FAQ: 1.6 SOHC to DOHC HEAD & Vice Versa Myth

Limegreen mx-3 · Post by **Limegreen mx-3** » July 27th, 2006, 11:09 pm

Like the title says BUT i am going to check if both heads are interchangeable between both blocks. DOHC block with a sohc head and a sohc block with a dohc head. just want to see if everything match up or not.

I have no intentsions of getting them running. Since i have both engine and have the spare time to play around with them. since i am turbochargeing the sohc if it blow as a spare i would to use a DOHC block with a sohc head. i'll take pic's and update on the interchangeabely of the topic. laters

Limegreen MX-3

Also i was looking into adjustable cam gear and to my surprise i check if a BP cam gear would match up and it did every teeth match up. got me thinking.

Tunes67 · Post by **Tunes67** » July 27th, 2006, 11:16 pm

To my understanding.. the blocks are the same except the DOHC block has 2 more oil passages than the SOHC block. The SOHC head could probably go on a DOHC block since the head would probably just block off those oil passages. The DOHC head needs those oil passages though and if they werent there as with the SOHC block.. premature valve train damage would definately occur. This is what I have been informed of anyway. Best of luck on your experiments

Tunes67

Josh · Post by **Josh** » July 28th, 2006, 12:19 am

Tunes67 wrote:To my understanding.. the blocks are the same except the DOHC block has 2 more oil passages than the SOHC block. The SOHC head could probably go on a DOHC block since the head would probably just block off those oil passages. The DOHC head needs those oil passages though and if they werent there as with the SOHC block.. premature valve train damage would definately occur. This is what I have been informed of anyway. Best of luck on your experiments

Tunes67

nope, the ports will still be half way exposed. like i said in previous posts, the 1.6 miata head will work and the 323 head will work. they will swap on with no problems, but the b6de head had bigger ports so a little bit more power.

Tunes67 · Post by **Tunes67** » July 28th, 2006, 12:45 am

Didnt the miata's come with the DOHC B6 engine before they switched to a BP?

Tunes67

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 11:10 am

i compared both blocks side by side heads taken off. the head gasket looks very much the same like twins. i don't know where this (the ports will still be half way exposed Josh ) (DOHC block has 2 more oil passages than the SOHC block. Tunes67) I NEED TO TAKE PIC WISH I STILL had metiatext. The top of the blocks look very much the same i don't see 2 more oil passages on the dohc. going back to check it out more. laters

When i am done with experment hopefully some of them mod. woll put it as a sticky do stop them dumb newbies & sohc guy that want to convert to a dohc 1.6 from asking the damn same ? over and over again.

Bochek · Post by **Bochek** » July 28th, 2006, 11:12 am

i allways thought this was a myth, its not like mazda to change a block to make a different head fit, as far as im concerned all of the b6 blocks should be identical. same with the bp blocks, altho there might be a difference between the b8 block and the bp.

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 11:18 am

Bochek wrote:i allways thought this was a myth, its not like mazda to change a block to make a different head fit, as far as im concerned all of the b6 blocks should be identical. same with the bp blocks, altho there might be a difference between the b8 block and the bp.

the B8 block looks very much like the BP seen some with a gridle guard like the BP i bet there probly the same if i do what iam doing with the 1.6 SOHC DOHC engines.

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 11:45 am

I took out the Head Gaskets from both blocks and to my surpise every hole that on the dohc is on the sohc i did find one difference . Two holes above the water pump. The two holes are 9.75mm on the dohc where the sohc two holes are 6.15mm. thats withe cooling system. only difference i found between both blooks.

As close as the head gaskets look they both are different. They fit fine on either block. in other words the dohc head gaskets uses ports that the sohc has sealed off and the sohc uses ports that the dohc has sealed off.

If u wanted to use a dohc head on a sohc block u are going to need to use the dohc head gasket as well. clean up the ports that the sohc seal off and u 'll have the sohc block ports matching withe the dohc head gasket. u'll also need the dohc water pump and misalance timing belt setup.

But in my opinion i think its a waste of time to convert a sohc to a dohc lots of parts u'll need like the ecu and wiring harness from a 94+ models to run the hybrid dohc correct. with i don't think its a hybrid. waterpump convert the sohc timing system to a dohc timing system. exhaust and intake manifold. lot of stuff u have to do.

know some info is done but for u guys that a have a sohc mx-3 just swap ot for 1.8 dohc BP a lot easier than converting ur sohc to a 1.6 dohc. just my opioion.

Limegreen mx-3

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 12:23 pm

The dohc head fits just fine on the sohc block with the dohc head gasket.

The sohc head fits just fine on the dohc block with the sohc head gasket.

the 12 head bolts line up right on both swaps..

Bochek · Post by **Bochek** » July 28th, 2006, 12:31 pm

problem solved, so the blocks are the same, and the head/headgasket makes the difference on wich ports get used?

Tunes67 · Post by **Tunes67** » July 28th, 2006, 12:38 pm

What year SOHC and DOHC engines did you use? Just for the record

Tunes67

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 2:33 pm

i used a 92 sohc engine and a 94 dohc engine both from MX-3's

(Bochek)
so the blocks are the same, and the head/headgasket makes the difference on wich ports get used?

That is correct.

Limegreen mx-3

NO STICKY should BE

MechaManZero · Post by **MechaManZero** » July 28th, 2006, 8:23 pm

One thing though Limegreen, the plug ins should all be different if I remember cause a lot is different enough for me to need to change a whole harness for my swap

. You should see if you can get your hands on an early 90s miata head or even the beautful AWD 323 late 80s.

Limegreen mx-3 · Post by **Limegreen mx-3** » July 28th, 2006, 8:39 pm

MechaManZero wrote:One thing though Limegreen, the plug ins should all be different if I remember cause a lot is different enough for me to need to change a whole harness for my swap . You should see if you can get your hands on an early 90s miata head or even the beautful AWD 323 late 80s.

I know that but i got tired of reading what other people say and never tried out. As i stated at the i just want to know the turth and if both bottom block could interchange with either head and they do. I know both wiring harnness are different that why i said this

Limegreen MX-3 wrote:Like the title says BUT i am going to check if both heads are interchangeable between both blocks. DOHC block with a sohc head and a sohc block with a dohc head. just want to see if everything match up or not.

I have no intentsions of getting them running. Since i have both engine and have the spare time to play around with them. since i am turbochargeing the sohc if it blow as a spare i would to use a DOHC block with a sohc head. i'll take pic's and update on the interchangeabely of the topic. laters

Limegreen MX-3 .

Limegreen MX-3 wrote:But in my opinion i think its a WASTE OF TIME to convert a sohc to a dohc lots of parts u'll need like the ecu and wiring harness from a 94+ models to run the hybrid dohc correct. with i don't think its a hybrid. waterpump convert the sohc timing system to a dohc timing system. exhaust and intake manifold. lot of stuff u have to do.
know some info is done but for u guys that a have a sohc mx-3 just swap ot for 1.8 dohc BP a lot easier than converting ur sohc to a 1.6 dohc. just my opioion..

I have a early 90s miata head and i even have a AWD 88 323 GTX. READ the post man u sliping on me MechaManZero i like the work ur doing to the mx-3 AWD thing ur doing which i think ur doing right or not.