On the expressway without having the engine explode and/or getting 6mpg?

It just seems like this thing needs an extra gear. In chicago during rush hour the left lane is an understood 75+. I went to pass someone and I noticed that at 80mph you cruise at a delicate 4000 rpm. I mean seriously??!!?

Am I getting 10mpg at 80mph and is my car going to explode? For the first time drove home in rush hour at 55 in the right lane, it felt weird. I didn't like it.

 

Year/make/model of car?

What engine/transmission are in the car?

 

We ned to know the make model of the car, engine and transmission...

Gear ratio's can vastly effect how fast ur motor spins at WHAT speed...but to see 6mpg???? I'd wager you'd have to at LEAST be dash boarding on both ends..

I've taken my LS-V-TURBO to about 160-165 on multiple occasons and that'll be the ONLY time i'd see THAT Poor gas mileage.

 

80mph 4000rpm sounds like a gsr trans...I get 35~mpg doing 75mph b18a1/gsr trans.

 

Well tire size/OD also affects rpm/mph. Here are some really cool gear ratio calculators I like to use:

M-Factory <-- clickable

Zeal Autoworks <-- clickable

4000rpm is pretty high cruising rpm, but depending on the engine itself it's probably not a big deal. A B16A at 4000rpm steady isn't as sketchy as a D16Y series engine at 4000rpm steady.

 

at about 75-80 i'm doing 3500 or just over, i don't think it'll hurt anything. My old mustang used to do that speed under 2k, haha.

 

You even going to reply to any responses or even update YOUR little thread you've got going here?

 

BTW:

I crunched a few numbers since the OP isn't telling us what he's got.

Using 195/50/15 tires as the tire size it's possible to get to 4000rpm (or very close) with just a stock D16A6 transmission (which I assume he has since an Si is in his signature)

22.68 OD tire with .771 5th gear with .425FD = 3800rpm @ 80mph

We have to include that the indicated rpm could be off at the cluster too.

If 3800rpm is bothering the guy then he'd probably cringe at some of the other transmissions if running 195/50/15 tires...

92-93 YS1 GS-R transmission at 80mph = 4500rpm

 

Well he only posted less than two hours ago, I assume he has a job and can't be on here all day. Give him some time. If he doesn't respond by this time tomorrow, then chastise him.

 

I have a 90 CRX Si with 185/60/14 stock size tires and it is dead on 4000 RPM at 80 MPH. I want to do research on doing the HF 5th gear swap into my Si transmission. If any of you can summarize here then please do. If that is an involved convo then I can search for it.
I run a Y5 motor withOUT VTEC right now and get right around 40MPG. I would LOVE to drop the RPM down about 500 to 3500 at 80 when I swap the A6 back into the car.

 

Wow! Lots of active people on this board! Thanks for the replies so quickly

A lot of people asking about tires/engine/etc...It is a 1991 si hatch, stock wheels, I'm not sure on the tires, but they seem to be stock-ish looking, no weird rubber bands or anything. I can tell you guys for sure tonight.

I'm not really getting 6mpg, it's sarcasm I just imagine that running an engine that high kills it's efficiency (or does it not on these things?). I'm still on the first full tank of gas in this thing, just picked it up and not even enough miles to try to calculate anything.

I'm new to Honda's and I just don't know if it's safe for a si engine to be running at the ~4000rpm range for a long expressway drive. It's got over 150,000 on the motor and I hear just about the only way to break a honda motor is to throw it off a building. Still kind of nervous about that though.

If i can still get gas mileage over 30 at that kind of rpm's like speedooo says I am more than thoroughly impressed with these cars Do any of you guys drive with the car consistently at 3500-4000rpms?

 

You have the SI model and the transmission has shorter gears to make it a little quicker. Because of that the gas does suffer a little on the interstate, but not nearly as much as you'd think. you should still get about 32mpg if not a little more.
I have an Integra GSR and at 80mph I am at 4000rpm. I still average ~30mpg Its perfectly safe for hondas to rev that high constantly. A 6th gear would be nice though. Seems like its making a lot more power than it needs to just for cruising down the interstate.

 

Exactly what I was hoping to hear!! Surprising too.

Now i might not be as nervous flying to work tomorrow. Imagine if this thing did have a longer 6th gear for the expressway, 40+mpg?!!? Why would someone buy a lame azz prius when they could have a sweet civvy from back in the day

 

That is what I have been wondering sense day 1 with the prius, even the CRZ. "omg! 120hp 40mpg car!" we've had them for 20 years.

 

I certainly agree that I'd rather be driving a 20 year old car getting excellent gas mileage, but plenty of people would also raise the points that:

Again I'm all about older Hondas and their simplicity, fuel mileage, etc. I drive a 1990 Civic wagon with a B18B swap netting 30-33mpg if I'm super ginger with the gas. It would absolutely RAPE a Prius, CR-Z, Insight, etc. in a dragrace, and has room for five adults and more cargo!

 

I guess the safety thing does make a lot on sense. Maybe if I had the money I would drive a newer civic/crz.

Where are you at on the southside? I am in Stockbridge. are you on ECEFC?

 

Who needs air bags, power steering and ac thats for hippies and girls.

 

I also have an integra, and was also wondering about my MPG at that RPM range. thanks for the info

 

From what i've read, slowing the motor down in 5th such as doing a DX/HF 5th gear does not net gains in fuel economy. I know its very hard to believe but these motors were designed to run in the 3000-5500 RPM range for optimum performance. There is a guy on d-series.org who LOST fuel economy by running a taller gear in 5th but his ears love him. That is one of the main things for me. I want the engine running slower at high speeds to keep the noise down and give me piece of mind knowing the engine is turning far fewer times per minute.

 

I have a 1991 HB STD with a D15B and a STD Tranny I cruise at 80 MPH at 4000 RPM and still get great gas milage even after doing a MPFI Swap. The funny thing is with only 1000 more RPM I can get up to 110 MPH. Gotta love those long gears.... haha

Gear ratio for 4G civics.
D15B6-Civic/CRX HF
1st- 3.250
2nd- 1.650
3rd- 1.033
4th- .823
5th- .694
Reverse- 2.954 or 3.250
Final Drive- 3.880

D15B2- Civic/CRX DX
1st- 3.250
2nd- 1.894
3rd- 1.259
4th- .937
5th- .771
Reverse- 3.153
Final Drive- 3.880

D16a6- Civic/CRX Si
1st- 3.250
2nd- 1.894
3rd- 1.259
4th- .937
5th- .771
Reverse- 3.153
Final Drive- 4.250

I do not have the Gear Ratios of a Four speed infortunately...

 

true that. i love my old EF plain and simple. i love short gear ratios too. idc about gas mileage at all. i miss being at 4000-5000rpm in my b16 swap. well that was my old hatch with 205 50 15s now im sohc with an si trans 7-9lb flywheel on 195 50 15s its not as bad on the fwy. i dont have a tach so i dont know what rpm im at doing 70-80mph, i would assume 3000rpm?

 

I think it safer to run a little high in the power band than a little lower at that speed. Air resistance increases with the square of speed so you are really pushing against some serious force just to cut thru air at 50,60, 70. I'd rather be on the high RPM side, than risk lugging the engine with too high a air-resistance load and causing pinging.

You notice that newer Lexus, BMW, and whatever have 6 and *7* speed transmissions to solve this very problem. They get excellent low end power in 1st and 2nd, but really crank out the MPG up in 6th or 7th. Problem is, those kind of transmissions start to be really expensive, especially back in the 1990s.