Target carrier (2 Viewers)

[J Mack]

About 13,000 miles on this engine this go around.

Beyond "acceptable" practice for a stock engine is a tough call for the Cummins engine, I was definitely at the upper limit for a single turbo but compound guys are pushing a lot further on seemingly stock bottom ends so I would assume I would be at the upper middle limits of “acceptable limits”.

The working theory right now is I floated the valves when I was running my second turbo the BorgWarner EFR 7064 Turbo, that turbo would start making boost around 1800 rpm and pull hard up to the 4000 rpm defueling point of my pump (from memory boost was 45+ at the time of defueling) and the engine sounded unhappy and this upper limit, I remember thinking it sounded like someone was shaking a tin can full of nuts and bolts under my hood in hindsight it was most likely valves hitting the tops of pistons.
Thinking back my blow buy issues started at about this same time but I never put two and two together, I removed that turbo and put a smaller more reasonable turbo on the “super” HX30 and I’ve kept the RPM down around 3000 RPM mostly because the new turbo flattens out above that.



New engine should be reasonably bullet proof with the current turbo but able to handle the higher RPM and boost if I get a bug in my butt and put the EFR back on..

 

[J Mack]

The 60# springs are supposed to address the valve float at my boost/RPM levels but as it appears they don’t.

New engine number two is going to get new valve train again and we are looking into exactly what that will be now.

 

[scrapdaddy]

I never thought that a diesel would float valves, but I guess when you start building one up it's like any other motor. Stronger springs = faster wear on the cam. Can you get a roller cam for the Cummins? It just keeps going!

 

[boots4]

Thanks for finding the limit for the rest of us. I think I've been to 2900rpms once, can't imagine what 4K feels like. Seems like you're starting to enter sled puller territory at those rpms. These dumb little engines are just too easy to get more power out of and do it whether it hurts them or not. These things sure do hold up to some serious abuse.

 

[J Mack]

I never thought that a diesel would float valves,

With the boost I was running pushing on the valves at the RPM it appears I needed to jump up in weight springs. Assuming this is an issue because all the aftermarket pistons offer fly cut valve reliefs.

Thanks for finding the limit for the rest of us.

This is the reason I can’t have anything nice or as my dad used to say “son you can (F) up a steel ball in a rubber room”

Something tells me I’ll find the next limit of Cummins vs Toyota soon enough..

 

[boots4]

I'd beg to differ that your FJ55 isn't nice and I'm pretty sure more than I would say you've done an incredible job on your pig. That thing is gorgeous. I'm with you though on having the "little more" disease.

I just want to see what it's like with just a little more.
Surely a little more will be enough.
Maybe a little more would be better, etc.
​

I don't think this disease has a cure but it can be managed with just enough.

 

[GLTHFJ60]

About 13,000 miles on this engine this go around.

Beyond "acceptable" practice for a stock engine is a tough call for the Cummins engine, I was definitely at the upper limit for a single turbo but compound guys are pushing a lot further on seemingly stock bottom ends so I would assume I would be at the upper middle limits of “acceptable limits”.

The working theory right now is I floated the valves when I was running my second turbo the BorgWarner EFR 7064 Turbo, that turbo would start making boost around 1800 rpm and pull hard up to the 4000 rpm defueling point of my pump (from memory boost was 45+ at the time of defueling) and the engine sounded unhappy and this upper limit, I remember thinking it sounded like someone was shaking a tin can full of nuts and bolts under my hood in hindsight it was most likely valves hitting the tops of pistons.
Thinking back my blow buy issues started at about this same time but I never put two and two together, I removed that turbo and put a smaller more reasonable turbo on the “super” HX30 and I’ve kept the RPM down around 3000 RPM mostly because the new turbo flattens out above that.



New engine should be reasonably bullet proof with the current turbo but able to handle the higher RPM and boost if I get a bug in my butt and put the EFR back on..

Valve float should be fixed with the 60# valve springs *assuming* the stock cam. If it's not, then I probably have the same problem that you do with valves contacting the pistons The 4BT absolutely sings above 3200rpm man, I love it I've hit the defueling point with my 3800rpm governor spring, usually when trying to get up a slick trail as fast as possible. Your throttle operates like an on-off switch too, right? Weirdest thing

I'm very interested to see what you do with the internals. I'm going to run my motor until I get blowby like you do consistently, then almost certainly go the same route.

 

[boots4]

...The 4BT absolutely sings above 3200rpm man,

Oh man... now I'm going to be tempted to try it. It was at 2900 rpm when my first side freeze plug let go so I've been gun shy about higher rpms.

 

[GLTHFJ60]

I've been lucky I guess

 

[J Mack]

If you’re starting to get blow by then I would get after it sooner than later, I would use very little oil under normal driving around town but gallons on long trips with extended run times under boost.

