Hey there <img src="/forums/images/graemlins/smile.gif" alt="" /> Its been a while. Last time I was here someone was talking about swaping from 12V SOHC heads to 24V SOHC but I can't seem to find the post anymore <img src="/forums/images/graemlins/scared.gif" alt="" /> So I was wondering if who ever mentioned actually went throught with it, or at least did some more reaserch? Since I have a cracked intake plennum I thought I could start doing some reaserch on the cost of the sawp before replacing it.

Hmm im not sure why you would want to?

It would involve swapping more than just the heads. The 12V has a drive for the distributor, while the 24V used coil packs. This would also probably mean changing the whole engine management system. Another difference is that the 12V has a mount on the right head for the alternator that the 24V doesn't. Actually, all the accessories are located differently on the 24V engine. Physically, they will bolt on, but you will need to do a lot more research on what else has to be changed. It could be done, but I'm not sure it's worth it.

151 hp to 177 hp
174 ft-lb to 188 ft-lb.

just a thought.



you are probably right. maybe getting the whole engine from a donnor instead of rebuilding when the time comes...

hmmm, I will probably never have money to do it anyways <img src="/forums/images/graemlins/zombie.gif" alt="" />

Here in the states, the 12V 3.0 Diamante did 175HP. If you search Car-Part.com, they will show the Diamante head and the Montero as interchangeable. Wonder how the Diamante made the additional 24HP?

probably same head just milled differently with different cams.I just think if your going to go to all that trouble you might as well swap in something that will be a considerable gain.I mean you have to redo the wiring harness anyway and that the brunt of the work on an engine swap.

If they were milled different and had different cams, I would not think that C-P.com would call them interchangeable, though.

Seems to me that the compression ratio is up around 10:1 and that's why it makes more power. Plus, it had a different intake, exhaust, and probably different cams.

Compression is higher on the Diamante due to different pistons (which in theory would work in our motor).
I've considered the 24v swap, but given the intensive conversion with accessories, engine management, etc I'm leaning towards the Diamante pistons and having a replacement set of 12v heads built up with better flow.
I bet the increased compression alone would get you pretty close to the horsepower goal. Though this would have to be done carefully as the Montero ECU is expecting the lazy CR, so you'd have to run higher octane fuel and if you want to do it right, tune with a knock detector to make sure your timing is OK.

Expect an increase of only 5HP by going from the stock 8.9:1 to 10.0:1....

CR Horsepower Change

You would get a much crisper throttle response, but the ECU would be somewhat helpful on ignition timing issues - particularly EGR equipped models. I don't know what the timing curves of other 3.0L engines are, but the '89 3.0L Federal model with base iginition timing set at 5 degrees BTDC runs ~ 40 degrees BTDC max under light load cruise (downhill) and is retarded to ~ 15 degrees BTDC under load/uphill/overdrive (no downshift) when all manifold vacuum is dumped around 2000 rpms.

IMO, for such a modest increase in HP, it's not worth the fuel cost of increasing CR unless other modifications are also made - like full head porting, larger intake valves, a different cam profile and an ignition timing controller - expensive, since it's mostly all custom work. A resulting change to low-end torque output from a different cam pattern would also be a question mark on driveability.

There are 2 reasonable answers for better all-round performance from the 3.0L in a truck - a blower or a stroker crank - both also expensive. IMO, anything less is probably a waste of time, effort and money.

Frank