Shower thought, Diesel 4.0

[ftpiercecracker1]

Let's suspend our disbelief for a moment and assume money is no obstacle for this project.

 

I have often wondered if it's at all possible to convert a 4.0 into a diesel engine.

 

1. Could we screw in direct injectors into the spark plug holes?

 

I know ideally the injectors are directly above the piston, but this is just proof of concept.

 

NOTE: Redrilling/taping the spark plug holes is allowed, but a completely custom, 1 of a kind, cylinder head is not.

 

2. Could we use the distributor shaft to turn and potentially time a high pressure pump?

 

2.a If not, what about using the serpentine system?

 

2.b If mechanical timing is out, let us use a stand alone engine management system.

 

3. Can an unbored 4.0 block handle the pressures a diesel engine makes?

 

NOTE: High strength replacement internals are allowed (pistons, rods, crank)

 

4. Can the head handle the pressure or is there not enough clamping force? Can this be overcome?

 

Solid copper headgasket?

 

ARP head studs?

 

Is there room to add more head studs?

 

I seem to recall boosted 4.0s blowing out head gaskets at as little as 8-10psi.

 

5. How can we increase the compression ratio high enough to ignite the diesel?

 

 

What other hurdles am I missing?

[Dzimm]

I think the biggest problem would be the head gasket.  There really isn't much if any room for any additional head bolts anywhere although it wouldn't be too complicated to come up with some sort of external clamping mechanism to add additional clamping force if it were necessary.

 

The question I have is, would a 4.0 even be able to create the pressures required to ignite the diesel?  Doesn't a diesel engine have a really small gap between piston at TDC and the head?  It may require grinding the head flat around the valves and longer rods but then you'd be pushing the piston rings past the head gasket to get the piston closer to the head.  It may be possible to get it running but not sure how it would do revved up.  I think a custom head would solve most of the problems you'd run into.

 

It's definitely an interesting concept, I'd be interested to hear from someone who knows a lot about both the 4.0 and diesel engines. 

[derf]

It's an interesting idea.  However, history has shown that trying to convert a gas engine to diesel doesn't usually end well.  The only ones that worked out were the industrial gas engines in medium and heavy duty trucks that were way overbuilt.

 

If you lift some of your restrictions like allowing a fully custom head, it would be easier.  Managing a turbo with a cross flow head is much easier.  But you still have the clamping force restrictions of the head bolts and that's going to be a huge limitation.  You'll have a limit on how much torque you can make.

 

There's also the issue of being over square.  The bigger bore and shorter stroke isn't the best way to design a diesel.  You want it to be the other way around.  The smaller bore and longer stroke of the 258 would be better.

 

I like the idea.  In theory anyway.  I'm just not sure it would work well.

[eaglescout526]

The Oldsmobile 5.7L from the 80’s comes to mind when I read this idea. 

[FrankTheDog]

6 hours ago, eaglescout526 said:

The Oldsmobile 5.7L from the 80’s comes to mind when I read this idea. 

We had an 80 Olds Regency 98 my Dad bought new. It got 26 mpg if l remember correctly. Big luxobarge.

It was good highway car its first 100,000 miles at least. It needed the injector pump rebuilt a couple times at $600 a pop in the 80’s. I think he replaced the engine once.

 It wasn’t a bad car but it wasn’t a good engine.

[ftpiercecracker1]

Ok some more ideas. .  .

 

 

Using a stock and unbored block, press in sleeves.

 

Couple this with a 258 crank for increased stroke

 

The sleeves will strengthen the block while reducing the bore diameter.

 

The goal of this is for the engine to become "under" rather than "over" square per Derf's recommendations. I'm not sure why this is important and even though it will probably impact the power output it doesn't matter. At this point we are just trying to work out the major kink just as a proof of concept. Can we get it to run and run reliably. Power will come later.

 

Next, to increase clamping force is there enough real-estate to drill out the studs for the next size up?

 

Is the issue with HG being literally ripped apart or with studs stretching?

