-----Original Message-----Date: Monday, November 26, 2001 10:45 AM
Subject: Re: Cam, Crank, Twist
>I don't know anything about all this stuff but I do know that I pulled the
>center main bearing web out of my first Plymouth 4 (3 mains at best) at El
>Mirage one November. It finished the run and was turning over but when I
>pulled it down the #2 and3 cylinders had just over .200 more stroke than #1
>and 4. Since the pistons couldn'tgo much past .041 out of the block before
>hitting the head, I assume the stroke was changing every revolution.
>It didn't break and Al polished it and now has it on display in his crank
>shop. Rich Fox
>-----Original Message-----
>From: Dave Dahlgren <ddahlgren@snet.net>
>To: rtmack
>
>>It might bend that much but I find it pretty hard to believe.. Easy test
>for it
>>though. With the crank in the block lock the front of it down so it can't
>move.
>>Put a degree wheel on the rear of the crank and a pointer. Install a lever
>with
>>the appropriate amount of weight for the amount of torque you have in
>mind..Read
>>the degree wheel for torsional twist. That should simulate worst case
>scenario.
>>In real life the amount of torque should be about 8 times less than that
as
>only
>>one cylinder fires at a time with one other part way through the power
>stroke in
>>the case of a BBC that would be #2... I don't think any of the twist
>theories
>>hold up that well in real life unless you ar working with a stock bottom
>end and
>>a pro-mod top end. What happened to the valve to piston clearance with all
>this
>>twist. Most push rod engines lose about 0.010 for every degree of cam
>movement
>>relative to the crank. Do you run an extra 0.040 on cylinder 7 and 8?
>>The best way to check this would be to put another trigger wheel on the
>flywheel
>>and phase it identical to the one on the front. Either on the dyno with a
>o'scope
>>or at the track with a good data acq system monitor the phase shift from
>front to
>>rear... That would tell the real story for each individual case.
>>
>>I think most of the cylinder to cylinder problems are more related to
>thermal
>>problems and flow problems in the intake and exhaust. If this problem were
>true
>>most cranks would break at the #1 main journal too.. Seems like most break
>around
>>#4 main....I work with electronics all the time that can trim the ignition
>on
>>each cylinder along with the fuel for each. Typically there is not much
>there
>>tuning each one unless the injector does not flow right or the pick-up for
>the
>>ignition is poorly made. This is working to the extreme right of the
>decimal
>>point...
>>
>>As far as a flathead twisting the crank or an Ardrun have a superior crank
>.. how
>>much power do they make? I just finished a BBC for a street car with
>injection
>>and a mild roller cam 555 inches and pump gas. 745 ft lbs at 4600 and 735
>hp at
>>5600.. I was not worried about the timing on # 8 cylinder and that ran
just
>>fine.. With a little more cam I am sure it would of made 800 hp but it was
>not
>>the design goal for the engine, it had to make a lot of torque off idle
>which it
>>did 580 ftlbs at 2500...and 640 at 3000 rpm.. What I did learn on this
>engine was
>>that even though it was pump gas and low rpm the amount of power increase
>with a
>>MSD 7 over a MSD 6..
>>
>>Dave Dahlgren
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