Re: Issues of Engine Reliability (LONG AND TECHNICAL BUT INTERESTING!)

[David <ravee@lamere.net>]

My 1992 Corrado VR6 has 126,000 miles on it and I try to redline it every
day, especially when hitting 140+ on the highway!  :)

-David
'92 slc - chipped...

At 05:10 AM 12/4/98 -0800, RPC Products wrote:
>Engine Life
>
>Hello everyone!  Mark Radelow here  In an effort to bring some technical
>discussion to the table I want to bring up the topic of engine life.  I
>know I know, it's been discussed before.  But after perusing some
>technical engine documents I came across something interesting.  We all
>know that revving your engine high is definitely hard on the motor.  The
>question is how hard is it.  Well I came across an interesting article
>that talked about engine life, specifically related to piston head speed.
>It was talking about the top ring area and that you need to be especially
>careful how fast your piston goes in relation to this.  Well I look at
>some posts and stuff and a guy was talking about a discussion in one of
>his tuning books about this.  Basically it breaks down like this.  
>
>
>I copied this from a post on the BMW list.  I don't know who did itSorry
>if you know who you are:
>
><quote on>
>
>1. Normal Condition
>   Gas pressure in the upper cylinder holds the ring down
>   against the bottom of its groove and out against the
>   cylinder wall, forming a seal.
>
>
>        Gas Pressure
>              :
>              :
>           \| :
>           \| v
>           \| :|----------------------------|
>           \| v|                            .
>           \| :|             Left           .   Right
>           \| v|-------   Cross-section     .  Side of
>           \| :.v.... |     of Piston       .  Piston
>           \|[[[]] <: |\                    .  (not shown)
>           \|  |-\----- \                   .
>           \|  |  \       Ring Groove       .
> Cylinder  \|  |   \                        .
>   Wall    \|  |     Piston Ring            .
>           \|  |                            .
>           \|  |                            .
>           \|  |                            .
>           \|  |----------------------------.
>           \|
>           \|
>           \|
>
>
>
>2. Too Much Piston Acceleration
>   Piston acceleration lifts the ring, shutting off pressure
>   behind the ring and breaking the seal.  The ring groove
>   is damaged by constant mechanical pounding. Hot
>   combustion gases get past the ring, overheating it and
>   the piston.
>
>
>         Gas Pressure
>             :
>             :
>           \|:
>           \|:
>           \|: |----------------------------|
>           \|v |                            .
>           \|: |             Left           .   Right
>           \|v |-------   Cross-section     .  Side of
>           \|:[[[]]   |     of Piston       .  Piston
>           \|v  \     |\                    .  (not shown)
>           \|: |-\----- \                   .
>           \|v |  \       Ring Groove       .
> Cylinder  \|  |   \                        .
>   Wall    \|  |     Piston Ring            .
>           \|  |                            .
>           \|  |                            .
>           \|  |                            .
>           \|  |----------------------------.
>           \|
>           \|
>           \|
>
><quote off>
>
>The result?  Increase wear on the piston, piston ring, rods, crank, etc.
>etc. etc.
>
>Thanks whoever made the great diagrams!
>
>
>
>Okay simple enough.  Now comes the question of determining at what RPM
>this occurs.  I turn to an article out of Gordon Jenning's "Two Stroke
>Tuner's Handbook".  True we have a four stroke, but the principle should
>remain the same.  Anyway, the formula is as follows to determine the
>maximum speed allowable before things turn bad:
>
>Cm = 0.167 x L x N
>
>  Cm = mean piston speed in feet per min
>  L = stroke in inches
>  N = crankshaft speed in rpm