 

Stud stretching should be alleviated with either higher grade studs, larger studs or more numerous studs.

 

HG failure should be alleviated by solid copper or similar extreme duty materials.

 

Next the head. Deck it as close to the valves as possible and have a custom cam ground to accommodate new clearances.

 

 

I have a feeling there could definitely be some useful parts on a olds 5.7 diesel. From what I understand the injectors are almost the same size as a spark plug.

 

Can a high pressure pump be ran off the distributor shaft? What about the serpentine system instead?

[gogmorgo]

I don’t think you could run an injection pump off a rubber belt. Even a timing belt style cogged belt would be marginal. Injector timing has to be very precise, and any stretch or bounce at all in the belt would cause problems. One degree in either direction away from where it should be can be the difference between advanced into dangerous running conditions and running like crap because it’s too retarded. There’s a reason diesel injection pumps are almost exclusively gear driven. You could probably figure out a gear drive either via flywheel or the timing gears, but you’re doing some serious machine work there.
If you were to go to a common rail injection system you could eliminate the need for precise mechanical timing. I don’t know if you’d have enough strength in the distributor drive… it’s not like it’s supposed to see much torque, and you’d probably also want to hang onto it as a cam position sensor. You’d need a pretty sturdy belt drive to run an injection pump. Hypothetically you could run an electric pump, then you’d just need to figure out your fuel injectors. 
Now most injectors live under the valve cover to keep them clean and lubricated. Some also run directly off camshaft, but we can’t really do that because the cam is on the wrong side of the head. If you were putting the injectors in spark plug holes you’d need to keep them covered and clean some other way, not a huge obstacle. I think the biggest thing is just going to be figuring out how to get injectors down the spark plug holes. Almost all diesel injectors are clamped in, so figuring out how to get them to screw into a hole will be something. Possibly just screw an injector cup down into the hole and drill some holes into the head nearby for the clamp system. You also need pretty good connections to get fuel to them at such high pressure. The spark plug holes also aren’t ideal for spray patterns because of the angle, but the higher pressure from the common rail system (30,000psi!) would immensely help with atomization. 
Something else the better atomization will help with is accommodating lower compression ratios. Most diesels are double typical gas engine compression ratios. You don’t necessarily need to be at 20:1, it just helps. Shaving the head down will help, sleeves and smaller pistons are a good idea but you don’t want to get the coolant too far away from the pistons walls either. It’s common practise to run “wet liners” in heavy diesel engines. Basically the sleeve goes straight through the cooling passage instead of just pressing down into cylinder wall. If you’re boring out the cylinder walls for sleeves I’m sure you could figure out a way to knock some holes clear through the factory cylinder walls to accomplish this while you’re in there. Also get a good solid o-ring around the base of the sleeve. 
I don’t know if you’d really need to mess with the cam to account for shaving the head. That would just be pushrod length. You likely will end up with an interference engine, but that’s only an issue if you lose a timing chain. 
As to head bolts and gaskets, the 4.0 turbo guys have kinda figured some of that out. Doubling compression ratio isn’t really much different from running 15psi in terms of cylinder pressures. I don’t think it would be too big a deal for a naturally aspirated diesel. If you want to stuff 30psi of boost down the thing on the other hand… yeah different story. 

[ftpiercecracker1]

Fantastic stuff Morgo, thanks for the info. A lot of stuff I had not considered.

 

I figured the high pressure pump could be driven by the belt system, but timing would have to be electronic.

 

A purely mechanical system would be superior for what I have in mind, but I'll take anything at this point.

 

What is different about diesel injectors that require them to be covered? Aren't they only lubricated internally and that is done by the diesel fuel it self no? They aren't connected to the vehicles motor oil system right?

 

I'm extremely surprised they are clamped in place and not threaded or some other more secure way. Clamping seems to be the least sturdy way. Do they use some kind of integrated collar that bolts them into place?

 

That's a great point about cooling and sleeving the block.

