kidturbo

Not that long ago a 6.6l Duramax piston upgrade involved taking stock pistons and cutting the bowl lip back to reduce the chance of cracking. Right after my second piston failure I lucked out and scored the first set of Mahle improved castings for testing. This new piston design included a reshaped bowl, better oil cooling passage, lower 16.5CR, valve reliefs and graphite coated skirts.

[ATTACH=CONFIG]553140[/ATTACH]

These held up well for me, and are still in the boat today with around 350hrs at just over 650hp. Many of those hours at high RPM's for extended runs. While some racers have cracked them, they are actually rated to around 950hp. So we used this piston with a 16.0CR in Dave's new 700hp build. One of the original Duramax gurus has expanded on the design by taken this same piston and machined the bowl into an oval. This change along with ceramic coating the top has provided a piston that's so far been unbreakable. More on this Fingers Oval Bowl Duramax Performance Piston

[ATTACH=CONFIG]553142[/ATTACH]

Many people ask "why not just run a forged piston?" It's actually not cost related, it's a longevity thing. Custom forged piston are now available and proven in 2000hp Duramax race engines. However the forge and machining process doesn't allow for using a hardened upper ringland like factory cast pistons. In the pic below you can see the "cheetah pattern" in the top of the cylinder wall. The upper portion of the linerless cylinder bore is induction hardened to reduce wear. Due to the very high heat and cylinder pressures, the forged aluminum piston ringland will actually wear out long before the rings.

[ATTACH=CONFIG]553143[/ATTACH]

What we don't see yet for the Duramax is a "steel" Monotherm piston as use by Cummins and other industrial level manufactures in marine engines. I have a feeling a couple sets may be out there in engines for testing by another OSO member... But nothing officially has been released by Mahle to date.

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More about these Dmax piston designs at:

http://www.dieselarmy.com/engine-tec...otherm-piston/

http://www.duramaxforum.com/forum/af...pistons-2.html

kidturbo

Had to finish up a couple projects last week, so will try to catch up where I left off.

Next internal part we need to address is the connecting rods. Once again the choices depend a lot on the power level your looking to run, and engine model your starting with. HP / Torque limit on stock first generation LB7 LLY rods was considered to be about 600/1200 at the crankshaft. If you think about it, that's not bad for a 2001 OEM 403ci bottom end. And when they do fail, they usually just bend rather than break. The factory LBZ/LMM and LML rods were upgraded, and those have been pushed up to 800-900hp in trucks without failure.

For typical marine use I don't feel bending the stock rods are a huge concern, and here is why. I pushed factory LLY rods to almost 700hp in my boat without failure. In the chart below we can see the torque vs HP curve on a newer 2011+ LML engine. Look at the peak toque RPM, it's at 1600R's then falls off a good bit. My experience was a 4 blade 32P Bravo prop couldn't begin to hold that power and would blow out with full down trim. I switched to a 5x37 and even that would start to cavitate if you stabbed it. So my theory is, these rods typically fail at peak torque RPM, and if you can't hook up that torque in a boat, then you can't bend them...

[ATTACH=CONFIG]553456[/ATTACH]

While bending stock rods at double factory rated power isn't a big concern, there is still a slight problem with them. And this one you won't find much about on the Dmax forums either, cause it typically only occurs in boats.. Wrist pin bushing wear... I was made aware of this by a very well known engine builder who is likely the first guy to ever marinize a Dmax. Curtis Halvorson at Extreme Engine Development in Calgary, Alberta, Canada. When I was ready to give up on the Duramax boat, this guy reeled in my expectations and pointed me in the right direction. I followed his advice and try to pass along everything he taught me.

Curtis tried spinning a pair of LB7 engines 5k all day in a race boat way back in like 2005. He told me he was only getting 100hrs on wrist pin bushings. So when I tore my engine down to upgrade pistons, we checked the pins and bushings closely. He was spot on, rod bushings were about shot with only 100hrs of high RPM boating on the stock bottom end. Curtis gave up on the whole marinisation idea BTW. Here is a video of his latest Dmax build though. https://youtu.be/0DRfjH-dVQI

What I took away from his advice was, 1) use a better bushing material, 2) increase the oiling to the pin, 3) stop trying to spin the engine 4000+ Rpm. You have to consider that in a truck this engine has a peak power range of 3000R, and red line of 3200R. While you can spin them 4k, it's not likely your gonna do that very long in a truck. Luckily the rod selection and options today are much better than my build date of 2010.

GM increased wrist pin dia on LBZ, and today the aftermarket rod selection is much better. You can now buy rods with pressurized piston pin oiling from at least two manufactures. Which I would certainly suggest for any build over 500hp. A good set of rods will run ya between $2400 - $4000. See the comparison picture below and see if you can spot the factory LB7/LLY rod. I will get into the "cheap fix" I used in the next post.


