VX head on DX engine?
Hey folks, few questions about my Civic. It's a 94 Civic DX Coupe with a D15B7 engine and a VX transmission. I'm trying to get the VX MPG figures with my car without the engine swap, so my question is, can I put the D15Z1 cylinder head on my D15B7? I know I have to run the D15Z1 P07 ECU and possibly the distributor, but I want the lean burn function of VTEC-E, and the better MPG's! I've already dropped the weight of my Civic with a $100 carbon fiber hood that was cracked, and I repaired, and my DX has no A/C or power steering from the factory. (Might add the A/C though). I'm trying to shed 200 lbs. off my coupe to bring it down to VX level. I also have 98 Honda Civic HX 14" wheels, which are very light weight, and comparable to the VX 13" wheels. Any help is appreciated!!
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You can probably do the swap. BUT, your compression ratio is going to be quite outlandish due to the small chambers on the VX head. This is NOT a good thing if you are going to be running lean burn. And although higher compression ratios typically do mean better FE, you might be stuck running premium (which could negate cost savings). My advice? Just do a full VX swap.
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Just to clarify what he's saying: the VX pistons are different than DX pistons.
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I wouldn't be SO concerned about the cars weight either. My friend has a VX swap in his heavier-than-VX del sol and he is still able to get the same mileage as my VX and as his old VX. I think lean-burn, tranny gearings, the "3-valve" swirl mode, and driving habit has more to do with MPG than anything else. You might want to address some Aero issues on the coupe since that is something that will affect your MPG if you do a lot of highway driving. Good luck on the swap! |
Maybe you can put a thicker head gasket on the motor to get rid of some of the high compression. Not sure if they make a gasket thick enough to supplement your problem. Just a thought...
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this might help:
https://www.zealautowerks.com/dseries.html FYI I did a hx onto cx d16 mini-me swap and raised my compression to 10.3/1 from 9.6/1 and still run regular with no pre ignition. Quote:
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You could put the VX head on your B7 if you also installed VX pistons. |
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https://en.wikipedia.org/wiki/Honda_D_engine#D15B7 https://en.wikipedia.org/wiki/Honda_D_engine#D15Z1 Look at the compression ratio listed there. |
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The trick is to find a combination that nets you a nice, workable compression ratio. 10 or even 11:1 can be streetable, but Honda tends to keep D-motors around 9:1 for the sake of reliability and consistent performance in all operating conditions. Cranking up the compression can improve combustion efficiency, yielding more torque and better fuel efficiency, but also makes the engine more prone to knocking/detonation in unfavorable conditions (high ambient air temperature, combustion chamber hot spots, lean air/fuel mixture, etc.). This can be managed by requiring higher octane gas, but nobody likes the premium price tag that comes with premium gas, especially if they're buying an economy car with an economy engine (the whole D-series lineup really). |
I like this. Its interesting that people on here are interested in civic's. I've been a member of other forums where the focus is more on HP and repairs and not so much mileage. but even so you have to do a lot for a honda to not get good mileage regardless.
Well anyway, there's one other person that I know of, well a person thats recorded his build that's running high compresion on 87 with minimal timing retard in certain areas. I personally am running up to 7psi on 87 with 9:1:1 cr (more or less depending on what some head work did to the chambers and the 3 layer HG I running). I'm really not pulling any timing at all. -.6-.7 per lbs of boost. and non out of boost. the effective ratio is 13.7:1. no detonation |
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IMHO if you're going to go through the trouble of wiring up the car for the Z1 head, you might as well just swap in a full Z1. It's safer and easier to deal with should any issues arise.
There is a person local to me (we shall call him Mr. Uninformed Ricer) that swapped a Z1 head onto a B7 block. He retained the B7 intake and exhaust manifold along with the B7 injectors. He also used the P06 ECU though. The car will not even run for him anymore, he can barely even get it to start. The car did run for about a month though. But then he told me that it started misfiring and running worse and worse. I told him that was because the motor was knocking severely. And now it won't even stay running anymore. I told him that when he swaps the head out for a Z6 head to give me a call so I can inspect his pistons and see how bad they look. |
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