High Compression Pistons

[Bugracing]

Hello All;



I am looking to increase the compression ratio of my '05 5. 9 liter from the soft 17. 2:1 to around 21 to 22:1.

Does anyone know of a piston manufacturer, who makes pistons for our 5. 9 liter Cummins that will achieve the higher compression?



Many thanks

 

[lmills]

There is no need to raise compression on a turbo diesel, ever. .

 

[Bob4x4]

Hello All;



I am looking to increase the compression ratio of my '05 5. 9 liter from the soft 17. 2:1 to around 21 to 22:1.

Does anyone know of a piston manufacturer, who makes pistons for our 5. 9 liter Cummins that will achieve the higher compression?



Many thanks

:-laf:-laf:-laf



These trucks don't work like Bugs



Bob

 

[rbattelle]

I would tend to agree with lmills and bob4x4. I doubt you'll find anyone to carry pistons for that purpose in this application.

Peak pressure would be extremely high, and would likely require major changes to the fuel control, head bolts, and possibly structural changes on the bottom end. I assume you've already considered this, so I apologize if this is repeating what you already know.

If you have the knowledge to perform this level of work, then I assume you also have a machine shop (or access to one). Have you considered making your own pistons? The trick would be getting the piston bowl small enough to provide the desired compression, but large enough to permit a sufficient quantity of fuel to be injected. The new fuel control would play a big part in making it work right.

It's like they say, with enough money anything's possible.

Ryan

 

[BigEasy]

doesn't increasing boost do the exact same thing to an engine as raising the compression?

 

[rbattelle]

doesn't increasing boost do the exact same thing to an engine as raising the compression?

A naturally aspirated engine at 22:1 won't make nearly as much power as one with 70 psi boost pressure with 17. 2:1 compression.

The difference is boost brings in more air, whereas compression simply produces more pressure with the same quantity of air. That's a subtle but very important difference!

The engine with higher compression will be more efficient (efficiency being a function of compression ratio), but won't necessarily make more power.

Ryan

 

[betterthanstock]

The engine with higher compression will be more efficient (efficiency being a function of compression ratio), but won't necessarily make more power.



Ryan

He didn't say he wants more power.



Are you after more power, or less power with better mpg? By upping compression ratio, you should also lower the max boost by reprogramming the ECM (I don't know if anyone, Smarty or other, allows this option) or by installing a mechanical boost wastegate at about 20 psi.



You'll get easier cold starting (although it will be harder on the starter and batteries), better throttle response "off boost", cleaner running at low power levels, and better mpg, but less max power, unless you want to really beef up the engine.



You can also raise compression by machinning down the head, a lot less work than pistons. (unless you now have a hole in one piston and this is just an attempt to make you feel less bad about the situation, to kinda justify the expense to yourself?) Just make sure the pistons won't hit the valves with whatever cam you go with. You could machine some valve clearance in the pistons even as they sit in the block. (by making a template and going with a router with a proper end mill, one piston at a time).

 

[Vaughn MacKenzie]

rbatelle I wonder what kind of cylinder pressures my old Blazer with the 6. 2 diesel and Banks turbo would run . . . let's see, 21. 5:1 compression ratio, and up to 11psi boost boost? After 110,000 miles with some trailer towing it never lost a head gasket or had any issue other than a lifter. I think the Cummins could handle 21:1 and ~25psi boost just fine, at least if it had head studs & O-ringed block or head.

betterthanstock. . . milling the head does nothing to raise compression on a diesel.

 

[betterthanstock]

betterthanstock. . . milling the head does nothing to raise compression on a diesel.

huh?



Isn't the Cummins a dome? I can see your point

on a flathead.



All right, I looked at the sectioned engine. It looks like aflat head.



So, you need to use an endmill (not a surfacer), and only remove where the head gasket contacts. Leave alone the part inside the cylinder, so it will stick in lower, and sort of act like an O-ringed head too, if done right. It will change the depth of the injector, so it may need a thicker copper shim??? (and possibly leak around the fuel connector tubes)

 

[Vaughn MacKenzie]

Picture of Cummins head

#ad

 

[TAbbott]

I doubt the new CR heads look like that... . Poster said he had an '05?

