DOHC head on SOHC block & pistons

[Crunkrich]

I posted this in the KA forum but didnt get any responses so here ya go...

"Shave the head(dohc head), run a SOHC block with SOHC pistons(DOHC timing chain still though) have the crank micropolished. port and polish. get a nice header and port match it. SR 370's. walbro 255, some nice ignition **** (this part is personal preference, the stuff i'd use is not what a lot of others would) and finally the hardest part..........a way to manage it all."

I read this on another forum and just wondering if anyone can validate it?

[180fan]

You can run the sohc block with dohc head. The compression will vary from which set of sohc pistons you run. The compression will be over 10:1 regardless. IIRC, the compressions are 10.6:1 or 11:1 depending on which type sohc pistons you're using.

A way to manage it all? Run very high octane gas. I'm not talkin 93 either. 93 should detonate pretty readily on that engine. Retard the timing a bit. There was another board member and local to me who had that setup run for about 200 miles before it detonated itself to the metal recyling yard.

[SR20drftSX]

sooo could i just take my stock SOHC and put a DOHC head on it easily and still use it as my daily driver? like could a average mechanic do this? or is it for non streetable racing setups?

[180fan]

No, the front cover and the front of the head will not line up. Look for "high compression" or "high comp" ka and you should find what you're looking for. I would not suggest it as a daily driver.

[nuts510]

cheap way to make a good running double overhead cam engine car, is to use 90 model single cam pistons, a good-quality header, a decent intake, and if you can afford it and Jim Wolf cams or colt cams. A tuned ECU would help but this is also a little pricey. This will run off of premium gas with no problems actually produce good gas mileage and make some decent horsepower also if you can find it the manifold off of a 94 does not have the flapper valves and this does seem to let the motor pull a little bit better strangely enough the 94 ECU seemed to be the best running ECU.

[Veriest1]

When you're searching Nico search for content created by Dauntless. IIRC he had a sohc block with a DOHC head in a Datsun 510 but he ended up selling it and since then Nico has lost track of it.

The major issue was the front cover as another member mentioned. I do believe he was running on pump gas but I've seen many people who say it won't work so it may just be my memory failing me. It would probably a good rather than mediocre tune to do so.

Honestly it'd probably be easier to buy and rebuild a DOHC motor with a SOHC pistons than to do the head swap.

[Crunkrich]

Do the SOHC pistons drop right into the DOHC head and block? I have an almost complete (missing throttle body and has a broken timing chain gear) SOHC motor sitting in my garage so I was just gonna use those.

[Veriest1]

That's what people say. Compression would be the same as with the head swap.

[rogoman]

Do the SOHC pistons drop right into the DOHC head and block? I have an almost complete (missing throttle body and has a broken timing chain gear) SOHC motor sitting in my garage so I was just gonna use those.

Yes, the SOHC pistons will drop right in, however as was mentioned in previous postings, the CR will very high resulting in detonation.

You'll have to run racing gas in order to keep the detonation down; if you can find racing gas, it'll cost you anywhere from $4 to $6 per gallon.

Early 1990 pistons will net you about 11.6:1 compression on a DOHC motor. Also the combustion chamber area in the head is MUCH different from SOHC to DOHC, DOHC pistons have a very large dish, whereas SOHC pistons are nearly flat top. Early SOHC pistons in a DOHC will give you ~11.6:1 compression.Later SOHC pistons in a DOHC will give you ~11.1:1 compression.

[Veriest1]

^ Where are these compression ratios coming from? I keep seeing people post different ones. People used to say the later pistons would yield a 10.5:1ish ratio. It didn't just change over night.

EDIT: You can drop the ratio slightly by running a thicker head gasket.

You should be able to get high enough octane gas at your local municipal airport. Just don't let them know it's going into a car (use a jerry can or something).
Modified by Veriest1 at 12:27 PM 8/27/2006

[dragnsoul28]

ok so overall.....it is a bad idea to put the DE head on a E block? true or false?