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
rtmack wrote:
> List:
> from Bill Smith's comments below-- and from some of Bill Hoddinott's a couple
> days ago-- it is clear that at least part-of the cylinder-to-cylinder timing
> differences can be calculated. In other words, you shouldn't have to use
> expensive experimental methods (tuning on the dyno) to get some benefit from
> individual cylinder timing. Can we get some input from Dave D. on this?
> Russ Mack
>
> "Smith, Bill" wrote:
>
> > for emmesion reasons the manufactures are begining to allow for cam and
> > Crank torsional twist and that why more and more are using individual cyl
> > timing. at full load I hav read that the rear cyl on a BBC can be up to 4
> > degs. off. probably is the reason why the front cyl. is the one you time.
> > wmts
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