D15B vs D15Z1
 

So I've needed to replace the engine in my 88 crx si and after doing a bit of research it seemed like the d15z1 with the hf transmission was the way to go. But just as I was about to get the engine, it got snatched up and I ended up with the 3 stage VtecE d15b instead, on t the advice of my very knowledgeable "car-guy." Basically he was saying that while B probably wasn't quite as fuel efficient, it wasn't much of a difference and well worth the additional hp. My question is what kind of economy could I expect from both of these engines in an otherwise stock Crx Si, and whether I should still go ahead with the HF tranny with the B?

From my understanding the trouble you will have with the 3 stage v-tec engine is finding an ECU that will work with it as that engine was never sold in the USA and the intake on that engine is larger for the higher revs, that is the main reason why you can't get the same kind of mileage out of it, also I don't think (could be wrong) but the 3 stage v-tec ECU might not allow for learn burn either, so what can you do about it? you could get an intake an exhaust from a D15z1 engine, along with the 5 wire o2 wide band o2 sensor and a civic VX 49 state ECU and at that point the 3rd stage in the v-tec, opening up the valves a bit more would be the only part you would be lacking, of course that could be controlled outside of the ECU with it's own Arduino or some other micro controller to trigger that solinod.
Can any one confirm or deny that the D15b engine doesn't have lean burn?
Otherwise it seems like folks are getting in the low to mid 50's with the D15z1 engine as long as they are not running A/C and I would think that the D15b would be about the same if you have the smaller intake and 5 wire o2 sensor on it and this is just a guess, but mileage around 45mpg or so otherwise?

that is a TOUGH swap I am told. If you look at the driver's side motor mount, the older D series engines like your's have a weird weird motor mount compared to the more modern stuff.

there are a surprising number of 86-89 acuras out there which all have DOHC which give 125 or so horsepower and are a lot easier to bolt in. They have the same motor mount your car has I believe.

For mileage, you are probably better off with the stock engine you had - they are good engines generally but only have 80 or so horsepower.

The stock engine I have is a 1.6l with 108 hp, that at best has gotten me 35 mpg. I'm pretty sure either of these engines would beat that. That and it's about to blow up on me anyway haha. As for the lean burn, I know that in low rpms the B only operates on 12 valves which is supposed to reduce fuel consumption. Dunno if that's the lean burn or not, but I still think it's pretty cool. Also, the ecu issue was a known concern going in, so we are rigging up a switch and a button so I can control the various stages manually (the switch will control the changeover from 12 to 16 valves, and the button to toggle the 3rd stage (which I hereby refer to as the boost) I don't plan to use the boost much and will probably use it less than the computer, but it's nice to have in a pinch. That's also part of what I wanted to know with the HF transmission. Would that keep my rpms lower and in turn allow me to use the first stage (efficiency) longer?

Lean Burn is when the engine leans out the fuel to air ratio, Honda does this when the engine is under a light load, like while cruising down the highway, going from a standard 14.7:1 ratio to a ~20:1 ratio, allowing the engine to burn a lot less fuel after you get up to speed but to do this you need an ECU that allows this and you need a wide band o2 sensor, this is the 5 wire o2 sensor as it has a heater and more or less two different o2 sensors in one package.
A few people have swapped wiring harness so they can use the Civic VX ECU, and it seems like I saw a few of those on Ebay the other day, you would still need a button for that 3rd stage V-tec.
Getting the engine to fit in the car seems like more of an issue, but that is up to you and your skill set.

You could expect 45 to 50 mpg with the HF engine and 49 state HF 5 speed transmission, but it depends on your driving style.

Thanks Ryland. We were able to alter the engine mount with no real problem and it's in there. For now I'm stuck with the jury rigged vtec, but getting the ecu and the 5 wire o2 sensor will definitely be my next big priorities. I will update this with my results.

As far as the "boost" button is concerned, Hondas use electronic controls for the cam phasing correct? Toyotas use vacuum for the phasing if I'm not mistaken. I've heard of the fart can group doing this sort of thing so they can drive around on the v-tec cam all the time.

Yes, it's an electronic valve that opens up an oil passage to move a pin that locks the rocker arm to the follower that rides on the other cam lobe.
On the Civic VX engine (D15Z1) that happens at around 2,500 RPM.

So after my first set of testing I'm averaging a combined mpg of 41.2 mpg. (about 100 miles on the highway averaging 70 mph and about 100 miles in town shooting for 40 mph whenever possible) This is without the ecu and with the stock SI transmission.

