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Old 11-19-2007, 11:38 AM   #1
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rebuilding D15Z1 1.5L Civic VX engine...what to change??

I just picked up a '92 civic HB w/ 155K miles as a commuter car...I'm in the process of buying a D15Z1 1.5L Civic VX engine to rebuild myself, then swap into the civic.

*I've been searching this forum (and google too) regarding my questions...found lots of great info, but still have questions:

what internal engine modifications should I do for FE?

here's what I was thinking:

1) shave head (this should increase compression ratio, and FE, right? any ideas of what compression ratio to aim for?)

2) smooth out all casting surfaces and port match (intake/exhaust manifold, ...)

3) lightweight pistons/rods...is this worth it?


any other ideas (or comments on my ideas) would be great!

*I'm coming from the opposite side of FE...I autoX a BSP 350Z...so I understand most of the ideas for FE, just haven't thought about it enough!

thanks!
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Old 11-19-2007, 11:45 AM   #2
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Originally Posted by first350 View Post
I just picked up a '92 civic HB w/ 155K miles as a commuter car...I'm in the process of buying a D15Z1 1.5L Civic VX engine to rebuild myself, then swap into the civic.

*I've been searching this forum (and google too) regarding my questions...found lots of great info, but still have questions:

what internal engine modifications should I do for FE?

here's what I was thinking:

1) shave head (this should increase compression ratio, and FE, right? any ideas of what compression ratio to aim for?)

2) smooth out all casting surfaces and port match (intake/exhaust manifold, ...)

3) lightweight pistons/rods...is this worth it?


any other ideas (or comments on my ideas) would be great!

*I'm coming from the opposite side of FE...I autoX a BSP 350Z...so I understand most of the ideas for FE, just haven't thought about it enough!

thanks!
First of all, a 350z and a vx will be day and night, but about the internal mod, I don't think you will gain a LOT of FE, because stock, the vx is already getting around 50mpg, and going more than that, it will take aero mods.

Look at that, 2 members on this forum with civic hb 92-95
http://www.gassavers.org/showthread.php?t=774

http://www.gassavers.org/showthread.php?t=5614
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Old 11-19-2007, 12:51 PM   #3
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Originally Posted by BIBI View Post
First of all, a 350z and a vx will be day and night, but about the internal mod, I don't think you will gain a LOT of FE, because stock, the vx is already getting around 50mpg, and going more than that, it will take aero mods.

Look at that, 2 members on this forum with civic hb 92-95
http://www.gassavers.org/showthread.php?t=774

http://www.gassavers.org/showthread.php?t=5614

thanks for the response...I saw those threads, and have started a long list of "To Do Aero Mods"...I feel weird getting so excited about modding the civic for FE .
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Old 11-19-2007, 01:01 PM   #4
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Remember that you want turbulence after the injectors leading into the combustion chambers to encourage atomization of the fuel mixture. IIRC most everything is already port matched on the D15Z1.

I'll have to check since I'm in the middle of rebuilding a spare Z1 that I have. the only thing that I am making sure I do is to radius the oil passages and rebuild the oil pump. Other wise replace the valve stem seals, piston rings and other gaskets and call it a day and spend just around $100 to have a mighty mighty gas saver engine.
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controversy is an idea thought up by weak people who are too afraid to hear the truth.
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Old 11-19-2007, 01:11 PM   #5
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Remember that you want turbulence after the injectors leading into the combustion chambers to encourage atomization of the fuel mixture. IIRC most everything is already port matched on the D15Z1.

I'll have to check since I'm in the middle of rebuilding a spare Z1 that I have. the only thing that I am making sure I do is to radius the oil passages and rebuild the oil pump. Other wise replace the valve stem seals, piston rings and other gaskets and call it a day and spend just around $100 to have a mighty mighty gas saver engine.
so you don't replace pistons? I had found a complete VX rebuild kit for around $500...I was planning to just get that. Where did you buy your rebuild kit?

thanks!
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Old 11-19-2007, 04:06 PM   #6
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I've also seen those ebay rebuild kits with pistons, but I would use the factory pistons before an ebay piston. I would go with new rings, main and rod bearings (maybe get the crank rebalanced), and replace the valve guides and seals. Other than that I don't see how you could improve the VX much more.
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Old 11-19-2007, 05:55 PM   #7
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I've also seen those ebay rebuild kits with pistons, but I would use the factory pistons before an ebay piston. I would go with new rings, main and rod bearings (maybe get the crank rebalanced), and replace the valve guides and seals. Other than that I don't see how you could improve the VX much more.
Exactly my point. If it ain't broke, don't fix it.

