Transmission/gearing question
 

I have a couple of questions about converting my 2005 Honda Civic with a 4 speed auto to a 5 speed manual. My first question is what would the overall effect on gas mileage be if I install an EX 5 speed trans? I initially thought that highway MPG would stay approximately the same and city mileage would improve.

However, I found out that the trans that I am looking to install (An EX 5 speed, which has more aggressive gearing than an LX or HX trans) would cruise at a high RPM. With my auto, the engine runs at around 2300 RPM going 70 with the converter locked, but with the EX 5 speed, the RPM would be more like 3000 going 60. I am not sure if that would mean lower highway MPG. You would think it would, but the manual transmission has much less losses, even cruising with the converter locked, so the mileage may not drop.

The other option I have is to get an EX 5 speed trans and swap the 5th gear to a taller gear from the LX trans before I install it, which would drop cruising RPM at 60 to around 2800 IIRC. Would that help gas mileage measurably?

Thanks in advance for your input

Also, I forgot to mention that I am also wondering about the effects of a higher cruising RPM on engine longevity. I can't imagine that cruising at 4000 RPM all day going 80 (like you might on a road trip) would be great on the engine. However, the load on the engine would be lower too, so for all I know the higher RPMs might not cause any more wear.

The manual transmission will provide better fuel economy around town, but the automatic will likely get better fuel economy on the highway, due to its taller gearing, unless you regularly do engine off coasting in the manual.

With many ecomods and slow, careful driving, my '04 auto Civic had a best highway trip of a hair over 60 MPG for over 300 miles. To get that kind of mileage in the city required extreme hypermiling techniques.

To beat the auto's highway fuel economy you would need to use a taller geared transmission.

Thank you, that's pretty much what I thought. Oh and btw 60 MPG highway is seriously amazing, the most I ever got on the highway was around 40.

I am not going to go with the LX or HX manual trans, so I guess the best I can do is get the EX trans and swap to an HX 5th gear.

The major difference between EX and HX transmissions is in the final drive. Swapping the 5th gear would help but I think you're still going to lose fuel economy on the highway.

*However* pulse and glide can largely eliminate losses from too-short gearing, if you're willing to use it.

I'd personally use an HX transmission if I had your car. If you need more power you always have a lower gear, with the exception of first.

I agree with these posts. I'm not sure what the specific gearing on the automatic transmission is. But if your swap is going to make your car hum along like a buzzsaw on the freeway, you are going to see a decrease in fuel economy. And someone is really, however, the main advantage of a manual transmission is the ability the cut the fuel injectors and Coast, to do the so-called pulse and glide technique. So it's true that in the city with a manual transmission you'll be able to get better gas mileage in an automatic almost no matter what manual transmission you have. It's just nothing better than for gas mileage averages than Infinity.

Great point! I know it would be hard to say, but what do you think the difference in mileage would be between an EX and HX trans? The EPA says that there is a 1 MPG loss on the highway with the manual vs the auto with a Civic EX, but that doesn't really mean much to me.

Also, that's a great point that you can always downshift for more power unless you are already in first gear, but when you are in 5th gear you can't upshift. However, I do like having good off the line power. Even though I have substantially improved the mid range and top end power from stock, the low end torque hasn't improved a whole lot. And besides, I would like the clutch to last as long as possible.

As for pulse and glide, sorry, but am not willing to do that. I understand that pulse and glide is efficient because it basically eliminates pumping losses, but it is inconvenient, illegal, causes extra wear, and it is (by my standards) not safe.

Thanks. With the gearing of the EX 5 speed, the RPM would be 3000 going 60, 3500 going 70, and 4000 going 80. However, my buddy Rudy has one of these cars with similar mods and he gets 38 MPG on the highway going 70, so that's pretty good IMO. He said that these engines like running at a higher RPM, especially with the cam that I have.

EPA figures I found say 34 vs 39mpg EX vs HX, and most of that is going to be in the transmission. Lean burn helps a bit but I don't think it's the holy grail some others make it out to be. Now, that's an average fuel economy mind you, and the highway test has mixed driving, so I'm going to guess at 15-20% increased economy during steady-state driving.


