Should a diesel be longstroke/undersquare?

[Christ]

Originally Posted by robertwb70

I remember reading somewhere that smaller bore longer stroke engines are inherently more efficient. It was somehow related to vintage race car motors (old Ferrari and Jag engines were WAY oversqaure). Smaller engines are also generally more efficient so I'm not sure a 300 is a good starting point for any vehicle smaller than a dump truck. I used to drive a Ford dump truck that had a small (for the job) car-type (didn't have replaceable bore sleeves) engine in it and IIRC it was around 300 CID and while it wasn't ideal it did move the 70,000 lb truck down the road at 70 mph everyday.

Best parts source would probably be dodge/ cummins stuff since it's also inline 6 cylinder configuration and there is a pretty good after market developed around them. Might could even use internal parts, I'm not sure but it's definetly worth a look.

On gas engines static CRs range from around 6 to 1 up to around 15 to 1 but if you look at dynamic CRs there is a MUCH smaller range, ie it's the dynamic CR that sets the limit and this is largely dependent on the cam timing I would assume diesel is the same way but to what extent I'm not sure.

I think it would be more fun to find a way to bolt 2 of them together and make a flat 12 boxster out of it

Normally, I'd agree with the size thing... problem is, I don't have anything else readily available (read: free) with an Iron block, heavy duty crank, and decent specs... not to mention multiple copies of something fitting that description.

I guess the 300, for me, is just kind of a "proof of concept" tinker-build.

Also, the 240 is the same engine with a shorter stroke and longer rod combination, IIRC. That would put the next size down to being the 170 and 140 L6, also from Ford.

Remember - Cheaper is part of efficiency. If I have to pay a bunch of money over the course of a tinker build, I'd have to recoup that in the final product. If I spend less money, I can have lower (read: realistic) expectations without being disappointed in the end.

[gone-ot]

Originally Posted by robertwb70

I remember reading somewhere that smaller bore longer stroke engines are inherently more efficient.

...the efficiency was from reduced sliding friction due to less sliding surface area of the smaller pistons: stroke is constant but bore is squared and times PI/4...ie: area vs. volume.

[bbraden]

The older 1st generation cummins (89-93) have what is called a VE rotary pump. It is just a rotary injection pump which (relative to the new Common Rails) have a low injection pressure. These would be probably the easiest to time onto a gasoline engine. There's no electronics to fool with. These should inject PLENTY of fuel to way over-do your 300.

[Christ]

That's what I want, a standalone setup with no computer controls, like my 240D engine. They're easier to work with.

[Peter7307]

It is worthwhile to mention there are a whole basket of factors determining the bore/stroke ratio of any production engine ranging from legal influences (in England there was for many years a "bore tax" where engines were taxed on the bore diameter and in many countries in Europe the tax on engines skyrockets over about 2.7 litres and 15CV) to manufacturing "conveniences" which is a nice way to say they pick from existing components and do a mix and match to get it all to work ; technical theory and details are often shove abruptly to one side.

Pete.

[dremd]

I'm NO EXPERT but I'd "guess" that the ideal rod/ stroke ratio will be different for gas than diesel.

[dremd]

Originally Posted by bbraden

The older 1st generation cummins (89-93) have what is called a VE rotary pump. It is just a rotary injection pump which (relative to the new Common Rails) have a low injection pressure. These would be probably the easiest to time onto a gasoline engine. There's no electronics to fool with. These should inject PLENTY of fuel to way over-do your 300.

Also look at Benz I6 Diesels

Similar pump in my VeeDub; just electronic controls on a VE pump
There is an "M" pump for VW that is full mechanical; not that it matters (4 cylinder) but . . . .

[rmay635703]

I seem to remember an individual I met claiming he converted his metro motor to diesel, he said the compression ratio was high enough to be left alone so long as it was WARM outside.

My estimate would be follow KISS.

Diesels have come many different ways dimensions strokes and compression ratios.

Leave your motor alone, replace the heads to a bit higher compression than you need which tends to hover in the 14to17-1 area depending on how warm it typically is), deal with the less than ideal bowl by placing the fuel intake/"injector" in a "mini" bowl (aka suido precombustion chamber) you bore out of the head and live with the less than perfectness being happy that it works with minimal work. Of coarse you will have to find some very thick heads to fit your unit.

The main issue is getting fuel into the motor at the right time, the rest is moot so long as the block doesn't overheat in the wrong place and break on you.

Good Luck

[Christ]

Originally Posted by dremd

I'm NO EXPERT but I'd "guess" that the ideal rod/ stroke ratio will be different for gas than diesel.

R/S ratio has more to do with piston speed and engine wear than anything else. The efficiency/power benefits are a byproduct of frictional losses, from what I understand.

[gone-ot]

...remember, GM "made" their diesel burner engines from basically stock V8 engine block assemblies...and that was why they didn't last (among other reasons).