VX head on DX engine?

[jasonty]

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!!

[StorminMatt]

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.

[suspendedhatch]

Just to clarify what he's saying: the VX pistons are different than DX pistons.

[Danronian]

Originally Posted by StorminMatt

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.

I agree.

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!

[civic lover]

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...

[mini-e]

this might help:

http://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.

Originally Posted by jasonty

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!!

[GasSavers_bobski]

Originally Posted by mini-e

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.

If you bolt a 'Z1 head onto a 'B7 block, it will put the compression around 12.3:1. While you may be able to tune an engine to run at those compression levels, it's not going to work well with the stock VX ignition maps. Adding lean burn on top of that would likely damage the engine, if it ran at all.

[mrmad]

Originally Posted by bobski

If you bolt a 'Z1 head onto a 'B7 block, it will put the compression around 12.3:1. While you may be able to tune an engine to run at those compression levels, it's not going to work well with the stock VX ignition maps. Adding lean burn on top of that would likely damage the engine, if it ran at all.

Plus the VX piston domes are dished or concave and the B7's are flat. The lean burn swirls into this dish if the VX piston domes to function properly.

You could put the VX head on your B7 if you also installed VX pistons.

[imzjustplayin]

Originally Posted by StorminMatt

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.

I don't think you guys are aware of the fact that the B7 has a HIGHER compression ratio than the Z1.

http://en.wikipedia.org/wiki/Honda_D_engine#D15B7
http://en.wikipedia.org/wiki/Honda_D_engine#D15Z1

Look at the compression ratio listed there.

[GasSavers_bobski]

Originally Posted by *************

I don't think you guys are aware of the fact that the B7 has a HIGHER compression ratio than the Z1.

Yeah, but we're not talking about stock engines here. The various D-series heads have different volume combustion chambers (the domed area the valves operate in) and corresponding amounts of dish and dome in the pistons to keep compression reasonable. When you start messing around with the head/piston combinations, you can get very high (small combustion chamber with a high-domed/long compression height piston) or very low (the opposite - large combustion chamber with a heavily dished/short compression height piston) compression ratios.
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).