Running like this for the last 4-5 thousand miles wore my cylinders to the point I needed the .040” over pistons, if I had stopped when I first noticed I’m sure I could have got away with STD or .020” over giving me one more rebuild on this block.

From what I’ve been told Mahle OEM makes the OEM Cummins pistons and Mahle performance makes their performance pistons from the same castings or forgings depending on what you buy. I’m switching to the large bowl Cummins piston because they handle the heat a little better (top ring land is a bit lower) and you can run a bit more timing, I’m also dropping my compression a half a point to help me use my boost a bit more efficiently without effecting my cold starting like dropping by a full point or more, Mahle is also machining .120” valve reliefs to prevent any future valve contact.

After hours on the phone with various venders trying to sell me full sets of 6BT pistons Pure Diesel Power ( puredieselpower.com ) got me exactly what I needed in the time frame I needed it.

Look in to the aluminum piston squirter when you do the piston switch, cheap insurance when you run the boost and fuel we are pushing into these little engines and have a heavy right foot..

 

[GLTHFJ60]

If you’re starting to get blow by then I would get after it sooner than later, I would use very little oil under normal driving around town but gallons on long trips with extended run times under boost.

Well damn, that's what I've seen. I thought it was a stuck ring that unstuck itself.

If you're running the large bowl pistons then you have to have a 155* spray angle injector, right?

 

[J Mack]

If you're running the large bowl pistons then you have to have a 155* spray angle injector, right?

You need 145° injectors if you run small bowl pistons and much over stock timing or you chance spraying outside the bowl, 155° injectors will chance spraying outside if you run the small bowl with very little over stock timing. I have 145° 5-12 injectors narrower pattern and large bowl will allow for more safe timing but honestly the 16° I currently run seems to work fine and I don’t see a need to run more.

The main reason for me going to the large bowl on this go around is the lower top ring land and the advantage that gives with the higher cylinder temps associated with my driving style.

 

[J Mack]

I thought it was a stuck ring that unstuck itself

I was thinking the exact same thing, history will show I was wrong..

 

[scrapdaddy]

Question... On the pistons with the recess milled in for the valves, do they have a thicker dome, which would move the ring land down or ? If they recess for valves, does that make a thinner area on the piston dome and does that jive with the higher cylinder temps.?

 

[GLTHFJ60]

Question... On the pistons with the recess milled in for the valves, do they have a thicker dome, which would move the ring land down or ? If they recess for valves, does that make a thinner area on the piston dome and does that jive with the higher cylinder temps.?

I'll try to address this before @J Mack gets here. I think you're mixing a few things together.

"Flycutting" the pistons, aka milling in recesses for the valves, is only to prevent piston to valve contact at higher RPM, nothing else. It's a custom modification.

J Mack runs his engine pretty hot. You could call it a "high strung" engine. Running a larger bowl in the piston will reduce combustion pressure by a little bit which will allow you to run more timing. The larger piston bowls also happen to have the ring land a little lower down from the crown which somewhat insulates the compression ring from the (super) hot combustion temperature. It is possible that Cummins engineered the ring land lower with the larger bowls due to the thickness of the piston wall at that point, but it's speculation.

Flycutting the pistons does thin out the top surface of the piston, but not significantly enough to affect it's durability or robustness.

HTH.

 

[scrapdaddy]

Flycutting the pistons does thin out the top surface of the piston, but not significantly enough to affect it's durability or robustness.

This what I was wandering about. So the piston isn't made thicker to accommodate the flycutting. It can be done to a stock piston.

Thanks! I've always found this stuff very interesting.

 

[J Mack]

GLTHFJ60 pretty much hit the nail on the head.

The pistons I ordered are also referred to as the marine piston or marine bowl and are popular upgrade to performance Cummins engines for all the reasons GLTHFJ60 mentioned. If you look at the picture of the Mahle piston below its machined from OE castings (retaining the steel top ring insert) and the top ring is a bit lower than the standard 4BT piston this will give you a better idea of what we are talking about.

When you add timing to a direct inject diesel engine EGT’s go down and cylinder temps go up as with cylinder pressure, if you get greedy pistons melt. Cummins used 155° and 145° angle spray nozzles on their injectors to accommodate factory bowl size with factory timing, when you start working too far outside the factory window you spray outside the bowl and chance washing down the cylinder walls with fuel. I’ve talked to guys running as much as 32° of injector timing but my engine started to lose bottom end around 20° and I settled at 16° as my best average.

 

[J Mack]

Same piston with "fly cut" valve relief.

Or the video,

 

[GLTHFJ60]

Same piston with "fly cut" valve relief.

Or the video,

The guy in the video is dullllll, but that two minute bit sold me on Mahle pistons for the next reman of my 4BT. Improvements across the board!

 

[scrapdaddy]

I never seen pistons like that before. Sounds like they have it nailed.