The off-the-line power isn't too substantially different, but pick the gearbox that's right for you. Don't let me tell you what to go with.

:thumbup:

Final drives:
EX: ~4.41
DX/LX: ~4.11
HX: ~3.84
Hybrid: ~3.60

For what it's worth the HX actually has a shorter first gear (10%) which offsets half the difference of the taller final drive.

https://ecomodder.com/forum/showthre...ios-26279.html

^ Looking at the ratios here, a pretty good frankentransmission might be a DX/LX transmission with the HX final drive - you get a shorter 1st/2nd/3rd/4th and keep the tall tall tall 5th. Either that, or put the 1st/2nd/3rd from a DX/LX into the HX box.

I know it's not remotely apples-to-apples but in my Insight I'm still on the original clutch at ~250k miles and it still feels like a healthy clutch to me. It has an even taller 3.23 final drive, and power is "fine" in 1st gear even without the hybrid system enabled (accelerating with only the 66HP 3-cylinder). It's only the very tall 2nd gear that I take issue with; I'd prefer a shorter 2nd gear when lacking the torque from the hybrid system.

They produce good power at high RPM and run smooth as butter, but ultimately it won't be good for the lifespan of the engine. You'll probably still get 250k out of it, sure, but at that point I'd bet it will be drinking a lot of oil. Get the RPMs down and you'll keep your cylinder walls and piston rings much longer.

Thank you for all the great information! My plan was to get the EX 5 speed and swap to the DX/LX 1st gear for even better off the line power, as well as swap to the HX 5th gear for less noise and more MPG on the highway.

Also, it's not just in the numbers for me. I personally don't think I'd like the way the car feels when it is cruising at a high RPM for a sustained period of time because it would sound noisy and to me it would feel like it is working harder than it needs to. I also imagine that when cruising at 4000 RPM at 80, releasing the throttle in gear would feel like hitting the brakes.

As for engine longevity, unnecessarily high cruising RPM probably wouldn't be great. Even though the load on the bottom end would be lower, a lot of parts that are unaffected by load would be moving a lot more than necessary, which would have to cause more wear. Parts like the water pump, tensioner pulley bearings, camshaft, rocker arms, valve stems and guides, timing belt, and maybe piston rings would wear out more quickly without a doubt.

However, I am not as concerned with engine wear as I am with performance and how the car feels driving. My thought is I needed to replace the engine after 200K hard miles because of a water pump failure. I was really upset and disappointed because I did EVERYTHING I could to take care of it to the absolute best of my ability and make it last as long as possible, and everything I did ended up being for nothing because the water pump failed, despite being an OEM part that I installed 20K miles ago. :(

So nothing I did ended up mattering anyways. It's possible that I could install the HX trans to try to get the engine to last as long as possible and then something stupid happens and I could lose this engine too for some stupid reason anyways.

Very true. Lightning can strike anywhere.

Maybe the LX transmission is a happy middle? Any way you could test drive a car with these various transmissions?

A very small turbo might be an option too. Small enough and it won't hurt economy, and will spool up very quickly. Not a cheap option but you could keep your power while gearing the car very tall for phenomenal highway economy.

Great advice, thank you. I may see if I can find similar cars to test drive to at least get a feel of the gearing. However, the EX, DX/LX, and HX have different engines, so even if one feels faster or slower than the other, it would be hard to say if the difference is the engine or the gearing.

As for a turbo, great idea but no. I am going to eventually K swap this car, and the time and money involved in installing a turbo would never be offset by any fuel savings.

I'm K swapping my Insight, and have put together what is possibly the tallest K series transmission ever assembled. I'll let the high level of torque take care of off-the-line acceleration and will be turning ~2200rpm (possibly less) at 70mph, hopefully allowing me to keep my 60+ mpg. Highway economy is really all about gearing and aerodynamics.

