Miata Mailing List: September 1996, Message #0191
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   From: dans@dmscomp.com (Dan Scolnick)

Subject: RE: Response to Norm's long message

   Date: Mon, 2 Sep 1996 23:19:50 -0500



>A few comments

>

> 

>>        The greatest stress on the bottom end of the engine occurs at Top

>>Dead Center on the exhaust stroke when the cylinder pressures are the

>>lowest, the piston is flying up and has to reverse direction. 

>

>You got this from one of Corky's old articles.

            

This one?  Broken connecting rods, detonated pistons, spun bearings you

refer to 'this one'?  I don't think that QUITE dismisses it.  And NO I

didn't get it from one of Corky's 'old' articles.  Are you saying that

because you think you know the source that it doesn't make a difference?







>You are totally ignoring

>piston scuffing, which is the major component we are talking about.

>

        Funny, I haven't heard you or anyone post anything about piston

scuffing yet.  I believe you used the term 'piston slap' in one of your posts.







>

>  The real issues

>>regarding blowing engines have more to do with detonation control, which is

>>taken care of by

>>

>>        1.  High octane fuel

>>        2.  Electronic devices

>>        3.  YOUR EARS AND JUDGEMENT

>

>Your ears are the worst thing to trust in a convertible 85 db car like the

>Miata. Trust me, you can be melting your engine to death at 100 mph and

>never hear a ping.

>



        Yes this is true.  Yet we have heard from many people with blowers

that routinely run far more than 6psi and drive much harder than merely

100mph and they don't seem to be melting their engines.  How about it.  how

many melted engines do we have out there?







>>        IMHO the supercharger crowd shouldn't be casting aspersions with

>>veiled references towards the increased boost of the turbos.  

>

>Turbos cause a back up of exhaust gases, even if ever so minute, that cook

                                                                  ^^^^^^^^^

>the exhaust valve and create lower thresholds of detonation. At best, the

 ^^^^^^^^^^^^^^^^^

>air trying to get out of the combustion chamber can't get past the turbine

 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

>impeller,

^^^^^^^^^



        Interesting theory you have there, Norm.







> and the impeller can't put more in than can be pushed out, so

>turbos become self-balancing on stock engines at some point. Superchargers

>have no such problem, they just push and push while the exhaust just draws

>and draws. And if someone tells me they can't feel turbo lag, they'd make a

>pretty poor test engineer...

>

>>

>>        Bottom Line,  If non-detonating 6lbs won't kill your engine, neither

>>will non-detonating 8 lbs.

>

>Uh, excuse me, but that 8 psi is making more power, isn't it? Sending 175 ft

>lbs of torque down four connecting rods, across four big end bearings, down

>a crankshaft and through a clutch, etc. is the same as sending 159 ft lbs?

>You're onto something here. 

>



Yeah I am.  I noticed that in the first paragraph you dismissed spun

bearings, broken rings/piston lands, connecting rods, crankshaft as the

major components that we were discussing.  Now they're important.  If you

measure the 6 lbs of boost to the 8 lbs of boost in what it really is,

ATMOSPHERES then quite simply we have 



14.7 lbs  (the atmosphere)

Plus one lb (or 8psi for the turbo)

minus one lb (or 6psi for the sebring)



Plus/minus less than 10% in a physics calculation is easily 'in the ballpark'.





>I'd better call Mazda. They can put that Miata tranny in the MPV after all.

>I'll call you when your royalties come in...

>

>NG

>

  No need to be nasty Norm.



/^\dans

















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