now, ive been building performance engines for myself for 10 years, working on cars and engines since i was 6. BUT im new to the whole diesel world. only had my truck for about a year. just learning as i go. now, when you build a gas engine, you make sure the block and heads are true so you dont get head gasket failure. i would assume diesels need the same working? and when running dome pistons, or with extreme cams you have to check for valve clearance between the pistons. if you need to space the heads, there are spacers to buy. head gasket, spacer then another gasket (i usually run copper gaskets) are there the same for diesels? if so, that would drop your compression ratio down as it does for gas. that would allow you to run more boost without having to do any machine work to the pistons, or in addition to. im sure if you you could always have one made. might cost a bit for the r&d but any ones made after that wouldnt cost much at all. sell them, spread the cost of the r&d though out.

 

never heard of someone trying this on a diesel, I'd be a bit concerned about the lifespan of the spacer with how high our cylinder pressure/temp gets

on the other hand I'd love to be wrong on account of the posibilities it would open up for performance builds

 

ya, compression isn't a big deal. Steel can handle it no sweat. The heat is another story. Warping shouldn't be an issue with arp head studs.

 

Even if you drop your compression to around 18 pounds but add 20 pounds of boost, the compression is getting up there to the limit even with studs and on the intake to. I would worry about spacers.

 

ya, you can add more boost. That's the point.

 

I've never heard of anyone using a spacer like that on a diesel, let alone an IDI with over 21:1 compression. Somehow I don't think its a good idea especially when you start adding boost on top of that. For dropped compression you can get pistons that are about 10 thou lower than stock. If you have to re bore the engine for whatever reason, then that would cost you no extra since the price seems to be the same as stock height pistons.

 

There are some diesel engines that use a thick steel spacer between the head and the block. But they are designed with steel pins to locate both the spacer and the cyl head

In this case though, I would use the lower compression pistons since you will already have the engine apart. Having spacers built would probably be more expensive than the pistons. Plus, you are risking the possibility that they won't work and having to do it over again.

Jason

 

well, the head studs would be the same as locating pins in that case. and ya, im going to look into pistons. but a spacer would be something for everyone. why tear your engine apart and install lower compression pistons when your lower end is fine and looking for lower compression. great alternative if its possible. and price like i said isnt in the making of them. its the design of them. once you get it right, then its a matter of materials plus maybe $100 to have them waterjet a set out.

 

But, the studs aren't meant to locate the heads. The diameter of the head bolt holes are larger than the stud dimension. So, there is a chance for movement. Being off even a little may mean a coolant or combustion head gasket leak.

The spacers that I am thinking of are used in applications where the cylinder liners are above the deck surface. The spacer spreads the clamping force across the entire surface.

You're right. Making them is inexpensive. But the R&D is going to be expensive and time consuming to you. Especially if you are planning on selling them. I guess it depends on how many times you want to disassemble your engine for trial and error. I don't like doing things more than once, though.

Jason

 

shouldn't even be any major design elements, just bring em a head gasket for a template

but I'll wait for someone else to test out a set

 

You're asking for twice the issues with 2 gaskets and a shim.

The thicker the gasket the more likely it'll fail.

-Enjoy
fh : )_~

 

To drop from 22.5 to 1 down to 18 to 1 usually takes about 80 thousandths off the pistons.

If you use a second head gasket between the spacer and head you are looking at a very thin spacer.

My opinion is it would be more trouble and expensive than just milling the pistons.

 

yes, you can get very thin shims for gas engines. not much thicker then a head gasket itself. and my point is, what is easier..... to pull of the heads of your engine, spin on some head studs, 2 gaskets and a spacer then the heads OR pull your engine, tear it apart, take your pistons to a machine shop to have the work done. then put the whole engine back together with new rings and bearings when your lower end wasnt in need of it to begin with?

 

You've got me intrigued oreo, cuz that would be alot cheaper and easier for more boost.

 

If the engine has any amount of miles on it, it would be a good time to refresh the bottom end anyways. Especially when you are planning for more than double the boost and a substantial power gain. I wouldn't install a supercharger on a 350 with 80K miles on it.

Another issue that you may run into is intake manifold fitment and sealing (even more critical with increased boost) and valvetrain geometry/ pushrod length.


Jason