Thanks for letting me know how far things have moved in F Prod SCCA.
My Series V racer did not run a generator, just spun a water pump, with a
small idler pulley to hold belt tension. Power losses through the
tranmission and welded rear axle gears and axle bearings etc. might not
have been 20hp and I sort of estimated (back then) that flywheel hp lost
about 15hp enroute to the ground. Amazing amt of power lost through having
the wrong U-joint angles !!! Pays to get exactly the same angle on front
and rear and above all....to have as close to zero as possible !
Appreciate seeing your proposed new engine specs and your request for my
comments. I will offer the following remarks in the hope you may see
something of value, or new to you or which might alter your own ideas:
1. Moly rings do afford a power increase of perhaps 1.5 to 2.5 hp on this
size of engine.
2. Use of flat top pistons would be surpassed with a forged domed piston.
At Venolia, my die gives a slanted dome roughly the shape of a slightly
larger combustion chamber. The height of the dome is perhaps 1/4" sloping
to about 1/16". While the piston was originally designed for .060 OS bore,
it could easily be turned to .037" OS bore. I assume the moly rings would
have to be supplied to venolia so they could properly machine the grooves
and oil return holes etc. This piston also uses floating Chevy pins and
they fit all this for you at Venolia. They also furnish teflon end plugs to
prevent pin ever touching cyl wall (which I never used because pins are
such a tight fit into the rod). Pin boss's have little oil holes on top of
boss. This piston has PROVEN 100% trouble free and long life etc. Don't
know the final CR it would give you but obviously more than a flat top.
Also..we would need to consider valve/piston clearences but I think I ran
about as much lift as you will have and there was no past problems.
3.Carrilo rods must cost a fortune? Z28 rods with tiny brazed buttons work
fine and NEVER have failed below 8100rpm but did let go once when a
suspected 9000 was touched. The Z28 has a husky bolt size as well.
I used many std. Chevy rods throughout the years and did only the usual hot
rod polishing and balancing work. None of these failed to my knowledge.
4.Clevite 77 bearings.....these were always reliable in the race engine.
Perhaps there are better today, but I know these hold up.
5.Your huge valve sizes sound awesome. I never got into this aspect of
engine mods due to having to stay legal in SCCA.
6.Re. the valves...is it possible to obtain valves with your 8mm stems and
which are sodium cooled? These would add a nice reliability factor.
7.I assume you have spring pressures known to keep all the valve train "in
contact" at high revs. While valve float will put a stop to further rpm,
what is sometimes unsuspected is that the train is NOT accurately following
the cam profile at somewhat lower rpm's. The hp below peak rpm suffers
badly but the driver never realizes this. It can be seen by charting the
HP curve completely (on a graph). if you were seeing a nice curve building,
and it then has a dip or flat area near the peak rpm this indicates the
train is floating on the cam lobe...at that speed. The English GKN Ltd.
published a large engineering paper on just this problem and it was found
that many stock rocker arm engines do have this problem, which is usually
(But not always) cured with having more spring pressure.
8.I would suggest lightening the valve train wherever possible and this
includes making "swiss cheese" holes in the lifter walls. Even tiny amounts
removed can have an affect at extreme rpm's.
9.Your combustion chamber deshrouding of the valves is of course SOP and
will pay off in filling efficiency...and net power gains. The 11.5:1 CR is
nice but perhaps the domed piston offer would push you over 12:1 .
10. The Weber carbs are a dream come true. Ah! if only my car could have
run them. I somehow feel 34mm choke size to be a bit too small for really
peak hp and rpm. More like 37-38mm sounds better to me??? The 34mm would
however make the engine produce better low and mid range hp.
11. Cam specs look nice but without having my old Crane data I cannot
comment on yours.
12. Will your 10+24 deg. distributor be enough? I know you can set to 36
deg or whatever the engine likes, but for easier cranking and likely faster
starting, it might be better to have say 5 deg BTDC at cranking, as a basic
static setting, then let idle (around 1000) be say 10 deg. I advise this
because in the event of a spin out where the engine may stall, you have to
crank it over and restart. Some guys have the timing set at a fixed
setting which is quite high and things run great..but restarting is almost
chancy with a hot engine.
All your other comments and specs sound fine and I have no more comments or
suggestions at this time. If something comes to mind I will send it.
Dick T.
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