EDIT:

https://i.imgur.com/TLkSCnp.png

I'm actually less than certain about the 4.4 final drive in the EX. That's what California98Civic's Honda transmission guide says, but Honda says it can be either/or:

https://owners.honda.com/vehicles/information/2003/Civic-Coupe/specs#mid^EM2123PW

Confusing. I got my data from Honda.com in 2013. But you are right for the link you offer for the 2003. Still, elsewhere, today, Honda.com lists only "Final Drive Ratio 4.41" for the 2002 MT EX. Oddly, their AT EX FD specs also change. See: https://owners.honda.com/vehicles/information/2002/Civic-Coupe/specs#mid^EM2192MW

Hard to confidently decide what is true without laying hands on the actual gears from an actual car.

??

EDIT: the Honda site also now labels the 2001-2005 EX as a "VTEC-E" engine and the HX as a "VTEC-E lean burn." But the EX was never vtec-e as far as I know. It's just VTEC. So I think over time, as they've updated that website, Honda may have introduced errors, which would be a bummer. Getting the original hard copies of the factory service manuals would be the way to resolve it.

What program or website are you using to compare transmissions, Ecky?

This is what I use:

https://www.zealautowerks.com/transcalc.php

In a way having tall gearing sounds nice. Maybe it’s just me, but I don’t really like cruising at a high RPM for a long time because it sounds noisy and it feels stressful on the engine, even though I know it’s fine. If I regularly took long road trips I would probably get sick of the EX transmission’s short 5th gear pretty quickly. The idea of cruising at 4000 RPM all day doesn’t sound appealing to me.

But I also like to push it hard sometimes, so I think the best option for my needs may be to get the EX trans and swap to the HX 5th gear, and possibly the DX/LX 1st gear for more off the line power.

Call me crazy, but I am starting to think about the possibility of installing a CVT from a Civic Ferio 1.7. It would probably be the most fuel efficient, and also possibly the fastest since it could hold the RPM high for maximum acceleration at full throttle and there would be no shifting.

But one major problem with a CVT is I am not sure how well it would handle the extra power that this engine is making. From my understanding CVT’s are problematic enough as is, and I’m sure pushing more power through it than it was made for wouldn’t help.

My understanding is that Honda's early CVTs didn't do well with high torque, and typically didn't last very long even with stock engines; failures before 150k weren't rare. They're also not very quick to "shift", giving a noticeable delay in power while the engine revs up and the belts find their new positions. Newer CVTs are faster to shift and more durable. Dunno about the 1.7's.

Automatic 4 speeds with a second Overdrive.
 

I am thinking that a second overdrive added to a stock 4 speed auto with a OD gear can work and in fact greatly increase a stock car/van’s MPG, just by lowing the cruse RPMS from around 2400 RPMs to 1700 RPMs.

This seems to be the best of all worlds, stock gearing until the added Over Drive is engaged then the advantage of super highway gearing.

Your thoughts and knowledge is invited.

Rich

The devil is in the details. Do you mean turning a 4 speed into a 5 speed, or just swapping the 4th gear for a taller one?

I am planing on adding a old Borg Warner over drive taken off and converted from an old 3 speed with OD behind the stock transmissions.

It also can be used as a gear spliter giving me up to 8 gears.

But the main one is a large drop in forth to fifth(both ODs)

Rich

Just a guess, but I'm thinking the benefits of increased load and lower friction / parasitic drag from accessories would outweigh the increased parasitic losses from the OD, but only on the highway. More gears to go through to the wheels = more losses.

That has been a concern as well and the added weight of the old cast iron over drive its self.

But there is Gear Venders selling add on ODs all over the place.

Rich

It would basically be impossible to add a 5th gear to a 4 speed auto. However, it would theoretically be possible to swap the 4th gear to a taller one, although I don't think that would work well and you may not gain anything for several reasons:

1. The PCM would have no way of knowing that the gear ratio has been changed, so it would likely shift to overdrive early and then lug the engine or shift back and forth between 3rd and 4th, so you would probably need to lock out overdrive by putting the shifter in 3, pressing "OD OFF", or similar (if your vehicle even has this option) until you are at a high enough speed to shift to 4th gear. The PCM will likely also set a code, likely for an incorrect gear ratio.