[ATTACH=CONFIG]553464[/ATTACH]

kidturbo

Ok we have examined the two weakest internal parts, and here is the most important points I feel allows these engines to live or die in a marine environment. Oiling, Oiling, and Oiling...

A good read that explains this along with the different Dmax internal changes over the years can be found here.
http://www.sbintl.com/tech_library/a...max_diesel.pdf

In 2006 with the LBZ model release GM / Isuzu strengthened the connecting rod, along with increasing diameter of the piston pin, and adding bushings in the piston. Obviously they were aware of some weak points by examining common failures and felt the piston pin area needed to be addressed. I can't say for certain if these LBZ changes resolved the LB7/LLY pin bushing issue or not, because I've never tore one down that was used in a boat for any extended periods. However a simple mod I used on the LLY to increase piston cooling and pin oiling [which didn't cost me an extra dime] was to simply increase oil volume flowing into piston bowl cooling passage by some 30% or more.

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These cast pistons are oil cooled. While now becoming common in high performance gasoline marine engines, all modern diesel engines use oil squirters to remove the heat from the piston. In the first pic above, see the little copper tube pointing towards the piston. In the second photo it's labeled (A). This squirter takes oil from the main rail and sprays it directly into a hole under the piston [pic3] when it reaches bottom dead center. There is a cavity in the piston under the bowl that drains back onto the rod. In top of the rod, there is two holes that oil the pin bushing. See where this is going?

That little copper squirter tube is crimped down on the tip to reduce the oil flow, so to increase flow we drill it out. Some salt flats racers have even found that by adding a second squirter and modifying the piston to accept 2 of them has stopped most piston failures. In the base or bolt area of the squirter GM uses a small spring and ball to stop the flow of oil if rail pressure drops below 30psi. So at hot idle, they don't flow any oil into the piston cavity. I can't say for certain if that mattered, but both of my stock piston failures came right after a long idle period, within 10 seconds, soon as I jumped hard on the throttle. Like they heat soaked and couldn't cool quick enough when I put the fuel to it.

But if you remove that ball and spring, you'll need a better oil pump setup, or idle pressure will drop below a safe level. Eight of those little tubes move some oil volumes. So for my build we left the check balls in place and just drilled out the tips. It sure didn't hurt anything... This is another point that Curtis from my last post turned me onto. I recently had a long discussion about this mod with the company owner who originally maninized my boat while helping chose components for my friend Dave's new engine. These guys build a bunch of Dmax engines and had never modified those oil squirters before, and claimed we would have to switch to a dry sump oiling. To which I replied; "If you recall I fixed all your screw ups some five years ago, and my engine is still running strong at 350hrs. How many hours is on your boat engine again?" LOL.. He agreed to the modification with my specs and a stock oil pump.

I found this MaxTorque.com study on oil cooling and the Duramax from 2008 that explains these principles and shortcomings with the factory oil cooler setup. This graph below fits well, and shows why we need to change coolers and monitor oil temps our Dmax conversions.

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From the study. The most notable result from the 2001 SAE Study is the effect of RPM on oil temperatures. The effect of doubling RPM, with no additional workload, raises oil sump temperatures 54 degrees! This effect is explained with a couple of phenomena. There is more friction, obviously. But also, oil flow rate (and thus heat transfer) rises almost linearly with RPM.

Oil flow and sufficient oil cooling is the life blood of any marine diesel engine...

kidturbo

So far we have covered the major internal upgrades for those looking to exceed 500HP marinized. Along with the simple oil squirter mod I would do to any stock engine before dropping one in a boat. Only a couple last points to address on the internals, then we can button it up.

If you've decided to tear the engine down for anything above, you need to KEY THE CRANK & CAMSHAFT while in there. For unknown reasons GM / Isuzu thought it would be OK to use a small roll pins to align the crank and cam gears. The stock cam itself is cut from billet steel with a profile that's typically good for 800-1000+hp without question. There is aftermarket profiles to raise operating RPM range, along with an alternate firing order option that came about to address harmonics felt to be causing broken crankshafts. While it makes for good opinion based topics on the Dmax forums, I just can't see spending $1500 on a camshaft unless there is some major performance gains... One thing everyone can agree on is the factory pin setup should be address for any performance application.

Below is some pics of the stock cam vs a keyed cam. I did mine [last pic] on the first tear down using a 50yr old milling machine in a buddies garage. There is plenty of online shops that will do this mod on your cam or even offer cam exchanges for around $150. I would highly advise it just to be safe.

