short stoke and fuel economy - Fuel Economy, Hypermiling, EcoModding News and Forum

rx191 · 03-23-2012, 12:26 PM

i'm putting together an experiment, i have picked up a 88 crx for real cheap, the previous owner swaped in a 1.8 dohc engine, it has 2 rods out the block in it's current state. i have a b16 block i'm swaping in the car to get it going. so it will have a very short stroke, large bore, smallish port head and high compression. what do you guys think it will eco wise.
the wife drives 80 miles a day and is getting 32mpg right now in the current car. I'm hoping this will get 45+ untill i can find a good vx swap for the car.

just checked the gearing and found it will spin about 3800 rpm at 70!

some_other_dave · 03-23-2012, 07:18 PM

The cylinders are in the block, so you should wind up with the stock bore and stroke. Unless you're sleeving the engine for some reason?

-soD

cbaber · 03-23-2012, 08:52 PM

Whats in the car now, a B18C Vtec or B18A/B18B non-Vtec? I hate to burst your bubble but 32 MPG in your current car is probably better than you will do with your new CRX. B-series engines are designed for performance, not economy. The B16 block you have developed about 170HP in its original form. Hardly qualifies it as being economical. Whats even worse is if the current motor in your car is non-Vtec b18. A non-vtec head on a b16 block will not be fast or economical. The only good thing that I can think of from having the non-vtec motor in your car now is that you probably have the tranny from it to. The b18 non-vtec transmissions are geared taller than the B16 and B18C's which will aid in fuel economy.

The 1.6L size is misleading in this case. In my civic I have a 1.6L but its a D-series. I can get over 40MPG but a B16 (no matter what head) will not achieve this. I had a couple of cars with B series motors. A had a civic hatchback with a B18B in it. Around 28-30 MPG was normal. I had an Integra with a B18C. Could get around 28-30 also. You will get better than those because of less weight in the CRX chassis, but no where near 40MPG. You need to find a D16 engine. With that light of a car, any D16 engine will get you around 40 MPG.

By the way, I noticed you were looking for a VX engine. If you are willing to rebuild it, I have a 1998 Civic HX D16Y5 longblock sitting in my garage. The #2 cylinder is bad. Only about 25 psi compression. But it did run until I pulled it out for a new engine.

Ecky · 03-23-2012, 09:16 PM

Sounds like you have the B16's tranny. To be clear, you want to run a B16 block with an LS (b18a/b) head? I don't think you'll have the clearance, it won't work.

The B16 is a hell of a motor but as others have said, it's not an economical one. It develops torque way too high in the RPM range and has a short stroke, better to get a new B18B block, or the whole motor. You can probably find one for less than $500 with low miles.

I run a B18B with the B16 tranny and I've been averaging about 34mpg since it warmed up, your car is lighter and more aerodynamic so you can probably do a little better.

I'd rather have the B18B tranny too, though.

drmiller100 · 03-23-2012, 10:50 PM

if you put the B motor in, sell the car and find something stock - preferably 90 or newer.

Optionally, find a newer d15, but it will be a PITA to install - the older crx's had that goofy engine mount which is NOT easy to change to a modern version.

Sularus · 03-23-2012, 11:43 PM

I wouldn't go short stroke. Short stroke=high RPM for power= less fuel mileage.
Long stroke=low rpm power= better mileage at lower rpm.

To illustrate this think of indy cars and F1 cars. Both have really short strokes and have to rev extremely high to make power. In the case of F1 cars that can get up to 18,500 rpm. On the other hand "stroker" motors have longer than factory strokes and are able to make more torque and power lower in the rpm band. In the case of fuel economy the longer stroke is preferable. Of course it all revolves around the transmission. If the transmission isn't geared for the speed and the engine it won't matter too much.

rx191 · 03-26-2012, 11:16 AM

it will be a b16 block with b18b head, the combo can be done it's just not optimal for performance. i got the head with the car and block was free, it needs rod bearings but that's it (copper on 2 of them, none spun) i figure i may be able to advance the cams to be able to get better mpg out of it, or at min decrease overlap. I will tune the ecm also to help out my chances.

I know this is not an optimum combo but i don't have more than about $50 in it at this point, so i figure why not try right? if anything maybe it will make a fun tinker toy until i can find a d15z1 and trans

Ecky · 03-26-2012, 10:35 PM

Maybe you could disable one intake valve per cylinder? What's the C/R with the LS head?

EDIT: Is that a good idea? If I'm keeping the revs below 4k, would it be better to run with only 12 valves instead of 16?

rx191 · 03-27-2012, 12:13 AM

the cr will be about 10.25, i thought of disabling an injector but then fuel would pool on the unused valve, i would have to make a custom intake to aim the injector at the one oping valve.

I have thought of making only one exhaust valve open, this arrangement was quite common years ago, and ford still uses it today. it seems to produce good low end tq and still let the engine "rev out"