Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - D15Z7 head to D16 mini-me advice

Madact · 10-31-2014, 09:21 PM

Goal is fuel economy, naturally (for its own sake rather than economic reasons w.r.t. this particular mod, break-even point might be 5 years if there are no hitches, so it's not justifiable just from that). A little more top-end power wouldn't hurt, of course.

Since reading your post I've played with a couple of compression calculators (didn't know they existed

), but I suspect you haven't set it up to stock specs first? 12-13:1 doesn't seem very likely, unless you're starting with a *very* odd combination of parts in the first place. I really hope this is the case, anyhow

D16Y4 has a compression ratio of 9.4:1 ... the combustion chamber volume is quoted here as 32.8cc, but though this info has been repeated a few times on the net, I couldn't find source material confirming this. The guy posting here says the combustion chamber looks identical to a D16Z6 (34.6cc), which makes more sense... also, D16Y4 and D16Y7 share the same head code (P2A-2), and the D16Y7 has a 34.6cc combustion chamber. I'd go with this as the figure.

By the same token, the info I could find D15Z7 all said 32.8cc for the combustion chamber. The head casting for this is a P2J, same as the D16Y8, which also is quoted at 32.8cc, so this passes the sanity check.

Setting up a compression calculator for a stock Y7 gives a compression ratio of 9.39, which is a match for the Y4 by part numbers and compression ratio - swapping to a Y8 head (same volume as the Z7) in the calculator gives 9.72, which would let me keep running 'regular' unleaded safely ('regular' is 91 octane here). For reference, the D16Z7 compression ratio is 9.6, so this seems like it should be fine w.r.t. not hurting lean burn performance/reliability AFAICT.

Only way I could get the kind of compression ratio you mentioned was with a D15Z1 head (completely different spec. and casting), combined with some crazy mismatched pistons.

From the tables here it looks like the Z1 has *massive* piston dishing, to go with its tiny combustion chamber size (25.3cc, much smaller than any other D-series).

Let me know if you think I've gone wrong anywhere there!

10-31-2014, 09:21 PM	#3 (permalink)
Madact EcoModding Apprentice Join Date: Aug 2014 Location: Adelaide, Australia Posts: 120 Emerald - '97 Honda Civic CXi 90 day: 40.13 mpg (US) Thanks: 53 Thanked 53 Times in 32 Posts	Goal is fuel economy, naturally (for its own sake rather than economic reasons w.r.t. this particular mod, break-even point might be 5 years if there are no hitches, so it's not justifiable just from that). A little more top-end power wouldn't hurt, of course. Since reading your post I've played with a couple of compression calculators (didn't know they existed ), but I suspect you haven't set it up to stock specs first? 12-13:1 doesn't seem very likely, unless you're starting with a very odd combination of parts in the first place. I really hope this is the case, anyhow D16Y4 has a compression ratio of 9.4:1 ... the combustion chamber volume is quoted here as 32.8cc, but though this info has been repeated a few times on the net, I couldn't find source material confirming this. The guy posting here says the combustion chamber looks identical to a D16Z6 (34.6cc), which makes more sense... also, D16Y4 and D16Y7 share the same head code (P2A-2), and the D16Y7 has a 34.6cc combustion chamber. I'd go with this as the figure. By the same token, the info I could find D15Z7 all said 32.8cc for the combustion chamber. The head casting for this is a P2J, same as the D16Y8, which also is quoted at 32.8cc, so this passes the sanity check. Setting up a compression calculator for a stock Y7 gives a compression ratio of 9.39, which is a match for the Y4 by part numbers and compression ratio - swapping to a Y8 head (same volume as the Z7) in the calculator gives 9.72, which would let me keep running 'regular' unleaded safely ('regular' is 91 octane here). For reference, the D16Z7 compression ratio is 9.6, so this seems like it should be fine w.r.t. not hurting lean burn performance/reliability AFAICT. Only way I could get the kind of compression ratio you mentioned was with a D15Z1 head (completely different spec. and casting), combined with some crazy mismatched pistons. From the tables here it looks like the Z1 has massive piston dishing, to go with its tiny combustion chamber size (25.3cc, much smaller than any other D-series). Let me know if you think I've gone wrong anywhere there! Last edited by Madact; 11-01-2014 at 12:42 AM..