>
>This gives you the actual piston speed in feet per minute.  Then you go to
>this handy little table (I don't know how the determined it, but they did)
>to figure out where your engine stands.
>
>Mean Piston Speed      	Result
>  ------------------     ------
>  Under 3,500 ft/min     Good reliability
>  3,500-4,000 ft/min     Stressful, needs good design
>  Over  4,000 ft/min     Very short life
>
>Okay, this is all good and well, but how does it apply to our car  Well
>let us see:
>
>VR6 Engine
>
>Stroke = 	90MM (out of technical manual)
>		90MM = 3.54 inches (courtesy of handy HP 19BII Calculator)
>
>Okay so plug this stuff into the formula:
>
>First with stock rpm
>
>CM = 0.167 x 3.54 x 6500 (I think this is stock redline)
>CM = 3,842.67 ft./min
>
>Okay that isn't SO bad.  We have already determined the VR6 is a fairly
>robust motor and is quite well built.  Now let's figure it out for two
>tuner chip rpms (6900 my P-Chip, 7300 Garrett's)
>
>P-Chip
>CM = 0.167 x 3.54 x 6900
>CM = 4,079.14 ft./min
>
>Garrett 
>CM  = 0.167 x 3.54 x 7300
>CM = 4,315.61 ft./min
>
>Okay now it is true these speeds are reach for only a few seconds
>(providing you don't hang at the rpm) but there can be no doubt that
>revving above the stock redline can, and will, be harmful to the life or
>your engine.  Even if the rings float just once, hot gases would escape to
>the bottom end.  Figure this, let's say you hold the engine at 7,300 rpm
>for 2 seconds. 
>
>7,300RPM = 121.67RPS (Revs per second, 7,300/60)
>Divide by six to figure out the revs for each cylinder
>121.67/6 = 20.28.
>
>That means that each cylinder has its rings float and gases escape to the
>bottom end 20 times  (providing the rings are indeed floating).  Or a
>total of 121 times for the whole engine!  All in the space of 2 seconds!!!
>I don't care what anyone says, if the rings are floating damage and/or
>increased wear is happening.
>
>Now these formulas are just the opinion of people, but I think that even
>if you add a bit of safety into the formula even then 7,300 rpm would seem
>to cause extreme wear on your car.  Here are some examples of other cars
>with what would be considered OVER BUILT engines.
>
>Redline   			Stroke 		Piston Speed
>Engine     	(rpm)    	in,	mm  	(ft/min)
>  --------   -------  --------    ------------
>BMW E36 M3 	6,800    	3.38,	85.8 	3,838
>BMW E28 M5 	6,900    	3.31,	84    	3,814
>BMW E34 M5 	7,200      	3.39, 	86   	4,076
>Just for comparison
>CBR600 (bike)  13,250 		1.78,	45.2 	3,939
>
>
>
>Okay, I know they are all BMW engines, but they are ALL M engines.  And
>not one of you, even Wally ;), can argue these are not well built engines
>built to take a load of stress.  Hell the rumor is that BMW picked old M3
>four cylinder engine blocks right off the factory line to make F1 engines
>out of them.  I find it funny that only one of them goes over the danger
>zone (barely), but even then it's at ridiculous RPM and not even close to
>what the VR6 pistons are doing at that speed.  Plus this is with a Dinan
>Chip that STILL recommends maximum constant engine speed be limited to
>6500 RPM.  
>
>What's the point of all this?  Well I am not gonna be as happy to spin my
>motor to redline anymore.  I think this shows a very good valid point that
>the tuners don't do all their homework; including Garrett.  I will be very
>weary of what they called reliable from now on.  It also shows you with
>stroker kits out there should be even MORE careful.  
>
>Now will this reduce the life of your car noticeably?  Maybe yesMaybe no.
>There is no way to be sure.  But if you are like me and would like the car
>to actually live BEYOND it's powertrain warranty then it is definitely
>something to consider.
>
>One thing, I am not an expert so I would like some responses from the
>group (Todd, Don, etc. etc.)
>
>I am sure this is gonna start something
>
>Mark Radelow
>(MEGA FLAME SUIT ON)
>1997 Jetta GLX "Dear Lord What Have I Started" Version
>
>
>