The first owner of my 93 Civic DX must have had a mishap that destroyed the engine, because it does not have the stock D15B7 engine in it. Instead it has a non-vtec D15B engine. The non-vtec D15B is one of several Honda JDM engine models commonly purchased by companies for re-sale in the United States. Typically these engines have 40-60k miles on them, all driven in Japan. Tough emission standards in Japan mean the engines are replaced at a very young age. All of the following are indications that the engine is from a Honda driven in Japan:
- The engine code on the front of the block a little below the distributor level is D15B (not D15B7 nor D15B2 nor any D15B[fill in with a number].
- The upper timing cover is in Japanese and gives the specs for a dual carbureted D15B's spark plugs, not a D15B7's.
- I measured where the timing marks are on the D15B's crankshaft pulley. The center mark of the three red marks is at 18 degrees BTDC. The center mark on a D15B7's crankshaft pulley is at 16 degrees BTDC.
- There is an external block-off plate on the upper rear of the engine sealed in place by liquid gasket and two bolts and nuts. The D15B2 and D15B7 also have cylinder heads with this aperture cast into it, but the blockoff plate is inside the aperture, about one-inch in, and it has no bolts. The aperture is for those D15B--s that were designated to become dual carburated at manufacture. Specifically, a mechanically driven fuel pump driveshaft fit through this aperture.
- My D15B's camshaft has an extra lobe on the end to drive the carbureted version's fuel pump. See the left end of the camshaft below. (Photo appeared on the net; can't remember where. Apologies for not crediting the person who put it up.) The D15B7 stock camshaft just has a gap, so to speak, where this extra lobe is.
The non-vtec D15B appears to replicate the D15B7 as follows:
- Same cylinder bore and stroke, 75 mm x 84.5 mm. These numbers are well-publicized.
- Same compression ratio, 9.2. This is well-publicized.
- Same duration for intake and exhaust valves: About 190 degrees and 208 degrees (at 0.05 inch lift). These numbers are not official but rather derive from reports from numerous aftermarket cam sites and measurements people at d-series.org took. Duration does not appear in OEM shop manuals.
After modifying the non-vtec D15B to have MPFI (and so using the USDM DX's original throttle body and intake manifold), the only differences that might affect engine performance are
- The cam lobe heights and the valve spring free length. These may be found in the OEM shop manual for the USDM D15B7. Unfortunately nowhere online is there an OEM shop manual for the JDM D15B. From much study, I think the D15B's camshaft is the same as the USDM D15B2 and Australia's D15B4. But what normal wear is for these parts might make the matter moot.
- Setting the timing correctly. The D15B7 specifies 16 degrees BTDC. The carbureted non-vtec D15B specifies 18 degrees BTDC. So if you have the D15B crankshaft pulley, you want to find the three, usually red, marks that are close together. Set the timing to the red mark closest to the white TDC mark. Generally MPFI burns the fuel air mixture more efficiently than a carbureted engine would, so the spark should occur closer to the maximum pressure in the cylinder or closer to TDC. Hence it makes sense that, all other things being equal, the timing for an MPFI would be a bit retarded (= closer to TDC) compared to a carbureted engine.
- Head codes -- My non-vtec D15B has PM3-8 stamped on it. At the junkyard, four United States origin (per the VIN) D15B7 heads had PM9-3, PM9-6, and PM3-4 stamped on them. Three Japanese origin (per the VIN) D15B7 heads had PM3-3, PM3-8 and PM3-13 stamped on them. See also http://www.automotiveforums.com/t691522-head_codes.html and http://www.honda-tech.com/showthread.php?t=2082366
- Camshafts -- See the discussion about the three different part numbers for the D15B7 camshaft at http://www.d-series.org/forums/engine-building/22640-sohc-non-vtec-cam-specs.html. Also see http://www.hondahookup.com/forums/showthread.php?p=2137331#post2137331
- JDM D15B Dual Carbureted Specs -- See http://www.cr-x.org/home/jdmspecs.html and http://www.honda.co.jp/HOT/ModelData/civic/92cv-k-109b/mx_sy.html (google for a Japanese-to-English translator), and http://d-series.org/forums/engine-building/23877-d-series-carbs.html
- Duration -- http://www.d-series.org/forums/engine-building/22640-sohc-non-vtec-cam-specs.html http://www.sohchonda.com/forums/index.php?showtopic=6622 http://psytronix.org/engine/local_copies/d16camshafts.html (I think intake and exhaust are reversed at this psytronix site) http://webcamshafts.com/index_blank.html?pages/vehicle_search.html
- JDM non-vtec D15B vs. USDM D15B7 and USDM D15B2 -- See moozregie post in particular at http://www.d-series.org/forums/engine-building/89846-d15.html#post1225448