Install BP DOHC head on BP SOHC engine

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August-15th-2003, 02:21 PM

#31

mike323

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Join Date: Aug 2003

Location: Montreal, Quebec

Posts: 68

Quote:

Originally posted by Protoss
most of the compression ratio is effected by the piston.

Miata BP piston compression 10:1
DOHC pistons produce a compression of 9:1
SOHC pistons produce a compression of 8.9:1

if you put a DOHC head on a SOHC pistons, you will get a lower compression ratio, than that of the stock DOHC. therefore more clearance from the valves. but if you go the other way, you MIGHT, maybe have valve issues.

Yes, your info on the pistons is correct but is the block height the same. What I'm trying to say is that maybe the DOHC block has more volume when it's pistons is at TDC, than the SOHC block.

On the Miata site it says if you install SOHC pistons on your DOHC block you'll end up with 8.2:1 compressionratio. That tells me that either the volume in the head is different on the volume between the piston's TDC and block height is different.

August-15th-2003, 04:34 PM

#32

zenilder

The Horns of Jericho

Join Date: Feb 2002

Location: Southern Californ-I-A (909)

Posts: 320

one other bad point of doing the SOHC->DOHC swap is that you'll be left with a cast crank. The crank out of a DOHC engine is a forged unit, and therefore a stronger crank.

you're better off getting a DOHC long block from a yard or something and having it checked. have anything that is out of spec replaced or rebuilt.

why exactly are you doing the swap and what kind of money are you planning to spend?

August-15th-2003, 10:18 PM

#33

kcbhiw

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Join Date: Sep 2002

Location: Atlanta, GA

Posts: 563

Quote:

i mean you aready have to changed everything but the block pretty much, why not get the thing pre-assembled and drop it in?

My sentiments exactly.

August-16th-2003, 12:22 AM

#34

spooki

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Location: texas

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amen brother

August-16th-2003, 01:27 AM

#35

kagekun

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Join Date: Jul 2002

Location: Grand Forks ND

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cause in some places its cheaper to just swap the head out yourself then pay for labor of having a engine lifted and then dropped.

September-11th-2003, 11:10 AM

#36

abeaujuin

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Join Date: Sep 2003

Location: Atlanta

Posts: 5

Harness

I have did the swap 92 dx block with the 92 lx head. I didn't change the ecu and the harness. the check engine light comes on and it fails emissions. I need to know where to get the harness and is it an easy job to do?