Reader Question: Diesel Conversion?

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Here’s the latest reader question, along with my reply!

Alex asks: I’ve been looking at the Nissan https://www.engine-specs.net/nissan/hr12ddr.html 3 cylinder engine as a potential diesel conversion candidate. Here are some of the questions I need answered before making a commitment to purchasing a quantity of them for modification.

1. Will the 84mm stroke allow these engines to rev to 7500rpm if the cetane is sufficiently high and if so, what is that cetane number?

2. Will the all aluminum engine be sufficiently durable for 2 bar of boost if the engine bolts are up to spec?

3. As a general rule with turbo diesel, should my exhaust “trim” value move more OR less exhaust than if I were using pump gas given all else being equal.

I’m patient. I don’t care how long it takes to answer as long as the information is reliable. Thanks in advance for your replies.

My reply: This is a little beyond my orbit, so to speak – but  I do have some general thoughts:

First, from what  I have read, converting an engine that was designed to burn gas using spark ignition to a diesel compression ignition engine is not a good idea because the block and crank and other critical hard parts were not designed for the much higher compression/pressure experienced inside a diesel engine. Diesel blocks, cranks, heads – and so on – are usually specifically designed for that role and built of stronger stuff.

Second,  I have never heard of a diesel engine that revs to 7,500 RPM. That is very high RPM for a gas engine. 

On aluminum: Some new automotive diesels are made of aluminum and I  assume the engineers have done their work. I myself would prefer cast iron – because I prefer a conservative approach, which is usually the more reliable and durable one when it comes to engines!

Hoping some of the engineers reading this will add their 50 cents…

Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!

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3 COMMENTS

  1. Such a “cluster-FOOL” attempt to convert a gasoline engine to run as a diesel would likely fail in spectacular fashion. Not only do diesel have a much higher compression ratio, which necessitates differences in piston, rod, and crank design, even the head gaskets, head bolts, and cooling passages are different. You’d be better off to adapt a small diesel like out of an old VW rabbit to run your Nissan, or even source some Nissan engines themselves.

    The (in)famous Soviet-built V2 diesel, which was a 60 degree, V12 design, made out of ALUMINUM, was an early attempt, as it was an adaptation of a French AIRCRAFT diesel design (yep, in the 30s, aircraft diesels were all the rage, in attempts to get adequate range and fuel economy to make the new airliners a workable proposition) to make a “hot rod” diesel…it was the only way their new T-34 tank, at its introduction considered a “Heavy” tank, fast AND have decent operating range. With its air starter, it also started readily in cold weather, which is definitely a Russia thing. However…this was, contrary to what’s often thought, a very UNRELIABLE engine, which would break down after 200 to 300 hours…which didn’t actually pose a serious problem for the Soviet tank divisions, as the average combat life of a T-34 was about seven hours!

    https://en.wikipedia.org/wiki/Kharkiv_model_V-2

  2. Never knew this was possible – i know they convert fuel a lot back in Karachi (say petrol to CNG/LPG), but when a conversion from petrol to diesel is done the whole engine (and usually matched gearbox for a more compact front wheel drive car) is swapped out.

  3. I have never seen a conversion. Some say that GM engine put into cars and light trucks was just a 350 but that’s not so. While many did give it up for apparently no reason, there was a reason, they had no water separator on the fuel line. Ever tried to compress water with any engine? You only get one try. Back in the day water separators were not throwaway filters and you just turned screw type petcock till fluid ran out. It was easy to see if it was water or fuel. I guess that’s asking too much for the typical diesel owner these days.

    I saw Gale Banks turn a Duramax up to 6500 rpm and that was amazing and dangerous looking at the same time. I believe he was getting something like 1400 lb ft or torque out of it but it was on the edge as in close to blowing up. Wouldn’t want to be in the same room with it running that fast.

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