Honda motor swap, opinions?

[owendavidj]

I currently have a 88 civic hatch dx, with stock d15 motor.
Summer driving gets me a steady tank after tank of 45mpg.
Winter driving obviously varies dramatically, anywhere from 30-40mpg avg/tank.

Well the previous owner didn't take care of my baby like i do most cars, and I'm burning oil faster than a lantern. Is time for new internals. I call my mechanic, explain my desires and also asked how much to shave the head slightly, and possibly find some higher compression pistons. He calls me back 2 hours later with options and pricing.

1 first option is a full rebuild of existing motor, replacing most parts and machining/polishing the rest. He did he'd also shave my had for very slight compression gains. Unfortunately there are no mods available for this older d15 without some serious expensive custom work. But he assured me when he's finished the engine would be BETTER than band new.

2 he happens to have a d16 Vtec motor from a 94 civic on hand. This motor has been rebuilt (but not quite machined/polished/tuned to the extent he would perform on my old d15). This wasn't an economy motor, as it's got about 135hp he claims. Vs. my old motor, this is multi point injection and also vtec. But this motor has mods-a-plenty, as one of Hondas more popular engines, and I'll admit that little extra hp would feel nice on step long freeway hills in the mountains that are oh so aggravating... This will match up to my old transmission fine, and i believe he did we can keep my old smaller alternator as well.

So...dilemma:

Obviously the rebuild on my old motor is going to be a great eco boost for me, no questions about that, but probably not going to help in the getting up steep mountain freeways dept.

What is your guys experience with the d16? My worry is that the swap for the new motor may leave me with WORSE mileage than my current beater. My mechanic points out that if i stay "under vtec" keeping the rpms low (which i drove this way anyway), and since I'll now have the more efficient multi point injection he thinks my mileage might stay the same. And he also points out that the options are virtually limitless with this motor, as opposed to no custom options with the old. (crankshaft, pistons, bolt on mods, etc etc etc).

The kicker: both jobs are quoted at $2k. The swap actually being slightly cheaper.

Sorry i don't have specifics on the EXACT motor, but this would be an (aprox) 135hp Vtec d16 from a 94 civic.....who has had real-world mpg existence with this motor? What do you guys think?

[Ecky]

I assume you have a D15B2?

Depends on the D16, but I'd probably stick with the 15. The 16 likely as some miles on it already, and is tuned for higher output, which will result in worse economy no matter how you look at it. If it's a D16Y5 (from the HX model) I'd take the D16 though.

[cosmick]

Originally Posted by Ecky

The 16 is tuned for higher output, which will result in worse economy no matter how you look at it..

That's not even a wise assumption, let alone set in stone. Part of the extra output is from the extra displacement, the rest must therefore be from greater efficiency.
Obviously the extra displacement shouldn't have to work as hard, anyone could claim that, but relevant experience shows that even with the extra displacement, the other changes to increase power can help MPG once you find what cruise RPM it wants.
I'd ditch the whole thing, let some kid pimp it out or whatever, and choose anything but a Honda.

[owendavidj]

Nice.....well, I'll never ditch the Honda, cheap, best mieage (in general) eat and cheap to work on. last 2 made it past 400k miles, with NO engine work. And prob had another 400k miles, if one wasnt stolen, wrecked, and the other rear ended by s teenager.

[owendavidj]

Sorry for small typos...thus forum doesn't read easy on a smart phone.
I'm still leaning towards the d16, bc i agree that it's a more effecient performance...can't i get it tuned to beat the d15 in economy?

[owendavidj]

And just found out the swap would be the d16z6

[some_other_dave]

Originally Posted by cosmick

Part of the extra output is from the extra displacement, the rest must therefore be from greater efficiency.

Different measures of efficiency. That efficiency is power per displacement, not power per fuel consumed. Either one can be labeled "efficiency", and they are parallel but not identical.

That said, your FE will probably not be much worse with the D16 versus the D15. I'd be surprised if it were better, though.

-soD

[Randy]

The D16z6 should be similar to your current motor. I drove a 4-door civic EX 5 speed with this motor and got 37 mpg averaged over 6 years. The exhaust and short geared transmission don't help mileage, so you'd want to keep yours if possible (it looks like the earlier D series were exhaust to the firewall, so that might not work). It's got the nice VTEC top end, but I'd think very similar performance otherwise.

To the central question: $2k is a lot of cash. You're getting great mileage as-is, but that's got to be more than what you could buy your own car for. Perhaps you could find something even better for the same price if you search around, especially with the low gas prices.

[Baltothewolf]

OP, another option would be looking around for a used D15Z1 to drop in. That would net some really nice numbers.

[Ecky]

Originally Posted by Randy

The D16z6 should be similar to your current motor. I drove a 4-door civic EX 5 speed with this motor and got 37 mpg averaged over 6 years. The exhaust and short geared transmission don't help mileage, so you'd want to keep yours if possible (it looks like the earlier D series were exhaust to the firewall, so that might not work). It's got the nice VTEC top end, but I'd think very similar performance otherwise.

To the central question: $2k is a lot of cash. You're getting great mileage as-is, but that's got to be more than what you could buy your own car for. Perhaps you could find something even better for the same price if you search around, especially with the low gas prices.

This is a fair point. Though the motor wouldn't be "new", you're getting into the range of being able to get a high mileage Insight in that price range and get 60-80mpg. There have been several in Florida for $1800-2600 lately.