Is everything 100% hooked up? I don't suppose VTEC is engaging like it should, is it?

si trans is pretty low geared I believe. Probably about what you should expect for mileage from that engine.

There pretty much is no Vtec at the moment. I hooked the 12 to 16 valve switchover to a switch, but without the ecu, the lean burn doesn't activate at all yet. I usually keep it at the 12 valve setting and have had no problems with acceleration or power even at highway speeds. If anything, the car is actually more fun than it was with the SI in it.

I don't know how it compares to other transmissions, but I know it has the highest gearing of any of the CRXs by quite a bit. That's a big part of why I'm debating throwing in the HF tranny. With the lower gearing I should be able to keep the RPMs lower and maintain lean burn longer (once the new ecu is chipped and installed), even at highway speeds. Right now in 5th gear 50 mph is the fastest I can go while keeping it under 2500 rpm, and typically I drive quite a bit faster than that.

low geared means it revs high.

There are a LOT of people who want your SI trans - you can probably find someone who will do the swap for you.

Haha oh my bad.

With and HF transmission you should be going 65mph with the engine spinning 2,000rpm or so and that engine should have enough power to keep that car at 30mph in 5th gear with an HF transmission on a flat road.

I have alot of experiance with hondas. I had a DX crx, sold it to get a 98 DX civic hatch. Anyways. You dont need vtec, or to ever worry about it or hook it up. They say you need to hit it every 5000 miles or so so it doesnt gunk up the vtec oil passage. but! if you dont ever want vtec (and lower gas milage) then dont hook it up. You motor still has more power than a stock si without it.

The HF or DX tranny is what you want for gas millage, or a 5th gear swap from one. The HF is better. I dont see any reason why you wouldnt be getting 45-50 mpg combined after a tranny or 5th gear swap.

Again this is just my 2 cents

Yea, that is what I was thinking. Would it be better to swap the whole tranny or just the 5th gear? I feel like the tranny would be easier to do if it was all the same.

Although I do plan to at least hook up the vtec E properly.

Swapping the whole trans would be easier. You have to pull the trans out and open it up to swap gears, and you only have to remove the trans from the car if you're swapping.

The HF has a taller top gear, and it also has a different ring and pinion ratio ("final drive") so that every gear is even taller than it would be in a DX or an Si transmission.

The DX (standard) and Si actually have the same gear ratios, but the final drive ratios are different which effectively gives the Si shorter gears all around. The individual gears for the HF are all taller (except possibly for reverse?) and the final drive is taller as well.

-soD

yeah the gear swapping is a ninja task lol. I may consider it myself to keep power and still have good cruising MPG. But my feeling is that this is not your concern? then why hook up vtec? it will only hurt your MPG. Vtecs only purpose is power. Bigger cam lobes and more fuel and timing = less MPG. honestley your better off without it

My interest is the vtecE which does help fuel economy

...supposedly

yeah I dunno. to my knowledge vtec has always been about power. efficient power by allowing 2 camshaft profiles, one for mid range normal driving and the other for power. combined they make the most power and fuel efficiency you can get out of these small motors. but take the vtec out and I believe you will get better mileage. just make sure you have a way of tricking the ECU so your not running the check engine (closed loop) program, or you will have terrible mileage.

I suppose you can make or brake the theory by testing it yourself.

As I understand it, the vtecE is a little different. Instead of using more gas to get more power it drops to 12 valves instead of 16 and goes into lean burn to use less gas when cruising under 2500 rpm. That is the first stage of the engine. The second is the normal 16 valves and is really no different from any other D15 engine, but the third stage is standard vtec and is exactly what you are saying. More power from a smaller engine by switching the cam shaft profile. At the moment I have hooked up the different profiles to switches I can control manually, but really the lean burn is the part I'm most interested, but I need to have the actual ecu for that. I have noticed a small boost I in fuel economy when I keep the car set to stage 1 without too much loss of power though, so that's cool. As for the third stage, you're right, I'm not terribly interested in it, and I never get the rpms high enough to acutely use it, so I may just opt against it.

any update?
 

how did this turn out? has anyone successfully mated a d15b with vx intake and exhaust incl 5 wire sensor and vx cat, coupled to tall hf tranny? i found the thread informative but vtec-e/ecu issues seemed unresolved. thanks for any update