[ATTACH=CONFIG]553617[/ATTACH] [ATTACH=CONFIG]553620[/ATTACH] [ATTACH=CONFIG]553621[/ATTACH] [ATTACH=CONFIG]553622[/ATTACH]

While not as prone to failure, if you have the crank out you may as well key it also.

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The rest of the bottom end is pretty good to go from factory. The main caps are cross bolted into the block, so it's not likely they can walk. Just remember to replace those torque-to-yield bolts. If you want added insurance, SoCal Diesel makes this stud girdle setup.

[ATTACH=CONFIG]553626[/ATTACH] [ATTACH=CONFIG]553627[/ATTACH]

Last point is to use good aftermarket rod and main bearings. I used the H series bearings back in 2010, but there may be better materials out by now. Also check out the oil pick up tube, no upgrades needed there.

[ATTACH=CONFIG]553628[/ATTACH]

sprink58

OK...so now I'm neck deep in the theory and application. Understanding that marine application is a full time bearing and wrist pin load I see where those parts that are sufficient for an automotive application will fail prematurely in a marine environment. I suppose it comes down to inferior metallurgy yielding to improved superior metallurgy for the application.

What I'm trying to wrap my head around is why the 32" and stronger bite props are blowing out with these huge applications of TQ. Seems that the answer would be in a larger diameter prop if I understand hydro dynamics at all.

Thanks for all the information...great read !!

kidturbo

Yeah its all that low end torque when the turbo lights off at around 1500rpm if your on the throttle. Engine goes from 400ft lbs to 1200ft lbs in under couple seconds. Soon as that prop starts to boiling the edges, its done. Bravo1 drives being limited to just under 15.5" diameter props, and 36" pitch off the shelf options doesn't help. That 4 blade 32P at 15" dia I first ran was like a 13" radial on a drag car. You can drive on it, just don't jump on the throttle.

Once I changed to 15.5" with 5 blades and stepped up to 35 pitch it wouldn't blow out, but you could still feel it cavitate until you backed off the throttle for a second. I see this same thing happening on my friends boat with the 6spd Allison and ASD8 between shifts. He can log the output shaft speeds, and that surface piercing prop will jump like 600-700rpm when shifted from 4th to 5th [OD]. After 5 or 10 seconds you can see it slow back down and hook up again in the logs. It's a torque thing...

The easy fix, that also helps protect the Bravo drives is using the ECM's torque limit table to map power curve by RPM. Once I modified the torque table you could slam the throttle down from a dead stop and she would climb nice and mellow until up on plane. [See Pic Below] Above 2000 R's I left it maxed out and unrestricted. After breaking the shift lever bolt off inside the outdrive, I used that same table to limit idle torque to 50ft lbs. Nice feature you get with EFIlive...

[ATTACH=CONFIG]553735[/ATTACH]

kidturbo

With the new internals installed there's not much left to do but button it up. Depending on cooling system plans, you may wish to switch to appropriate freeze plugs at this time. Stock cylinder heads are fine for most applications. At minimum they should be inspected, cleaned, and trued before reassembly. One safety upgrade might be switching to titanium keepers.

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Also now is a good time to paint the block and powder coat all the covers, intakes, and brackets if you want. Just be sure that who ever does the powder coating plugs all the bolt holes and masks off mating edges. I forgot to stress that, and it became an issue on assembly. Should also be noted that the oil pan, intakes, and front cover don't have gaskets. These parts use grey GM engine RTV sealant. Only the two piece valve covers actually have gaskets.

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Last two points worth covering are regarding the crank damper and factory fan mount / idler pulley. The factory crank pulley and damper assembly does ok in most lower HP applications. Since we have keyed the crank, spinning the ring is only possible issue. I paint marked my damper after assembly to catch any movement. If not keyed and the pin sheers, they will pick up a violent vibration. For any high power application the ATI super damper is a good upgrade choice.

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The center pulley in normal location of a water pump on gas engines is actually just a cooling fan drive. It has a 1.5" long threaded snout that the cooling fan mounts on. When I moved the charge cooler to front of the engine, I was 1/2" short on space. So I chalked the pulley up in a band saw and removed that snout. This mod makes for a cleaner looking setup on any marinisation project.

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That concludes our internal upgrades section.

Unlimited jd

iTrader: (5)

Curtis had me drill out the piston oilers on mine way back when also. Great info with the how's and whys.

Blueabyss

Most Factory Marine Diesel engines have after coolers on them. How are addressing that issue?

Chris

999JAY

[ATTACH=CONFIG]553860[/ATTACH][ATTACH=CONFIG]553861[/ATTACH]In comparison to a Seatek that makes 700-1200hp the rods look small, Seateks are only 6 cylinder though.