Hi,
I'm here in seek of answer to secret behind the unmatched fuel efficiency offered by the Honda CRX HF with D15B6

According to fuel economy.gov, the 1986 model was rated 42mpg city, 51mpg highway, this is matched, perhaps only by a Geo Metro, but with a 1.0 liter displacement which probably have less low-end torque.

more than 20 years later, the Civic Hybrid have the same highway mileage and better city mileage, but there is not a single gas only car that can match the HF from 20 years ago.

The Honda Fit is only 28 city, 34 highway, sporting the same displacement, 1.5L engine, built with 21st technology.


So... what's the secret and why can't none of today's gas car match this?

 

Good question. There's not really one thing that makes a vehicle more efficient, so much as its a combination of many factors. The modern efficient vehicles of today have many of the same characteristics that the HF had, like good aerodynamics, modest power in the engine (in lieu of gained fuel efficiency), and tall (aka slow) gearing.

But the one thing the modern cars dont have that the old HF did was extremely low curb weight, and weight is a (the) big factor.

Today's cars are just plain heavy compared to the cars of 17 years ago.

The 07 Civic Hybrid weighs roughly 900lbs more than a CRX hf

 

the 1988 hf weighed like 1700 lbs or something stupid.

the crank also has smaller rod journals = lighter.


the axle hubs and brakes are smaller = less rotating mass

 

The fuel rating system has changed slightly over the years.There are more safety and emissions regs now too that add weight.And remember the Civic Hybrid and Prius are really "green" cars and not directly built for fuel mileage.

 

the crx hf had aluminum steelies and aluminum drums.

the insight has the drums, but no honda has aluminum steelies anymore.

 

That is a really good question. I've heard that modern hybrids are built as more of a showcase for technology than they are for function though, and I kind of believe it. Ie, if you got rid of all the batteries, electric motor, and control systems in a hybrid, the large reduction in weight would be enough to offset the lack of regenerative braking, etc. However, as the technology advances, that won't be the case. And when you drive around with the a/c/defrost on in a hybrid, you're really killing your mileage.
Does that crx really get 42/51 mpg? Without even SEFI, or any type of advanced chamber design, like their old stratified charge motors? What is the comp ratio on the hf?
What I don't get is how every year, all the midsize/bigger cars keep getting better economy, even with bigger and more powerful motors, and the little cars don't change. Neither do the trucks..

I would agree with fireant on this and say if the hf really does get that extraordinary mileage, it is due to a lot of factors, but the biggest one is probably weight. 900lbs is definitely not a small difference.

What about a/c, power steering, 4 dragging disks, etc, too? Does the hf have any of those?

I would say if you're trying to build a fuel efficient car, keep the weight low, with good aerodynamics, the compression ratio high, and the cruise rpm down. I think the celica gts is a good example of most (I don't know about the cruise rpm) of these, esp the 11.5:1 comp ratio. I know that if you're cruising at 4400 rpm in an integra, that isn't going to compare to 2700 or so rpm in another "less performance" oriented car, but everybody here loves those stupid honda gears..

One more thing, since we can't get a motor with stratified charge chambers, by using egr, (inert gas + same air+same fuel=higher dynamic compression=more efficient) you can almost achieve the same thing, as can you by simply running leaner than chemically correct, with a little more timing. I've read about carbureted cars of the past cruising at ratios of almost 18:1, but I have no personal experience with this though.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by rorik &raquo;</TD></TR><TR><TD CLASS="quote">That is a really good question. I've heard that modern hybrids are built as more of a showcase for technology than they are for function though, and I kind of believe it. Ie, if you got rid of all the batteries, electric motor, and control systems in a hybrid, the large reduction in weight would be enough to offset the lack of regenerative braking, etc. However, as the technology advances, that won't be the case. And when you drive around with the a/c/defrost on in a hybrid, you're really killing your mileage. </TD></TR></TABLE>

I bet an insight with all the hybrid and batteries stripped out, then replaced with a CRX HF drivetrain (hell, put in a DX transmission to make is zippier) and it would be a funner and probably just as efficient car.

I have been commuting with my 91 CRX Si on the highway only for the last month, and with it being lower to the ground and using taller-than-stock tires, I've averaged 38mpg, using the AC... I'm shooting for 40mpg once it gets cooler. That's higher that it was originally rated for!