mike323

Can I install the BP DOHC head on my BP SOHC engine?
I know it can be done, since they same part # head gasket is used but what else needs to be done.

Do I need to install the BP DOHC intake manifold or can I keep my SOHC intake manifold? Are they the same intake manifolds?

I've searched but didn't find answers to my questions.

kagekun

lol i would have to call you a lie since ive started like 2 threads that ask the same question. But yes you can, it requires more then the head tho.


ill just give you the parts minus the chatter from my swap notes.

-water pump from a DOHC engine (so grab that while you're getting the head. check for rust on these puppies, too)
-oil cooler (sits inbetween block and oil filter, you'll need this to have the water hoses fit properly, otherwise you're on your own to get custom fitted water hoses)
-water hoses from DOHC
-DOHC timing belt
-DOHC timing belt cover (not a necessity)
-Distributor
-DOHC Intake manifold (sohc doesn't have VICS)
-DOHC exhaust manifold (bolt pattern is different)
-DOHC ECU and wiring harness

kcbhiw

Don't forget the pistons. The DOHC pistons have clearances for 4 valves while the SOHC has clearances for only 2. You'd probably find it much easier to just drop in an entire DOHC engine.

mike323

The pistons have nothing to do with the swap. If you know how the otto cycle works than you wouldn't bring this up. The valves never come close to the piston during motion, unless you alter the cam timming but allot. The reason for the grooves on the piston is if you're timing belt snaps than you can salvage the pistons and valves.

mike323

Why do I need the water pump, is it because they have different size pulley, or does it have something to do with the timing belt?

Are the distributors from the BP DOHC and SOHC different, they use the same cap and rotor?

What's VICS and what does it do? Is it some kind of internal plates in the intake manifold that open/close at different rpms?

If I use the DOHC ECU what do I need to do keep my existing wiring harness?

kcbhiw

I'm totally familiar with how engines work and why things are where. But why do a half assed job?

hotrod0001

Who said it was a half assed job? Yeah you need alot of parts, but hey he can do what he wants. And performance wise the sohc block with the dohc will yield a higher compression then the Dohc motor. Oh and does this mean you are calling Bizob car a half assed car since he did this exact swap??

kagekun

You do need the water pump, i cant remember off the top of my head why. But the dizzy is infact differant, its like the bolt pattern is differant. VICS are the butterflys that are inside the manifold, trust me you want them. Im not sure about what you would have to do to keep your existing harness.

sweetprotege93

The SOHC has 4 valves per cylinder also.
How would you yield a higher compression from lower compression pistons?

I think you should just go with a BP swap personally. But whatever floats your sail.

owinbush

i'm in the process of doing the same swap except i'm going to bump up to a turbo in the process. basically, you'll need to get everything that is attached to the cylinder head and preferably from one engine...thats how i got mine.
the guy i got the parts from had just learned the hard way that apparently there are several different distributors for the sohc and the dohc. they all fit but the timing gets really hard to deal with if you don't have the correct distributor. also make sure you get the ecu and harness. i've been hunting for the harness for a couple of weeks now.

speaking of harness anyone out there have one for sale?

mike323

I beleive my SOHC engine has 2 valves/cylinder. My BP engine is from a 92 323 LX and they have 8V.

mike323

Why would I get a higher comperssion if I use the SOHC block with the DOHC head?

Does the volume in the SOHC head larger than the volume in the DOHC head? That would be the only reason why it affect compression ratio.

kcbhiw

It's just a safety factor. If you ever snap your timing belt, the valves and pistons will clash.

I stand corrected. I'd forgotten that the SOHC does, indeed, have 4 valves/cylinder. However, I'm not sure if they are the same size (doubt it).

Good luck with your head swap. Personally, I'd rather save myself the effort and just drop an entire BP in.

Bruce95fmla

you guys know you can get a BP dohc on www.car-part.com for as cheap as 250 dollars.

I have even seen some as cheap as 100 ..

midnightblue97

NONE of the Mazda 4 cylinder engines are an interference design except for the F2.
Don't worry about the timing belt breaking.