What engine/tranny for best GPM potential?
 

Hello all. my 95 civic HB is on it's last leg and after reading this GREAT site for a few weeks, I've decided to swap out everything in my SI in favor of a high efficiency powerplant. What combo will have the best potential?

I have somewhat gathered that the D15B8 will be the best choice while converting the gear ratio in the tranny to that of the HF. Does this sound correct, or should I go with the Z1 or B6? I just want to have it all figured out before I go buying parts. Should I also start looking for a VTEC-E ecu? Any help would be greatly appriciated! Thanks.

The good way to get high gas mileage would be to swap a small motorcycle engine into the car. A single cylinder 250 - 400 cc motor would give a lightweight car 60 mpg. How about a Suzuki GZ250? It gets 82 mpg as a motorcycle.

the B6 is going to have the OBD-0 where both the B8 and the Z1 are going to have OBD-1, the Z1 is also going to have the v-tec bits, along with the JDM D15B engine, of course if you can find a JDM D15B engine that has the 3 stage v-tec (you can either hack it for the 3rd stage, or keep the engine under 5,500rpm), but I would vote for for the D15Z1 or the D15B as they would both be able to take advantage of the v-tec wiring that is already in your SI, and as for a tranny, you have a hydrolic clutch, so sticking with a 1992 and newer tranny is going to be your easiest, and it's going to bolt in, for that the vx/cx tranny is most likely going to be your best bet.

Get a d15z1 and cx/vx tranny, that'll be the best combination. :thumbup:

OK, so purely MPG speaking...
 

So the D15B6 was only used up to 1991? That?s good info because in my state I have to keep the powerplants and auto series the same, (ie. OBD-1 for OBD-1).

When you say JDM d15B engine, does that include the JDM D15B8? If so, that narrows me down to the D15Z1 or D15B8. I am a very conservative driver anyway and I rarely reach 5K rpm so would the JDM D15B8 with the 3-stage v-tec have the most potential for efficiency? Or will the 16 valves of the Z1 (SVOboys choice) enable me to use a higher gear ratio resulting in higher MPG? I want to break the 50-MPG mark so if I need to sacrifice power and torque so beit.

I'm sure some of my questions are very amateur, but then again I am an amateur so... Thanks for all the help so far.

Sorry I think I replied in the wrong place. ob1coby.

good comments so far!

A couple of things I would like to do.

1st an underbelly pan is out of the question for this truck. Would never be smooth enough So I will need to build a HUGE air damn instead. Would not do much for my coasting however!

2nd is to find a taller rear axle. The gears are something like 5.61:1!!!!!!! That's horrible! They must make a gear set taller than this somewhere?

Did you mean to reply to this thread? Not that it matters, but you might get better help in a different topic.

has a whole page on the D-series of engines, including HP and toruqe, and years that it was used, and what type of OBD it has.
the JDM D15B appears to be differnt then the D15B8, just to avoid confusesion, of course the other advantage of the Z1, is that it uses commen, and avalible off the shelf parts, and if you keep things simple, and all in one family, then if you need to fix something, or go to sell the car, it's going to be much simpler.

Well I just looked at the JDM D15B specs and it has a lot more power and torque than the other two. I thought the Best efficiency will come from the engine with the least amount of horse power and torque. That leaves me with the D15B8 unless there are other factors involved that I'm just not getting (Not unlikely). I like your suggestion of eveything being bolt on and having easy access parts, but I would seriously consider any engine that has the most potential for efficiency even if that means buying JDM and doing some part chasing. I am feeling the pressure to go with the D15Z1 though. It is the most suggested. Is it the only one that will be direct bolt on? My only problem with it is that it has 8 more valves and 12 more horses over the B8. I hope my questions aren't getting cumbersome. Thanks again for the help.

There are three versions of jdm d15b, on like the z1, one like the z6, and one like the dx motor, whose engine code I have forgotten, I feel old now.

Anyway, z1 for the win, no matter what.

Really? That surprises me since the Z1 has more valves, HP, and trq, but that is also a pleasant surprise. OK, you've convinced me. Now all I have to do is find one. Anyone?

Hey, just out of curiosity, can I do any better with the JDM version of the Z1? It would have the three stage v-tec that Ryland was talking about, or would getting a JDM v-tec ECU do the same thing...?

The jdm d15b vtec-e is not the 3 stage d15b, the 3 stage is only 96-00 and is very hard to get up and running properly since you need to go obd2 and find the proper (rare) ecu.

the z1 engine acts like a 12 valve engine under 2,500rpm, and puts out a fair amount of low speed toruqe (good), and because of this, it's valve timing is tuned to alow it to run rather efficently at lower rpm, but if you do happen to rev it up past 2,500rpm that is when the variable valve timing (v-tec) kicks in, and opens up those extra 4 valves (giving it a total of 2 intake, and 2 exaust per cylender) preventing the engine from being totaly gutless, this ability is really handy when mearging in to buisy roads, or highways, if you were to take a look at the power band of the z1 it would be much wider/more useable, with just enough power where you need it, and a bit more waiting, if you down shift or rev it up.

Ok, I've have a couple lines on a vx motor/trans/ecu, but my next question is.. do all VX engines have the VTEC-E ECU? do I need the harness from a VX or will my SI be fine. Last question is what if I were to talk to a custom ECU maker like HONDATA. Think they sell or could make an ECU that would really fine tune for economy?

I haven't set an SI and a VX side by side to compare, but as I understand, the SI has all of the v-tec wiring, altho the ECU is not the same, and the ECU is in the car, pasenger side, under the carpet right under the dash, next to the door hinge, the only part of the wiring out side of the ECU that I think is differnt, is the o2 sensor wiring, the vx has that 5 wire sensor, and I think those wires all go to the ECU, so that's pretty simple, but as I said, no personal expearice, just reading stuff, and owning a vx.