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Thread: MPS L5 Frankenmotor

  1. #1

    Default MPS L5 Frankenmotor

    After seeing a few other people doing this and finding there is minimal information I decided to do a write up on what I have found out through research.

    We will see if I actually get around to building it.

    Part 1: THE RESEARCH

    I've not heard of this being done too much in the MPS groups although the Miata crew seem to look at the L5 as a viable option for them.

    First; why do this?
    The MPS now is getting old and there are a lot of cars out there with worn or damaged motors, spun bearings seized etc L3-VDT motors are getting a bit harder to come by and they're expensive. The CX7 is a good source of engines as more were built and they were less likely to be thrashed.

    I found my MPS 6 especially a bit hard to get moving off the line stock as it is quite a heavy car and could use a bit more bottom end torque and boost coming on sooner etc.

    What are the differences between an NA L5 block and the L3-VDT one.

    For a start; not a lot, the block casting is actually the same height (about 320mm) which is a bit of a win from a fitting point of view. The L3-VDT crank is forged whereas the L5 crank is cast. For medium horsepower applications this *should* not be a big deal.
    The big differences are the rods are short and the wrist pins are small. Why is this a problem? From my reading short rods lead to high stresses on the rods crank and lower bores. Not the best in high horsepower applications but would have been cheap to produce. Considering that in a non turbo application keeping the rotating mass down improves fuel economy.

    Here is some reading on the subject:

    https://www.hpacademy.com/previous-w...tio-explained/

    http://blog.diamondracing.net/unders...nkshaft-stroke

    https://www.rodauthority.com/tech-st...ng-rod-length/

    https://www.enginebuildermag.com/201...ng-rod-ratios/


    Ok so a stock L5 isn't going to be a high revving engine.

    The next step is really to decide what you want out of your build horsepower wise and how much money you're prepared to sink into it. This is really the key, as there are two ways it can go: Under build my motor and then decide later on I want more power. or overbuild my motor and spend loads of money on things I'll never use.

    Decide which one of these camps you're in. Hopefully you choose exactly what you want and stick to it.

    My intention is not to make this a sinkhole money wise and live with the limitations and so 300-400hp is about the limit.

    Now lets look at the options for an L5 build:

    1. Cheapest.

    If I was doing the lowest cost option I would look for the lowest mileage CX7 2.5L engine and then take the head off it and sell it to recoup some of the purchase price. Swap the L3-VDT head on using the L5 gasket and do minimal other work to get it running and then set my HP target at about limit of the stock turbo. I've seen stock L5 motors around the $800 mark plus say $200 for shipping. $1000 delivered.

    2. Next step up.

    The biggest issue with the L5 will probably be the rods (my guess) so swap out the stock rods with a cheap set of after market H-beams. Probably $700 to purchase maybe a small cost to swap the pistons if you do the rest of the work yourself.

    3. Durability.

    Short rod motors tend to wear taper more quickly in the bore, the stock cylinder liners are not particularly durable and so boosted L5 motors are probably going to wear really quickly so maybe picking up a motor in need of a rebuild and putting a set of Darton dry sleeves into it might improve durability plus you can then re use the stock pistons as there are no stock oversize pistons for the L5.

    https://dartonsleeves.com/sl_import.html#


    However this is where the money starts happening, The best price I can get dry sleeves is $700AUD and then preparing the block would probably be that again and so we are up to about $1500 with me building it. Add $70-$100 per hour for someone else to do it. So we are up to about $2k. if you go down this road make sure your engine machinist knows what they are doing and are not the sort of people who bash the new liners in with a hammer!

    4. Fixing the lousy rod ratio

    I came across this: https://esslingeracing.com/pistons-5...and-piston-kit

    It seems to be a better solution for the L5 it has longer rods larger wrist pins, but look at the cost! At a guess 2k AUD delivered!

    The upside with this set up though is that it might open the door to using a bored out L3 block; why is this good? you can keep your original block and engine number which might matter for some people.
    I am yet to prove this but if you look at this: https://dartonsleeves.com/mid_04.html

    Darton make a mid sleeve only for an L3 not an L5. Looking at the dry sleeve catalogue from above the liners in an L5 sit about 0.3 inches lower (7.62mm) and so at a guess it is not possible to just put an L5 crank into an L3 block without the piston hanging below the end of the liner. Mid sleeves are probably a better option for higher horsepower as the cooling is better but this is for really serious applications.

    With the Esslinger racing setup the pistons sit 4mm further up in the bore thanks to a longer rod and even with the longer stroke (100mm vs 94mm) the rods only get pulled 3mm lower and so boring out an L3 and fitting mid liners and then opening them up to whatever you like up to 90mm might allow something workable.

    However the mid sleeves are about twice the price of dry sleeves and the machine work is probably about twice the price too. Lets say 4k.

    I'd bore to 89.5mm cos you might as well at this point; it wont cost a lot more and the Esslinger pistons come in that size. This will give a capacity of 2516cc

    So we are up to about 6k!

    Is it all worth it for 11% of extra capacity? I guess if you were going to rebuild your motor anyway with these sort of components then why not.

    5. Go nuts:

    I'm not sure whether this would work:

    https://esslingeracing.com/rotating-...ec-stroker-kit

    You could see if this would work, I am not sure however how much difference the Duratecs have over the Mazda engines. In the early days they were the same but after Mazda and Ford parted ways about 10 years ago who knows.


    Part 2 will be next where I'll take photos and measurements of the different parts from the L3-VDT and L5

  2. #2
    Join Date
    Jun 2009
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    Newcastle
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    Default

    SP63 have dabbed into 2.5L, you may find some relevant info if you haven’t yet come across it.

    Rod length and piston combination should be your main focus to see if your able to achieve a more favorable dwell angle for the rod, that’s going to weigh heavily on piston design.

    Darton MID sleeves open up another can of worms if not executed correctly, the webbing area of the block near the main tunnel is weak and may not offer the rigidity to support the liner, not to mention the potential movement they may be subject to causing them to potentially sink. Although the closed deck arrangement of the MIDs may offer upper support for the liner, significant material removal can pose other issues with counter bore distortion. You may get cavitation issues but prob not at low HP. Won’t mention head gasket issues. Sleeve preparation processes are critical!

    I don’t use Darton but use LA Sleeves, flanged type dry liners, the disturbance to deck thickness isn’t as intrusive, they offer good cylinder wall thickness and support. They also have specific instructions to ensure correct heat transfer, but at the levels of power you’ve mentioned the control of your cylinder and cooling system temps shouldn’t a problem with a reliable and experienced tuner. Head gasket issues shouldn’t be a problem if you do your homework on liner protrusion.

    Cost And practicality against what’s achievable with the 2.3 aside, if the favorable measurements appear it’s a cool thing to do but make it count for the effort! 400HP isn’t enough
    Every man should have a V8 ute.....with a Chev badge.....and a Southern Cross sticker! Mods? What mods?

  3. #3

    Default

    Thanks to MPS2NV for the comments, I'll definitely look into LA Sleeves: https://www.lasleeve.com/auto-high-p...ormance-sleeve

    I also looked into SP63, I didn't find much on the 2.5 but found this which is an interesting read: https://www.speedperf6rmanc3.com/pag...al-papers.html

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