The pistons are fine on my motor, don't need to replace them.

Things I am replacing:
  • Piston rings
  • Valve stem seals
  • Crank bearings
  • Main bearings
  • Water pump
  • Timing belt
  • Head gasket (since the head will be off for the rebuild)
  • Rear main seal
  • Front main seal
  • Oil Pan gasket
  • Valve cover gasket
  • Spark plug tube seals
  • Distributor o-ring seal
  • Camshaft seal

That is all I can remember at the moment.

The sleeves were in perfect shape along with the pistons and crank. I will be inspecting the condition of the oil pump while I'm radiusing the oil passages and such.

I've spent right around $130 for all the gaskets, rings, bearings, and parts. It's good to know the right people.
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controversy is an idea thought up by weak people who are too afraid to hear the truth.
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Old 11-20-2007, 01:57 AM   #8
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Exactly my point. If it ain't broke, don't fix it.

The pistons are fine on my motor, don't need to replace them.

Things I am replacing:
  • Piston rings
  • Valve stem seals
  • Crank bearings
  • Main bearings
  • Water pump
  • Timing belt
  • Head gasket (since the head will be off for the rebuild)
  • Rear main seal
  • Front main seal
  • Oil Pan gasket
  • Valve cover gasket
  • Spark plug tube seals
  • Distributor o-ring seal
  • Camshaft seal

That is all I can remember at the moment.

The sleeves were in perfect shape along with the pistons and crank. I will be inspecting the condition of the oil pump while I'm radiusing the oil passages and such.

I've spent right around $130 for all the gaskets, rings, bearings, and parts. It's good to know the right people.
I personally am not a big fan of reringing. If you do this, you are increasing piston to cylinder wall clearance (due to material removed by honing). And this will only increase the odds that you will experience piston slap. The honing process (if not done after boring) will also exaggerate any imperfections in the cylinder wall. If you are going to go into the motor and replace stuff, but don't want to replace the pistons, then it is robably best to leave things as they are. Otherwise, get new pistons and bore/hone your cylinders.

As for compression, increasing compression will indeed increase fuel economy. BUT, you could end up having to buy midgrade or premium fuel to prevent detonation. This could result in increased fuel cost, despite imroved fuel economy. So increasing compression might not be a good idea.
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Old 11-20-2007, 06:47 AM   #9
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I personally am not a big fan of reringing. If you do this, you are increasing piston to cylinder wall clearance (due to material removed by honing). And this will only increase the odds that you will experience piston slap. The honing process (if not done after boring) will also exaggerate any imperfections in the cylinder wall. If you are going to go into the motor and replace stuff, but don't want to replace the pistons, then it is robably best to leave things as they are. Otherwise, get new pistons and bore/hone your cylinders.

As for compression, increasing compression will indeed increase fuel economy. BUT, you could end up having to buy midgrade or premium fuel to prevent detonation. This could result in increased fuel cost, despite imroved fuel economy. So increasing compression might not be a good idea.
1) So if I am going to bore/hone the block, I assume I should get a slightly larger piston/ring set-up, right? (This will be my first engine build...I've done just about everything else, except a full rebuild)

2) Any idea of what compression ratio to aim for that will allow me to still run 87 octane?

thanks for all the help guys, this forum is great!
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Old 11-20-2007, 12:12 PM   #10
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Well, my experience with Honda engines is in 100% favor of TomO's recommendation. I have several engines I have done exactly what he described and from my experience it has just greatly extended the engine life, increased the oil pressure and worked great.

I did rings, rod bearings, main bearings, valve guides, new oil pump and new gaskets. I honed the piston walls and reused the original pistons. It doesn't seem to use any oil and runs fine.
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