to answer your question;
Is there a stock combo that I could use to achieve this?
answer; yes
but
If you overdrive your water pump at idle, to get some fan-speed, this will also overdrive it at 7000 rpm...... just saying. Which will or may, increase the likelihood of throwing a belt, resulting in possibly, an engine meltdown.
Therefore
IMO, it is better to solve your low speed/idle heating problems in the conventional way.
Just so you know;
I run the same underdrive ratio that you currently have, on my 400hp 360/4-speed, and she will idle down see, note-1
IMO, and it may be mine alone, I get it, but here it is anyway; see note-2
But consider this;
your current pully ratio is 6.5/6.875= .945:1
Going to 1:1=1.00; at 700 idle rpm this is
a difference of 38rpm.
In another life I would have said; gimmee a break, if your combo has to depend on 38rpm, your system is way effed up.
If you have overheating problems, start a new thread and tell us what you have, what you don't have, what it's doing and when. see note-3
In my case,
I had to take the engine apart and loosen the skirt clearance and increase the ring-gaps.
Note-1
I run the same underdrive ratio that you currently have, on my 400hp 360/4-speed, and she will idle down
to 550 in gear and pulling herself in a parade, with 5 measly degrees of advance.......... and she has cruised all day geared at 65=1600, with normal advance, so, jus saying .......... it can be done.
And the 20 plus years old belt, stays on, at 7200 and more.
Note-2
Too many SBM guys make too big a deal about pully ratios, and way too big a deal about radiator sizing. My rad is a factory rad out of a 73 to 75 Dart 318-auto- A/C car . Even the patches have patches.
My secret is that I also use the shroud, and the 7-blade all-steel fan, both from that same donor-car, but mounted it on a Ford pick-up thermostatic clutch fan, that keeps the coolant at 205 to 207 degrees, by cutting in and out as may be required. and that's a 26"rad running in the factory-stock 6-cylinder core support, in a 68 Barracuda.
My hot-running ended in 2002 or thereabouts.
Jus saying.
Note-3
If you have overheating problems, start a new thread and tell us what you have, what you don't have, what it's doing and when.
My Engine went from running hot and locking up at shut-down, to, afterwards it won't hardly heat at all. and it gained some low-rpm torque, and now has a sweet idle. even down to 550 with that cam.
How many guys on FABO had to go this route?
Mostly, they just throw parts at the problem, and live with it.
Btw, at the time I was having this problem, the engine was running a 292/292/108 cam @11.3 Scr, @ any idle-timing, and no amount of idle-timing would cure it, nor idle-rpm.
Afterwards, like said; it would idle down to 550 in gear, and pulling itself, with just 5* of Idle-advance, with a starter gear of 2.66 x 3.55= 9.44.
My attempt at solving this prior to tear-down included;
A) the engine was already set-up with the aforementioned rad, a 5-blade direct-drive fan, a shroud, an 8-vane factory pump, alloy heads, an Airgap intake, and TTI unwrapped headers with full-length dual 3 inch pipes and 3-pass dynomax mufflers.
B) my changes included;
pully ratios, more fan blades, several different sized restrictor washers, bypass restriction, a hi-flow Milodon pump WITH a hi-flow stat, a 7qt roadrace oilpan with lots of surface area for oil-cooling, and
Nothing worked;
Until I took it apart, and got to the source.
Good luck
