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Discussion Starter · #1 ·
I have a 1994 Isuzu Rodeo that has a broken 3.2L motor. I currently have a donor motor from the same year, but I would like to swap my cylinder heads to bump up the power to 190 hp. From what I've gathered there are two options for this, 1) go with the DOHC cylinder heads from a 92-95 Isuzu Trooper or 2) go with the SOHC cylinder heads from the 96-97 Rodeo/Trooper. I'd like to fully understand the pros/cons of each before i choose an option.

92-95 Trooper DOHC cylinder head Pros:
-uses 7 stud exhaust manifold pattern. Current exhaust down pipe would simply bolt right up to my old exhaust manifold (2 stud design). Similarly, EGR pipe should easily bolt between the exhaust manifold and the SOHC intake manifold
-ticking noise should be reduced versus the SOHC heads
-meant to work without a cam sensor, I think.
-sometimes I've seen horsepower figures slightly higher than 190 hp. I don't know whats accurate though.

92-95 Trooper DOHC cylinder head Cons:
-more difficult to find
-interference engine
-different timing belt setup on the DOHC motors may need get some new timing components
-may need to swap to the trooper fuel injectors

96-97 Trooper/Rodeo SOHC Pros:
-easy to find
-non-interference engine
-timing belt setup is the same
-if this mod was chosen, the exhaust would potentially be adapted for the second generation 6VD1 or 6VE1 motor for a second revision motor swap

96-97 Trooper/Rodeo SOHC Cons:
-uses 8 stud exhaust manifold, new exhaust manifolds and probably new down pipes/cat would be needed to bolt to the 3 stud manifold to down pipe flange.
-is the EGR port on the exhaust manifold in the same location as on the earlier year rodeos? If not, may need to fabricate an EGR pipe.
-ticking noise
-would this cylinder head work properly without utilizing a cam sensor? I assume it would work.

Which fuel injectors would you go with for both options?

Did I miss any pros/cons? Which option would you go with and why?
 

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I've never had the 3.2 engine in one of mine but I was under the impression that all the 3.2's were non- interference engines. Same for the 3.5's except for the direct injection engines in the 2004.
 

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Discussion Starter · #4 ·
I'm leaning towards the trooper DOHC cylinder head because it would be a cleaner install for me (considering exhaust), plus I like the novelty factor of having a rare setup. However, I did think of another con...I'll need to getthe DOHC valve covers and the bolts and plates that mount at the back of the cylinder heads.
 

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Go with the DOHC heads, use the SOHC intake and injectors. It is a very easy swap. There are different timing belt/pulley parts, timing cover, plug wires (the SOHC wires fit but don't seal out water), and of course the valve covers are different. You do not want to swap injectors, as the DOHC ones are different resistance and would need a different ECU.
If you grab the heads from a pick n pull type junk yard you should be able to get them complete, cams, timing pulleys, valve covers, etc. Then just have a machine shop do the valves and resurface, then install with new head bolts. Put your SOHC intake on it just like it was the SOHC engine and go. Only fit issue is the coils need to sit a bit higher to clear the DOHC timing covers, a few washers is enough but make sure you get the mount grounded.
 
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Discussion Starter · #7 ·
Tim,
Thanks for the feedback! I've already looked through DutchBro's build thread, but I'll check out the thread you made also. Thanks for the specifics on figment, those were the details I wasn't sure about, but now I'll make sure I get all the parts you listed. I'll be heading to the junkyard next week to locate a DOHC trooper. My build will be pretty close to your recommendations.

Another pro for this motor is that it makes slightly more torque. From the specs I've seen 195 ft-lb vs 188 ft-lb in the SOHC.

-Alex
 

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I'm not sure how much of the timing belt parts you will need from the donor. I believe we used everything from the dohc including the timing pulley on the crank. I think I'd grab all of that to be safe. You'll probably want to replace the belt, the tensioner, the water pump, and the idle pulley while you are rebuilding anyway.

There are some other things I might consider adding to the build. I'm working on swapping Multec 2 injectors from a 98+ Isuzu into my SOHC Trooper now, mostly based on the work of mtman on here. He also has another of the DOHC hybrid motors using the SOHC intake. He changed out his injectors and had had some success with it. If nothing else you get rid of the Multec 1 injectors that can end up being unreliable with ethanol blended gas like we have almost everywhere now.
 

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Discussion Starter · #9 ·
Tim,

On DutchBro's motor did you use the SOHC fuel rails or the DOHC fuel rails? Or were they the same?

Yea, I plan to be pretty thorough with building my motor. I'm going to get valve jobs on the cylinder heads and the block/crank rebuilt at a machine shop. I'm definitely going to replace the timing components with new parts. I've already put a bunch of labor and parts into my vehicle and I want it to last me a long time.

I have skimmed through mtman's thread before on the multec 1 vs multec 2 injectors, but I didn't understand the "multec" terminology. Are you recommending that I use none of the injectors from the 92-97 motors, but instead use injectors from a 98-03 Rodeo or Trooper?

-Alex
 

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Discussion Starter · #10 ·
Tim,

Do you have a part number for the multec 2 injectors that would fit the SOHC intake manifold? I just looked online at the 98-04 rodeo/trooper injectors and they have a different form (skinnier and taller looking). Or would those fit even with the different shape?

-Alex
 

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They are different, but the height is the same or near enough. You do have to adapt the wiring. I pulled this idea from this thread which gives the details:
viewtopic.php?f=22&t=77480

I have just pulled some injectors from a couple junkyard trucks and intended to clean and rebuild them. The rebuild parts are available on eBay from a seller called Mr Injector.
 

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Discussion Starter · #12 ·
I went to the junkyard today and there were 2 DOHC troopers. I grabbed some valve covers, timing covers, and plates that bolt onto the valve covers...I didn't have enough time to get the cylinder heads yet. I hope to go back on Friday to get the rest of the parts.
 
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