A Little Makes A Lot Of DifferenceI'm building an EG hatch with a JDM D15B swap and I've been waiting to boost it for a while. But I need to make a decision on fuel management. Should I use a rising rate FMU or an SAFC? This is a daily driver/weekend drag car. Also, have you heard of people using Suzuki Vitara pistons for the D15B? Sounds kind of sketchy to me. I have a block from a '92 VX and was wondering if anyone makes aftermarket pistons for it, or if I should just build a Z6 bottom end.Devin ChouinardNew Hampshire
To answer your first question, no. While rising rate fuel pressure regulators do work, they are a band-aid fix for lack of a real engine management solution. Rising rate regulators limit tuning. Even the ones that are adjustable can only add or subtract fuel from the whole rpm/map range, rather than from specific points on the table.
A piggyback computer like an SAFC is great for tuning mild N/A cars, but not for properly tuning a turbo car. Usually, people team the AFC up with a set of big injectors (typically 450cc blue top injectors from a turbo DSM) and then subtract a substantial amount of fuel via the piggyback to compensate. This works better than the FMU because you can tune individual RPM points, but they aren't dependent on map sensor readings.
Instead, there are basically two maps divided by a user-set throttle position point to choose from. This is great because you can write separate maps for low throttle and high throttle (say greater or less than 60 percent), but if you think your car needs the same amount of fuel enrichment at 5000 rpm under 75 percent throttle as it does under 100 percent throttle, think again. Your best bet is to save your dimes and go for stand-alone engine management like Hondata or AEM. If you have a background in circuitry or are willing to learn, there are grassroots options available at pgmfi.org.
As for your bottom end, you're better off going with a D16 block. The bottom end geometry in any variant of D15 is different from that of the D16. The two D15's you have both come with 137mm rods similar to the D16 offerings, which means you can get them off the shelf, but the pistons are about 3mm shorter than the D16 slugs to make up for the shorter deck height.
The smaller pistons are not available off the shelf. Custom pistons will cost $200-300 more than a set of D16 pistons and since a D16 block can usually be found for $100-200, the price is offset and you'll gain a little bit in displacement.- Dr Barrios
ObscurityI was pleased to read the B16 vs. single-cam article in last month's issue. I have a '97 Civic EX with a D16Y8. My car was equipped with the 4-speed auto and I'm wondering if I can swap in other D series transmissions. If I were to keep the automatic, can I just swap in gears from the other tranny?
Some JDM transmissions have higher third and fourth gears for better acceleration, for example. I know I might lose top end and fuel economy, but I want better acceleration.
Also, can the D16Y5 (Civic HX) exhaust roller rockers be used in the D16Y8 head?Glen HagiwaraSunnyvale, CA
I'm not absolutely positive if you can swap D-series auto gears or not. I assume you can, but my sense is that it's not going to be worth it. The performance gains are likely to be minimal. A better option is to swap in the EX/Si S20 5-speed tranny. Your costs and labor will be the same as swapping in the auto, but you'll be going manual, which will give you the biggest gains.
The first time I saw under the valve cover of a D16Y5, I had the same reaction you did. "DUDE! D-series roller rockers!! NO WAY!!!" Upon further research, I found that the rockers are not swappable to a conventional SOHC VTEC head.
It doesn't stop there. If you really want to make this happen, you'll have to use the VTEC-E head. If you make a pin to lock the rocker arms together (essentially making a non-VTEC 16-valve head out of it), you'll be left with a head similar to that of a D16A6, but with roller rockers. Make a big, huge billet cam to make use of your new roller setup, and you've got a hell of a combination.- DB
Confuse-DMy step mom is giving me her EK hatch and I wanted to step up the game of the lil' four-banger. I got some used ZC pistons from a CRX Si at U-Pull-It and I was also looking for the D16YZ8 VTEC-E head, along with a header from a '99 EX (like you used in your B vs. D article). Can I take the five-speed from a '93 del Sol and swap it with mine (along with the clutch pedal, brake pedal, clutch master cylinder, and clutch lines)? The del comes with a D15 and a different kind of intake. I don't know if this interferes with mounting points or anything, but will it mate with my D16? Jonathan OgdenAtlantic City, N.J
Hmmmm, first of all, ZC pistons come from ZC motors, which are found in JDM CRX's, not the CRX you found at the junkyard. They're also found in '88-89 Integra motors, of which, there were probably 10 or more at the yard. The head you should be looking for is from a D16Y8 or Z6, not a YZ8, which does not exist. Both the Y8 and Z6 heads are VTEC, not VTEC-E.
The del Sol parts will fit your EK and you'll need to pull everything involving the transmission out, including the mount. Keep your eyes out for a '92-95 EX/Si tranny or a '96-00 EX tranny. These have the shortest gears available in a D-series transmission and make the driving experience loads more fun.- DB