Install BP DOHC head on BP SOHC engine

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August-15th-2003 | 03:21 PM

#31

mike323

Thread Starter

Registered User

Joined: Aug 2003

Posts: 68

From: Montreal, Quebec

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 | 05:34 PM

#32

zenilder

The Horns of Jericho

Joined: Feb 2002

Posts: 320

From: Southern Californ-I-A (909)

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 | 11:18 PM

#33

kcbhiw

Hoosier daddy?

Joined: Sep 2002

Posts: 563

From: Atlanta, GA

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 | 01:22 AM

#34

spooki

Protege Enthusiast

Joined: Jan 2003

Posts: 131

From: texas

amen brother

August-16th-2003 | 02:27 AM

#35

kagekun

Protege Enthusiast

Joined: Jul 2002

Posts: 151

From: Grand Forks ND

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 | 12:10 PM

#36

abeaujuin

Protege Newbie

Joined: Sep 2003

Posts: 5

From: Atlanta

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?