D15B vs D15Z1

[Viceral]

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?

[Ryland]

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?

[drmiller100]

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.

[Viceral]

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?

[Ryland]

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.

[arcosine]

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.

[Viceral]

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.

[Ragnarok Warrior]

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.

[Ryland]

Originally Posted by Ragnarok Warrior

As far as the "boost" button is concerned, Hondas use electronic controls for the cam phasing correct?

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.

[Viceral]

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.