2. The torque converter clutch will probably not lock very much or for very long since lockup is controlled in large part by engine load, and the load would probably be too high for the TCC to lock, even cruising down the highway at a steady speed on flat ground. The converter is also likely to lock and unlock quite frequently, which is inefficient and will quickly destroy the clutch. You could get around this with a manual lockup switch, but again, this will probably set a code, and may even cause the PCM to enter limp mode.

3. The trans will also frequently need to downshift to 3rd gear to accelerate a tiny bit or climb a tiny hill, which will eat into your savings, especially if you manually lockup the converter. Unlocking the TCC may provide enough power to climb a hill or accelerate without downshifting, but again will eat into your savings.

4. When driving in the city, your speed will probably be too low to cruise in 4th gear, especially with the converter locked. I have this problem with my car when I manually lock the converter in 4th gear below 35-40 MPH, which is a speed that I drive at a lot around town. A taller 4th gear would make this much worse. So you will need to cruise in 3rd gear a lot at lower speeds, which will also eat into your savings.

So for those reasons, I would advise against installing a significantly taller 4th gear on an automatic transmission vehicle unless the vehicle is driven on flat highway almost exclusively, you have workarounds for those other issues, you are okay with the vehicle being miserable to drive around town, and you don't care if it sets a code.

As for the CPU throwing codes I will be running a combo of a 93 Plan Jane TBI PCM (runs ONE O2 Sensor..._)and a 86 Camaro TPI PCM OBDI Running the fueling system, I don't think they are smart enough to throw such complex codes.

As for using the second OD I agree only on the highway at a easy cruse speed around 75/85MPH. SO in the city it will drive normally, one of the reasons I like the add on OD.

The nice thing is I can easily lock the second over drive out.

I plan on adding a VSS sensor/sender to the rear of the OD so the truck/car PCM will be able to see a normal speed reading.

My thinking is the convertor clutch and PCM will see 5th gear like a very tall highway gear and act as it is stock.

Good points makes me think.

Thanks.

Rich

Oh I see. So you replaced the trans with a 5 speed auto rather than changing out 4th gear? That would be a good idea IMO

Well a 4 speed with a second transmission that is a in/out overdrive.

So it is a 5 speed or even a 8 speed as the over drive could work as a gear splitter, giving a First and first OD, or second then 2nd. w/OD and so on.

I used to play 6 speed in the 60s with my 56 Studebaker with a 3 Speed w/OD, I would drop OD in each gear, 3 + OD = 6 gears.

Rich

Oh that sounds like fun to have more gears and something else to play with LOL. :D But as someone else said, that makes me wonder if having a second transmission would actually be of any benefit. That would depend on the engine's efficiency at different RPMs and how much frictional loss the overdrive unit adds. It is quite possible that such a setup would be of no benefit to MPG.

But like I said, cruising RPM isn't all about gas mileage. Some people (like myself) don't like the noise of cruising at a high RPM, especially since I made this car so loud as it is. Also, even though I know that it's illogical, I don't like the feeling of cruising at a high RPM for extended periods of time because I feel like the engine is working harder than it has to. To me, driving down the highway is more relaxing at a lower RPM :)

Pretty simple to slow down.

Not really LOL. The people here in Memphis drive like jerks and if you go less than 60-65 you would get rear ended. I often have to exceed the speed limit just to not hold traffic back or get rear ended.

I have never been rear-ended.

Then I am glad you live in an area where people drive in a civilized manner unlike Memphis. The speed limit on one of the highways around here is 70 MPH, and a lot of people go 90 or more.

Also, the other factor here is that the left lane is often much more nicely paved than the right lanes. The right lanes are generally quite rough with a lot of pot holes, lumps, and harsh transitions that rattle my insides out and frequently scrape my car.

Well I have an update. My transmission went out after 243K, so I installed that JDM SLXA transmission that's been sitting around for the last 3 years. This transmission is geared shorter than the OEM trans was since it's from a Honda Stream (heavy station wagon), which I like. The car feels somewhat quicker since the gearing is shorter, but that also means my cruising RPM has increased.

