Hi Mike, here's my 2 cents:
At a steady 60 mph, a specific amount of horsepower is required to maintain
speed. This is determined by the aero drag and friction of the various
mechanical components. It doesn't matter what mod's you've made to the
engine, if you need 20 HP to go 60, that's all your engine is called upon to
produce when going 60. Heat is a by-product of HP production, so your problem
may be either:
a. An abnormally high amount of HP required to drive your car at 60 -
something mechanical in the drivetrain causing higher friction at speed,
anything from the trans, u-joints, bearings, rear end, dragging brakes etc?
Does the car 'coast down' normally? Are you sure Bielat didn't pack a chute
on the back of your car, but it worked this time? (sorry, obscure TT
b. Produces an abnormal amount of heat at running speed and load. Either
internal drag w/in engine, or wrong spark timing or too lean mixture at the
rpm and load placed on the engine. On the full skirt and four ring pistons -
lot's of old cars use this design - it was stock for the Sprite, and I doubt
the small extra friction from this is your problem. Of the stuff in this
category it's far more likely to be spark or mixture. WST's comment on head
gasket leak could be right on target here, also.
c. Makes a normal amount of heat at running speed and load - but it isn't
shedding it fast enough. You know all of this cooling system stuff that
could be wrong.
I know the blower pre-heats the charge by compression, but agree the blower
is not likely the problem, unless the blower is abnormally 'tight'. If this
were really bad enough to be the problem I'd guess the belt would break, slip
like crazy, or you'd break a mount before long. You'd have noticed that kind
I know my stone stock '66 1098 Sprite will run at about 180-190 at a steady
55 to 60 mph in warm weather (Oh, and BTW, you Cal and Southern whiners
didn't happen to have several hundred people keel over dead from the heat
like we did in Chicago a few years ago, did you?). But if I try to run much
faster temps definitely rise. I slow down when this happens so I don't
overheat, I've never pushed it to see if this would level off at 200 or 210
or whatever. The ambient temp makes a big difference to my running temps. A
stock system (at least mine, which is probably pretty representative) doesn't
seem to have a great amount of 'margin'.
If the car coasts down well, is pretty fast and responsive at lower speeds
and pulls well when you drop the throttle at higher speeds, then it's most
likely your cooling system needs improvement or maybe you have a head gasket
leak (which is a cooling system problem of sorts). Good Luck!