[automotivebreath]

Originally Posted by shrinker

First off I would get rid of the HP carby and go with an old 60's 850 or I'd
retune the HP's emulsion, but it wont work as well as an Oldy. At least don’t
run it rich. The carby is the start of the process and there is no point
analyzing anything if its not right and an out of the box is not going to be right.

What would be the best way to upgrade the HP for improved emulsion? Can
I replace the metering blocks with aftermarket units? I do understand how
improvements in fuel atomization affect the combustion process, when the
carburetor is in the main circuits. Running rich is not my doing; the
owner/tuner is convinced that his over rich setting is ideal.

Originally Posted by shrinker

I would use a wider LSA on the cam if the revs are 7000 max and probably at
smaller duration. The cam is in the zone for 7500 max however If you fixed
the push rod pinch choke on the as cast heads it will be a very big benefit.
Those AFR heads won’t support 7500 properly with there as cast push rod
pinching ports. It’s probable that the LSA on the cam in use is to overcome
this problem.

The engine pulls great to 7500 RPM, a smaller cam would likely require a gear
change. As for the wider LSA you lost me there, what would this benefit?
The push rod pinch is now as delivered from AFR, I haven’t measured the
CSA. I could open it up with-in the limitations of the casting with out offset
rockers, Is that what you are referring to? Here we are talking about
improved VE and resulting increased cylinder pressure, I’m with you on the
impact this has on combustion at WOT in the engines RPM range.

Originally Posted by shrinker

The compression is fine, I wouldn't use a fuel that’s
too high octane for the job because I'll bet it is at the moment. I would
suspect the VE to be lower than it could be at max revs so that alters the
dynamic comp and hence the octane. It’s just that it’s common for people
to use fuel that’s too high octane.

Yes the owner runs more octane than needed with C12 heavy leaded racing
fuel, again not my choice. What impact does this have on combustion?

Originally Posted by shrinker

When the carby is set better and the vaporization is improved the octane
requirement goes down. If these things were done the engine would have lots
more power and it wouldn't be comparable anyway to what it is now with the
grooves. It would burn cleaner at all points with a correct carburetor to start
with. That’s just some quick ideas. Really need lots of info and time to make
a better posting.

Thanks for taking the time to explain.

I’m certain that the cylinder head wet flow characteristics are poor with the
current carburetor (as is with a large percentage of engines world wide). This
I will explore, if you will get me started in the right direction.

As for improving the cylinder heads, I’m willing to do the modifications, many
people refuse to spend additional money porting CNC ported heads, this
owner is the same. I agree improvements can be made to effect cylinder
filling, trapped charge and dynamic compression resulting in improved
combustion.

I’m all ears on changes in camshaft design; first I need to understand the
benefit of widening the LSA with this combination. As for shorter duration,
the cam matches the current engine RPM.

I understand the benefits of most of the above and can visualize
improvements implementing most of this with the current combination. This
could result in improved combustion at WOT in the engines RPM range and
throttle response.

The question now is would the grooves help the combination with the
recommended changes? I say yes, but I do get your point, some people
that work at higher levels in the sport feel they have accomplished more
of the same benefit using other methods as described.