My RPM going 60 has increased from around 2300 to around 2900, but I need to verify that the torque converter is locking because that seems high to me. I have been getting about 33 MPG average lately with the old trans. I will report back shortly with how my MPG changed.

EDIT: I was concerned that I might not like the way the car feels or sounds cruising at a higher RPM, but at least up to 70 MPH (which is the fastest I have gone so far), it feels fine. If anything, the engine actually sounds quieter oddly enough. It's possible that maybe the actual decibels aren't lower, but the frequency is higher and is IMO more tolerable. The noise before was more of a deep roaring, but now it is kind of a higher pitch humming, which is less disruptive when trying to have a conversation IMO.

Also, unsurprisingly, I noticed that the car takes less throttle input to maintain speed on the highway, and it doesn't seem to have as much difficulty climbing hills in 4th gear. It didn't really feel like it lacked power climbing hills with the old trans, but I barely notice when I get to a small hill with this trans when I am cruising down the highway.

My 2008 manual Hyundai Accent had 2980rpms at 60MPH. Wanted a higher geared transmission, but settled for used, but bigger wheels/tires. Over 3 years ago, I went from 175x70x14 inch wheels/tires to 195x65x15 inch wheels/tires. Eventually, I moved up again, to 205x65x15 inch tires(nice fit in wheel wells, but close to mudflaps), with rpms reduced to 2730 at 60MPH. Very happy with my decision, specially for the dirt cheap, but well performing tires I've gotten. Big bumps to the Accent are swallowed much better with the big tires, handling is much better & the Accent belongs on the highway, now. Last summer, eighteen tanks in a row were over 40MPG with highs of 45, 47+, & 48+MPG. Never had over 45MPG, previously. Have a second car that got the big tire treatment & that car is sweeter to drive, also.

So your buns are still cute? :o :rolleyes:

Not necessarily. We have both a 2013 automatic Elantra AND a 6% lower geared 2016 manual Elantra (same series). Both are rated the same EPA highway mileage. As a featherfooter tho, I try to keep speeds down, & would say the manual gets slightly better MPG on highways. On back roads with both transmissions in high gear, the manual gets somewhat better MPG. Of course, going over mountain passes, the manual gets about 6% better MPG. With its lower gearing, the manual has much better acceleration & speed holding ability on mountain slopes.

Good to know, thank you for the information! I suspect that the manual transmission gets better highway MPG because it is more mechanically efficient than the auto since it has less moving parts and no internal oil pump.

You're probably barking up the right tree. The manual 2016 seems more powerful, & NOT just because its geared lower. The 2016 Elantra has 2 or 3 HP LESS than the 2013 Elantra. However, the 2016 engine seems smoother & more responsive than the 2013. I do love the 2016 manual in the mountains to 4000 feet. Soon, I'm going up to Mt. Rainier & Chinook Pass (5500 feet). Expect the manual to continue its mountain superiority over the 2013.
Both Elantras have a total of 135,000+ miles, & nothing has ever had to be repaired on either one.

Good to know, thanks for sharing. One possible explanation for why the manual trans may feel faster is because it has no torque converter. The energy wasted by the torque converter never makes it to the wheels. Assuming that the torque converter is 90% efficient at full throttle, it could be wasting up to 15 horsepower on a 150 horsepower engine that could be going to the wheels, which certainly would be noticeable.

That and a manual trans is a lot lighter than an auto and likely has less rotational mass since a clutch is probably a lot lighter than a torque converter.

Here is a thread I made about manually controlling my torque converter lockup if you want to check it out. https://ecomodder.com/forum/showthre...-new-post.html

The road that shows the most benefits from the larger tires, is the Highway 2 west bound trestle as it approaches Everett, WA from the East. Within the last year & a half, it was repaved with very smooth & quiet pavement. However, the joints on the trestle are wide & they didn't pave close enough to the joints. With our larger car, which doesn't have the large tire treatment like our smaller car, the trestle tire thumping is disconcerting. The smaller lighter Accent, with tires that are 6/10's of an inch GREATER in diameter, than on the larger car, has a nicer(less thumping) time on the trestle.