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What are the mechanical limitations of the R28?  RSS feed
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LOSTCRD

Joined: 18/07/2009 22:51:54
Messages: 26
Location: San Antonio, Texas
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Pertaining to 1)Boost 2)HP 3)Torque

What are the safe limits when it comes to these parameters? I know the Aluminum Head creates some limits...I think you have mentioned possible cracks in the block at the ports at some point...Just would like to know the 99% safe limits.

2006 Jeep Liberty CRD...OME Lift...ASFIR Aluminum Skids and Steps...

DarbyWalters @ L.O.S.T.
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GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 371
Location: Southeast Michigan
There are no defined limits for horsepower or torque, it is a function of cylinder pressure during combustion. 160 bar is no problem for this engine and it can handle up to 180 bar for shorter periods of time. The amount of torque produced at a given cylinder pressure depends on how long the combustion event lasts. If the burn lasts for 45 crank angle degrees verses 30 degrees the effective torque may be more. Many different parameters will play into this, but the area under the curve when measuring the cylinder pressure is vital to determine torque. Sorry for the engineering speak. The other limit is turbo speed, 180000 rpm is good all day and the bearings can handle up to 200000 rpm for shorter durations.

With a cast iron cylinder head and studs the engine would be able to achieve upwards of 230 bar and the bottom end should still be fine...unless someone designs a cast head we will never see those numbers.

In the end, you do not want to get too crazy with a 4-cylinder engine as the torsionals get too high and will wreak havoc to the transmission, a 6-cylinder is a much better option for overall driveline life.
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LOSTCRD

Joined: 18/07/2009 22:51:54
Messages: 26
Location: San Antonio, Texas
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So, if at idle we are running pressures of say 40bar (600psi), what kind of pressures are we running at WOT with the HOT Tune? Maybe the 40bar is high at idle...but that is just an example. I know that diesel is a slower buring fuel than say petrol (Otto cyle engines) and that limits rpms in a inline 4 like the R28, I was just concerned about a post highlighting a weak point in our block near a port area.

2006 Jeep Liberty CRD...OME Lift...ASFIR Aluminum Skids and Steps...

DarbyWalters @ L.O.S.T.
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GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 371
Location: Southeast Michigan
There is not a weak point in the block. The weakest link is the bridge area between the ports on the aluminum cylinder head. With the hot tune we measure about 170 bar peak firing pressure at peak torque between 2000 and 2400 rpm at WOT. At peak power (3800 rpm) the pressure is down to about 130 bar. The engine just does not breathe enough at high rpms to increase the system pressure...it will just make more smoke at a certain point and not useable power.

The durability testing on this engine in Europe included several tests where the powertrain was ran for 2000+ hours on a WOT cycle that includes idle time between runs. Each cycle was about 1-2 minutes. This puts the maximum stress on the cylinder head from a cyclic fatigue failure point of view. The test has a very high load factor compared to a real life automotive application. VM does a good job of flogging their engines to the limit to find the weak links.

The on road equivalent of this test would be running 0-90 mph back down to 0 and repeat for the life of the vehicle. Definitely much more aggressive than real life. The constant load of cruising down the highway is much less stressful on the engine even if pulling a trailer.
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LOSTCRD

Joined: 18/07/2009 22:51:54
Messages: 26
Location: San Antonio, Texas
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That is good to hear about the extensive testing. The bridge area in question...problem caused by heat or pressure? I wonder if some kind of "coating" would remedy the problem? When I raced for Mazda, I experimented with many ceramic, thermal, slick, heat dissapating permanent coatings with some great success. I would love to get a spare head and try some stuff!!!

2006 Jeep Liberty CRD...OME Lift...ASFIR Aluminum Skids and Steps...

DarbyWalters @ L.O.S.T.
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GreenDieselEngineering
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Joined: 10/07/2009 07:25:47
Messages: 371
Location: Southeast Michigan
The bridge area between the valves has the smallest cross section of aluminum. The pressure causes cyclic stresses on the aluminum, the heat is generally slow to respond due to the mass of the head. Coatings are used on the pistons of some performance diesels as a method of heat control and extending piston life.
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