 

[TCluff]

Milling The Deck Is Asking For Trouble With Stock Pistons, Unless You Run A Smaller Cam, That Would Put You Back To The No Air, Lots Of Pressure, Black Smoke And No Power, Making The Bowl Smaller Might Mess With The Spray Pattern, I Think Cummins Has It Engineered Pretty Good Stock, High H. p. Guys Run Shorter Pistons And Less Compression To Use The Extra Room For More Fuel And Air Which Will Produce Power Building Pressure At The Rpm They Like To Run, A Daily Driver Will Lose Some Daily Drivability Due To Lower Compression And Might Lose A Little Power Spending Energy On Pushing The Higher Compression Pistons Through The Compression Stroke, Also Alot Of Fuel Timing Would Be Involved

 

[TBartlett1]

Your signature leads me to believe you are into racing, Y/N?

Please explain what are you trying to do?



Unlike gasoline engines to make extreme power from a diesel you do not increase compression you would lower it and increase fuel and boost.

As stated in previous posts the clearance between the piston & valves is extremely close.

As a matter of fact Cummins supplies thicker head gaskets if you need to machine more than . 010 or . 020 from the block surface to maintain proper clearances.



The only reason I have heard of anyone increasing the compression significantly in a diesel was to aid cold staring in extremely cold, high altitudes and this application was for a diesel generator.

 

[rbattelle]

He didn't say he wants more power.

Good point.

I think the Cummins could handle 21:1 and ~25psi boost just fine, at least if it had head studs & O-ringed block or head.

As usual, you're right. But I still think you'd probably want to change the fuel control to limit peak pressure, right? I mean, if you ran without changes to the fuel control your peak pressure would go up considerably. From what I've read, diesels are normally designed to run to a limited peak pressure (constant volume cycle through part of the stroke, followed by constant pressure once the maximum peak is reached).



What if you just filled the piston bowl in a bit with "something" to make it smaller. I don't know what "something" is, but maybe a ceramic material? The danger there would be the "something" breaking up while the engine is running.



Feasibility aside, it's an interesting discussion!



Ryan

 

[ThrottleJockey]

As Vaughn was saying, the Cummins head surface is flat, on the 05s, too. Milling it won't do anything.



Arias Piston will custom make pistons, tell them want you want and get the forged versions, they're a little tougher. They'll cut valve reliefs in them, too.



Arias Pistons

 

[Bob4x4]

Indirect injection diesels need more compression than a direct injected engine to operate efficiently. More power will be made by increasing boost (with increased fuel) than adding compression. With the electronic timing and fueling control there is no reason to increase static compression.



Bob

 

[Bugracing]

Many thanks for everyone's feedback about compression ratios on diesels.

If one takes a look at younger (current) diesel engines it is very obvious that compression ratios have been dropping. The sole reason this is done is to reduce burn-temperature, which reduces NOx emissions. OE's are required to achieve governmentally regulated tail-pipe emissions, which has brought us , common-rail injection, diesel cats, and now diesel particulate filters (DPF).

The downside to lower compression is the reduction of engine's responsiveness and efficiency. Of course you could stuff more turbo boost into the engine (like 70psi), but that exponentially increases loads on all components.

The goal is to burn more of the current fuel load. (Yes, head studs will have to be upgraded to deal with the higher static compression ratio and higher operational pressures when the turbo goes to full boost. )

Higher compression ratio does increase burn efficiency, which will lead to improved engine performance and better mpg as you are now burning more of the injected fuel.



In short, I am still looking for a supplier who makes high compression ratio for the 5. 9 liter Cummins.

There is one advertiser in Diesel Power magazine: Ross Racing Pistons, yet I like options - so: does anyone else know of any forged piston suppliers for Cummins Diesel engines?





PS - What is interesting is that some folks here think that our oil burners don’t behave like gas burners – sorry to disappoint you , but any fuel burning engine is an “air-pumps” no matter what the fuel is.

 

[Vaughn MacKenzie]

Bugracing, if we were talking about 12-valve engines I think you could get higher-compression pistons such as those used in non-turbo applications of the B-series engines, but I'm guessing they may not be as durable as the turbo variety. I'm not aware of any naturally aspirated 24-valve applications though.

 

[AH64ID]

The sole reason this is done is to reduce burn-temperature

This may be a silly question, but how does increased EGT's come from a cooler burn temp? Does it have to do with where the majority of the burn is?



Also I feel the compression has been dropping based on stock boost, were up to 32 psi on the HPCR 5. 9, thats a lot... Like you said, they are similar to gassers, and gassers have to drop compression to run boost.

 

[moonranch]

There are several custom piston manufactures out there: Arias, CP, JE,Mahle, Ross, Wiesco... . Most os them can build a piston to your specs, but I have only seen Ross, Mahle and Arias mention diesel applications.