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Old 01-25-2021, 11:57 AM   #1 (permalink)
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3 cylinder water cooled vs 2 cylinder air cooled thoughts on possible conversion

Hi all,
As a possible project, I've an option to replace a 2 cylinder air cooled motor with a 3 cylinder water cooled motor.

The AC vs WC
652cc vs 989cc
~23hp vs ~57hp
Carb vs MPI

Obviously there's quite a lot of work involved to swap and to throw a slight curveball, the project vehicle is RE/RWD.
Initial swap if done would look to retain the 4spd box currently fitted. (Top speed would be around 80mph gear limited)
With the engine in the back air cooled, this gives an option to basically do anything wanted with aero shaping of the front, currently housing spare wheel and battery and not much else, but they could potentially be relocated. Fuel tank is 'midship'.
Moving to the 3 cylinder would bring the requirement for a radiator and associated piping, hardware and weight.
The rad could potentially be fitted in the rear (issues of airflow not withstanding) but may have to be front mounted to allow enough cooling airflow.

What are peoples thoughts on keeping the AC setup vs moving to the WC option?

All thoughts welcome.

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Old 01-25-2021, 12:22 PM   #2 (permalink)
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My thought is you left out the most important constraining variable: Year, make and model.

Via duckduckgo.com/?q=652cc+air+cooled+rear+engine+-motorcycle the likely candidate is the Fiat Panda.

According to www.classicandsportscar.com/features/square-space-fiat-panda-40:
Quote:
At its launch, the Panda was primarily offered with two engine options: the 30 edition employed the air-cooled 652cc two-cylinder unit from the 126 Personal, with power boosted by a giddying 6bhp; the Panda 45, meanwhile, used the 903cc pushrod ‘four’ from the Fiat 127 that, remarkably enough, produced 45bhp.
23hp sounds like not too much.
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Old 01-25-2021, 02:35 PM   #3 (permalink)
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WC generally means it can have higher compression, which is good for FE. An extra cylinder/more displacement is generally bad for it. Of course, that depends on the power requirements of how you use/drive it. FI generally gets better efficiency, could make up the difference. As could the design of the engine.

Can't tell ya what's more important for you. FE? Power? Ease? For me, unless I was looking for a project, and if it was good enough as is, I wouldn't put myself through the bother of an engine swap. Diesel or electric swap might catch my attention more.
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Old 01-25-2021, 06:29 PM   #4 (permalink)
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Are you willing to fit a Daihatsu engine into a Fiat 126?
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Old 01-25-2021, 06:47 PM   #5 (permalink)
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Quote:
Originally Posted by freebeard View Post
My thought is you left out the most important constraining variable: Year, make and model.

Via duckduckgo.com/?q=652cc+air+cooled+rear+engine+-motorcycle the likely candidate is the Fiat Panda.

According to www.classicandsportscar.com/features/square-space-fiat-panda-40:


23hp sounds like not too much.
Year/make/model is somewhat not applicable in this case as it is a v low volume kit car hence the option to change most things.
It's not currently on the road and hasn't been for a few years so it's somewhat a reasonable option to approach from either viewpoint for engine choice.


But current drivetrain is from an air cooled fiat 126 (presumed 1978-86)

They were originally speed limited to around 65mph @ ~4800, max bhp @4500
Wheels are only 12"

The 3cylinder is an EJ-VE daihatsu unit and is sat in a complete donor vehicle hence is an option with all parts available.
6k rpm would give a top speed north of 80mph with power being made up there on the EJ motor anyway would give the benefit of something in hand for safety in all gears.
Donor config is FE FWD AT
Parts other than the engine will likely be donated to update the project where possible.

A relatively low cost 'recycling' project using mostly parts already 'in stock' for a 2 person commuter with FE, some reliability and a bit of future proofing as well as not ruining the handling with a reasonable chance to would be a good set of goals.

Power is not a goal here and definitely would require a new transmission from the offset.
I'd even be willing to potentially detune the 3 cylinder in the future as anything north of 35 should be adequate.

A diesel/diesel hybrid would be a great end solution or possibly full electric and was a consideration;
But this doesn't fit in entirely with the low cost recycling project as well as using the above doner or keeping the current drivetrain would.
It may be a future option.
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Old 01-25-2021, 07:12 PM   #6 (permalink)
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Air-cooled engines are interesting to say the least, even though a water-cooled one might give you more freedom to deal with the aerodynamics. Well, had it been a front-engined model which would be likely to have a more effective cooling flow, I would be quite partial to keeping it air-cooled.
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Old 01-25-2021, 07:13 PM   #7 (permalink)
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cRiPpLe_rOoStEr called it.

Are there picture of one on www.undiscoveredclassics.com/forgotten-fiberglass/?

I was hoping for the BMW 700, but it had the 697cc flat twin.
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Old 01-25-2021, 07:23 PM   #8 (permalink)
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Quote:
Originally Posted by freebeard View Post
I was hoping for the BMW 700, but it had the 697cc flat twin.
AFAIK the BMW 700 had some units assembled in Argentina, with some local content added to them. But anyway, I like flat-twin engines because of how the cooling flow is usually better distributed among both cylinders, unlike what may happen in air-cooled engines with more cylinders or even in a longitudinal straight-twin.
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Old 01-25-2021, 07:33 PM   #9 (permalink)
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Quote:
Originally Posted by cRiPpLe_rOoStEr View Post
Air-cooled engines are interesting to say the least, even though a water-cooled one might give you more freedom to deal with the aerodynamics. Well, had it been a front-engined model which would be likely to have a more effective cooling flow, I would be quite partial to keeping it air-cooled.
The air cooled engine already being in the rear and designed to be there both in the kit and the original Fiat plus the front end being a 1 piece replaceable 'clip' and the body 'tub' being fibreglass including the rear engine bay and mounted to a separate steel chassis means that aero options should very much be possible regardless of keeping it air cooled or switching to water cooled or even future electric/hybrid etc. As long as rules for lighting etc. are adheared to.
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Old 01-25-2021, 07:54 PM   #10 (permalink)
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Since it's already set for the air-cooled engine, and you don't seem so likely to look out for all the different positions where a radiator could be fitted, maybe it's worth to keep it air-cooled anyway.

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