Cummins QSB 5.9 480 hp 3400 rated

BillD

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For interested Cummins motorhead readers. :D

I found an old post to a question I asked on boatdiesel forum a few years back when the Cummins QSB 5.9 appeared on the market replacing the Cummins 6BTA 5.9.

The mechanical 6BTA 5.9s were replaced by the "new at the time" QSB 5.9s that are EPA Tier II engines. The top hp rating went from 370 hp (3000 rpm) on the 6BTA to 480 hp (3400 rpm) on the QSB 5.9

The QSB 5.9s will be out-of-production after this (2013) year, replaced by the "new" Tier III QSB 6.7s. The 6.7s are available now along with the QSB 5.9s.

My question @ the time was "base engine design" of the new QSB 5.9 block to withstand the 480 hp level spinning 3400 rpms.

Paul Foulston, a boatdiesel forum Cummins moderator from the UK was on the engineering design team @ Cummins. He's retired now but "stays in touch" with the engineering innards @ Cummins. The following response is the answer to my question. I think the date was 2010 ish.

Paul Foulston: Bill, There is actually very little common about the block B Vs QSB. However lets get down to some basics. The plain old B loved to scream with no ill effects as the Dodge Ram guys know, in fact it loves to spin around 3200 all day where there no hint of crank activitity at all. Bearing in mind that the B crank does not run into trouble until 4200 rpm, other than a torsional grumble at 2700 rpm bottom end is incredibly robust and torsional free. If you ever get to lay a Yanmar LY crank on the floor alongside a B the 3,300 rpm Yanmar crank which looks like a bent pin and nobody questions it. QSB did not need anything doing to the bottom end up to 380 Hp. The big deal is heat. Power equals heat. Once over 350 Hp the old B block has difficulty getting the heat out of the piston crown. The 91 block refinements improved piston cooling. The 370B has had a small piston design change since it first came out to make it more tolerant to abuse. ISB base motor design recognised the need release more power out of 5.9 liters to match the capability of the bottom end. As I said power is heat. The radical and simple piston cooling nozzles in the main bearing saddle of the B were no longer up to the job. ISB was designed from the outset with ´J´ jet under piston cooling nozzles just under the bottom of the bore in order that the oil jet travel was far shorter and better targeted on the underside of the piston. New higher capacity lube pump and cooler came as part of the ISB. The whole ISB block was redesigned and has far greater tensile strength than B Storm block as well as noise reduction benefits. QSB marine was slow off the blocks, the original top rating of 380 was all about using the 370B cooling package, bear in mind QSB 380 is 375 proper Hp 370B is 355 proper Hp. Higher ratings had to wait for a more capable cooling package. Right out of the box ISB proved to be a potential powerhouse and Cummins subcontracted Ricardo to develop ISB for military ´funny´ applications and 500 Hp came straight out of the box. That was in 2001. However what was apparent was the need to get the fluids pumping around the engine and this work saw the capability of the four valve head to continue to follow at high rpm´s. The four valve head actually demonstrated a better valve control than the two valve B at high rpm, probably due to the lower inertia of the valves. QSB 425 came out with a large heat exchanger an even larger oil cooler, still 3000 rpm rated speed. However Cummins is ultra conservative and they developed a unique con rod with an even larger pin bore than a normal 5.9 which is already generous. I think the larger pin bore is borrowed from the 6.7. If you take the QSB 425 as a base platform and improve the coolant flows by spinning it faster the power grows accordingly. If you consider the 480 will have been signed off at 10% overfuel overspeed for 500 hours before anybody even considered letting it loose to the public you realise what the capability of the engine is. Although the 440/480 benefit from the more muscular rods of the QSB425 the part#´s are different even though they look identical, I suspect they a balanced assemblies. I have been very close to a pair of QSB´s in a raceboat running at 3600 rpm all season with calibrations of over 600 Hp at times. Yes an engine blew. Why too much oil, same old story, oil level becomes super critical at 3600 rpm, increased windage in the pan causes aeration of the lube oil and lube temperature rockets. Boat ran a race with 20 psi lube pressue at 3600 and 600+ Hp! and the crank held out but the block split around the area of main bearings, but it held together. Problem solved with CAREFUL calibration of oil pan. New engine sat at 60 psi at 3,600 at the end of a days racing without any issues after that. To sum up the 3400 rpm QSB certainly not a marginal product it is not the Cummins way. What limits the engine from developing even more power? Just the lube oil cooler design, you just cannot cram any more plates in there. Once Cummins have solved that one like they did with the piston cooling jets somebody will be asking all the same questions about some even higher rating.

FWIW,:p

Bill D
 

cb34

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Qsb

Thanks Bill, I am looking foward to my first start up. 350 at 2800rmp, should be real robust.
 

John 40

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Thank you for the info Bill. I too look forward to start up, might have to have it cranked up from 440 to 480.
 

petrel

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Good stuff, Bill D. I especially enjoyed the comparison to Yanmar. Will be interesting to see how they hold up over the years. Of course, a lot of operators who have them in twin engine apps could probably break an anvil w/ a rubber hammer...
 

BillD

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Good stuff, Bill D. I especially enjoyed the comparison to Yanmar. Will be interesting to see how they hold up over the years. Of course, a lot of operators who have them in twin engine apps could probably break an anvil w/ a rubber hammer...

I used to know how much a 6B crank shaft weighed,
Can't remember.
 

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