 

Spill the beans. What do the forced induction guys do to get around the clamping/head studs issue?

 

[gogmorgo]

Don’t really know for sure why they go for clamps rather than screws. It could be because they don’t want any sort of twist on the thing. The internal clearances are extremely small and you could damage one pretty easily. When I say clamped, I do mean usually there’s hold down bolts, but the injector itself doesn’t thread in. Some of them likely are doing this in part to make sure the injector sprays in the right direction to ensure intended flame propagation, and also that the fuel delivery system lines up properly to the injector to seal the connection point. I guess precise orientation and placement, proper load on the injector, not twisting the injector body on the way in all add up to not screwing the injectors into the bore.
As far as whether they need covered or not, that’s probably an obstacle that’s easily overcome. I haven’t encountered any yet that were built to survive outside the engine, but that doesn’t mean they can’t. But they are usually buried pretty deep in the engine. I don’t really know what the reasoning is again but it might be to avoid getting damaged, bent, leaned on, twisted, anything, if not just that firing from the centre of the cylinder is a better place for distribution. A fully electronic injector that acts the same as a gasoline injector might be a different matter, but again I haven’t really encountered that. The pressures acting on the parts demand some serious effort to move and open the injector, and it all has to happen really quickly. You need the mechanical action to happen up at the top end of the injector where there’s space, but you need the timing to be precise so they open as close to the injector tip as they can, with the clearances between all the moving parts so tight that 30,000psi won’t push fuel between them. Even if you were actuating it with a solenoid you would want that thing in tip-top shape all the time, and leaving it exposed to the elements, even just what ends up in the engine bay, isn’t the best idea. The better sealed it is, the more it just means whatever makes it in will be trapped to do the most damage it can. So I guess there’s no particular reason you wouldn’t want to hang the injectors out the side, it’s just not a thing that’s done. Even with electronic control, a lot of them still rely on the camshaft to mechanically open the injector, and the electronic part mostly determines how much fuel gets distributed without as much control on the when. 

Some fuel injectors are actually connected to the oil system. There’s a separate high pressure oil pump that hydraulically actuates the injectors. I don’t actually recommend using those, though. Cat used them for a while but I don’t know of any others, there’s probably a reason.

 

I guess a high pressure pump could probably be driven by a serpentine belt system, you’re probably only looking at 10hp to turn it, which isn’t more than a supercharger. And you’d need to be putting that much power into your alternator anyway if you went electric. I was thinking there’d be some advantage not tying its rpm to the engine speed, but that’s no different than driving it with the crankshaft, because that’s exactly what it is. 

 

[derf]

The 7.3 powerstroke uses an oil fired injector.  High pressure oil, 26,000 psi or so, pushes the 40 psi fuel like a syringe into the combustion chamber.

 

It works but it's not ideal.

 

If I was going to convert a 4.0 I'd probably go with a common rail setup.  You could go with the cam position sensor that came in the 2000-2001 XJ to replace the distributor and drive the common rail setup. I'd also go with a gear drive for the camshaft to eliminate chain stretch.

[ftpiercecracker1]

2 hours ago, derf said:

The 7.3 powerstroke uses an oil fired injector.  High pressure oil, 26,000 psi or so, pushes the 40 psi fuel like a syringe into the combustion chamber.

 

It works but it's not ideal.

 

If I was going to convert a 4.0 I'd probably go with a common rail setup.  You could go with the cam position sensor that came in the 2000-2001 XJ to replace the distributor and drive the common rail setup. I'd also go with a gear drive for the camshaft to eliminate chain stretch.

 

Any idea how to drive the high pressure fuel?

 

Electric? Off the cam using the distributor hole? Belt drive?

[derf]

4 hours ago, ftpiercecracker1 said:

 

Any idea how to drive the high pressure fuel?

 

Electric? Off the cam using the distributor hole? Belt drive?

A lot of diesels drive a fuel pump off the timing gears.  That would be difficult to retrofit into a 4.0.  An electric pump would be the easiest to integrate into the system.