Building a 23 EFI motor out of a carbed 21: DX vs DX2 vs DX5 differences?
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  1. #1
    GGR
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    Default Building a 23 EFI motor out of a carbed 21: DX vs DX2 vs DX5 differences?

    Hello,

    I live in the US and I would like to make a DX5 2.3 EFI motor out of a DX or DX2 motor. the DX5 was never imported in the US. I however have both a DX and a DX2 available to me in the US. I also have a complete DX5 motor at a friend's place in France. The engine needs a complete rebuild. to avoid huge shipping costs, and as the engine needs to come apart anyway, I was thinking of picking all the DX5 specific parts out of that engine in France next time I get there, put them in my luggage and bring them in the US to graft them onto the DX or DX2. So I would need some help to identify all the DX5 specific parts I would need to recover from the donor engine.

    The obvious ones are the pistons. My plan is to bore out the 21 liners to 23 specs and fit the pistons in there. Will this work? I read somewhere the 21 block would need some work for the 23 liners to fit. Is this true? What would happen by just boring out the 21 liners? Would they become too thin in some places? If so, I may get some 23 liners. But then what modification would be required on the 21 block?

    The head: I noted the studs for the intake manifold are positioned differently. So is it just a matter of relocating the studs on a 21 head? Or am I going to end up drilling through water ways? What about valve size? I know they are different between the DX and DX2. But are the DX2 valves the same as the DX5 ones? What other differences?

    What about the camshaft? are they the same between 21 and 23s? between carbed and EFI versions?

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    What about the flywheel? I know it changed at some point. do the DX2 an DX5 have the same flywheel? Or did the change occur in between theses two versions?

    I know I will be missing the oil cooler on the 21 block but it's OK. I would also have to block the port for the mechanical fuel pump. Am I missing any other difference?

    Thanks for the help!
    Last edited by GGR; 9th January 2017 at 04:22 PM.

  2. #2
    Fellow Frogger!
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    A good place to start would be the parts manuals, and compare part numbers for camshafts etc, as well as valves. Roger Wilkinson gave the link to the online manuals recently.

    The flywheels were different for automatic and manual transmissions, I suspect both your engines would have manual gearboxes.

    The heads are different and I think you would need the injection head to match the manifold and would give the injection valves.

    I think you mean manual fuel pump not oil pump ?

  3. #3
    Fellow Frogger!
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    What you are suggesting is not a small undertaking, off the top of my head you're going to need:

    • the complete intake manifold with all of its brackets, if its going into a BVH car you will also need the hydraulic device for the accelerated idle
    • Whilst on the subject of the BVH, the gear selector also has a different part number for EFI cars
    • throttle cable and associated brackets
    • the air filter and its bracket
    • radiator and the metal pipe connected to the bottom hose
    • If you swap the entire head it removes the headache of relocating studs and worrying about valve sizes
    • I believe the EFI engines had a different type of clutch



    are you intending to use the original bosch EFI system or use a modern one?

    The parts catalogs and manuals can be found here https://www.dropbox.com/sh/tv0b25gpmd5ux8e/e-HYMQrA3e

    catalog 648 d-parts 71-75 should tell you what you need

    also useful would be manual 639-6 DS23ie technical data https://www.dropbox.com/sh/tv0b25gpm...0data.pdf?dl=0
    Last edited by faulksy; 9th January 2017 at 04:46 PM.

  4. #4
    Fellow Frogger
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    Was the 23 from an auto? EFI or carby? There are some bottom end differences between the auto and manual versions of the 23 engine.

    The flat faced / diaphragm clutch flywheel was first used with the EFI cars, but adopted for all of the engines shortly after. It should bolt up to a crankshaft that had an earlier 3xtoggle clutch and recessed flywheel. The release bearing also changed.

    The EFI head has four intake tubes bolted on that also mount the injectors. These are held to the head by one stud and one setscrew and one of them, I think the setscrew, goes into the water jacket and needs a thread sealant. So, the factory has already drilled into the water jacket! There would be an extra hole in the left side of the EFI head for the thermotime switch, not needed in a carby version. Maybe another at the front left for the EFI coolant sensor mount. There could be other detail differences.

    The 'technical data' books that can be downloaded with the manuals will also be useful in determining detail differences between parts fitted in different years / models.

    Perhaps, consider fitting a monoport EFI system (Megasquirt?) to the 21 carby engine and save yourself a lot of work. You would also avoid having to find and install the original EFI harness and all the related hardware outside the engine, including losing part of the passenger footwell to house the ECU.

  5. #5
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    May I suggest you stick with the 21. There is only 2 mph difference in top speed and more importantly the 21 does not have the over-heating issues of the 23;same block and less water=overheating,regards.

  6. #6
    Fellow Frogger! marc61's Avatar
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    There's an oil cooler on a DX5 bolted to the side of the engine roughly where the regulator and accumulator fit on a carb car. It's not obvious how that could be transferred. I guess they went to the trouble of fitting it to keep the oil temp down when driving hard in hot weather.

    Camshaft is the same. Inlet ports in an EFI head are larger, would need to match the carb head ports to the 4 outlets of the EFI inlet banana. Holes would need to be drilled for the EFI sensors and the hole blocked in the carb head for warming the inlet manifold. Also there's a water fitting on the side of the EFI head near the water pump that would need to be taken. Swapping the heads is probably a better idea.

    Engine mount support plate with throttle cable will need to be taken from DX5 car. An EFI fuel tank will be required so the return fuel line can be plumbed in.

    Cheers

    Marc
    Cheers, Marc.

    1987 CX GTi T2 Maikonics
    1972 SM 2.7 carb
    1972 DS21 EFI

  7. #7
    GGR
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    Thank you all. this is very useful information. To answer some of the questions:

    yes, I meant fuel pump, not oil pump.

    All my engines are BVH.

    I am intending to use Megasquirt.

    My donor engine is a 23 EFI, with oil cooler (23 EFI with 5 speed manual didn't have the oil cooler if I remember well).

    Yes, keeping the EFI head seems to be the best option.

    By looking into the parts manual, all 23 blocks, including carbed ones, have a different part number compared to the 21 block. This may be due to a different machining to accomodate the 23 liners. Any info on this would be welcomed. Surely someone must have already tried to increase the capacity of a 21 motor?

    Thanks again!

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