far as MPG strategy, the most fuel efficient gear is the highest one. If you are going any speed, say 30 mph, higher gears will be more fuel efficient than lower gears because of the lower RPMs. The higher load required in the higher gears doesn't matter, as long as you are not going high enough to enrich the mixture (~90% load, WOT).

Adding to the confusion is BSFC. Keep in mind that the ideal RPM and load range set by the BSFC chart might be the most power efficient, but it is not necessarily the most fuel efficient. People that do P&G accelerate based on the BSFC chart because they want to maximize the efficiency of getting back to the top end speed so they can glide.

People that use the DWL (driving with load) technique need to use the lowest possible load for each situation, because lower loads = higher MPG's. We are not concerned about the BSFC while cruising at a steady state, only when accelerating. So going up a hill on a highway you need to find the highest gear you can maintain your minimum speed in.

Sounds like the engines in hondas have more balls or torque to them then Suzuki? I know Japanese made engines are funny about spark plugs and love to rev. I have experience with Suzuki sidekicks 2&4 doors, swifts and gem metros with 3 and 4 cylinders.

So, for the suzukis it seems they are rather gutless til about 3 grand, then the power band starts about 5. In my zukis I use a 5-10 degree advance on the cam to drop that.

The Honda insight I have has the IMA assist and vtec that kicks in at 2700 rpms. It does rev rather low than some 6 or 8 cylinder engines in vehicles I have driven. Then again it has the ima for the lower speeds and lower end.

Yeah, I agree. If you can accelerate in that gear, its fine. I try to stay around where the max torque is in the rpm band vs the BSFC.

My car isn't exactly happy below 2500 RPM, but I've learned to sacrifice speed and power for fuel economy. I try to shift below 2500 RPM, but I accelerate with about 80% load so I can get to top gear as quickly as possible.

Many Honda's come with shorter gear transmissions which encourage higher RPM driving to compliment the VTEC system. But for the VX, HX, HF, CX, and some DX/LX models, the longer geared transmissions make it pretty easy to drive like a grandma. It might not be exciting or fast, but thats where the better fuel economy is.

cbaber, when does your vtec kick in?

Just for notes, 55 mph was 1700 rpms, 70 mph was 2300 rpms. Not bad for a 1.3 engine. My sidekick runs 3 thousand rpms at 60 and it just climbs from there. :eek:

My TSX 6-speed runs 3000 RPM at 70 MPH and the VTec kicks in at 6,000 RPM.

I'm envious of everyone that has more usable and efficient gears and VTec engagement.